So I've got a '78 mainly stock camaro (350 auto trans)... looking to upgrade my old slow rear.

I can get a 3.73 posi, probably all original, for $200 (steal!).

Or i can get a 3.90 posi with new richmond gears for $350 (also steal).

How important is the new gears in the rear? Should I be happy with the great deal on the 3.73 stock rear, or would it be wise to just pay the extra for the one with newly installed gears?

Always have to wonder if an ancient factory posi unit is still working. Not sure if they're rebuildable or not (some stock GM posis aren't) but it's a pain to buy new parts just to find out you need to pitch them or rebuild them before they ever get installed.

Always have to wonder if an ancient factory posi unit is still working. Not sure if they're rebuildable or not (some stock GM posis aren't) but it's a pain to buy new parts just to find out you need to pitch them or rebuild them before they ever get installed.

well on the rear with the new gears in it, i'd imagine whoever had the rear apart to install those gears would've either looked over the posi or had it replaced. i'm starting to think it's a better idea to just pay the extra for the rear with the new gears in it, right?

pay the extra for the rear with the new gears in it,ditto that.

A lot depends on who set the new gears up. Some after market gears are noisy even when installed properly. Sounds like both units have used posi carriers in them.
So buy the one that has an Eaton type posi in it, the Auburn style are not rebuildable. If both are Eaton's then the decision has to be made based on the gears...for me the GM gears would win out.

well I bought the one with the new richmond gears. what should i have looked over before installing it?

personally, I would mark the teeth and verify the gear contact & confirm backlash.

This is something that is extremely easy to do with the rear out, and there are a few selected members (biggearhead)n that are professionals when it comes to rear ends.

If it were me (as I am no rear end expert) I would get the gear pattern, measure the backlash, and then post the results and see what some of the "experts" say.

well I bought the one with the new richmond gears. what should i have looked over before installing it?
Everything.
If unable to ride in the car before it was pulled to listen to it I would have pulled the rear cover off, removed the cross shaft, c clips and axles. Inspected all the parts for wear, replaced the seals and measured the thickness of the clutch packs.
At the very least the rear cover would have come off and the wear pattern on the ring and pinion checked to see if it was set up properly and that there was no shiny flecks in the gear oil before purchasing it.


I got burned one time on a used rear end that once torn down was complete junk inside, it will not happen again.

$400 down the toilet on this one.

http://i80.photobucket.com/albums/j199/64elcamino/Buick%20Regal%20project/GN%20rerar%20end/P2140004.jpg

http://i80.photobucket.com/albums/j199/64elcamino/Buick%20Regal%20project/GN%20rerar%20end/P2140005.jpg

http://i80.photobucket.com/albums/j199/64elcamino/Buick%20Regal%20project/GN%20rerar%20end/P2110007.jpg

As I see it, here’s your dilemmas.

1). How “savvy” are you at looking inside the rear end to know what you are looking at? If you are knowledgeable enough to see if it’s good or bad, then by all means buy one of them. If not, then you are taking your chances.

2). Do you know the person that is selling them and/or can you trust them? If not, then you are taking your chances.

3). What is your budget? If you have an unlimited budget then by all means buy a new Eaton posi unit, new gears, and an installation kit. If not, then your are relegated to buying a used unit and being at the mercy of the person selling it not selling you a piece of junk.

4). ASSUMING that you decided to buy all the parts to make the rear you have over into a posi unit assembly, who is going to install it for you? Honestly, even with all my mechanical knowledge, I have a good friend install any rear gears as he’s done hundreds of them successfully whereas I haven’t done any (because he's done them all!). Some things are best left to people who are better at it ESPECIALLY when you have HUNDREDS of dollars invested in parts!

I personally wouldn't worry as to whether or not the stock posi unit is “operational” as they are VERY simple to rebuild. If I were to buy the stock posi rear, I’d install it in the car, and see if it worked. If it didn’t, I’d buy a clutch pack kit, a cover gasket, new gear lube, posi additive, new wheel bearings, new wheel seals, and rebuild it. Even if it did work, I’d change the fluid and add new posi additive anyway.

You can make an easy check of the condition of the posi plates without taking anything apart. Look at a GM factory service manual. They show you how to connect their special tool to the lug bolts on one wheel and turn it with a torque wrench while holding the other wheel solid. This will tell you the breakaway torque of the posi plates and is a very good indicator of their condition.
You don't need to buy GMs special tool to attach to the wheel lugs. You can make your own using some scrap metal. Mine looks like this. It appears to be a piece of scrap, but it has been a very valuable tool for me to evaluate posi rears before tossing cash at them.
http://webhost.btinet.net/~gstegmiller/jig.jpg
A simple torque test with a jig similar to this plus a visual inspection after removing the cover will save you a lot of possible bad surprises.

well, like I said, I bought it already. I bought it through ebay and am paying with paypal. I understand that I'm fully at the mercy of the seller. But I've talked to countless guys selling rears and gained (what I thought to be) a good perspective of which sellers were pushing garbage and which were honest. This guy seemed real honest, a nice guy, had very good ebay feedback, and appears to have been in the classic car business for a while. he has a few parts car camaro's as well as a few other projects he's restoring. he's also willing to drive 360 miles round trip to bring it to me.

so I'm still weary that I'm going to get screwed, but of all the guys I've talked to that I was close to buying from, I feel most comfortable with this guy. I've also got a friend who's really good with chevy's, especially with rears, so I'm going to have him look over everything before we bolt it in. i'll also point him to this thread and see if he knows these techniques that you guys have posted up.

thanks for the help guys

The tool and proceedure that Gary S talks about has never worked for me. I've always had to pull the cover to see what was inside. I'll bet that you're going to pull the cover anyway to inspect everything.

BTW, the BEST sealant to use on the diff cover is a Locktite product called "The Right Stuff". I called Locktite because EVERY time I put a Moroso diff cover on they LEAK! The Locktite tech said to use The Right Stuff product as it is specifically formulated for EP/gear oil covers. I used it on the narrowed 12 bolt's Moroso cover and AMAZINGLY it doesn't leak!

It is a gamble buying any part. Hopefully you did OK. I agree that sometimes you can tell from talking and/or emailing someone if they're a criminal or an honest person.

I've always used the factory paper gaskets and no sealer of any kind. Many of the carrier bearing failures like the pictures shown above are a result of using silicone or gasket sealer. All it takes is for you go get a tiny amount of sealer squeezed into the oil holes on the housing and the carrier bearings run with insufficient lube. Expect them to fail early.

My 70 Camaro still has the original factory paper gasket in it. All I had to do was remove 12 bolts, remove the cover and gasker, drain it, and put it back on. Unless you are unlucky enough to tear the gasket, you can reuse it and it won't leak with a factory cover. Aftermarket covers are a different matter. You never know what you get until you use it.

If the factory gasket tears, I replace it with a good quality replacement like FelPro.

So far, I haven't had a factory gasket (new or reused) leak in 40 years on my vehicles.

yeah the guy said it just needs new gear oil and a cover gasket... recommendations?

cgibsong002: any good quality synthetic hypoid gear oil with the correct viscosity for the differential will be fine. Amsoil, Castrol, Valvoline, Mobil 1, etc. plus posi lube with "get'er done". As for a cover gasket, Felpro is a good choice.

Gary S: you are correct in your assumption that TOO much RTV is a bad thing. If, however, the user follows the directions on the sealant, it will tell them to use a skim coat of sealant (being careful not to plug any circulation passages), let it dry for 20 minutes so that it is skinned over, then install the cover. Usually what is found is a HUGE amount of sealant that has made worms that then plug every thing they can = mechanical failure. I as given a 1980 Caprice with a new Targetmaster 350 in it because it lost oil pressure. I pulled the oil pan and found a cerial bowl full of blue RTV snakes in the oil pump pickup. Removed the offending RTV snakes, put it all back together, and had 35 psi oil pressure at 1500 rpms.

I don't reuse a differential cover gasket because if it does leak, then you have to remove the cover (spilling all the new gear oil), then put a new gasket on (which should have been done in the first place).

I've been doing mechainical work for 53+ years and have seen both covers that leaked and covers that didn't leak. Since we started using The Right Stuff, we haven't had one differential cover leak ESPECIALLY that Moroso POS! Youngest son just installed a "new to the truck" S10 Blazer diff cover and used The Right Stuff + a new diff cover gasket with NO leak afterwards.

one thing on the rearend of our cars the like to melt if you use the stock gasket there are two tabs one on either side that need to be trimmed trim the gasket to match the cast housing to keep the sides lubed up

if you decide on a eaton posi they've got (3) versions for our cars or different pre-load springs that are yellow,blue and red/black .yellow is street only with 400lbs preload ,blue is street/strip with 600lbs preload and strip only with red/black springs rated at 800lbs preload and that's what i'm running in my camaro and you can definately feel it on corners !!!

i just had fun coming up/down the mtns in my friends rock crawler jeep today with a detroit locker !!!:eek::eek:...everytime you lifted off of the throttle then got back into it on corners you would feel the rear of the jeep move around and bark the tires entering a corner when lifting off of the throttle

I had the rear delivered yesterday. Looks good from what I know (not much). I haven't opened it yet, I'm waiting for my buddy to come and look at it, he knows a lot more. But for now I'm going out and getting some rust-oleum professional to paint it. How should I go about painting it? Just do some minor sanding to get rid of any grease and dirt, then have it it? Or do I need to really sand it well and then tape off certain areas?

Now mine was a steal at 375 for a posi set up with 4.56s and an eaton carrier...works great still

I used a wire brush fitting on a grinder to get all the crud and grime off mine. Then I primed it and painted it semi-gloss black with Dupli-Color 500* engine primer and paint. I had a bunch left over so I figured I'd put it to good use. It came out pretty good. :bowtie:

wire brush fitting on a grinder to get all the crud and grime off , then use rustoleum semi flat black, but grind it well and she will look brand new, mine is 12 yrs old and still looks good.

well I don't have a grinder, think I'll manage to have some success with a powered sander?