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Old 11-21-2015, 11:05 AM   #1
Cabinetman
 
Drives: 2015 ZL1
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My differential woes

I really want to love my '15 Z, but I'm about fed up with Chevrolet regarding my noisy rear diff.

Within the first week of ownership I noticed some gear whine on coast between 40 and 50mph. I took the car in to the dealer for repair. The service manager heard the whine and agreed to replace the diff. However, the next day I'm told that GM denied my repair and I needed to come get my car.

After the repair denial I contacted one of the GM reps on this board and she set up an appointment with another dealer. I took the car in and went with a ride with the service manager who heard the noise and agreed to fix it. This time GM allowed my rearend to be rebuilt with a new gear set, but would not supply a complete diff. The parts came in this week and the new gears were installed.

The new gears that were installed are more annoying than the gears that came out. I still have some whine on coast, just in a different speed range, and now I have a whine under power between between 62 and 72mph. The service manager agreed the noise is there, but he said they can't do anything until I put 500 miles on the car. He acted like this was a requirement from GM.

It is my understanding that once gears are whining it is not going to go away. I don't understand why I have to drive 500 miles, which may take 2 months, before GM will step up and fix my car. I just want my 5 month old car fixed so I can't stop jacking with this rearend noise and enjoy my Z.
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Old 11-21-2015, 12:50 PM   #2
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I think 99% make some whinning. I just had my whole different replaced with a new one and it wines on deceleration between 50-60. The one they replaced whined around same speeds but the clutches were bad. I've had alot of gear changes in ford's and I was told 500 mile breaking and sometimes the wine did get less audible.
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Old 11-21-2015, 01:33 PM   #3
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Most rears with a manual shift have a little whine on Decel.
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Old 11-21-2015, 01:34 PM   #4
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Originally Posted by cbarile View Post
I think 99% make some whinning. I just had my whole different replaced with a new one and it wines on deceleration between 50-60. The one they replaced whined around same speeds but the clutches were bad. I've had alot of gear changes in ford's and I was told 500 mile breaking and sometimes the wine did get less audible.
I appreciate the input. Most of my gear experience is with Jeeps and if they whined after install they never seemed to get better. Maybe things will improve after some mileage, but I'm not getting my hopes up.

When they replaced the first set of gears there was notation on the paperwork that the tech found excessive metal shavings and uneven wear, so the noise I was hearing didn't appear to be normal. Sadly those gears were quieter than the new set.
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Old 11-21-2015, 01:40 PM   #5
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I have had my 15 ZL1 for just over a month and a half now. I just passed the 1500 mile break in finally. My rear diff also had a whine on decel, not that bad though. Its hard to tell how bad it is, cause I have nothing to compare it to. So I changed my diff fluid last week, and the noise is hardly even noticeable now. Changing out the fluid is very easy to do. Mine took like just over three quarts.
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Old 11-21-2015, 04:16 PM   #6
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Quote:
Originally Posted by sengli View Post
I have had my 15 ZL1 for just over a month and a half now. I just passed the 1500 mile break in finally. My rear diff also had a whine on decel, not that bad though. Its hard to tell how bad it is, cause I have nothing to compare it to. So I changed my diff fluid last week, and the noise is hardly even noticeable now. Changing out the fluid is very easy to do. Mine took like just over three quarts.
What brand fluid did you use? I was considering Amsoil, I have 600 more miles to go on my break-in.
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Old 11-21-2015, 04:35 PM   #7
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I would never trust a dealer mechanic to install rear gears. It takes experience, skill and time to get it right. Mine had the gear whine when new, but almost completely disappeared when I changed the fluid. I used the correct GM fluid and added extra limited slip additive to help.
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Old 11-21-2015, 04:38 PM   #8
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Yeah, mine is noisy when cruising at slight accel and slight decel when at the 62 to 72 speed range. Mine started by 500 miles and just got worse with time. It really takes away from enjoying the car. I got jacked around by the dealer and gave up on them ever fixing it. Some day I might do something myself or just get a different car.
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Old 11-21-2015, 06:19 PM   #9
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Originally Posted by DrkPhx View Post
I would never trust a dealer mechanic to install rear gears. It takes experience, skill and time to get it right. Mine had the gear whine when new, but almost completely disappeared when I changed the fluid. I used the correct GM fluid and added extra limited slip additive to help.
I agree. This was why I pushed for new complete rear diff, but GM balked. Now things are worse than before and I have to live with it until I can get 500 more miles on the car.

I'm surprised how many Z owners appear to be fine with a little gear whine. I have owned a few other high hp cars including 2 GT-Rs, '11 GT500, 997 C2S, IS-F and an E90 M3 and none of those had gear whine. I know the Z rearend is very strong, but that doesn't mean that gear whine should be a given.
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Old 11-21-2015, 07:01 PM   #10
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I can hear a faint whine also. Doesn't bother me though. My 2000 SS with a Moser 12bolt whined incredibly loud. It held up to years of abuse from 5k launches at the track on a nitrous, so I couldn't complain. On the other boards some people complained about that on the 12 bolts. They went and had them adjusted and then they would break the gears latter. I read that Moser set their backlash a little farther in to help with strength of the gears. I just figured this is why the ZL1 rear had a little whine.
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Old 11-21-2015, 10:11 PM   #11
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Quote:
Originally Posted by Cabinetman View Post
I agree. This was why I pushed for new complete rear diff, but GM balked. Now things are worse than before and I have to live with it until I can get 500 more miles on the car.

I'm surprised how many Z owners appear to be fine with a little gear whine. I have owned a few other high hp cars including 2 GT-Rs, '11 GT500, 997 C2S, IS-F and an E90 M3 and none of those had gear whine. I know the Z rearend is very strong, but that doesn't mean that gear whine should be a given.
It's not that we are fine with it, it's just that we have given up on GM stepping up on what is a known backlash issue. 2 years ago GM monitored ths site and in a few cases replaced the pig and some of those owners had great success. The chances of finding a mechanic that could or would take the time to set up the backlash at a dealer is nil. Now that the 5th gen run is done I don't think you will see GM as willing to start a mass replacement of these bad pigs.

So Get use to the sound as the pig won't break, but is annoying. I am lucky to had 3500 miles of peace and quiet before mine started, and once it starts it will just get louder as the mesh widens. It is sad my 5 year old f150 just started whining after 56000 miles and my my Z just hit hit 10,000. Maybe we should start a signature page and forward it to Mary's desk...
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Old 11-21-2015, 10:43 PM   #12
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Originally Posted by ZMEnow View Post
It's not that we are fine with it, it's just that we have given up on GM stepping up on what is a known backlash issue. 2 years ago GM monitored ths site and in a few cases replaced the pig and some of those owners had great success. The chances of finding a mechanic that could or would take the time to set up the backlash at a dealer is nil. Now that the 5th gen run is done I don't think you will see GM as willing to start a mass replacement of these bad pigs.

So Get use to the sound as the pig won't break, but is annoying. I am lucky to had 3500 miles of peace and quiet before mine started, and once it starts it will just get louder as the mesh widens. It is sad my 5 year old f150 just started whining after 56000 miles and my my Z just hit hit 10,000. Maybe we should start a signature page and forward it to Mary's desk...
I intend to keep fighting. Ultimately I might throw in the towel and sell the car, but not until I have exhausted every reasonable course of action to get it fixed.
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Old 12-06-2015, 10:54 AM   #13
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Any updates?
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Old 12-06-2015, 04:10 PM   #14
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Any updates?
Not yet. I contacted the GM rep on this board and just heard back last week. I was asked for some more information, which I provided, and now I'm waiting to hear back. I probably could have gotten the ball rolling faster had I just called, but I like having a paper trail.

I have managed to put about 100 miles on the new gears and the high pitch whine between 62 and 72 has not improved. There is also still some lower speed whine on coast like I had before. The whine on coast is not as bad as before, however I would trade the new high speed whine for my old low speed whine in a second.
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Old 12-06-2015, 06:48 PM   #15
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I have a slight whine in mine also between 48-52 or so. I am just hesitant to take my car to a dealer...seems my local dealers usually do more harm than good to my cars. Mine is a 14 with 3500 miles.
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Old 12-31-2015, 02:40 PM   #16
Cabinetman
 
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Update

I finally got the 500 mile break-in completed on my replacement gears that whined from day one. I'm still not sure why I had to put 500 miles on the car when the service manager and I both could hear the gears whining right after the install, but such is life. Today the car went in again and I got a call that the dealership is going to replace the entire rear diff with a new factory unit. This is what I wanted from the beginning so I am happy with the outcome.

The interesting part of this latest development stems from the conversation I had with the service manager today. He told me that it is imperative that I follow the full 1500 mile new car break-in procedure after I get the rear diff. He told me that the area service rep told him that the gears are not fully hardened from the factory and have to have to be slowly broken-in to avoid gear whine. I guess the heat cycles finish the hardening of the gears. I did follow the original break-in procedure very closely and I'm not excited about going through another 1500 miles of easy driving. However, I will do it if I can end up with quiet gears.

I should have the car back early next week. I will update this thread once everything is put back together.
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Old 12-31-2015, 04:38 PM   #17
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I have 100 miles to go then fluid changes and game on!!! :-)
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