8.25, 4.56 ratio pinion shim size?

shmoken875 · Aug 12, 2006

A mechanic from work is helping me to swap 3.55 for 4.56 gears in my 8.25, the 3.55 pinion had a 31/1000 shim. We dont have the "special tool" that tells you what shim size to use without having to pull the pinion and bearing apart multiple times. Anybody that may have put 4.56 gears in the 8.25 recall what shim size you used? I'm just trying to get a starting point and from there I think we can close in on the correct shim size.

HaleYes · Aug 12, 2006

The only way to do it correctly is to "pull it apart multiple times".

xjtrailrider · Aug 12, 2006

Take your old pinion bearing and grind out the center some so that you can easily slip the bearing on and off to get the pinion depth set correctly. avoids haveing to press the bearings so many times!

I made my own Pinion depth guage out of some 1/2" tool stock(any straight edge will do) and a sliding caliper. Lay the tool stock across the the 2 flat surfaces that the caps bolt to, then rest the calipers on the edge of the tool stock and measure into the pinion(using the plunge feature of the calipers), and then subtract the 1/2"(or however thick your straight edge is) for the tool stock. All pinions have the depth marked on the gear end.

This is only a starting point, tooth contact pattern is the only true test of your pinion depth being right.

The short answer to your situation is to start out with what was in it and go from there, no two rear ends of the same type will likely be the same set up, so it is trial and error.

Make sure that you have enough preload on the pinion when checking tooth contact.
Make sure you have the carrier bearing preload/gear backlash set properly before checking tooth contact.

shmoken875 · Aug 13, 2006

xjtrailrider said:
Take your old pinion bearing and grind out the center some so that you can easily slip the bearing on and off to get the pinion depth set correctly. avoids haveing to press the bearings so many times!

I made my own Pinion depth guage out of some 1/2" tool stock(any straight edge will do) and a sliding caliper. Lay the tool stock across the the 2 flat surfaces that the caps bolt to, then rest the calipers on the edge of the tool stock and measure into the pinion(using the plunge feature of the calipers), and then subtract the 1/2"(or however thick your straight edge is) for the tool stock. All pinions have the depth marked on the gear end.

This is only a starting point, tooth contact pattern is the only true test of your pinion depth being right.

The short answer to your situation is to start out with what was in it and go from there, no two rear ends of the same type will likely be the same set up, so it is trial and error.

Make sure that you have enough preload on the pinion when checking tooth contact.
Make sure you have the carrier bearing preload/gear backlash set properly before checking tooth contact.

thats a good idea with the old bearing, hes was trying to get a hold of another mechanic he knew to borrow a pinion depth gauge, but it looks like we'll either have to go homemade or use the press alot. He was looking for a ballpark idea of where to start the shimming. He rebuilds classics cars in his spare time (camaro, 65 stang, continental, stingray, lemans, chevelle all waiting to be sold from his driveway) and said that hes used to just swaping same ratio gear sets where he keeps the shim size, not such a jump like mine (3.55-4.56)

Frank Z · Aug 13, 2006

Yep, make your own set-up bearing. I bought a bearing from NAPA and used a 1/2" diameter 80grit sanding drum on my Dremel. Takes less than 5 minutes.

FWIW, I swapped out my 4.10's in my 8.25 for a set 4.56's today. I ended up with a .030" shim under the bearing. Use the old crush sleeve during your set-up too. I would suggest starting there and seeing what kind of pattern you get. I would also strongly recommend using two adjuster tools so you don't have to keep going from one side of the axle to the other while establshing the proper backlash.

OlyWaXJ · Aug 13, 2006

Frank Z said:
Yep, make your own set-up bearing. I bought a bearing from NAPA and used a 1/2" diameter 80grit sanding drum on my Dremel. Takes less than 5 minutes.

What I used was a brake hone on a hand drill.Everytime I setup a diffrent type of diff I build a set of setup bearings.

OlyWa

Frank Z · Aug 13, 2006

Great Idea!

8.25, 4.56 ratio pinion shim size?

shmoken875

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HaleYes

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xjtrailrider

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shmoken875

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Frank Z

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OlyWaXJ

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Frank Z

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