Hello, Michael

I've got a Borg-Warner Australian 9 bolt in my 87 Trans Am. It has a 2.77 ratio now, but I bought a 3.7 ring and pinion set. I don't know what the pinion depth is. Does anyone know what is should be, or where I can find out what it should be?

big gear head

I never set the pinion depth with a gauge. The only accurate way to set the pinion depth is by reading the contact pattern. Start with the shim that is on the pinion now and make adjustments from there. I have found that pinion depth gauges are not accurate enough and always require additional adjustments.

AlkyIROC

If it's marked, the pinion depth is on the end of the pinion and is specific to that pinion. The pinion depth is the distance from the center of the axle to the rear surface of the pinion. Without a depth gauge, you'll never know the proper depth.

Because the pinion depth is adjusted by changing the shim behind the pinion bearing, the bearing needs to be removed every time you change the shim and since it's pressed on, it's not easily removed without destroying it.

A proper driveline shop will have setup bearings that have been machined to easily slide on and off the pinion making shim swaps easy.

The best you can hope for is to install a shim the same size as what was originally in the diff.

That's why I like a 9". It's quick and easy to swap the shims without removing bearings.

Hello, Michael

Does anyone sell these set up bearings?

jwscab

you can make set up bearings with your old ones. If you have a drill press, it's easy. set up a rubber mandrel with a sanding roll on it, and stick it in the drill press. stick the bearing on some thing so that the roll is inside, and sand out the race so that it's a nice snug fit on the pinion, but doesn't need to be pressed on. might take a few minutes as the bearing is very hard, and you might need to change out the sanding roll.

then clean it thoroughly, liightly lube it, and use that as your 'setup bearing'. start with the pinion shim that was on the old gears and adjust from there.

then when you are all done, stick the bearing in a box and label it. keep it or sell it off to someone that needs one!

AlkyIROC

It's possible but I doubt you'll get the old inner pinion bearing off without damaging it. You also don't want a used bearing to use as a setup bearing then install a new bearing on the pinion. What's the chances of the pinion depth being the same between a new and used bearing? I'd want a new bearing as a setup bearing.

big gear head

I have never recommended using these set up bearings because I have measured as much as .004 difference between the thickness of 2 new bearings with the same number on them. I always recommend using the same bearing to do the trial assemblies that will be used in the final assembly. I will admit that I have damaged the bearing on a 9 bolt, but of the hundreds of rear ends that I have built over the last 27 years I have damaged probably 5 or less pinion bearings by pressing them off. Just use the right tools.

gurkgurkgurk

to be as accurate as possible just use the new pinion bearings when trying to get within spec, sure youll have to press them on and off, but if your carefull you wont damage them. because if you use the old ones like mentioned before, its not likely youll get the same measurement later when u put the new ones on