How Tight should a rebuilt rear diff be ?
Thread Starter
Le Mans Master
Joined: Jan 2006
Posts: 9,054
Likes: 665
From: Norcal
How Tight should a rebuilt rear diff be ?
Had a 3.42 rear diff rebuilt with 3.90 gears and did the r/r over the weekend. Dont know if it matters but diff is assembly lubed but dry, and has been sitting my my cold garage about 3 months. Before installing the unit I took my of my axels and put it in while the diff sat on the ground to see how easy it turned and it DIDNT. Unit was very tight. It moves but not easy. Once in the care I grabbed a rotor to try and rotate it and again very tight. Is this what I should expect or should I take it out and send it back for inspection?
Pro
Joined: Apr 2008
Posts: 628
Likes: 4
From: Columbia SC
So from your post I gather that the diff is now installed and the car ready to run. If so, at this point you may as well put the proper lube/amount in and take the car for a SHORT drive. Go easy, listen for any bad noises, then come home and put the back of the car up. Does the diff then feel hot? How much resistance does the axle now have to turning? I'd guess the axle/wheel will turn with less effort after the short break-in/lube-up.
Did you speak with the re-builder about your concerns?
Did you speak with the re-builder about your concerns?
Thread Starter
Le Mans Master
Joined: Jan 2006
Posts: 9,054
Likes: 665
From: Norcal
I wish it were that easy. Car has a blown motor and I was putting in the new diff so I could get it on a trailer and over to the shop doing the motor swap. Builder told me it was tight but he "felt" it was perfect. I just wanted a general feedback as to how tight a rebuilt diff actually is. I could be overconcerned but I am afraid not. 
Former Vendor
Joined: Aug 2009
Posts: 1,184
Likes: 1
From: delware county pa
tigh as in gear setup ex backlash,heel/toe. something is wrong , you should be able to turn your diff by hand with the trans in n. .sounds like the backlash is way to tight. just to let you know it takes some special tools to properly setup a c5 diff most of which are kent moore. best wish's
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Either your side cover end play is too tight, the pinion to ring engagement is too tight or the pinion bearing is too tight.
Either case, (IMHO) its going to cause an issue and either damage a bearing OR damage the ring and pinion.
Can you feel any back lash between the ring and opinion?? That would tell you if the back lash is good.
Put a heat lamp on the rear and get it warm and eliminate the cold theory.
Either case, (IMHO) its going to cause an issue and either damage a bearing OR damage the ring and pinion.
Can you feel any back lash between the ring and opinion?? That would tell you if the back lash is good.
Put a heat lamp on the rear and get it warm and eliminate the cold theory.
Thread Starter
Le Mans Master
Joined: Jan 2006
Posts: 9,054
Likes: 665
From: Norcal
I had my cousin who is a GM tech rebuild it for me. He has done a couple others over the years for me but I think he just went to tight. I am going to have him come over in the next few days and take a look. I hate bothering him with it, but after some thought and your guys advice, I hate the R/R more. HAHA Thanks I will let you know what I come up with.
Burning Brakes
Joined: Sep 2005
Posts: 987
Likes: 1
From: Braidwood Il.
A diff should have between .006-.012 backlash and the preload on the pinion bearing should be set at 25 INCH pounds, thats INCH pounds.
If you set it up like that you should have no problems
If you set it up like that you should have no problems
Pro
Joined: Feb 2009
Posts: 651
Likes: 33
From: North Port Florida
tigh as in gear setup ex backlash,heel/toe. something is wrong , you should be able to turn your diff by hand with the trans in n. .sounds like the backlash is way to tight. just to let you know it takes some special tools to properly setup a c5 diff most of which are kent moore. best wish's
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Melting Slicks
Joined: Feb 2003
Posts: 2,966
Likes: 22
From: Frederick Maryland
St. Jude Donor '08-'09-'10-'11
Teddy, all the diffs I set up do turn by hand (at room temp). Make sure the diff is at room temp and try to spin it. If it doesn't, I would say it's little on the tight side.
Thread Starter
Le Mans Master
Joined: Jan 2006
Posts: 9,054
Likes: 665
From: Norcal
Thanks guys for all the info. Like I orginally stated he has done a couple others for me with no issues. I aware of the special tooling involved and know he has them at the dealer where he rebuilds them for me. I will get the thing warmed up and see if I can turn it by hand. Honestly though, I think he simply has it to tight. back to r/r
back to r/rThis is a Corvette diff and not your run of the mill GM diff. The .006-.012 backlash is correct but the pinion preload is incorrect. The pinion carrier is setup with the Kent Moore J42168 to set the initial shim. Then the new gear is pressed into the carrier and the spaner nut tighted to 370 ft lbs. YES! that's 370 ft lbs!
Teddy, all the diffs I set up do turn by hand (at room temp). Make sure the diff is at room temp and try to spin it. If it doesn't, I would say it's little on the tight side.
Teddy, all the diffs I set up do turn by hand (at room temp). Make sure the diff is at room temp and try to spin it. If it doesn't, I would say it's little on the tight side.
Burning Brakes
Joined: Sep 2005
Posts: 987
Likes: 1
From: Braidwood Il.
This is a Corvette diff and not your run of the mill GM diff. The .006-.012 backlash is correct but the pinion preload is incorrect. The pinion carrier is setup with the Kent Moore J42168 to set the initial shim. Then the new gear is pressed into the carrier and the spaner nut tighted to 370 ft lbs. YES! that's 370 ft lbs!
Teddy, all the diffs I set up do turn by hand (at room temp). Make sure the diff is at room temp and try to spin it. If it doesn't, I would say it's little on the tight side.
Teddy, all the diffs I set up do turn by hand (at room temp). Make sure the diff is at room temp and try to spin it. If it doesn't, I would say it's little on the tight side.
Melting Slicks
Joined: Feb 2003
Posts: 2,966
Likes: 22
From: Frederick Maryland
St. Jude Donor '08-'09-'10-'11
Burning Brakes
Joined: Jun 2005
Posts: 782
Likes: 45
From: Toronto Ontario
I'm not sure its the pinion preload thats too high here. if buddy rebuilt it, he may not have even removed the pinion bearings. Setting their preload requires changing the spacer until the proper bearing drag is achieved...not even sure different thickness pinion spacers are available. My guess is he f'd up the side bearing preload. Real easy to do that. I'd loosen the RH cover bolts and see if it frees up!
Melting Slicks
Joined: Feb 2003
Posts: 2,966
Likes: 22
From: Frederick Maryland
St. Jude Donor '08-'09-'10-'11
I'm not sure its the pinion preload thats too high here. if buddy rebuilt it, he may not have even removed the pinion bearings. Setting their preload requires changing the spacer until the proper bearing drag is achieved...not even sure different thickness pinion spacers are available. My guess is he f'd up the side bearing preload. Real easy to do that. I'd loosen the RH cover bolts and see if it frees up!
Burning Brakes
Joined: Jun 2005
Posts: 782
Likes: 45
From: Toronto Ontario
Haha...You're the last person I want to argue with about differentials, Rick. What I meant was this: If the tightness was coming from tight BEARINGS(too much preload), then its PROBABLY the side bearings that got screwed up. As you know, the RH side shims need to be measured with a J tool to come up with the right preload. There are no calculations or shim measurements for setting pinion bearing preload. Its pretty much factory set. If the old pinion bearings were left in it, the preload would not have changed. The tightness could also be coming from the GEARS, in which case the pinion housing shims could be wrong, or the side shims on the left could be wrong.
Melting Slicks
Joined: Feb 2003
Posts: 2,966
Likes: 22
From: Frederick Maryland
St. Jude Donor '08-'09-'10-'11
Haha...You're the last person I want to argue with about differentials, Rick. What I meant was this: If the tightness was coming from tight BEARINGS(too much preload), then its PROBABLY the side bearings that got screwed up. As you know, the RH side shims need to be measured with a J tool to come up with the right preload. There are no calculations or shim measurements for setting pinion bearing preload. Its pretty much factory set. If the old pinion bearings were left in it, the preload would not have changed. The tightness could also be coming from the GEARS, in which case the pinion housing shims could be wrong, or the side shims on the left could be wrong.
