Rear Differential Break In

BierGut

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Getting a diff rebuit (which I think means gear sets being replaced in the pumpkin) -- What is the break in going to be?
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JAJ

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Getting a diff rebuit (which I think means gear sets being replaced in the pumpkin) -- What is the break in going to be?
Same break-in as a new car - vary speeds and gradually increasing load for the first 1,000 miles or so - no cruise control.
 

matthewr87

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What happened to your diff?
 
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BierGut

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What happened to your diff?
Good question. Still working to get the best guess from the dealership. Vibration developed following a three day WGI event and I was sending it in for full fluid change and asked them to investigate the vibration -- I figured a hub, but the word came back it needed the diff rebuilt and a new driveshaft. (it's a 2017 with 28k miles - I am 2nd owner at 25k miles)

What I need answered is was metal found in the diff fluid? If so -- I'll demand a new diff cooler as well. We'll see. I'll report back.
 

JeremyPro5.0

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Best of luck.
Ive changed many a rear gear out and never had any break-in other than making sure the rear had a chance to come to temp before hammering on it.
Just listen for noise on acceleration, steady state cruise or deceleration while tranny in gear. It should make no noise if work was done correctly.
 
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BierGut

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Best of luck.
Ive changed many a rear gear out and never had any break-in other than making sure the rear had a chance to come to temp before hammering on it.
Just listen for noise on acceleration, steady state cruise or deceleration while tranny in gear. It should make no noise if work was done correctly.
Thanks...
Spoke to the dealership today and asked how they knew the diff and driveshaft needed rebuilding/replacing and was told that until now it was all based on noise. (facepalm) They have gone ahead and ordered bearings for the diff and a new drive shaft. They have not drained the diff so they have no idea about the gear sets. Car has been sitting there for two weeks ... typical dealership BS. :wink:
 

matthewr87

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Thanks...
Spoke to the dealership today and asked how they knew the diff and driveshaft needed rebuilding/replacing and was told that until now it was all based on noise. (facepalm) They have gone ahead and ordered bearings for the diff and a new drive shaft. They have not drained the diff so they have no idea about the gear sets. Car has been sitting there for two weeks ... typical dealership BS. :wink:
Are you sure the vibration is driveline related? I would want to be quite sure about that before tearing into the differential. It just seems odd that the diff would cause a vibration. The driveshaft or pinion sure, but the diff seems odd. I had the dealership replace my ring and pinion on my 2012 GT because of the infamous 3.73 whine and the car was never the same after that. They introduced a horrible driveline vibration at high speed which they could never diagnose or fix. I gave up after a while and switched to a one piece aluminum shaft which decreased the problem but did not fully fix it.
 

Hack

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Are you sure the vibration is driveline related? I would want to be quite sure about that before tearing into the differential. It just seems odd that the diff would cause a vibration. The driveshaft or pinion sure, but the diff seems odd. I had the dealership replace my ring and pinion on my 2012 GT because of the infamous 3.73 whine and the car was never the same after that. They introduced a horrible driveline vibration at high speed which they could never diagnose or fix. I gave up after a while and switched to a one piece aluminum shaft which decreased the problem but did not fully fix it.
So - just to make sure I understand - you're saying a dealer replaced your ring and pinion and that caused a horrible vibration? But then you are saying his rear diff shouldn't cause a vibration?

I see a conflict there.
 

matthewr87

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So - just to make sure I understand - you're saying a dealer replaced your ring and pinion and that caused a horrible vibration? But then you are saying his rear diff shouldn't cause a vibration?

I see a conflict there.
I don't see a conflict. The most likely explanation is that the dealership mechanics failed to properly index the pinion, driveshaft, or any of the internal axle components (likely all of the above) during the gear and pinion replacement procedure, which led to the horrible vibration I experienced at high speeds afterwards. It doesn't seem likely that any component indexing would change as a result of a track day, unless the OP lost a driveshaft bolt or something along the way. I was simply sharing my experience in an effort to save the OP any headaches if in fact the vibration is unrelated to his differential. To me, a proper diagnosis by a mechanic that knows what they are doing would be the first step, and based on my experience with Ford dealerships, I would be leery of the rather murky initial diagnosis OP has described.
 
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BierGut

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I don't see a conflict. The most likely explanation is that the dealership mechanics failed to properly index the pinion, driveshaft, or any of the internal axle components (likely all of the above) during the gear and pinion replacement procedure, which led to the horrible vibration I experienced at high speeds afterwards. It doesn't seem likely that any component indexing would change as a result of a track day, unless the OP lost a driveshaft bolt or something along the way. I was simply sharing my experience in an effort to save the OP any headaches if in fact the vibration is unrelated to his differential. To me, a proper diagnosis by a mechanic that knows what they are doing would be the first step, and based on my experience with Ford dealerships, I would be leery of the rather murky initial diagnosis OP has described.
Murky is an understatement... I'll no nothing until they actually drain the fluid and take a look. I am somewhat cornered in that I have a long term warranty that I purchased through the dealership when I purchased the Shelby. (the dealer is 4 miles from the house) I have had a ton of issues in the first 6 months and have had zero issues with getting everything repaired and completely paid for so I stick with them for service. (it's a 7 year 100k plan) I don't think the trouble is the technician, but just the general "F-150" mentality the dealership has toward service work overall. (Parts department won't hunt for parts if system says it's backordered, etc...) So I feel I need to be pretty proactive when it comes to getting timely stuff done during track season.

What had me confused this time is the car went in and I was told it needed a diff rebuild and a driveshaft... when I pressed them I learned they have only provided that diagnosis based on "noise" and a visual of the driveshaft. (insert facepalm here) Knowing you don't/can't "rebuild" a Torsen diff, I think a uneducated service advisor just said "diff rebuild". We have to wait until the diff fluid is examined and go from there. Like someone mentioned earlier -- it would much more likely be the ring/pinion. Fingers crossed. The bummer is I miss what was to be my final track event of the year -- three days at VIR. :headbang:
 

Hack

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I don't see a conflict. The most likely explanation is that the dealership mechanics failed to properly index the pinion, driveshaft, or any of the internal axle components (likely all of the above) during the gear and pinion replacement procedure, which led to the horrible vibration I experienced at high speeds afterwards. It doesn't seem likely that any component indexing would change as a result of a track day, unless the OP lost a driveshaft bolt or something along the way. I was simply sharing my experience in an effort to save the OP any headaches if in fact the vibration is unrelated to his differential. To me, a proper diagnosis by a mechanic that knows what they are doing would be the first step, and based on my experience with Ford dealerships, I would be leery of the rather murky initial diagnosis OP has described.
Good post. I somewhat agree with your thoughts. Indexing really shouldn't cause "horrible vibration" though. All of the components of the driveshaft assembly and differential assembly are spec'ed and produced to tolerances and they are assembled together randomly. They are not marked and indexed prior to initial assembly. Yes, when working on them it is recommended to keep the same indexing. I believe that is because the original indexing is proven.

In other words, the parts aren't assembled and then balanced as an assembly. They are balanced separately, put together and then inspected. If there's a problem, typically that means one of the parts has a flaw or they were assembled incorrectly.

This is the reason why a person can purchase a replacement drive shaft or a replacement differential and not require some kind of balancing machine to make it functional in the assembly. The new part bolts in and is expected to work well out of the box. Just like when the car was originally put together. All drive shafts and all differentials produced by the vendor are intended to be interchangeable.
 
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