Hi guys.
I know there were several threads regarding whining diffs after rebuild. But maybe someone has an experience with ZIP corvette rebuilt diffs. I ordered this one from them: https://www.zip-corvette.com/97-04-3...ferential.html. It arrived with a yellow paste on the ring gear teeth, that showed a reasonable meshing pattern, at least to my inexperienced view, the gear slack was ok, but it was impossible to turn the gear by hand, is this normal? So I installed it last weekend, and filled up with this: https://www.zip-corvette.com/driven-...il-80w-90.html adding amsoil friction additive. I did the first 10 minutes break in cycle, and the diff whines after around 30mph and up. It whines while accelerating, decelerating and coasting the sound and intensity is different but it always present. So my question is, whether it is normal for a first few miles, and it will go away? And should I continue break in procedure or I need to pull it out again and send it back?

 

Well, my RPM diff was quiet from the go, no that should not be making any whining. That said did you do a few tight turns right and left to get the lube into the clutch packs?
I used Valvoline 75 90 synthetic per their recommendations

 

I did a few tight turns while parking and maneuvering in my parking lot, but nothing intentional. The break in recommendations say that I need to use non-synthetic oil for the first 500 miles. Since it is whining during the straight forward driving the clutch packs are not in action during that time I guess.

 

Assume you followed this closely?

https://www.zip-corvette.com/downloa...nformation.pdf

Heat cycles are really important during break-in.

I had my diff rebuilt with 4.10 gears locally, and followed the break-in procedure above. I still get some whine at part throttle (only) at 30 (exactly) and then from 75-85. Shop said it can be normal. I know a number of people with rebuilt diffs that whine. I think it's just the nature of the beast.

 

I actually just started it and did "10 mins not faster than 50mph" cycle. Then stopped everything and waiting from ZIP Corvettes any directions on what to do next for a second day already. Customer service there is not perfect to say the least.
Anyway does your diff after rebuilt had a whine right from the start? And how it (the while) evolved during the break in period?

 

I've only bought one thing from ZIP (rebuilt steering rack), customer service certainly leaves a lot to be desired.

On my diff, the 30mph whine is new...but it came when I swapped from conventional to synthetic gear oil. Shop told me to stick with conventional gear oil because it's thicker at temp, and that these are quieter with conventional gear oil, so I may change back.

The 75-85 whine was present the first time I went that fast. Note that the break-in procedure specifies being under 55 mph for 4.10's, so I assume the whine was always there. Since mine is only under part throttle and only for that speed range, shop claimed that I'm experiencing what they best described as "gear float" where the pinion and ring aren't making consistent contact being at part throttle. Makes sense to me. Could be BS

There's people on here that swear up and down that aftermarket gears should be 100% silent. I'm not buying it. I know too many people like me with noisy diffs build by my local shop and some of the top vendors here. I think these diffs are just noisy with different gears.

 

Ok so it was not noisy from 30mph from the beginning right?

 

No, that one's new and I assume due to the oil.

 

Yeah that means I guess that I need to pull it out again. Gosh I hate that job)

 

It's really no fun. Might be worth finishing the break-in procedure and see how it is after you swap out the break in oil.

 

I still yet to hear from ZIP Corvettes on how to proceed. Whether I should continue or should I return it immediately.

 

 

Ok so I returned back my rebuilt diff to the Zip Corvettes, it turned out to be a burnt pinion bearing. I was told it happens when your transmission output shaft is bent, and it can burn the bearing in 100 miles. Not sure if it is a case since it started whining from the beginning, and I did not even put 100 miles on a diff, I suspect the pinion bearing preload was too high, but can not be sure. Anyway I got a refund, and went ahead and bought a complete pre-owned transaxle with gearbox and diff together, just to be sure I do not ruin another rebuilt diff if my old gearbox indeed has a bent shaft. The new one seems to have output shaft play within the tolerances, so I hope it will work this time. Did not have time to put it in yet though.

 

Every drivetrain shop has an excuse for the whine. Burnt bearing is a new one!

At least you got your money back.

 

Put a dial indicator on the trans and measure the output shaft run out. That will solve that theory.

I would have to say that an improper bearing preload would be a strong reason. I'm surprised to hear that you had poor customer service from ZIP.

Before you install it, I would be sure to replace the output shaft seals.

Bill

 

You know when you build as many as we do, you can find all kind of problems in cars that have excessive miles or have been abused. Normally this customer that sent his diff back, it would have not been under warranty for this as the diff or Zip didn't cause the problem. I gave him a refund on it because the of the amount of time it had been here under warranty and the amount of time it would have taken us to get it back out to him. I am not sure what his customer service complaint is about, because I refunded his money. It is still sitting in the same box in the back of the shop right now because we are busy. The diffs leave here with approx. 25 inch pounds of preload on the pinion bearings, it is always possible to mess one up, but we do not build this on an assembly line, it is one at a time so that this issue is eliminated. We also machine the spacers our self so it is checked and everyone is hand set. The factory spec on the output shaft runout is .003 and the spline section is .0025. I have a ton of respect for Bill and have known him for many years, but Bill you can't measure this in the car. The output has to be setup on the centers and spun. The is important on a new diff because there is preload in it and nothing is broken in. When the shaft is bent it applies a massive amount of pressure to one side of the spline in the pinion, during break in it can cause the oil to not lube the bearing correctly and this will cause the rollers to burn up. It is easy to spot when you remove them. A used diff you can get away with because there is plenty of clearance there for the oil. We pre lube them to try and help this during breaking but once it leave here, we do not know how it is being used.
Now that is not gear whine though so don't confuse it. Gear whine is completely different and that can be caused by just a improper setup which is easy to do on a Getrag diff you don't have the right tools for it, or even a bad set of gears. We have all seen a fair share of that where there was a hardening issue with the gears and they would be worn out by 1500 miles. Motive has had that issue solved for awhile though.

 

We actually didn't bring the pinion bearing issue to light being caused by the output shaft. Tremec and Getrag engineers did. We had a customer with an 05 who went through 3 of our differentials and one of another companies. They all had the same issue with pinion bearings being worn and the races actually being burnt. Luckily for us, I had been introduced to a engineer who works for Getrag many years ago by David Farmer. I sent him the unit, he got Tremec involves and that is how they figured our the issue. We had the customer send his transmission and we installed a output shaft. Never had another issue with it. It was insinuated above that it just an excuse, we are not out to make excuses, if we are at fault for something we take care of it plain and simple. However I expect the same from everyone and if your car or your handy skills are the issue that caused a problem then you need to be accountable for that. We will help you as much as possible but it is not up to any company to pay for you to learn or your mistake. When the part leaves here it is out of our hands and sometimes parts get installed incorrectly and it damages it. I've done it and there is nobody on here who hasn't, but you have to be accountable for you own mistakes, when Zip makes one we own it and we have made that known.
Justin

 

This is the most actual education I've ever read on this forum regarding differentials. Thank you Justin. Bravo.

 

Justin was quite helpful in this diff problem resolution especially when I shipped the diff back, and he could examine what was going on. The complaint regarding the customer service was at the beginning when It was several days I could not get any technical help. Closer to the end it significantly improved. Anyway I am glad we reached a consensus and I got my refund, thanks to Justin. I am planning to install my new transaxle next week, I hope that I will be finally able to drive my car after 6 month of it sitting in a garage.