[b-man]

On the GM rear ends being discussed here the differential contains the spider gears and side gears (and sometimes posi clutches too), the ring gear bolts to the differential. The differential unit installs from the back with the pinion gear already in place in the housing. This type of rear end where the differential loads from the back is known as a Salisbury design.

Same differential definition applies to the Ford 8" & 9" rear ends except the design of that rear allows you to remove the differential/ring gear assembly along with the pinion gear from the front as one unit making for easier gear changes. The Ford rear ends like this are a Hotchkiss design.

The '55 -'64 big Pontiac 9.3 rear ends as well as the '55 -'64 8.2 Chevy rears were all Hotchkis. The later Ford 8.8 rears are Salisbury.

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In order to accomodate different gear ratios the differential unit needs to be able to accomodate the different gear ratios. Sometimes a new differential unit with an offset flange to mount the ring gear is needed to do this, hence the 2 different differentials for the GM 8.5 and 3 different ones for the GM 8.2.

A 2.56 gear has a very large diameter pinion gear compared to the pinion on a 4.10 gear. The ring gear will be offset further to the side on a 2.56 rear than on the 4.10 to accomodate the larger pinion gear diameter. In the case of the GM 8.5 the 2.41 & 2.56 will work on one design, the 2.73 and higher gears numerically will work on the other one.

[russosborne]

Ok, I think I got it.
So from reading here if I were to buy an 8.5 from an Olds or Buick 71-72 A body I either need to make sure the differential it comes with will work with whatever gear ratio I plan on using, or plan on buying another differential as well?
The external housing of the rear end is the same, it is the internals that determine what range of gear ratio's you can use?
Sometimes I think I really am stupid. Other times I am sure. :-)
Thanks,
Russ

[b-man]

The axle housing will accept any gear set so it isn't specific to any gear ratio range, only the differential unit itself needs to match the gears you want to use.

[70temp455]

I was also a bit confused. Thanks B Man for the great information!
What are the original P axles (how many splines) that I have ? 72 LeMans.
I didn't look while inside the housing, are the 8.5 axles press-in or C-Clip.
I did however install a PowerTrax unit in my Tempest so I did get to tinker around in there a bit but appearently I I need to know more about what I'm gettin into.
So now I understand that I need a new Carrier if I plan on going up in gear.
How difficult is teh carrier/differential change.
I've rebuilt engines and I rebuilt a Trans but not a Diff. "yet".
Thanks,
Andy

[70temp455]

Currently running a old worn out 350-2bbl TH350.
Maybe next year a 400.
I want a decent street able gear but I also like going for country cruises and 200 mile drive to Norwalk. But then again I love to get on it hard also. I'm thinkingh the Tempest I had was decent enough with a 455 and a 3.08 gear.
I can get a 3.42 but I'm thing it may be a bit too high for long Highway cruising but I never had a 3.42 so don't have any experience here.
How would a 3.23 compare in the mix.
comparisons between 3.08, 3.23, 3.42 ? ?
What do yall have and what likes and dislikes about them !
Thanks,
Andy

[b-man]

I paid a pro to build my 8.5, some special tools are required to do the job. It's not like you couldn't buy some tools and learn to do it yourself, but I consider it to be cheap insurance to have an experienced guy do the work to make sure the gears don't make noise or wear prematurely.

-----------------------------------------------

A 3.42 gear is not a good highway gear, especially for a 455.

I would consider 3.23s as the highest gear to consider, with 3.08s being just about a perfect all-around gear for a 455 for street and highway. Running a tall tire will help take the sting out of running the 3.23 gears if you decide to go that way.

I picked the 3.42 gears for my 8.5 rear only because I will be running an overdrive auto trans with a lockup converter, the final drive ratio will be 2.394 in overdrive.

[70temp455]

"had was decent enough with a 455 and a 3.08 gear."
IKey word "had". I don't have a 455 anymore.
Currently 350, next year (hopefully) a 400.
I hear 1 vote for 3.08
Anyone else?
Andy

[b-man]

If cruising the highway comfortably is a priority the 3.08s are tops, but a 350 or 400 likes a little more gear.

With the smaller cube engine go with the 3.23s for the best compromise between acceleration and highway RPM.

The 3.23s are probably the most common performance gear that came in the majority of musclecars, regardless of car brand.

I had a '69 400 Firebird 4-speed coupe and the original gears were 3.23s. I can remember street racing against a 383 Road Runner back in the late '70s, it had 3.23 gears too. I beat him with my 1756cc 1957 VW that ran in the low-14s.

[67drake]

Andy, To set up a rear you will need a magnetic mount dial indicator to check backlash and runout,which you might already have if you have done engine and tranny rebuilds. And a beam type (not a clicker) INCH lb. torque wrench for checking pinion bearing preload.
I went to the home supply center and bought some 1"x1/4" steel stock,about 4 feet long. I drilled 2 holes in it,then bolted this to my pinion yoke using the u-joint bolt holes. This holds the yoke when crushing the crush sleeve. I also put a 4' long pipe on my breaker bar to get leverage to crush the sleeve. Worked great! I always hear people complaining how hard it is to crush the sleeve for proper preload,it was honestly easy this way.
If you have a press you can press your own bearings on,I don't, so I had my buddy do it at his shop.
I also honed out the old original pinion bearing to use as a "set-up" bearing on the pinion. You need to install the pinion with the set up bearing on it,then the carrier and ring gear to check your gear pattern. If it is not correct,you pull everything apart again and reshim the pinion till pattern looks good. Instead of pressing and pulling the pinion bearing each time,you just hone out the old bearing so it's a slip fit. Then press the new bearing on after you get the pattern correct.
Other then that just all common tools are used.
A hassle,yes,but that is why I think people get into trouble doing rear ends. I think a lot of times they get impatient ,figure it's "good enough",and then they have gear noise.

[70temp455]

I'll have to do some homework like reading up on how to do it.
I'm a machinist and actually have an old Mag base and indicator in the trunk of my driver that I brought home to check rims and bearing play etc. I was going to try to use it to make a camber caster gauge, but the wheel nut sticks out too far. I have a bid on ebay on a C/C gauge. The shop that I have had do a lot of work on the caddy wants $75/side to add or remove shims when aligning. I thought that that was part of doing an alignment. SO, I'll get the camber and caster set and have them set the final Toe.
I just finished redoing the whol front end when I figured I had better re-do the rear also before having the alignment done and that's when the SH*t went sour (broken Housing).
Andy

[Shiny]

Andy - You got great advice from 67 Drake. You can do this and his tips will make it easier. I am no mechanic nor machinist, but I was able to rebuild and set up my 8.2 with no previous experience. I paid a shop to remove and press new axle bearings, and also to remove the old pinion bearing. With the old pinion bearing removed, I honed it as described to set up the shims. It doesn't have to be real accurate, just so you can get it on and off easy as you adjust the pinion depth. I just ground mine with a stone in a drill until it slipped onto the pinion. I did not pay to have it pressed back on, I just hammered it on with a mallet and some kind of ring to spread the load.

For me, I tried to use the gear tooth pattern with the paint but found that to be impossible without any experience. I had no confidence in "reading the pattern", and finally gave up on that. I found out my gear set had been stamped with the exact pinion depth at the factory (I don't remember, but may have been Richmond gears ?). The gear set is run-in at the factory as a matched pair and they mark the depth so you can match it exactly - no guessing required. The depth is measured from the center of the ring gear (axle center lines). So I put a straightedge (a ground flat from Ace Hardware) across the bearing caps to provide a centerline reference for the ring gear, then used a cheap expansion guage and a caliper to measure to the pinion. This way, I did not have to guess about the correct pinion shims. I think this was probably accurate to +/- a couple mils, which got me way closer than I think I could have done trying to read the pattern with paint off the teeth. If I ever do this again, I will make sure the pinion is stamped with the target depth when I order the gears. I just got lucky when I did it. If I had to rely on the pattern, I would have paid an expert to set it up.

To set the pinion bearing preload, I did not have a low-value torque indicator, and found they were expensive so I improvised. Basically, I used a rubber band on the end of a 3/8" bar. I hung a dead weight on the rubber band at a measured distance from the breaker bar end to calibrate the spec'd in-lbs. Then when I started tightening the bearing, I checked/tightened/checked until the rubber band stretch matched the length I had targeted. Worked fine and avoided spending $ for a tool I'd only use once.

Setting the ring gear lash was very easy - I used a dial indicator and magnetic base, same as you have. You won't have any trouble with this.

Mike

[70temp455]

Don't know about the ruuber band thing but I'm sure I can find someone (hopefully) with a torque wrench. I used to have on but now I have a clicker.
What was (aprox) the measurement from the bearing caps to the pinion ?
I have up to 6" depth mics and if I need more (couldn't imagine it would be much more)
I could use one of many options at my disposal.
I deal with .0005 to .001 everyday.
Thanks Mike et al
Keep the info coming (I feel special- LOL)
Andy

[70temp455]

http://www.summitracing.com/parts/RMG-SGM7502/

[70temp455]

I am planning on buying Drakes 2.56 POSi unit and taller gears are supposed to work with a spacer if I understand all this correctly.
Andy

[GStage1]

Don't use Richmond Gears.....use US Gear or Yukon.

You need to list your city/state in your header info.

I know of an excellent rear axle builder in the Cleveland/Youngstown/Columbus OH area.

[67drake]

Got my torque wrench off of E-Bay. I didn't find any friends who had an in. lb. beam type to borrow either.
http://cgi.ebay.com/STURTEVANT-TORQU...#ht_500wt_1156

[b-man]

Do not use a spacer, get the correct posi unit.

A spacer can fail under load, causing great damage to your car and maybe to you too.

[70temp455]

How much of a spacer do the 2.56 carriers need ?
I assume it spaces out the ring gear and it seems as long as it is tourqued correctly it wouldn't fail, maybe the bolts would shear and fail but I'm in uncharted territory here.
Andy

[b-man]

http://forums.maxperformanceinc.com/...ng+gear+spacer

[Shiny]

Don't remember the distance for the pinion set-up but think it was around 1.25". B-Man's post reminded me it was a US Gear ring and pinion. Their web site says:

"PRODUCTS

Ring & Pinion Gear Sets
– Manufactured from forged USA Steel
– Pinion face marked for "checking" distance
– Each set comes with match set number and installation instructions
– Made in U.S.A."

Call them and they can tell you what a typical depth is, but I'm sure you can get it done with a depth micrometer if you have a ground reference bar to lay across the bearing mounts.

As for the rubber band, ya it sounds hokey, but the torque is really low, more like in-ounces, so if you get a 100 in-lb wrench, you will not be very accurate. At the time, I thought the right tool would be something like a 30 in-lb indicator, which I could not borrow nor find for under about $50 on ebay.