84-Z28-Canada

Hey guys,

Trying to come up with a plan for a rear end upgrade this winter. The car is an 84 Z28. The motor is as follows:

383 ci using Scat Cast Crank, GM HD rods, and SpeedPro Flat top HyperEutectic pistons. Compression about 10.5:1

Edelbrock Performer RPM top end including heads, intake, and 750 Carb

Lunati 0.490/0.504 lift cam, "268" duration and 110 LSA

This is in front of a 700r4, Vette Servo, B&M megashifter.

Current rear end is the 7.5" 10 bolt with 3.23 open gearing.

So, on street tires I ran a 14.55 quarter mile last year, and won my first few bracket race rounds. Thrilled to pieces, highly addicting. Now I want to run a slick to see what I can really do, but I don't want to break anything going 100 mph at the track. This winter I want to replace the rear end firstly to a Posi set, and possibly some better axles. My question here is... can I put an Eaton style "locker" in (Gov-Lock, or similar) and upgrade to 28 spline axles (Moser or something) and retain the 3.23's (this should put me around $600-$700) OR should I be looking for a 4th gen posi and get 4th gen wheels? not easy to find around here. OR go with something different entirely? Things to note, happy to do everything myself, but im a novice welder so fabbing up a 9-inch or 8.8 is kinda out of my wheelhouse. Let me know what you think.....I jus wanna go racin!!

big gear head

A 383 with a manual transmission and drag racing is going to scatter 7.5 parts all over the place. You need to completely upgrade the rear end to something a lot stronger. There are many after market bolt in rear ends for your car. Quick Performance is probably the cheapest bolt in 9 inch. You could use a ebay chunk in it and probably get by for less than $2000.

A Governor Lock is probably the worst differential that you could use in your 7.5 rear end. The Auburn is probably the second worst. A Eaton Posi or Eaton Truetrac would be good, and the Power Trax Grip LS might also work well. None of these will hold up well to repeated water burnouts.

Wife'sCar

iTrader: (1)

700r4 is an auto........

Any idea what kind of power numbers your making?

big gear head

He said he wanted to run a slick and I saw "I want to run a stick". I thought he was going to change transmissions. I've got the wrong glasses on.

The 7.5 might hold up fine with the 700R4. Just remember that if you spend $800 on the 7.5 and then break it you have lost that money and you still have to buy another rear end. You can invest that $800 into a stronger rear end and not have to worry about it. Then again, the 7.5 might hold up and you won't have to spend any more money. It's a gamble.

Wife'sCar

iTrader: (1)

Yeah, I'd run it till it broke then get something nice. Especially if you plan to track the car a lot.

84-Z28-Canada

Hey guys,

thanks very much for the replies, great info so far. No real idea of power numbers, and I don't want to be that guy who is guessing and making it all up. Without a Dyno test, can't know for sure, but if I built something that could stand up to 400hp/400ft lbs I'm sure it would be ok. That PowerTrax Grip LS is the one I was thinking of instead of the Gov-Lock, I got them mixed up. From what I've read, those PowerTrax units can be swapped in without much headache. I am planning on tracking the car quite a bit, and in the coming year I'd love to hit low 13s, maybe lower. I'll gain a lot with a slick, my 60 footers are atrocious. I have been thinking of the Grip LS unit with a better axle, and that might stand up just fine. Not running any power adders. The reason that I don't want to run what I have til I break it is that it isn't a posi rear, so I'm thinking I'm really not getting a good indicator of how well the car can actually do at the track. If I did go with the Grip LS and a decent axle (new bearings, maybe a diff girdle), are my 3.23s a decent gear for what I want? I'm about 50/50 street/strip. Thanks a million for any info guys.

dmccain

iTrader: (2)

As much running at the track as you plan to do you could definitely benefit from the 373s especially if you are already going into the rear to put in a limited slip differential. 323s are nice though if you are making trips. I will probably change mine from 373 to 323s in the future because I make a few long hauls a year.

big gear head

Are you getting the Power Trax Grip LS confused with the Power Trax Lock Right? The Grip LS is a complete limited slip differential and the Lock Right is a locker kit that goes in the oiginal standard differetnial case.

84-Z28-Canada

I must be getting them confused. I am thinking of a kit that I can put into my existing diff case without changing the gear set. I know that if the gears are changed the preload needs to be set (ie: lash) and I don't feel like I can do that just yet. So, from what I understand, one of the PowerTrax sets can be put into my existing set up to give me a "posi" set up using my existing gears. From what I understand, this could also be my opportunity to upgrade to 28 spline axles, and purchase good quality 28 spline axles (I think Moser makes 28 spline axles for the 10 bolt rear in the exact length we need for our cars). So, if i can do that, and have a "posi" rear with decent axles using most of my existing set up and adding the Powertrax unit, that seems like a reasonable way to increase the traction and durability of my rear end without any cutting/welding/swapping out gears or wheels (think 4th gen). All for under $1000. Let me know what you think, especially if you've done it! thanks guys

Wife'sCar

iTrader: (1)

Ah this is a ratchet locker, I have one right now and will be glad to be gone with it when I swap my new rear in. The clicking gets old real fast and when it's wet enough if you don't have good wet traction tires it will try to act like a welded diff and slip the back end easy.

It's nice for dry weather track driving but it's not real pleasant daily. It's doable but it's not real fun.

I'd vote get the gears you want, the diff you want, and pay a shop to install it for you. If you can remove the rear and drop just that and the new parts at a machine shop it's pretty cheap endeavor.

Shop down the road from me said they would install for 175 with a 3 year warranty if I pull the rear and buy all the parts.

big gear head

You can't put 28 spline axles in a 26 spline differential case. The hole in the ends of the case is not large enough for the 28 spline axles to go in. A 28 spline locker will not fit in a 26 spline case. The 28 spline cases are wider inside and you can't interchange the parts between them. So if you want to upgrade to the 28 spline axles you are going to have to swap the differential case too.

84-Z28-Canada

Thanks for all this info guys, this is great. Ok I didn't know that the 28 spline axles wouldn't fit in the case, or that the 28 spline unit wouldn't fit into the series 3 carrier. I was under the impression that the series 3 carriers (3.23 gear and up) were all the same size. Fair enough, so if I go this route, it will have to be a 26 spline unit. I have heard good and bad about the day to day use of these things, some people say they click and bang, other people say they're great. At the end of the day it's a noisy car anyway, I've got a complete 3" flowmaster kit from headers back, so I wonder if I'd hear the noise anyway. If the goal is to have faster ETs I don't know if clicking would bug me all that much. I guess the other route is to look for a set of 3.73s and have a shop install the gears and a posi unit if I can find one (like a ZT unit from an 01 camaro or something).

Wife'sCar

iTrader: (1)

I have full 3 inch as well. You will hear it, but that's the least of the issues. When you take turns at under 30 it feels like you are dragging the outside wheel over a series of tiny speed bumps. And on the occasions it pops you will swear it sounded like something snapped off under the car. It's fine for weekend warrior garage car but I highly don't recommend it for daily driver. And if you have a gravel driveway or park anywhere not paved, turning will tear it up. Gravel and sand isn't enough traction to overcome the locker.

Don't get me wrong it's not a bad setup, but it's not good for a daily. Not to mention the stares in parking lots and having to explain it to everyone gets old. I can't tell you how many people have to me I need to get my cv joints inspected because they are popping real bad. I've even told people I'd give them a grand if they can find a cv joint on my rear. No one's gotten a grand yet......... as someone who has daily driven one for a year I will not miss it at all.

Night rider327

iTrader: (13)

I'm a big fan of the power trax lock right locker. Ran one for years in my daily driven camaro. My dad now has that same locker in his.

Mistakes I learned from spending my hard earned money....

Don't waste your funds on the 7.5"/7.625" 10 bolt. By the time you upgrade it, you will be $800-1200 in... That's half the cost of a ford 9" or 12 bolt if you shop around.

I wasted $1000 upgrading my rear end with locker, axles, TA support cover, etc... Just to end up with the thing breaking anyway. All of those parts still can't fix the weak point which is the small ring gear and pinion gear.

If you are putting slicks on the car and running it at the track, you will break the 10 bolt.

Look at QT or moser for housing/axle package and some local or internet diff. shop for a third member.

I got the moser housing and 31 spline axles shipped for $1000
Valley custom differentials in CA built my third member with ford iron case, nascar take out detroit locker, and new motive gears and timkin bearings for $735 shipped.

I then used a set of second gen F body brake backing plates I had and enlarged the holes, and put in second gen F body wheel cylinders and brake shoes.

Used my same alum. drums

Cut rear brake lines and changed the fittings to SAE fittings and re flared them.

ES poly sway bar end links and bushings and 3" heavy duty exhaust clamps to hook up my rear sway bar.

I think all of mine came in around $1900 for complete working ford 9" with gear oil, brakes, and all.

Like I said I wasted $1000 before that trying to upgrade the 10 bolt. If someone had told me what I'm telling you now, I could have and would have just saved up another $900 and done the ford 9" the 1st time around.

sofakingdom

iTrader: (1)

I'd suggest a 12-bolt, for the simple reason, it fits the car better.

The advantages of a 9" are the VAST array of aftermarket parts to make the 9" PLATFORM as distinct from the original 9" which is a weenie oversize under-engineered POS, into a contender; and the ease of swapping the 3rd member. The advantages of the 12-bolt are weight, efficiency, and better fit. The ultimate "strength" of an aftermarket 9" is greater than a 12-bolt but with a N/A small-displacement small block like a 383 you're in no danger of having to worry about that, don't be misled into a non-optimal choice FOR YOU on that basis.

Evaluate which of those strong points are more important to YOU before biting off.

If you're serious about running this car at the strip with traction, don't waste a dime on your 10-bolt. Don't even bother changing the fluid. It's destined to become shrapnel.

Ron U.S.M.C.

Just to get a idea as to the difference between the 10 Bolt and the larger 9" and 12 bolt class.
This is the 10 Bolt and a 9".
Buy the way I "Built" my 10 Bolt with some of the best parts I could find. Its still there. I don't use real sticky tires and have an automatic 5.0.
The pinion is the photo that gets me. Incredible.

84-Z28-Canada

Wow guys, great advice. So the long and short of it is... if I'm going to run the car at the track with a slick tire, I need something stronger than a 10 bolt. I think this is a good call anyway, because the N/A 383 isn't the ultimate power plant for this build. Ultimately I'd like a blown big block, but who wouldn't!? So, save the money and run what I have for now, probably break it, and build a GM 12 bolt in the mean time (and have the cutting and welding done by pros). Awesome guys, thanks very much!

Wife'sCar

iTrader: (1)

That sounds like an awesome plan. Maximum fun, minimum money wasted learning the hard way.

Ron U.S.M.C.

I agree totally.

Night rider327

iTrader: (13)

No cutting and welded needed. Buy a bolt in ready aftermarket housing. Trouble free, pain free bolt in setup

All the correct mounts will be on it in the correct places... Then just build up from there, add what ever carrier, gears, axles, etc you want.

Check out quick time performance and moser for bolt in housings

big gear head

As far as a bolt in 12 bolt, I think Mark Williams has the best quality. It's probably also the highest price. Not sure about Strange or Moser. I sold a lot of Moser 12 bolt rear ends over the years, but I never installed one in a 3rd gen.

jbenge

iTrader: (2)

I agree with the others, don't waste any money on the 10 bolt. Save up and buy a 12 bolt or 9in rear, do it once and don't ever worry about it again.

I just put a Strange 12 bolt in my 91 this spring. No fitment issues and it came with the sway bar mounts, new end links, and gear oil. It also has LCA relocation holes already built into it which is a nice feature. Only downside is that is does have some gear whine.

I had a Moser 12 bolt in my 84 and ran it many years with no issues deep into the 10's and 1.4x 60' times. The Moser had no issues but the Strange rear seemed to be a more complete package, included everything while the Moser did not include sway bar mounts, LCA relocation brackets, gear oil etc. The Moser rear was purchased a long time ago though so what's included may have changed by now.

84-Z28-Canada

Wow guys, the info here is really awesome. I will definitely be pricing out a bolt in rear (either a Moser or Strange, hearing great things about both). Saves the cutting and welding, get a great product, and not have to set up the lash and so on if I can get a good center section. I'll start collecting parts now! I'm going to probably go with a 3.73, maximum 4.10 gear set. It is still a street driven car, but I have the 700r4 so the overdrive will help with highway RPM. Great advice guys, I'll update when I put it all together! Now to work on getting that blower...