Differential pattern question (pic)
Thread Starter
Pro
Joined: Jun 2008
Posts: 680
Likes: 3
From: charlotte N.C
Differential pattern question (pic)
I am doing a frame off restoration on a 68 vette. I have finish the frame and the front suspension so I moved to the rear end. I have been working on this differential for probably a month now and now that the posi is tuned I trying to get my RG pattern right. These are the original pinon and ring having 3.70 ratio. Here are a few pictures with three different pinion shims. Which one is acceptable or what do I have to do to get it acceptable. All of these were done with load apply while checking the pattern. Sorry for the bad pictures, my camera isn't the best at close ups. Thanks in advance for the help. 
029 pinion shim and around 007 backlash
030 pinion shim and around 007 backlash
033 pinion shim and around 006 backlash.
029 pinion shim and around 007 backlash
030 pinion shim and around 007 backlash
033 pinion shim and around 006 backlash.
Safety Car
Joined: Aug 2001
Posts: 4,883
Likes: 11
From: North Easton Mass
You might want to send a PM to Mike (Tracdogg2) and ask him to look at the thread. He is one of the ace differential rebuilders that is still on this forum. The other guy is over on DC.
Rick B.
Rick B.
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 38
From: Fremont CA
Looks like the 2nd one with the 0.030" shim but, I think you need to increase your backlash to 0.008-0.009". I have had to go out to 0.012" on some used gear sets to get a decent pattern (because of the wear pattern they had when running.) If you set the backlash too tight, you'll get a de-accelerration whine (coast side of gear.)
Because a Corvette differential is pretty close to the driver's compartment and only fibreglass seperates the 2, coast side noises are common problems in Vettes. I know you want the backlash tight, as it is commonly thought that the gear engagement is better for strength but, a little looser setting will not drastically effect the strength of the gear set.
There is a good reason why I have a honed/slide-on pinion bearing around my workshop to do differential set-ups with, sometimes it takes a few pinion shim changes to get the correct pattern on the gearset,
Because a Corvette differential is pretty close to the driver's compartment and only fibreglass seperates the 2, coast side noises are common problems in Vettes. I know you want the backlash tight, as it is commonly thought that the gear engagement is better for strength but, a little looser setting will not drastically effect the strength of the gear set.
There is a good reason why I have a honed/slide-on pinion bearing around my workshop to do differential set-ups with, sometimes it takes a few pinion shim changes to get the correct pattern on the gearset,
