JohnVallo
1 5 4 8 3 7 2 6
- Joined
- Feb 9, 2015
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- 49
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- 360
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- Venice, FL
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- racersreunion.com
- First Name
- John
- Vehicle(s)
- '16 GT350, Shadow Black, Whipple Supercharged
- Thread starter
- #1
I was a little surprised that my first gear swap from 3.73 to 4.11 wasn’t a more noticeable change.
To read about the 3.73 to 4.11 change
SEE LINK: https://www.mustang6g.com/forums/threads/gear-change-from-3-73-rear-gear-to-4-11-in-my-gt350.96590/
I ended up driving 4,000 miles with the 4.11 (Including two 1300 mi trips). Gas mileage was really no different with the 4.11 than the 3.73 gears.
That 38-point change to the 4.11 was not a significant change. Originally, I had considered a 4.30 gear ratio, but no-one produced one for the Super 8.8. When I learned that a 4.56 was available from Yukon Gear I decided to go for it. Another 45-points may give me the change, (or a little more), that I originally wanted.
Just so we’re on the same ‘Terminology Page’, here is the proper terminology for the following rear-end parts.
Differential/Carrier Unit - The inner differential component that the ring gear bolts to. This unit transfers power from the driveshaft/pinion gear to the axles. Carriers are available in various types that are used in different vehicle applications. Common types are open carrier, Traction -Lok, Limited Slip, Torsen, Detroit Locker, spool, etc.
Housing/Gear Case/Pumpkin - Cast iron (or optional aluminum) unit that houses all of the internal differential components such as the carrier and ring & pinion gears. When all of the internal differential components are installed into the case, the unit is sometimes referred to as a "third member". In the case of the ’15 up Mustang IRS rear, it is referred to as the ‘Pumpkin’, or Loaded Differential Housing.
The Story:
As with the 4.11 swap, I found a 2017 GT350 low mileage 3.73 take-out housing. I could have located other used Super 8.8 Mustang rear ends, but with the GT350 you know Exactly what you are getting: (A painted cast iron housing, a 3.73 gear ratio, and a Torsen T2R differential). The Pinion Flange was quite confusing at first. A lot of people were saying there was one Pinion Flange for Automatic cars (110mm), and another Pinion Flange for Manual cars (113mm). Well the GT350 (all w/Manual Trans) used the (110mm) Automatic Pinion Flange. -So much for that theory-
I purchased a Yukon 4.56 Gear (pn: YG F8.8-456-15) from Summit Racing Equipment. They had a pretty good price of $233.00, Plus a $40.00 rebate. On the Install-Kit, this time I decided to buy the parts I needed individually, for 2 reasons: (1) Because upon teardown, this take-out rear end looked amazingly new. All the bearings & other parts looked great. (2) I still had pinion shims and a few other parts left from the previous Ford R&P Install Kit I had used before.
I ended up buying: a Collapsible Spacer and Pinion Nut Kit (FORD pn: FL3W-4C121-BA), as well as a carrier bearing shim kit (RATECH pn: 1148), and a 2 qt. bottle of BG Ultra Guard LS Heavy Duty Synthetic Gear Oil 75w-140 (pn: 75364).
To keep my original/spare housings safe and sound I decided to make a couple of nice wood fixtures to keep them stored in.
Upon receiving and examining the Yukon gear set I noticed that the machining (On the pinion bearing surfaces) had been done after the heat-treat as they looked newly machined. This was a definite indication that the process used to manufacture this gear set was the (FM) Face-Milled Process, -or sometimes referred to as the 5-cut process-. Different than the (FH) Face-Hobbed process, now used for virtually all newer Ford OEM production vehicles.
When setting up the ring and pinion it is very important to know what manufacturing process was used to make your gear-set, because between the (two) set-up procedures they are are different for each. Other ways to tell the difference is if your ring gear has a non machined casting area or bevel toward the backside, or looking at the teeth on the ring gear, you see that the teeth are equal height from heel-to-toe, you have a (FH) Face-Hobbed, or 2-cut gear-set. If the entire outside diameter and bevel of the ring gear looks machined, and looking at the teeth on the ring gear, you see that the teeth are taller at the outside diameter than they are on the inside diameter, you have a (FM) Face-Milled, or 5-cut gear set.
For a complete understanding of the different manufacturing processes used,
SEE: http://gearsolutions.com/features/face-off-face-hobbing-vs-face-milling/
SEE: http://www.crownracegears.com/gear_cutting.html
Also, upon measuring the pinion surfaces with a micrometer (Both the inner bearing surface and outer bearing surface), I discovered those surfaces were about .001 thousands larger (OD) than the previous 4.11, and the original 3.73. This did require me to take some fine sandpaper and spend 45 minutes to get both OD’s down to ½ thousands within specs.
One thing that I was concerned with was heat. Although I don’t track my Shelby, but I do some pretty spirited street driving and since I have a base GT350 I don’t have the factory diff Temp gage display and cooler. Knowing that the 4.11 was maybe going to run a little warmer, what I did on it was put an 8 TEMP THERMOLABEL 210-280F on the rear end in 2 places (Under the pinion on the cast iron surface, and on the back on the aluminum cover.) At least with this I could tell if the Temp ever got between 210 and 280 degrees) Which it Did Not in 4000 miles.
While doing this latest swap (4.11 --> 4.56), I learned that I could actually get the Diff Temp Dash Display Gage activated/working and, also enable the Trans Temp Gage on the dash display.
Learning from the following thread, (These Guys are Truly Amazing !)
SEE LINKS:
https://www.mustang6g.com/forums/threads/gt350-forscan-tweaks.61884/page-3#post-1442254
https://www.mustang6g.com/forums/threads/oem-differential-oil-cooler-install.69499/
https://www.mustang6g.com/forums/th...lution-discussion.55937/page-175#post-1757692
For my Diff Temp Gage to work, I did the following:
1. Run (2) 20ga. wires from the left-side drivers kick panel Connector C-264 -Tap into wires #4, and #21) run to behind the back-seat area and to the rear of the Diff. cover connected to a Motorcraft Pigtail (pn: WPT 984), and a Brass Temp Sensor (pn: FORD 9L8Z-6G004-E , or Standard Motor Products TS-653) is needed to screw into the rear of the Diff. cover. (The threaded recess for it is already there).
I made a nice tape-wrapped wire harness and fished it thru the driver’s sill and rear seat left panel then down thru the body between the rear seat and trunk. (Right beside where the existing harness goes thru). A big Thank-You to @jwb for sending me the connector terminals.
2. After the wiring was completed and sensor was plugged in I went into Forscan and enabled both the Axle Oil Temp and the Trans oil Temp for the Dash Gage Display. (In the IPC module: 720-06-01 xxxx Xxxx xxxx) Just change the location (where the large X is) to a 9.
The Transmission already has a temp sensor, it’s Just not enabled in the Software for the Dash Gage Display.
SEE LINK: https://www.mustang6g.com/forums/showthread.php?p=1985119&highlight=@kgschrader#post1985119
UPDATE: To read about my own fabrication of a Finned Aluminum Rear Diff Cover that holds more fluid
SEE LINK: https://www.mustang6g.com/forums/th...-for-the-mustang-‘super-8-8’-rear-end.117720/
Concerning the Speedometer
I have read repeatedly that if you make a minor change to your rear-gear (Within certain percentages) your speedometer will remain accurate. (Taking that to mean if you made major changes it would not).
My speedometer remained accurate with the 4.11 gear, and also with the 4.56 gear, requiring NO changes.
Well, here is what I conclude. FORD -using the magnetic triggers (located within rear knuckle inner bearing, or on some on the half-shafts) to drive the speedometer reading- the computer doesn’t really care what rear-end ratio it has, concerning the speedometer. It only has to know the tire circumference to get an accurate MPH. Because it is sensing the rear axle revolutions at the wheel, the rear-end ratio doesn’t come into play. Being there is a sensor on both sides, if one side turns repeatedly faster/slower than the other side, this will trigger the ABS system. (Now when they used to sensor at the back of the transmission, both the rear-gear ratio and the tire size would affect the speedometer.)
For Automatic S550's the Gear-Ratio setting in the computer is used for transmission shift-points. So with Automatic transmission cars there may be other issues with a gear change.
I know the software has a location for the Rear Gear Ratio, (In the BCM Module: 726-12-01 XXXX xxxx xxxx (where XXXX is the Hex representation for your Ratio, Hence 0175 is hex for 373, 019B is hex for 411, and 01C8 is hex for 456. I did change mine, somewhat later after the gear swap, -but it did not seem to affect anything-.
Here's some more logical explanation and info on the subject:
https://www.mustang6g.com/forums/threads/speedometer-calibration.110607/page-2#post-2875272
Now the part where I may have gone astray.
While I had the rear end housing out I thought about doing 3 more things.
1. Some stronger diff bolts -Lethal Performance (pn: LP-550179), and a 14mm HS drill bit -There were reported problems with the factory original bolts shearing, mostly on higher HP mods, and launches from dead stop) . These are the strongest bolts available.
SEE: https://www.mustang6g.com/forums/showthread.php?t=74891&highlight=Extreme+diff+bolts
2. Definitely needed a Steeda Cradle Alignment Kit (pn: 555 4438) to properly center and locate the Cradle back to the body squarely, (As I did drop the Subframe (Cradle) this time to drill out the front Diff bushing holes to 14mm)
3. Possibly some BMR Red poly diff lock-out bushing inserts (pn: BK 051) to reduce diff to subframe movement.
This obviously violated my #1 sworn policy: (NEVER CHANGE MORE THAN ONE THING AT A TIME)
Anyway, this is what I did and I figured I could always remove the lock-out bushing inserts later if they caused too much NVH, which they Did!
Concerning the BMR BK051 Diff Bushing lockout kit
This kit consists of 4 polyurethane bushing inserts (And Hardware) that fit into the voids of the Differential-to-Cradle Rubber Bushings. I read/heard no real complaints or issues on installation from any regular Mustang, GT Mustang owners. On the GT350 one of the Diff Bushings is different. -The Left Side (Drivers) Rear bushing is slightly different, (The void space is slightly smaller (OD), and the Nub Pattern in the Bushing itself is different). This required modification to one of the Red Poly inserts.
SEE LINK:
https://www.mustang6g.com/forums/showthread.php?p=2212523#post2212523
Again, the rear-end build went relatively well
TIP:
A fact some may not know when setting the proper backlash, using the carrier shim packs.
To aid in easier removing/installing of Diff assy, Use .003 thinner shim packs -On Both Sides-
Then when ready for final assembly, add the .003 shims back to each side to give proper carrier bearing preload.
After the proper backlash is achieved and the carrier shim stack thickness (on each side is known),
(Sometimes the thinner shims get warped, beat-up and wrinkled from changing them several times.)
I always order the solid carrier bearing shim (1 piece) from Ford Parts for Final assembly.
Ford has them -in one solid piece-, from .242 thru .307, in 001 increments.
When installing the Steeda (Delrin) alignment bushings, I had read some people having trouble with having to pry excessively to align-up the holes in cradle bushings/Delrin to the threaded holes in the body. I saw that some even had thread stripping problems. I studied my situation briefly and noticed by the bite-marks -that my original Cradle-to-body alignment had been centered pretty well. I also noticed that when I jacked up the cradle to start to align the holes, my cradle was ½ bolt hole to the rear of being centered and lined-up, so I had to pry it forward for the holes to align. It seemed the rear springs were keeping the cradle from going forward enough to line-up perfectly. I pried the cradle forward with a small bar in the original factory alignment holes/slots) and started the Left Side (Drivers) front bolt first. Then the Right Front. After drawing the front bolts up close, (but not tight), I was able to start both rears without any prying.
After buttoning up everything and torqueing all the suspension bolts at ride height, I was ready for the road test.
Here was a Big surprise
I did run the drive-train (While still up on jack-stands) for about 5 minutes. Varying from First to Second at low RPM’s and even in Reverse for a couple of minutes. When the ABS lights all lit-up on the dash display, I thought it was time to stop.
On the road test I was surprised, and not very happy. On every up-shift the drivetrain had this noticeable (loud) clunking, (Kind of a metallic clunk every time I up-shifted and sometimes just pushing in the clutch when moving). Also, slight noticeable gear whine, -coming in at 48 MPH and lasting to 52 MPH- Only on very Light acceleration and Float. I only drove about 7 miles and went back to re-check all the drivetrain and suspension bolts again. (All were good).
Being very disappointed (After all, I had a pretty good pattern on the gear setup? What went wrong?)
I thought about it that night and got up early the next day and took a longer ride, this time really checking for drive train slack at low speeds, different shifting scenarios, and really getting a feel for what might be going on. That time I noticed that on normal shifting, I would get a clunk during up-shifting as soon as I let out the clutch, and then immediately another clunk on acceleration. A DOUBLE CLUNK, -If you will-. (It was pretty loud on all up-shifts except 5th to 6th.)
I wondered, could it be the Torsen?, did I need a better gear set-up?, why all the noticeable slack in the drivetrain?
After everything cooled down again I decided to remove the driveshaft, lock down the axles with the emergency brake on, and put an angle-finder at the pinion yoke to measure exactly how much slack was in the rear-end. (5-6 degrees), That’s not real tight but it is not too uncommon for the New Mustang’s drivetrain.
I then drove the car out to the interstate. This time I was moving a little faster. At (85MPH in 6th gear turning 3000 RPM), I noticed a slight ambient roar inside the cabin start to develop. (Sounded like it was coming from rear-end). Slowing down to 80 it went away. (Even more puzzling).
Just then I realized what may be causing some of this. -I had violated my #1 policy-, (I had changed more than one thing at a time…) THE POLY LOCKOUT BUSHING INSERTS.
Went back to the garage, again waiting till the next morning when everything was cooled off, I removed the 4 Poly Bushing inserts.
Here was a Little surprise
Again, a road test. 75 percent of the Rear-End whine (Especially at 48-52MPH) GONE.
The Clunking, (or Double-Clunking) syndrome turned into a kind of Thumping, or Double Thump when up-shifting -Not as loud but still unacceptable (To me). Removing the Poly inserts definitely had a big effect on all the noises. If I were to continue with normal and occasional spirited street-driving, I wouldn’t be needing/wanting those in.
Some insight on the clunking/thumping
Some of this phenomenon I learned may be due to the design of the Dual-Mass Flywheel.
There is actually up to 16 degrees of free-play in this (Dual-Mass Flywheel and Clutch unit)
The clutch-discs and pressure-plate can actually have 16 degrees of: Free-Play. In other words the Clutch-Discs/Pressure-Plate moves but the Flywheel/Ring-Gear does not.
Here is a page from the Ford Shop Manual describing the inspection/checking procedure for this Dual-Mass Flywheel
Now for the Comparison/Evaluation of the ratios:
This (.45) point change (From 4.11 to 4.56) was a little more than my first (.38) point change (From 3.73 to 4.11), For a total change of (.83) points. If you look at the chart below, it’s really only about 750 RPM difference from: 3.73 in 5th gear at 70 MPH, to: 4.56 in 5th gear at 70 MPH.
Too much gear?, Most definitely NOT !
Here is a chart of the comparison of all 3 gears, speeds, and approximate RPMs.
3.73 Rear Gear
Trans Gear/Speed(MPH)/Engine RPM
5th / 50 / 2250
5th / 60 / 2750
5th / 70 / 3150
5th / 80 / 3650
6th / 50 / 1400
6th / 60 / 1700
6th / 70 / 2000
6th / 80 / 2250
4.11 Rear Gear
Trans Gear/Speed(MPH)/Engine RPM
5th / 50 / 2500
5th / 60 / 3000
5th / 70 / 3500
5th / 80 / 4000
6th / 50 / 1600
6th / 60 / 1900
6th / 70 / 2200
6th / 80 / 2550
4.56 Rear Gear
Trans Gear/Speed(MPH)/Engine RPM
1st / 10 / 1900
1st / 20 / 3600
1st / 30 / 5400
2nd / 20 / 2500
2nd / 30 / 3600
2nd / 40 / 5000
3rd / 30 / 2700
3rd / 40 / 3550
3rd / 50 / 4450
4th / 40 / 2750
4th / 50 / 3450
4th / 60 / 4200
5th / 50 / 2800
5th / 60 / 3300
5th / 70 / 3900
5th / 80 / 4400
6th / 50 / 1750
6th / 60 / 2100
6th / 70 / 2500
6th / 80 / 2800
What to do now
After only 150 miles on this Rear Gear, I decided it was time to remove this Clunky-Assed setup.
I ended up putting the Original 3.73 back in. (Mainly for the following reason).
-I wanted to perform the slack test with the angle finder on the original rear end, so I would at least have a comparison on the amount of driveline slack difference between the two rear ends. The original 3.73, Torsen had exactly 5 degrees of driveline slack, measured at the pinion yoke, with the emergency brake on. And as referenced earlier, the 4.56 setup had 6 degrees.
So my plan now is to tear down the 4.56 and look closely at the Torsen, possible try some different pinion depths/backlash and look at the pattern again. Need to eliminate the whine and try to correct the thumping noise on shifting.
With the original 3.73 gears back in, the cars shifting (especially upshifts) is much smoother, (Definitely less jerky), than the other 2.
With the 4.11 gear I did notice I needed to use my (Rev Matching skills) somewhat to obtain the same smooth shifting. (Even on Upshifts)
With the 4.56 Even my Rev matching skills couldn’t produce perfectly smooth shifting.
For some more detailed info on the "Super 8.8" rear... SEE LINK:
Inside the "Super 8.8" Rear End | 2015+ S550 Mustang Forum (GT, EcoBoost, GT350, GT500, Bullitt, Mach 1) - Mustang6G.com
To read about the 3.73 to 4.11 change
SEE LINK: https://www.mustang6g.com/forums/threads/gear-change-from-3-73-rear-gear-to-4-11-in-my-gt350.96590/
I ended up driving 4,000 miles with the 4.11 (Including two 1300 mi trips). Gas mileage was really no different with the 4.11 than the 3.73 gears.
That 38-point change to the 4.11 was not a significant change. Originally, I had considered a 4.30 gear ratio, but no-one produced one for the Super 8.8. When I learned that a 4.56 was available from Yukon Gear I decided to go for it. Another 45-points may give me the change, (or a little more), that I originally wanted.
Just so we’re on the same ‘Terminology Page’, here is the proper terminology for the following rear-end parts.
Differential/Carrier Unit - The inner differential component that the ring gear bolts to. This unit transfers power from the driveshaft/pinion gear to the axles. Carriers are available in various types that are used in different vehicle applications. Common types are open carrier, Traction -Lok, Limited Slip, Torsen, Detroit Locker, spool, etc.
Housing/Gear Case/Pumpkin - Cast iron (or optional aluminum) unit that houses all of the internal differential components such as the carrier and ring & pinion gears. When all of the internal differential components are installed into the case, the unit is sometimes referred to as a "third member". In the case of the ’15 up Mustang IRS rear, it is referred to as the ‘Pumpkin’, or Loaded Differential Housing.
The Story:
As with the 4.11 swap, I found a 2017 GT350 low mileage 3.73 take-out housing. I could have located other used Super 8.8 Mustang rear ends, but with the GT350 you know Exactly what you are getting: (A painted cast iron housing, a 3.73 gear ratio, and a Torsen T2R differential). The Pinion Flange was quite confusing at first. A lot of people were saying there was one Pinion Flange for Automatic cars (110mm), and another Pinion Flange for Manual cars (113mm). Well the GT350 (all w/Manual Trans) used the (110mm) Automatic Pinion Flange. -So much for that theory-
I purchased a Yukon 4.56 Gear (pn: YG F8.8-456-15) from Summit Racing Equipment. They had a pretty good price of $233.00, Plus a $40.00 rebate. On the Install-Kit, this time I decided to buy the parts I needed individually, for 2 reasons: (1) Because upon teardown, this take-out rear end looked amazingly new. All the bearings & other parts looked great. (2) I still had pinion shims and a few other parts left from the previous Ford R&P Install Kit I had used before.
I ended up buying: a Collapsible Spacer and Pinion Nut Kit (FORD pn: FL3W-4C121-BA), as well as a carrier bearing shim kit (RATECH pn: 1148), and a 2 qt. bottle of BG Ultra Guard LS Heavy Duty Synthetic Gear Oil 75w-140 (pn: 75364).
To keep my original/spare housings safe and sound I decided to make a couple of nice wood fixtures to keep them stored in.
Upon receiving and examining the Yukon gear set I noticed that the machining (On the pinion bearing surfaces) had been done after the heat-treat as they looked newly machined. This was a definite indication that the process used to manufacture this gear set was the (FM) Face-Milled Process, -or sometimes referred to as the 5-cut process-. Different than the (FH) Face-Hobbed process, now used for virtually all newer Ford OEM production vehicles.
When setting up the ring and pinion it is very important to know what manufacturing process was used to make your gear-set, because between the (two) set-up procedures they are are different for each. Other ways to tell the difference is if your ring gear has a non machined casting area or bevel toward the backside, or looking at the teeth on the ring gear, you see that the teeth are equal height from heel-to-toe, you have a (FH) Face-Hobbed, or 2-cut gear-set. If the entire outside diameter and bevel of the ring gear looks machined, and looking at the teeth on the ring gear, you see that the teeth are taller at the outside diameter than they are on the inside diameter, you have a (FM) Face-Milled, or 5-cut gear set.
For a complete understanding of the different manufacturing processes used,
SEE: http://gearsolutions.com/features/face-off-face-hobbing-vs-face-milling/
SEE: http://www.crownracegears.com/gear_cutting.html
Also, upon measuring the pinion surfaces with a micrometer (Both the inner bearing surface and outer bearing surface), I discovered those surfaces were about .001 thousands larger (OD) than the previous 4.11, and the original 3.73. This did require me to take some fine sandpaper and spend 45 minutes to get both OD’s down to ½ thousands within specs.
One thing that I was concerned with was heat. Although I don’t track my Shelby, but I do some pretty spirited street driving and since I have a base GT350 I don’t have the factory diff Temp gage display and cooler. Knowing that the 4.11 was maybe going to run a little warmer, what I did on it was put an 8 TEMP THERMOLABEL 210-280F on the rear end in 2 places (Under the pinion on the cast iron surface, and on the back on the aluminum cover.) At least with this I could tell if the Temp ever got between 210 and 280 degrees) Which it Did Not in 4000 miles.
While doing this latest swap (4.11 --> 4.56), I learned that I could actually get the Diff Temp Dash Display Gage activated/working and, also enable the Trans Temp Gage on the dash display.
Learning from the following thread, (These Guys are Truly Amazing !)
SEE LINKS:
https://www.mustang6g.com/forums/threads/gt350-forscan-tweaks.61884/page-3#post-1442254
https://www.mustang6g.com/forums/threads/oem-differential-oil-cooler-install.69499/
https://www.mustang6g.com/forums/th...lution-discussion.55937/page-175#post-1757692
For my Diff Temp Gage to work, I did the following:
1. Run (2) 20ga. wires from the left-side drivers kick panel Connector C-264 -Tap into wires #4, and #21) run to behind the back-seat area and to the rear of the Diff. cover connected to a Motorcraft Pigtail (pn: WPT 984), and a Brass Temp Sensor (pn: FORD 9L8Z-6G004-E , or Standard Motor Products TS-653) is needed to screw into the rear of the Diff. cover. (The threaded recess for it is already there).
I made a nice tape-wrapped wire harness and fished it thru the driver’s sill and rear seat left panel then down thru the body between the rear seat and trunk. (Right beside where the existing harness goes thru). A big Thank-You to @jwb for sending me the connector terminals.
2. After the wiring was completed and sensor was plugged in I went into Forscan and enabled both the Axle Oil Temp and the Trans oil Temp for the Dash Gage Display. (In the IPC module: 720-06-01 xxxx Xxxx xxxx) Just change the location (where the large X is) to a 9.
The Transmission already has a temp sensor, it’s Just not enabled in the Software for the Dash Gage Display.
SEE LINK: https://www.mustang6g.com/forums/showthread.php?p=1985119&highlight=@kgschrader#post1985119
UPDATE: To read about my own fabrication of a Finned Aluminum Rear Diff Cover that holds more fluid
SEE LINK: https://www.mustang6g.com/forums/th...-for-the-mustang-‘super-8-8’-rear-end.117720/
Concerning the Speedometer
I have read repeatedly that if you make a minor change to your rear-gear (Within certain percentages) your speedometer will remain accurate. (Taking that to mean if you made major changes it would not).
My speedometer remained accurate with the 4.11 gear, and also with the 4.56 gear, requiring NO changes.
Well, here is what I conclude. FORD -using the magnetic triggers (located within rear knuckle inner bearing, or on some on the half-shafts) to drive the speedometer reading- the computer doesn’t really care what rear-end ratio it has, concerning the speedometer. It only has to know the tire circumference to get an accurate MPH. Because it is sensing the rear axle revolutions at the wheel, the rear-end ratio doesn’t come into play. Being there is a sensor on both sides, if one side turns repeatedly faster/slower than the other side, this will trigger the ABS system. (Now when they used to sensor at the back of the transmission, both the rear-gear ratio and the tire size would affect the speedometer.)
For Automatic S550's the Gear-Ratio setting in the computer is used for transmission shift-points. So with Automatic transmission cars there may be other issues with a gear change.
I know the software has a location for the Rear Gear Ratio, (In the BCM Module: 726-12-01 XXXX xxxx xxxx (where XXXX is the Hex representation for your Ratio, Hence 0175 is hex for 373, 019B is hex for 411, and 01C8 is hex for 456. I did change mine, somewhat later after the gear swap, -but it did not seem to affect anything-.
Here's some more logical explanation and info on the subject:
https://www.mustang6g.com/forums/threads/speedometer-calibration.110607/page-2#post-2875272
Now the part where I may have gone astray.
While I had the rear end housing out I thought about doing 3 more things.
1. Some stronger diff bolts -Lethal Performance (pn: LP-550179), and a 14mm HS drill bit -There were reported problems with the factory original bolts shearing, mostly on higher HP mods, and launches from dead stop) . These are the strongest bolts available.
SEE: https://www.mustang6g.com/forums/showthread.php?t=74891&highlight=Extreme+diff+bolts
2. Definitely needed a Steeda Cradle Alignment Kit (pn: 555 4438) to properly center and locate the Cradle back to the body squarely, (As I did drop the Subframe (Cradle) this time to drill out the front Diff bushing holes to 14mm)
3. Possibly some BMR Red poly diff lock-out bushing inserts (pn: BK 051) to reduce diff to subframe movement.
This obviously violated my #1 sworn policy: (NEVER CHANGE MORE THAN ONE THING AT A TIME)
Anyway, this is what I did and I figured I could always remove the lock-out bushing inserts later if they caused too much NVH, which they Did!
Concerning the BMR BK051 Diff Bushing lockout kit
This kit consists of 4 polyurethane bushing inserts (And Hardware) that fit into the voids of the Differential-to-Cradle Rubber Bushings. I read/heard no real complaints or issues on installation from any regular Mustang, GT Mustang owners. On the GT350 one of the Diff Bushings is different. -The Left Side (Drivers) Rear bushing is slightly different, (The void space is slightly smaller (OD), and the Nub Pattern in the Bushing itself is different). This required modification to one of the Red Poly inserts.
SEE LINK:
https://www.mustang6g.com/forums/showthread.php?p=2212523#post2212523
Again, the rear-end build went relatively well
TIP:
A fact some may not know when setting the proper backlash, using the carrier shim packs.
To aid in easier removing/installing of Diff assy, Use .003 thinner shim packs -On Both Sides-
Then when ready for final assembly, add the .003 shims back to each side to give proper carrier bearing preload.
After the proper backlash is achieved and the carrier shim stack thickness (on each side is known),
(Sometimes the thinner shims get warped, beat-up and wrinkled from changing them several times.)
I always order the solid carrier bearing shim (1 piece) from Ford Parts for Final assembly.
Ford has them -in one solid piece-, from .242 thru .307, in 001 increments.
When installing the Steeda (Delrin) alignment bushings, I had read some people having trouble with having to pry excessively to align-up the holes in cradle bushings/Delrin to the threaded holes in the body. I saw that some even had thread stripping problems. I studied my situation briefly and noticed by the bite-marks -that my original Cradle-to-body alignment had been centered pretty well. I also noticed that when I jacked up the cradle to start to align the holes, my cradle was ½ bolt hole to the rear of being centered and lined-up, so I had to pry it forward for the holes to align. It seemed the rear springs were keeping the cradle from going forward enough to line-up perfectly. I pried the cradle forward with a small bar in the original factory alignment holes/slots) and started the Left Side (Drivers) front bolt first. Then the Right Front. After drawing the front bolts up close, (but not tight), I was able to start both rears without any prying.
After buttoning up everything and torqueing all the suspension bolts at ride height, I was ready for the road test.
Here was a Big surprise
I did run the drive-train (While still up on jack-stands) for about 5 minutes. Varying from First to Second at low RPM’s and even in Reverse for a couple of minutes. When the ABS lights all lit-up on the dash display, I thought it was time to stop.
On the road test I was surprised, and not very happy. On every up-shift the drivetrain had this noticeable (loud) clunking, (Kind of a metallic clunk every time I up-shifted and sometimes just pushing in the clutch when moving). Also, slight noticeable gear whine, -coming in at 48 MPH and lasting to 52 MPH- Only on very Light acceleration and Float. I only drove about 7 miles and went back to re-check all the drivetrain and suspension bolts again. (All were good).
Being very disappointed (After all, I had a pretty good pattern on the gear setup? What went wrong?)
I thought about it that night and got up early the next day and took a longer ride, this time really checking for drive train slack at low speeds, different shifting scenarios, and really getting a feel for what might be going on. That time I noticed that on normal shifting, I would get a clunk during up-shifting as soon as I let out the clutch, and then immediately another clunk on acceleration. A DOUBLE CLUNK, -If you will-. (It was pretty loud on all up-shifts except 5th to 6th.)
I wondered, could it be the Torsen?, did I need a better gear set-up?, why all the noticeable slack in the drivetrain?
After everything cooled down again I decided to remove the driveshaft, lock down the axles with the emergency brake on, and put an angle-finder at the pinion yoke to measure exactly how much slack was in the rear-end. (5-6 degrees), That’s not real tight but it is not too uncommon for the New Mustang’s drivetrain.
I then drove the car out to the interstate. This time I was moving a little faster. At (85MPH in 6th gear turning 3000 RPM), I noticed a slight ambient roar inside the cabin start to develop. (Sounded like it was coming from rear-end). Slowing down to 80 it went away. (Even more puzzling).
Just then I realized what may be causing some of this. -I had violated my #1 policy-, (I had changed more than one thing at a time…) THE POLY LOCKOUT BUSHING INSERTS.
Went back to the garage, again waiting till the next morning when everything was cooled off, I removed the 4 Poly Bushing inserts.
Here was a Little surprise
Again, a road test. 75 percent of the Rear-End whine (Especially at 48-52MPH) GONE.
The Clunking, (or Double-Clunking) syndrome turned into a kind of Thumping, or Double Thump when up-shifting -Not as loud but still unacceptable (To me). Removing the Poly inserts definitely had a big effect on all the noises. If I were to continue with normal and occasional spirited street-driving, I wouldn’t be needing/wanting those in.
Some insight on the clunking/thumping
Some of this phenomenon I learned may be due to the design of the Dual-Mass Flywheel.
There is actually up to 16 degrees of free-play in this (Dual-Mass Flywheel and Clutch unit)
The clutch-discs and pressure-plate can actually have 16 degrees of: Free-Play. In other words the Clutch-Discs/Pressure-Plate moves but the Flywheel/Ring-Gear does not.
Here is a page from the Ford Shop Manual describing the inspection/checking procedure for this Dual-Mass Flywheel
Now for the Comparison/Evaluation of the ratios:
This (.45) point change (From 4.11 to 4.56) was a little more than my first (.38) point change (From 3.73 to 4.11), For a total change of (.83) points. If you look at the chart below, it’s really only about 750 RPM difference from: 3.73 in 5th gear at 70 MPH, to: 4.56 in 5th gear at 70 MPH.
Too much gear?, Most definitely NOT !
Here is a chart of the comparison of all 3 gears, speeds, and approximate RPMs.
3.73 Rear Gear
Trans Gear/Speed(MPH)/Engine RPM
5th / 50 / 2250
5th / 60 / 2750
5th / 70 / 3150
5th / 80 / 3650
6th / 50 / 1400
6th / 60 / 1700
6th / 70 / 2000
6th / 80 / 2250
4.11 Rear Gear
Trans Gear/Speed(MPH)/Engine RPM
5th / 50 / 2500
5th / 60 / 3000
5th / 70 / 3500
5th / 80 / 4000
6th / 50 / 1600
6th / 60 / 1900
6th / 70 / 2200
6th / 80 / 2550
4.56 Rear Gear
Trans Gear/Speed(MPH)/Engine RPM
1st / 10 / 1900
1st / 20 / 3600
1st / 30 / 5400
2nd / 20 / 2500
2nd / 30 / 3600
2nd / 40 / 5000
3rd / 30 / 2700
3rd / 40 / 3550
3rd / 50 / 4450
4th / 40 / 2750
4th / 50 / 3450
4th / 60 / 4200
5th / 50 / 2800
5th / 60 / 3300
5th / 70 / 3900
5th / 80 / 4400
6th / 50 / 1750
6th / 60 / 2100
6th / 70 / 2500
6th / 80 / 2800
What to do now
After only 150 miles on this Rear Gear, I decided it was time to remove this Clunky-Assed setup.
I ended up putting the Original 3.73 back in. (Mainly for the following reason).
-I wanted to perform the slack test with the angle finder on the original rear end, so I would at least have a comparison on the amount of driveline slack difference between the two rear ends. The original 3.73, Torsen had exactly 5 degrees of driveline slack, measured at the pinion yoke, with the emergency brake on. And as referenced earlier, the 4.56 setup had 6 degrees.
So my plan now is to tear down the 4.56 and look closely at the Torsen, possible try some different pinion depths/backlash and look at the pattern again. Need to eliminate the whine and try to correct the thumping noise on shifting.
With the original 3.73 gears back in, the cars shifting (especially upshifts) is much smoother, (Definitely less jerky), than the other 2.
With the 4.11 gear I did notice I needed to use my (Rev Matching skills) somewhat to obtain the same smooth shifting. (Even on Upshifts)
With the 4.56 Even my Rev matching skills couldn’t produce perfectly smooth shifting.
For some more detailed info on the "Super 8.8" rear... SEE LINK:
Inside the "Super 8.8" Rear End | 2015+ S550 Mustang Forum (GT, EcoBoost, GT350, GT500, Bullitt, Mach 1) - Mustang6G.com
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