hey guys i need some help with my project. i have a 1985 trans am with a 350 bored over .30 with edelbrock 650 double pumper carb, high rise rpm performance intake, mild cam, hooker header, etc.

it has a a700r4 racing transmission mildly built. engine and trans have abt 35,000 miles. car has 188,000

i will eventually have a 500hp+ 383 stoker or a ls1 build engine in there and be upgrading to either a mad dog level 3 a700r4 racing transmission or the a700 raptor level 3 racing transmission.

so i wanna get my axles right before i put in more powerful engine in there. i am pushin abt 300-380hp with the 355 i have in it now and transmission is doin fine. but i need help with how i show build my rear end. i have been told that the rear axle in it now is stronger than the dana 44s. but dont exactly know which axle is in there now. how should i build my rear end now to be able to withstand a 500+hp car? i want off line power and acceleration ,but dont want it as a straight drag car. will mostly be driven everyday expect in rain and snow. will have street/racing tires on it(not slicks) not the wealthiest person either so keep price reasonable.

 

i'm drag racing a stock rear with over 500hp. as long as you aren't launching with slicks and a trans brake you shouldn't have a problem, and if you did i would just stuff another stocker in there.

 

Assuming it's still a factory diff, I highly doubt it's stronger than a Dana 44. You may have the first version of the 9 bolt but it's not much stronger than the normal 10 bolt that just about every other third gen received and not as good as the Dana 44.

Crawl under the back of the car and look at the diff cover. Smooth cover and 10 bolts holding it on is a 10 bolt. Cover with a rubber plug and 9 bolts holding it on is a BW 9 bolt. If for some reason, some previous owner did an upgrade, you may have a rare Dana 44. It will have 10 bolts around the cover and will have a metal fill plug in the cover.

First advice is to drive what you have until you manage to break it, then decide how much it's worth to upgrade to something better. Even the weak 10 bolt which has been broken in street use has survived dragstrip action with some upgrades. It's not really worth upgrading either the 10 bolt or the 9 bolt. No matter how much you invest into upgrading them, they still have a small and weak ring and pinion which is what will fail first.

Your next option is to invest in an aftermarket direct bolt in diff. You have a choice of a 12 bolt, Ford 9" or Dana 60. There are many ways to option them out but generally, expect to spend close to $2000 for a proper upgrade. An inexpensive upgrade can be done for around $1000 by getting a 9" housing package. It comes with a bolt in housing and axles. You provide a center section with gears, posi etc and you swap over your brakes. Because of the third gen's torque arm suspension, there's no junkyard diffs that are a direct bolt in to give you something better.

When building a car with more HP that stock, the entire driveline needs to be upgraded to handle the extra power. GM never put a performance driveline in these cars to handle huge amounts of power. It's a package deal. You can't improve the engine without everything else. Factory stuff can survive for a little while but eventually something will fail.

 

thanks. so i think i am just going to put a 2500 stall converter on and some racing gears. i guess after my big engine upgrades i will wait untill stock breaks then invest in the 9" ford rear end build. oh yea i also heard another way is to put on the 4th or 5th gen rear end on it. that should give me the disc brake zo6, posi, and the gears. so now the question is which one would be better. cost? efficiently? which one will take more work?

 

I have no idea what kind of suspension the 5th gen has. 4th gen is a direct bolt in but the diff is slightly wider. The 4th gen diff is no stronger than a third gen ring gear wise however it uses 28 spline axles, the same as 90-92 third gens.

Unless you can get one for dirt cheap, it's not much of a strength upgrade compared to buying an aftermarket diff.

 

5th gen is definitely far from being bolt-in for us, as it's an independant suspension mounted under a completely differnt chassis design. - Apples vs oranges.

A 4th gen axle isn't really any sort of upgrade; it's still a 7.5/7.625 ring gear and will still grenade with much power, especially with lower gears(numerically higher than 3.73 = time bomb). It will also require special wheel offsets being almost 2" per side wider.


Bolt in upgrades are the 12-bolt, D60, and 9"; as noted by Alky. Unless this is a race only car, thus ok for a spool, expect to spend $2500+ for one of the bolt-in units(especially if you have to have it shipped to you). If you have access to a cheap 9" center section, carrier, and gear, then you could do the housing/axles package that Alky mentioned. A stock center section is not nearly as strong as the aftermarket equivalents, but still considerably stronger than the 7.5" 10-bolt or the BW 9-bolt.

 

thanks guys i am going to try to find a cheap 9" housing kit. wen all of that goes out i will upgrade to the ford 9". hopefully that wont be any time soon.

 

If it is the factory '85 rear end, it has 26-spline axles, about as weak as you can get. The 4th gen rear would be an upgrade over that; but it is longer, so either your tires will stick out beyond the fenders, or you'll need higher backspaced rims.

You can upgrade the stock rear end with 28-spline axles and a 28-spline center carrier (which is what I have done for now). Add an aluminum support cover and weld the axle tubes, and you'll have a stronger rear than the 4th gen. For your current power levels, I wouldn't be concerned about such an upgraded rear holding up.

When you get the 383: A 12-bolt would be stronger, of course. And, a 9" would be stronger than that (with the right parts), but a 9" is also about 50 lbs heavier and less efficient than a 12-bolt.

BTW, Edelbrock doesn't make a "double pumper" carb.

 

With an auto the stock axle will last a little longer, a lighter car will also help. To be honest, you'd have to try really hard to break one on the street, but at the track is another story.

the 3rd and 4th gen rears are almost the same, as has been said, the 4th gen axle is a little wider and, it also has 28 spline axles like the late 3rd gen, but the early one has 26. OTOH, typically the axles aren't what you'll break, usually it's gears first, then differential second.

 

If you decide to go with a 9" housing package, get it with 31 spline axles. I won't even recommend 28 spline 9" axles for a street car.

That just means when you're hunting for a junkyard center section with a posi and a gear ratio close to what you want, you also need to find one that uses 31 spline axles. You could mix and match parts. Pull a 9" center section, find a 31 spline posi then find a gear ratio you want. The nice thing about the 9" is that there's no carrier series. If you find a 31 spline posi with 2.50 gears, you can put any gear ratio available onto the carrier. I got lucky once and pulled a 9" center with 31 spline posi and 4.10 gears out of an old Bronco. Only cost me $100. 3.50 is a common 9" ratio.

The C7AWE is the most common center section. I caught mine before the pilot bearing support broke off. It was cracked and could have failed at any time. I was doing transbrake launches and running mid 9's with a stock case.

 

wht r some common places i can find some good 9" housing, gears, etc... ? like wht type of vehicles and years r common to have wht i am looking for?

 

o yeah my bad abt the carb. i did have a holley 650 dp, but needed to be rebuilt but i just found that elelbrock 650 new really cheap.