www.jdrace.com

I have a 8.5 1986 grand national rear I'm going to be upgrading.

What are the best brand of gears? (3.73 or maybe 3.90)
Are gm gears worth the cost? I don't mean strength wise, but quietest, most consistent gear set to gear set.

Well - If noise is not a factor any brand will do. Not to say you can not get the gears quiet...You just really have to work hard and know what your doing to get them dead on... GM gears and a larger sweet spot (domed area for the ear to ride on) AAM gears are pretty good and pretty expensive too.

3.90 gears will be harder to track down. 3.73 every company makes for sure.

Every gears set has to be set to the housing it is being installed in. Sooo not every gear will be abler to be popped into to just any housing with the same shim. Sometimes the shim works sometimes you will need to change it. .038 shim is usually a good starting point if you do not have one to start with for the 8.5 rear

I bought (what is supposed to be) aam gears. They came from rock auto, and were not cheap. My concerns are: there is no paperwork; there is yellow markings on them already. They don't appear to be used or previously installed, so is this normal?
http://i1145.photobucket.com/albums/o50 ... e3f835.jpg
http://i1145.photobucket.com/albums/o50 ... f03848.jpg

What paperwork would you be looking for? You have to set-up the gears. These are what normally go to the factory so you will not get paperwork. These are also 2 step gears the tolerances are much tighter than standard cut 5 step cut gears.

Hope you did not get in over your head on this. NO paperwork will tell you how to set up gears. You either know how or you do not.

Do you have Dial indicator (thousands of inch .001) Magnetic base- Setup bearing would be a good idea. This is a 8.5 / 8.6 gear set so a good start will be .038 shim. Then hunt for the pattern. NOW if you look at the gear set- they have run the lapping pattern for you. THAT is what you will try to get again. SO take another real good picture of both the drive and cost side. Jim

Not over my head (yet!). I've swapped gears in ford 8.8's before. I have all the tools except a press, including a new honed out pinion bearing. Been reading a lot on this, including posts on other forums by you. http://www.chevelles.com/forums/showthread.php?t=152807

I just expected a paper with backlash specs and maybe ideal gear pattern pics.

Here is one for you- 2 step gears are usually .002-.004 backlash... This is something I will check into further
Pattern is on the gear you have in the picture. It is basic diagonal swipe... and a finger cross.

I know the backlash is tight on the aam gears. I'll post pics this weekend when I get it together.
Thanks for all your help.

Finding a good 8.5 core, all the parts to build it, adds up quick. I regret not getting one of your bolt in 8.8 ford rears. I will definatly steer people your way for them.

After about a dozen tries, I have a pattern.
Stock shim was .038
I tried shims ranging from .028 to .044 and the pattern seemed off the edge. I set the backlash between .003 and .009 each try.
I reduced it to .012, got it a lot better, so using the thinnest shim of .010 got me this- http://i1145.photobucket.com/albums/o50 ... cc967a.jpg
http://i1145.photobucket.com/albums/o50 ... af7065.jpg

This is with .003 backlash (best I could do with my limited shims)


Here is the close ups of the pattern that was on them out of the box.
http://i1145.photobucket.com/albums/o50 ... 01877f.jpg
http://i1145.photobucket.com/albums/o50 ... dcd60b.jpg

I also wondered what is the .14 that is scribed on the pinion and ring gear for?

hum... Have a pic of that? Certainly not the backlash...lol. Jim

My1979chevy wrote:After about a dozen tries, I have a pattern.
Stock shim was .038
I tried shims ranging from .028 to .044 and the pattern seemed off the edge. I set the backlash between .003 and .009 each try.
I reduced it to .012, got it a lot better, so using the thinnest shim of .010 got me this- http://i1145.photobucket.com/albums/o50 ... cc967a.jpg
http://i1145.photobucket.com/albums/o50 ... af7065.jpg

This is with .003 backlash (best I could do with my limited shims)


Here is the close ups of the pattern that was on them out of the box.
http://i1145.photobucket.com/albums/o50 ... 01877f.jpg
http://i1145.photobucket.com/albums/o50 ... dcd60b.jpg

Please tell me what pinion shim and backlash the pictures are - It appears to be pretty darn good.
Running the pattern off the gear set is NOT bad the way you have it set. IF it goes off the gear in a triangular pattern THEN you have issues. Your pattern covers the peak and the valley as it should... Very nice swipe see how it move all the compound away. ONCE you get 300 ft lbs. and 3000# of weight across the gear it will swipe the complete surface. YOU WILL NEVER get a complete swipe from toe to heel. Richmond gears are usually heavy in the toe on both sides for competition strength etc. EVERY gear company has there way of contact- Just want to see where you are on the shim and backlash JUST to be sure. Jim

The pinion shim is only .010!
I could not get a pattern with shims around .038!
Backlash is .003

I think my pinion shims are too small on the inside diameter. After looking at a few that I had tried, they are bent on the inside edge where the pinion head radius goes.

Some times the pinion shaft will have a back cut and Yes sometimes the pinion radius will bend the shim....THIS is what is causing your in consistent reading. JUST can not believe .010 is going to work. NEVER...Never have we ever had a shim that thin in the housing BUT that does not mean it is not right. THE pattern is EVERYTHING. I just fear that if you press on the bearing the pattern may change. The pattern you have is pretty good and according to me you might even want to go a bit less shim by about .001 or .002 BUT your BACKLASH can also change the pattern ...

Only other thing I can thing is do you have a shim under the inner pinion race of the housing? Might want to pop that out and be sure it does not have a shim under it. and be sure the race is all the way seated into the housing. JIm

Thanks for all your help.

I'm going to step away from it for a day or two. I ordered some more shims and I will see what I can do with more playing.

No shim under bearing race, they are all fully seated, gave the pinion a tap on each end before bringing up preload as well.

More playing, better shims------

.036 pinion shim
.004 backlash
http://i1145.photobucket.com/albums/o50 ... ac9cd5.jpg

http://i1145.photobucket.com/albums/o50 ... cc35ee.jpg

Drive looks good to my untrained eye, coast looks a little funny?