ZL1 Differential Rebuild

[Torkenstein]

I have been looking into getting my differential rebuilt or getting the parts to do it myself but there seems to be very little out there on the web for our diffs. I have a 13 and ive seen where a few guys claim that 13s had some problems with the carrier. Mine likes to make a whailing sound when turning until the diff fluid gets hot. Also it has a fair bit of gear noise on accel and decel and appears to have a little to much endplay judging on how much slack the gears have. I know the GM fix is running the car around with multiple flushes of fluid and im going to flush it again here soon to see if it helps.

More or less does anyone know where to get parts or a shop that is recommended for the diff?

[ABM2SS]

When my Ring Gear broke, a mechanic friend of mine tried to find a rebuild kit. No luck, and like you say, not much information out there. He found me a good used one, and I installed it.

You could probably get a good low mileage one from Hawks Motorsports.

https://www.hawksmotorsports.com/

[1MtnGoat]

If I remember right there is good info in the factory service manual. I'll look when I go out to the shop.

[ZMEnow]

Originally Posted by Torkenstein

I have been looking into getting my differential rebuilt or getting the parts to do it myself but there seems to be very little out there on the web for our diffs. I have a 13 and ive seen where a few guys claim that 13s had some problems with the carrier. Mine likes to make a whailing sound when turning until the diff fluid gets hot. Also it has a fair bit of gear noise on accel and decel and appears to have a little to much endplay judging on how much slack the gears have. I know the GM fix is running the car around with multiple flushes of fluid and im going to flush it again here soon to see if it helps.

More or less does anyone know where to get parts or a shop that is recommended for the diff?

You are describing multiple problems, the 1st is a known TSB, which changing the fluid which must include the friction modifier ( don’t buy a fluid without and add your own for this problem). After the fluid change multiple figure 8’s at slow speed repeatedly. I personally like to do separate right and left circles before starting the 8’s. You are getting the friction into the clutch packs which are binding which is what your are hearing and feeling. The friction modifier gets old over time or miles, but some carriers were binding new from the factory.

Your second problem is gear lash, if it’s between 65 and 75 I would leave it. If it’s lower like 45 to 60 and it bothers you you are going to have to reset the lash. Depending on the amount of miles you may want to just replace the ring and pinion for one, it’s the only way to can get a crush sleeve and pinion seal as both are discontinued.

[Torkenstein]

Originally Posted by ZMEnow

You are describing multiple problems, the 1st is a known TSB, which changing the fluid which must include the friction modifier ( don’t buy a fluid without and add your own for this problem). After the fluid change multiple figure 8’s at slow speed repeatedly. I personally like to do separate right and left circles before starting the 8’s. You are getting the friction into the clutch packs which are binding which is what your are hearing and feeling. The friction modifier gets old over time or miles, but some carriers were binding new from the factory.

Your second problem is gear lash, if it’s between 65 and 75 I would leave it. If it’s lower like 45 to 60 and it bothers you you are going to have to reset the lash. Depending on the amount of miles you may want to just replace the ring and pinion for one, it’s the only way to can get a crush sleeve and pinion seal as both are discontinued.

I'm aware of the TSB and that the gear whine is a separate issue. Since it appears that no one rebuilds these diffs or can get parts for them then I'm just gonna have to run it till breakage then put in a 9". After I made the original post I dug deeper looking for parts and you can't even get most of the parts Direct from GM being that they are discontinued.

I've done a fluid change recently with Lucas 75w90, drove the car in a lot performing circles and 8s. The whining while turning did eventually stop but only after the fluid got hot. I'm going to try again with the GM fluid everyone recommends and give it one last try.

[gtstorey]

I’m not sure that the Lucas has friction modifier. It says can be used in Limited Slip, but I had to add in the modifier. At least the Lucas that I used.

[Torkenstein]

It claims to have it in it and I also added a bottle when I first put it in. I recently had the diff out to replace bushings. When it was out a very small amount of fluid spilled out and when it went back it I replaced what was lost with more friction modifier. Still groans when turning.

[Little Walter]

Can you still purchase a new Gen 5 ZL1 rear end from GM Performance?

[ZMEnow]

Originally Posted by Little Walter

Can you still purchase a new Gen 5 ZL1 rear end from GM Performance?

No longer see it in the catalog. Used to be in the Gen 5 section for SS upgrades, there is no Gen 5 section.

[Whisper1]

Originally Posted by Torkenstein

I'm aware of the TSB and that the gear whine is a separate issue. Since it appears that no one rebuilds these diffs or can get parts for them then I'm just gonna have to run it till breakage then put in a 9". After I made the original post I dug deeper looking for parts and you can't even get most of the parts Direct from GM being that they are discontinued.

I've done a fluid change recently with Lucas 75w90, drove the car in a lot performing circles and 8s. The whining while turning did eventually stop but only after the fluid got hot. I'm going to try again with the GM fluid everyone recommends and give it one last try.

Sorry for your issues. I bought my 2012 ZL1 for the transmission and rear end. And here we are. So on the 9" conversion are you aware of a direct bolt in that mates to a 5th gen ZL1? Looks like GForce makes a 9" but I am unclear if it would work with the stock half shafts. If anyone can chime in I would like to learn in case mine goes south. Good luck in your search. This board has some great knowledge.

[PoleCat2SSRS2010]

This is a sad time for the ZL1 since the major components like the rear differential are no longer available from GM. The original manufacturer was American Axle Manfacturing. A while back the entire plant burned down and then they just let all the employees go and closed the doors forever. I was bummed to learn about the closing of AAM since they made such great products. As a result of any possibility of my 2015 not holding up for any reason I had to start considering the availability of options.

If any of the service parts are still available a rebuild is worth it but as they are most likely a finite supply, they will disappear. Enter the options for differential conversions.

The only drawback with a conversion is the loss and disabling of the OEM ZL1 differential cooling system. Not my personal preference but if I had no choice then the only option left is a conversion.

I would recommend a call to G Force for all the unknowns and to DSS. Unless there is something I am missing, all of the 9 inch conversions I have seen require custom half shafts or at least the stub ends that go into the differential. This is a due to the original 9 inch width specifications and the difference between the carrier widths and the number of spines and bearing sizes because the 9 inch has large bearing sizes.
Then there is also the choice of case and pinion support bearing options all will require a revised driveshaft.

The other option is the Strange S60 Dana 60. Still, this too has physical dimensions that are different from the OEM ZL1 differential and will require those same phone calls about the half shafts and drive shafts. Some may even provide a one stop parts support.

Better to be properly informed from the aftermarket providers like G Force and DSS than to jump in and invest into a situation without being properly prepared.

I leave you with this; the final part of the puzzle is to decide on which center carrier to put into service when shopping for a conversion. My personal experience with a Detroit locker was sketchy on wet roads and not for the faint of heart. I had way too many spinout experiences, and I am still alive to say that it is no fun staring at oncoming traffic that was once traveling in the same direction a moment ago. If I had to make a recommendation it would be to set up with a posi-clutch style. It will be a more predictable and safer application. I have no experience with the Torson style and have yet to talk with anyone about their experience with it.

[Torkenstein]

Originally Posted by PoleCat2SSRS2010

This is a sad time for the ZL1 since the major components like the rear differential are no longer available from GM. The original manufacturer was American Axle Manfacturing. A while back the entire plant burned down and then they just let all the employees go and closed the doors forever. I was bummed to learn about the closing of AAM since they made such great products. As a result of any possibility of my 2015 not holding up for any reason I had to start considering the availability of options.

If any of the service parts are still available a rebuild is worth it but as they are most likely a finite supply, they will disappear. Enter the options for differential conversions.

The only drawback with a conversion is the loss and disabling of the OEM ZL1 differential cooling system. Not my personal preference but if I had no choice then the only option left is a conversion.

I would recommend a call to G Force for all the unknowns and to DSS. Unless there is something I am missing, all of the 9 inch conversions I have seen require custom half shafts or at least the stub ends that go into the differential. This is a due to the original 9 inch width specifications and the difference between the carrier widths and the number of spines and bearing sizes because the 9 inch has large bearing sizes.
Then there is also the choice of case and pinion support bearing options all will require a revised driveshaft.

The other option is the Strange S60 Dana 60. Still, this too has physical dimensions that are different from the OEM ZL1 differential and will require those same phone calls about the half shafts and drive shafts. Some may even provide a one stop parts support.

Better to be properly informed from the aftermarket providers like G Force and DSS than to jump in and invest into a situation without being properly prepared.

I leave you with this; the final part of the puzzle is to decide on which center carrier to put into service when shopping for a conversion. My personal experience with a Detroit locker was sketchy on wet roads and not for the faint of heart. I had way too many spinout experiences, and I am still alive to say that it is no fun staring at oncoming traffic that was once traveling in the same direction a moment ago. If I had to make a recommendation it would be to set up with a posi-clutch style. It will be a more predictable and safer application. I have no experience with the Torson style and have yet to talk with anyone about their experience with it.

Thank you for the knowledge on AAM closing up shop. Explains why there are no parts out there for our diffs. Currently mine is getting a little quieter as far as the turning noises when still cold. I did a couple of track days a week ago and the thrashing has possibly cleaned some of the gear paint out of the clutches. I'm hoping that the flush I'm doing tomorrow with the GM brand fluid will quiet that problem up for good. As far as the whine on decel I can live with.

[Whisper1]

Originally Posted by Torkenstein

Thank you for the knowledge on AAM closing up shop. Explains why there are no parts out there for our diffs. Currently mine is getting a little quieter as far as the turning noises when still cold. I did a couple of track days a week ago and the thrashing has possibly cleaned some of the gear paint out of the clutches. I'm hoping that the flush I'm doing tomorrow with the GM brand fluid will quiet that problem up for good. As far as the whine on decel I can live with.

Just wanted to throw out a little bit of info. I stopped by Hawks Motorsports in Easley, SC yesterday and spoke with the Manager, Tyler Hawkins. His Dad is Bruce, who seems to be easing out of the business and Tyler is running the day to day.
Anyway, talked ZL1 parts, and Zl1 diffs. Most are on the website but he said he normally keeps 8-12 5th Gen Zl1's at all times. When they come up at a salvage auction he's getting the lions share - they have a stream coming in and will continue to do so due to the parts situation.
On the Diff, he sells a lot of them. On rebuilding one he said it will be downhill business. They build rear ends in their shop and actually do some neat custom stuff for F bodies. On the ZL1 rear end he said they have rebuilt 1 and will not rebuild another. Said a rebuilt rear will run 2 to 3X times the cost of a used one and that they are a PITA to rebuild. Didn't get into all the aftermarket replacements - obviously you get new parts and it's very viable but just expensive.
Anyway, just wanted to mention that they are committed to supplying used parts for the ZL1 that are out of stock, as used F body parts, Vette parts, and 5th gen parts is their core business.
PS Tyler owns a street/autocross F body called Brutality. It was my car before I sold it to him in 2016 with 44K miles in immaculate condition so it was cool to see that he has taken it to the next level and also preserved the car.

[Triple5even813]

Reading this thread makes me nervous about launching my car at the track now.