4.09 Rear Gear Set

[EXP Jawa]

Had to:

yeah strange they could not have made it the popular and well known 4.10

I guess that depends on what axles you're familiar with - 4.09:1 ratios aren't unheard of either. However, what it comes down to is the combination of tooth numbers on the ring and pinion. If Ford decided to redesign the previous gear set (4.10) to make it stronger or more durable, one way to do that is to revise the size and shape of the gear teeth. Usually, that results in a different number of teeth for a give ring size (more smaller teeth or fewer larger teeth). The target would've been the same approximate ratio, but you've got to work with the tooth counts that fit. So, 4.10 might become 4.09:1 in that situation.

nice find, may consider this mod for faster acceleration.
so how does it work exactly? dose the entire diff need to be disassembled? and replace the 3.73 ring/pinon set with the 4.09?

I saw they have the installation kit, bolt kit, and seal kit as well for that, do I need that too?

lastly, is it DIY friendly?

Ring and pinion set up is not complicated, but it is tedious and requires specialized knowledge and a few special tools. Specifically, both the pinion gear and the differential need to be shimmed correctly to make sure that the mesh between the ring and pinion gear is correct. It isn't rocket surgery, but it does require that you know what you're doing - or, are very patient and have good reference material.

To do the job, the entire carrier assembly needs to be disassembled. The axle shafts out, the cover off so that the differential itself can be removed from the carrier, as well as the pinion gear. The previous ring gear has to be removed from the differential case/body and replaced with the new. The pinion is installed into the axle carrier, and must be shimmed for depth (fore/aft position). This controls meshing location on the gear teeth. Then the diff/ring gear can be put into place and shimmed for side-to-side placement. This controls backlash between the ring and pinion (see earlier comments).

Again, not technically difficult, but time consuming and finicky.

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[mustang_guy]

nice find, may consider this mod for faster acceleration.
so how does it work exactly? dose the entire diff need to be disassembled? and replace the 3.73 ring/pinon set with the 4.09?

I saw they have the installation kit, bolt kit, and seal kit as well for that, do I need that too?

lastly, is it DIY friendly?

depends what you consider friendly. If these get installed wrong the rear differential will whine. In my opinion if you have to ask, you're probably not suited for job. I mean no disrespect by that. Youd be better off paying someone that deals with rear differentials often for a living.

 

[Grimace427]

depends what you consider friendly. If these get installed wrong the rear differential will whine. In my opinion if you have to ask, you're probably not suited for job. I mean no disrespect by that. Youd be better off paying someone that deals with rear differentials often for a living.

I've been a tech at a dealer for 10 years but it's been since I was in school last time I set up a ring-pinion. I'd have no problem paying someone else to do it for me.

 

[mustang_guy]

I've been a tech at a dealer for 10 years but it's been since I was in school last time I set up a ring-pinion. I'd have no problem paying someone else to do it for me.

If you worked at one of the big three youd have done your fair share in 10 years. I cant see many euro dealerships doing that very often. Typically they just replace the whole differential. I know i did a few at toyota as well as ford. The tacoma, tundra (t100s back in the mid 90s) and 4 runners. Some guys were just so aggressive off road sometimes. Definitely wasnt super common at toyota. At bmw we just replace the whole thing. There is no inner working part numbers for gears. Its whole thing or nothing. Ive not done one in some years but i still remember enough to do one with no issues.

 

[GT P-TREE]

I'm all for doing installs myself, but I would have someone do this for me. Gear whine is f'ing awful to deal with.

 

[Grimace427]

If you worked at one of the big three youd have done your fair share in 10 years. I cant see many euro dealerships doing that very often. Typically they just replace the whole differential.

Yup, Benz dealer. Only repairs we do are seal replacements, otherwise any real failure gets a new or rebuilt diff.

 

[Hack]

I've set up a rear diff before and it worked great after installation, but I would also consider buying a pumpkin with the gear set installed in it, if the price isn't too high. It would be nice to be able to swap back and forth quickly. I think on the street the 4.09s will be an improvement over the 3.73s, but on the road course I would probably be faster with the 3.73s in the car.

 

[RBS550]

nice find, may consider this mod for faster acceleration.
so how does it work exactly? dose the entire diff need to be disassembled? and replace the 3.73 ring/pinon set with the 4.09?

I saw they have the installation kit, bolt kit, and seal kit as well for that, do I need that too?

lastly, is it DIY friendly?

Here's a link to my thread where I changed my gears a while back in my S550 DIY. I went from 3.15s to 3.73s, after several months of racing I went back to 3.15s. These engines unlike engines from my day have a very broad power band, so in my case using 4 gears in the 1/4 was no better than using 3 gears in the 1/4, my best 11.11 1.52 60' @126 was with the 3.15s, no doubt Circle D plays a MAJOR roll in the 60' number. In the old days our engines were very peaky in power, so we needed much gear to keep getting us back up to that peak. Today's dyno pulls look like rolling hills instead of mountainous terrain. Now once I install radical cams I'm sure my power will become more narrow, at which point I will visit the 4.09s so I can use up 4th gear in the 1/4 and if it doesn't pan out go back to what was better. I have a few more threads of all the work I've done if you search me on this forum. And some youtube vids of the car at rbs550. Below is the gear change thread. Hope this gives you an idea of the work involved.

http://www.mustang6g.com/forums/showthread.php?t=27136

 

[RBS550]

Another thing any experienced gear changer will notice is that Ford gears never come with a pinion depth written on the pinion, this is why it is common practice to use the size pinion shim that came out of the car, doesn't guarantee it'll be dead on, but that's what you have to start with when there's no reference depth given with the gear set. That being said the Ford gears are very good gear gears when it comes to set-up using the original pinion shim. I always make a note of what my car takes and just put that shim under the next ratio I'm trying, this way I'm not having to press off the pinion bearing again to steal the shim.

 

[Hack]

Here's a link to my thread where I changed my gears a while back in my S550 DIY. I went from 3.15s to 3.73s, after several months of racing I went back to 3.15s. These engines unlike engines from my day have a very broad power band, so in my case using 4 gears in the 1/4 was no better than using 3 gears in the 1/4, my best 11.11 1.52 60' @126 was with the 3.15s, no doubt Circle D plays a MAJOR roll in the 60' number. In the old days our engines were very peaky in power, so we needed much gear to keep getting us back up to that peak. Today's dyno pulls look like rolling hills instead of mountainous terrain. Now once I install radical cams I'm sure my power will become more narrow, at which point I will visit the 4.09s so I can use up 4th gear in the 1/4 and if it doesn't pan out go back to what was better. I have a few more threads of all the work I've done if you search me on this forum. And some youtube vids of the car at rbs550. Below is the gear change thread. Hope this gives you an idea of the work involved.

http://www.mustang6g.com/forums/showthread.php?t=27136

Just curious because the linked thread doesn't say anything. I can see being slower with a manual transmission using steeper rear gears due to more shifting, but I imagine the automatic shifts very quickly (I've never driven one). Were your times slower because you were spinning off the line, or did you hook with both gear sets and the difference was only shift time? I assume you have a stock transmission other than the circle D converter? Are you foot braking and then nailing it on the light, or did you have to ease into the throttle to avoid spinning? What RPM does the circle D converter stall to?

What tire are you running? Any changes to the shocks/suspension/front tire to improve weight transfer, etc?

Sorry for all the questions but I'd love to understand the details of how your car is working. I think it will help me quite a bit in my decision on whether I'm buying gears for the GT350. I think the character of the Coyote and Voodoo are very similar, so a greater understanding of the Coyote is useful for those of us in this forum. I remember driving my manual transmission 2011 Brembo GT on the street with 3.73 gears was crazy. The rear gears really seemed to wake up the engine from a seat of the pants standpoint. My 2015 GT seemed a lot more tame and boring with the 3.31 gear set or whatever it was that was the factory equipment on that car.

 

[Voodooo]

Although my gt350 is geared different then my LX. Going from a 4.10 to a 4.56 picked me up almost 4 tenths in the 1/4. I want to run my gt350 in the 1/4 with my mods, ARH long tubes, JLT, Lund e85 tune and slicks before I swap gears. You want to cross the line at your shift rpm. I won't know what that is until I run it down the track. Doing gear swaps isn't that big of a deal if you have the tools and equipment. The main thing is getting the pinion depth correct. Most gear sets have the pinion depth marked on the pinion head, some Ford performance gears do not. Once the pinion depth is set the back lash and pattern is set. You need a press, indicator, micrometer, bluing and torque wrench and locktite. I always install new bearings and races when I do them, but that's just me.

 

[RBS550]

Just curious because the linked thread doesn't say anything. I can see being slower with a manual transmission using steeper rear gears due to more shifting, but I imagine the automatic shifts very quickly (I've never driven one). Were your times slower because you were spinning off the line, or did you hook with both gear sets and the difference was only shift time? I assume you have a stock transmission other than the circle D converter? Are you foot braking and then nailing it on the light, or did you have to ease into the throttle to avoid spinning? What RPM does the circle D converter stall to?

What tire are you running? Any changes to the shocks/suspension/front tire to improve weight transfer, etc?

Sorry for all the questions but I'd love to understand the details of how your car is working. I think it will help me quite a bit in my decision on whether I'm buying gears for the GT350. I think the character of the Coyote and Voodoo are very similar, so a greater understanding of the Coyote is useful for those of us in this forum. I remember driving my manual transmission 2011 Brembo GT on the street with 3.73 gears was crazy. The rear gears really seemed to wake up the engine from a seat of the pants standpoint. My 2015 GT seemed a lot more tame and boring with the 3.31 gear set or whatever it was that was the factory equipment on that car.

My trans is stock other than the 4K stall, I didn't spin with the 3.73s, I just think that Circle Ds converter and the broad power is what makes the difference.
I've been out of racing for more than ten years and my knowledge is with pushrod engines, some as fast as high 8s N/A with a 5 speed and using all 5 gears in the 1/4. I was 100% positive I would instantly go faster with the gear change and much to my surprise I didn't. After several months my Tuner pressured me to get 3.31s, I had no luck in finding any so I reluctantly put the 3.15s back in and much to my surprise I had my best times. No don't get me wrong were not talking about a lot, but the the fact that I make my best passes N/A in a heavy auto with 3.15s amazes me. I can only attribute it to Circle D and the broad power of the Coyote Ti-VCT.
I'm actually a stick guy. Sticks eat less HP and when you never lift off of the gas time lose is minimal. I only went with an auto due to advice that there was issues with these stick cars when power shifting.
While an automatic may seem quick, there's still fluid that has to be directed and clutches compressed, this all takes time too. Also an auto eats a lot more power than a stick. Remember that thing is a huge hydraulic pump.
To do another comparison, back in the day 90% of all the race autos were 3 speed. I can't say I ever saw anyone use a 4th gear in the 1/4. And a lot of guys only run a 2 speed, the converter plays a huge roll. This my first car with a converter so I'm on a learning curve. I'm use to clutches.
Now as far as how I launch, if you watch & listen to some of my videos it sound like I take off at idle, but when I read my data log I have it at about 1,800 then as the tree comes down when I floor it but only release the brakes when I think they can't hold it any more. Doing this shows on the data that most times I reach 4K before the tires start moving. The other very important thing I do to get good 60' times, is I barely turn on the second bulb, this doesn't help your reaction time, but it gives you what we call rollout and that's movement before the timer starts.
Tire, here's another area where my Old School thinking is out dated. I thought for sure a bias-ply tire would do the best, well it didn't. My bias-ply tire set-up is on 15" wheels and combined weighed 35lbs less, but never gave me my best numbers. My best numbers came from Mickey DRs 29/45/17s ET Street Radial II. I never thought a heavy steel belted tire would be better.
Now I could be screwing up again, but I'm going to try 15" DRs ET Streets and use my transbrake this spring. It's hard for me to give up on 15". Here's some vids, there's more at youtube rbs550

DRs
[ame]

Bias-ply tires
[ame]

Barely staging
[ame]

Barely pushing, shows I'm reving up then release brakes, I'm a little late on releasing the brakes.
[ame]

This is with 3.73s, I go into 4th gear.
[ame]

This one shows loading the tire before launching.
[ame]

 

[FTD]

Anyone compiled a speed in gear delta with these gears?

 

[Voodooo]

Anyone compiled a speed in gear delta with these gears?

Huh

 

[Nataphen]

Rear gears need to be matched well with the Coyote manuals, but the autos seem to run the same no matter what gear you have. Guys have tested this over and over, and there's no appreciable difference between gears with these cars' automatic transmissions. Best to run 3.15s or 3.31s and keep your gas mileage up.

For a manual NA Coyote, run 3.73s with a Boss, CJ, or even possibly a Voodoo IM. For the stock IM, run 3.55s.

Where these 4.09s are really going to help is on launching the GT350 harder. As we all know, the car has pretty weak torque below 3,500RPM, and first gear is extremely tall. After it gets moving, it builds speed like crazy, but it needs help off the line for the guys who really want to drag race them. It would probably be a little more fun on the street too. It would be worse for a road course with 4.09s, which is what it's designed for. Like Hack said, buy a second center section with 4.09s and swap them out depending on your application.

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