zcamaro28

OK i have an 1984 z28 and i have a mildly built 383 with about 500 hp and i had a 87 700r4 built by a race trans shop but my question is what kinda hp can the stock 10 bolt hold. Also its not posi who would make a cheap ($2-350) posi diff for it. thanks

89_ho_rs

i would go with an eaton posi. check summit or jegs

zcamaro28

will it hold all the hp if i didnt run slicks. plus what are all the things i need to know when getting a new posi unit like how big the center pumpkin is and what not

TKOPerformance

Assuming it's a 7.625" 10-bolt go with an Eaton posi for 28-spline axels. Moser 28-spline axels. TA girdle cover. If everything else is in good shape that should allow it to live behind your 383. Slicks will probably grenade it.

If it's a BW 9-bolt your in luck because they are stronger than a 10-bolt. You're gear selection is limited though. I know TA just came out with a girdle cover for these. That would be a good first step.

zcamaro28

Well its a 10 bolt. I have another question i thought all Z28 came with posi rears. Either it didnt or maybe i broke a spider gear or something.

kevinc

Nope, plenty of non-posi Z28s rolled off the assembly line. Even if yours had a posi in it, chances are it's worn out by now anyway. If you've broken a spider you'd be hearing about it.

Eatons are OK for drag racing but the clutches eventually wear out. Auburn makes a nice heavy duty unit with cone clutches that may last longer, not much comparison data around. My favorite for drag duty is a Detroit Locker...no clutches.

TKOPerformance

Yes, my fully loaded Z28 IROC didn't have a posi rear from the factory, so plenty didn't get it. The stock GM posi is weak anyway, and by now it is most likely dead, especially given how most Z28s were driven.

The Auburn is a sturdier unit, but the Eaton's a little cheaper.

I've got a Detroit in my car now, and I wish I didn't. If it was a strip car that woudl be one thing, but on the street it is harsh. Lots of clanging, and understeer in truns until it unlocks and then it transitions to snap oversteer. Not that much fun. If I had to do it again I'de use a limited slip. When I upgrade to the 9" that's what I'll be using.

kevinc

Yup, that's why I specified drag duty but maybe not as clear about the bad points for non-drag duty as I should have been.

I use a Torsen HD personally. Not ideal for drag service on launch but it gets both tires turning as soon as I'm rolling.

It's perfect for street and road course service, which is where it spends the majority of its time. Doesn't drag the inside tire thru turns on acceleration like Eatons are prone to, no lock/unlock action to unsettle the rear when I accelerate at the apex.

TKOPerformance

The Torsen is the same concept as a Truetrac or a Quaif I believe. Helical spur gears. It works on applied torque rather than breakaway torque, sort of the opposite of a limited slip or locker. A lot of drag guys criticize them for exactly the the reasons you noted, but I've read several articles from autocrossers, particularly in the Roundel (the BMW CCA magazine, I've got a friend that is a BMW fanatic, so that's how I came by it). All have praised the Quaif and Torsen. I just read an article about using a Truetrac (made by Detroit Locker) in a 12-bolt destined for a Chevelle. They handle a lot more power and never wear out, which is another benefit.

Maybe I'll give that a try in my 9" instead. The Detroit in my Camaro was an experiment. I knew the 10-bolt wasn't going to be in there forever. Plans were to beef it up so it would live, then sell it (provided it doesn't break), and buy the 9" when I get the turbo motor up and running. I wanted to see how the car drove with one. I don't like it.

Strangely, I run a Detroit in the rear of my K5 Blazer and it is seamless in operation. Occassionally on a really tight turn it will make it's prescence known, but otherwise I could swear it wasn't even there. The two tire marks prove it works though! I've got an ARB in the front, so it's the best of both worlds. Locked to unlocked with the press of s button. Great for 4-wheeling, particularly in the front where I can unlock it to get a tighter turning radius, but I wouldn't use one in a street car. Too much to think about.

zcamaro28

so whats one is better detroit, auburn, or eaton

kevinc

You're seeing above that it depends on how you want to use the car. I inferred drag racing since you were talking about holding HP and slicks.

Detroit is great, doesn't wear out, but is clunky/noisy on the street.

Eaton and Auburn are about even in terms of capability, in my limited experience the Eaton is my recommendation as I've seen three Auburns break during launches. One of them was in a 12-bolt rear end.

I haven't seen or read about an Eaton coming apart, just the clutches worn out but that tends to take years.

65panhed

If you have time to wait I will give a review of an auburn pro series diff and Yukon 3.73 R/P and Yukon axles..........Just installed today...........

zcamaro28

OK i kinda wanted a street/strip kinda thing you know go to the strip throw some slicks on then put on some regular street tires. But i want something very streetable

Pro Built Automatics

I carry both types of posi's, Auburn & Eaton. Between the two, the Eaton is the stronger one. This is from past experience (since the mid 1960's). Auburns are good for most street setups with modest horsepower. For more HP the Eaton, then for even more... HP the Detroit Locker.

TKOPerformance

If you want a street/strip car that won't act like a strip car on the street then go with the Eaton. They even have that guarantee now that if the diff fails in the first three years they will send you a brand new on for free.

zcamaro28

so then everyone is saying eaton

65panhed

Not me not yet Also Auburn has the DREX program to back up their parts. My ? is, an Eaton might be stronger than an Auburn hi perf series or OEM, but is it stronger than the pro series? Check out Auburns website.

Nightrider350

I read that all 82-88 F-Bodies got 26 splines, 89 was the changeover year, and all 90-92 F-Bodies got 28 splines. Just somethin to think about cause u said urs was an '84 and someone told you ur axles were 28-spline when, according to this http://www.uspowertrain.com/axlesGM.htm they are 26-spline. This is all new to me as well cause i got an '88 lookin for a posi also, so don't take my word for it but look into a little more and make sure you know exactly what u need to get.

TKOPerformance

Yes, you have 26 spline axels stock. My advice was to upgrade them to 28. It is all bolt in parts, and if you are changing the differential anyway it makes sense. The 26s are too weak your your application. They are too weak for a stock car IMO.

Also, the beak point isn't an exact science. That is when 28 spline axels started production. I've pulled 26 spline axels out of a '90 before. When dealing in the '88-'90 range the only way to know for sure is to look. GM had piles of 26-spline rears lying around in various ratios. They didn't just junk their inventory, rather they used it until it was gone. Less popular ratios stayed around longer, which is why you will occassionally find 26-spline axels in '90s.

demetri

Is there a way to check how many splines you have? Sorry if this is not related to this topic.

TKOPerformance

Pull an axel and count. Sorry no other way to tell.