Pinion gear install question

[EarlR]

I have a question for the hard-core rear end guys (not that kind of rear end - I know we all fall into that category:naughty:) - if I'm just replacing the carrier & bearings(all four), and keeping the old R&P shouldn't I be able to use the original size shim between the bearing and pinion? Or could there be enough difference in the bearings that it could change (significantly) the pinion depth? Btw the diff is a stock 10-bolt from an '02 Camaro.

The reason I ask is that I'm to the point in the install where I am checking the depth of the pinion, but the measurements aren't working out. The depth I calculated that the pinion face should be is 2.356", which is the standard depth for a 10-bolt (3.780") less the thickness of the gear (1.424"). The depth I read now, after installing the gear is 2.305", or about .051" too shallow. The original shim between the pinion & bearing was .029", so I used the closest one I could find in the installation kit which was .030". The two things that concern me about my measurements are 1) I'm using one of the cheap (~$110) Proform depth gauges from Summit, and 2) the thickness of the pinion gear was tough to get - since the caliper doesn't easily reach the top face of the gear.

So, what do the experts think? Can you usually rely on the original set-up, or should I go back and re-do all my measurements to see if I screwed up royally? Btw, I also found something on the Richmond Gear website that pretty much said for the 7.5" GM diffs if you don't have a pinion depth gauge you can either go with the original shim size or just use a .035" shim. That also made me wonder how critical the pinion depth really is; if I can still get the backlash right and the gear contact patterns look good should I be ok?

Sorry for the long post, and thanks for any help.

[bigbrian442]

Re: Pinion gear install question

Where are you getting the "standard depth for a 10-bolt (3.780") "? These rears are 7.625. That makes 3.8125. Minus your pinion head 1.424 = 2.3885.

What is wrong with your stock shim? If you didn't damage it you should be able to reuse it with no problems. If it's damaged you can use more than one shim to make one that size up.

I have both the Mark Williams/T&D machine pinion depth tool (http://www.tdmach.com/page18-19.shtml or http://www.markwilliams.com/detail.aspx?ID=1405) and the PMS ( Proform bought the rights to make their tool from PMS) and find they are within .0005 of each other ( that's 1/2 thousandth).

[EarlR]

Re: Pinion gear install question

Where are you getting the "standard depth for a 10-bolt (3.780") "?

Here, here, and here. Since GM elected not to stamp the depth on their factory gear sets this is all I had to go by. That and I haven't gotten around to buying a factory service manual for this car yet.

What is wrong with your stock shim? If you didn't damage it you should be able to reuse it with no problems.

I just figured as long as I had a new set of shims I might as well use them. Since the new one was only .001 thicker I didn't think it would be a problem.

I have both the Mark Williams/T&D machine pinion depth tool (http://www.tdmach.com/page18-19.shtml or http://www.markwilliams.com/detail.aspx?ID=1405) and the PMS ( Proform bought the rights to make their tool from PMS) and find they are within .0005 of each other ( that's 1/2 thousandth).

The T&D tool looks nice, and similar to what I've seen guys use in the past, but they tend to be a little pricey for the average shade-tree mechanic. It's good to know that the proform tool is a quality piece - I'll recheck some of my measurements and see if there is something else going on.

Thanks.

[bigbrian442]

Re: Pinion gear install question

Here, here, and here. Since GM elected not to stamp the depth on their factory gear sets this is all I had to go by. That and I haven't gotten around to buying a factory service manual for this car yet.

What those instructions fail to tell you is the rears went to the 7.625 in the late 80's early 90's. Does the math work to the stock shim with the 7.625 pinion diameter?

Remember you need to use the old pinion nut and crush sleeve to pre load the pinion bearings when you check the depth. Only use the new stuff after you know it's not coming apart again.

[Skinny]

Re: Pinion gear install question

I would have reused the stock shim. If you are just changing the bearings, then it should go back together with all the same shims (pinion and carrier). If you really want a new pinion shim, you can get one at a GM dealership parts counter in the correct size (.29). I wouldn't even worry about pinion depth measurements, just make sure your bearing preload is set right. Spec for new bearings is 15-30 in/lbs. I usually aim for 26-27in/lbs, but definately do not exceed 30in/lbs. Do that then throw the carrier in with the original shims and check your pattern. 99 out of 100 times you'll be right on.

[EarlR]

Re: Pinion gear install question

Thanks guys - I've now had enough people (here and elsewhere) tell me the stock shim thickness should have be fine that I'm just going to go ahead and install the new carrier and see if I can get the right backlash and then look at the contact patterns. I really don't think using a .001 thicker shim is causing the problem, more likely I missed when measuring the pinion thickness. If it turns out my measurements were correct and it really is off .051 I'm sure that will show up when I try to install the carrier/ring gear.

Brian, if I were to use the larger diameter in the calculation it would throw me even further off, since I'm reading that the pinion is too shallow now. And yeah, right now I have the pinion in with the old crush sleeve, pinion nut, and no seal. I've torqued it to 25 in/lbs, which feels a little tight when turning it by hand, but I guess the new bearings will loosen just a little when it's under load.

And am I correct that the backlash on these diffs should be in the .005-.009 range? That seems a little loose to me, but then I'm used to working on my 240SX, which specs .002-.004.

Thanks again for the help guys.

[bigbrian442]

Re: Pinion gear install question

Put some oil on the bearings and they should free up a bit.

[Skinny]

Re: Pinion gear install question

You are correct, spec for backlash is .005-.009"