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What's in the rear end?

4K views 41 replies 6 participants last post by  Willem 
#1 ·
Hi, looking for a better mileage for my 67RS I came across a rear end which supposed to be a 1st Gen Camaro. I've decoded the numbers 3894859NF and and PA 0710G1. Being an 8.2 1st Gen 10 bolt Camaro. But there's also a posi or limited slip unit which I can't decode. The richmond gears numbers are 82-0368-1 and 8620. Tried to find the richmond numbers but couldn't find it. Counted the gears and pinion 37/12 being a 3.08. But what kind of posi is it? I can read Canada and patented. Thanks for the help. Cheers Willem
 
#2 ·
Factory used Eaton's Positraction™ clutch disc style with four springs to preload the clutch packs. This limits the slip with a stronger 800 pound springs slipping less for drag racing than the standard 400 pound springs, and 200 pound springs slipping more for road racing. Even if it is an Eaton Positraction™ you won't know if it has been modified by adding clutch discs or playing with the spring pressures with out taking it apart and measuring things.

Since Richmond gear wasn't the original OEM vendor to GM I must assume some one changed those gears at some point since the rear end was built. As such it can have any make or type of locker, or limited slip differential in it. Borg-Warner, Auburn Gear also make limited slip rears and Eaton make five different types and designs of limited slip and a locker. Yukon makes a knock off of Eaton's Posi. So it coul d be anyone's rear. Without at least a picture there is no way of us telling on line.

Big Dave
 
#5 ·
Auburns are disposable unlike an Eaton or Borg Warner that can be rebuilt.

Before you pop those caps off mark the housing L and R with a letter punch and put a matching cap L or R on the cap. They have to go back on in the same place facing the same way.

Then you can pry it out.

Big Dave
 
#8 ·
Auburns use a cone style clutch that wears away not only the friction material but the machined cone it seats into. Even if you put the money into a new friction cone it would make but a light contact with the steel surface inside; and as such quickly wear away again in a short while.

Like I said they are not rebuildable.

Best to leave cone style clutches to tractors where they are common for quick forward and reverse on Ford and Case front end loaders and Gravely tractors.

Big Dave
 
#11 ·
Ok. Any thoughts on Motive gears or Richmond?
Both those gear brands are made in Italy now but from different foundries. I just put Richmond in and they are quiet. I also have Motive 4:10 in another car and no issues with those either.

IMHO go with a Eaton 400lb LS diff vs any Auburn

Gear ratio choice can be subjective. If you don't have a OD trans and do a lot of Hwy driving than 3:08 may be a better choice to keep rpm in a decent range at 70 mph. If it is just street or short Hwy driving than lower (3:73) will give more acceleration.

You can use a RPM calculator entering your 411 to see what RPM's a certain rear gear ratio will be at X speed.

https://spicerparts.com/calculators/engine-rpm-calculator

and this to determine what driven gear you need to correct speedo because of a rear gear change

Speedometer Driven Gear Calculator

Don't use synthetic gear oil in a LS diff and you need to add a 4 oz bottle of friction modifier to the regular gear oil. FWIW my Eaton unit came with a bottle of the Ford additive, aka "soy sauce". I use the GM stuff also as either will work.
 
#10 ·
If you are looking for better mileage then why would you use 3.73 gears?

The Auburn in that rear end may or may not be any good. Some of them have small windows cut into them so that you can see if the cones have bottomed out in the case. If they have not bottomed out then it can be used and may last for a long time if you drive easy.
 
#12 ·
My current set up is 327(210 hp) th350 2.73 gears in a open diff. Great on the highway but not at the stoplights. I have a 200r4 laying around which I want to use. I've understood from various threads that combined with 2.73 or 3.08 the 200r4 will not like 4th gears. 0.67. So looking into the with higher gears range. (3.42-3.73). So highway combined with an occasional run at the stop lights is what I'm looking for. Thanks for the calculator. I'll use it.
 
#16 ·
If you're looking for mileage increases, make sure you're carburetor is dialed in correctly. If you're not running an AFR gauge, I highly suggest you think about it. If you're running a little rich on the cruise circuit, you're just burning fuel for no reason.
 
#17 ·
There are ring gear spacers available to use 3 series gears on a 2 series differential but I DO NOT recommend using one. They cause problems. The Auburn that you have now may or may not still be good. You will have to inspect it to see how much wear is left on the cones. It will be a 3 series since it has a 3.08 on it now.
 
#18 ·
Thanks again! Really appreciate it. Like you said the Auburn might work if it's not worn. Finding an open diff of an 1st gen Camaro 3 series 8.2" 10 bolt seems not to be an easy one. I'm located in The Netherlands and finding used American car parts is nearly impossible. I've checked Ebay a few are offered, taking into account shipping costs. The whole project is going to be a bit pricey. Any ideas?
 
#22 ·
Is there a notch at either end of the case that shows the end of the cone? If you can see the end of the cone you can tell how far it is from being bottomed out in the bore. If it's bottomed out then it's junk.
 
#24 ·
On either end somewhere around the bearing, is there a small window where you can see inside it? Some of the Auburns had these notches and some don't. If yours has them then you can see how much life is left in it.
 
#25 ·
OP

If running the 3.08 gear with the 200 trans that will be a nice street/hwy gear especially if Hwy mileage is a priority. Assuming the Auburn LS still works. Looks to have some surface rust so clean it up well before putting it all back together. If you want mor "getty up" off the line than 3.42 or 3.73 but RPM's on Hwy will be higher. You just need to use the calculator noted earlier to determine what is acceptable to your use

My 67 came with 3.08 but had 3.73 in it when I got it. I don't have a OD trans but have a TH350 in it now and the 3.08, for me is a good all around gear for a non OD...IMHO better with a OD trans if HWY RPM's are a concern

My diff is a Eaton
 
#27 ·
Looks like you have already removed the preload springs and plates. Remove the cross shaft. Stick the unit on an axle that is mounted in a wheel. Use the axle to turn the axle gear and spin the pinion gears out of the unit. When the pinion gears come out you can remove the axle gears.
 
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