[Scott Roberts]

Just looking for suggestions on a bolt in rear with disc breaks for a 1st gen firebird. Street use mostly and around 700hp. What is the best bang for the buck?

[Tom Vaught]

Bang for the Buck says 8.5" GM rear with 1LE rear Disc Brakes, ASSUMING THE REARS ARE CLOSE IN WIDTH. I know little about F-Bird Interchange.
I do know that a 8.5" rear can stand decent HP.
Tom V.

[mgarblik]

Strange Engineering I am almost sure has a drop-in unit for 1st gen F cars. Do not know cost but I can assure you it would be a one time purchase. Bolt it in and move on to some other potential weak link if any. 700 HP is allot to ask of OE parts that were designed for 300-400 HP maximum.

[Tom Vaught]

If he had not mentioned "BUCK" Strange would have been my 1st choice too. I have a couple of Strange 9" center sections and they are a very nice piece.

Tom V.

[torqhead]

I'm happy with the 12 bolt Moser I put in my car, not sure of the cost difference versus the Strange that's been recommended.

[64speed]

Quick performance if you are on a budget and want to use a 9 inch. I paid 2450 minus shipping for what I feel is a really nice differential with a Detroit true trac posi and everything plus they are super nice to work with.

[Half-Inch Stud]

Happy with the Strange S-60.

BUT you'd have to be happy with a 3.54:1 gear ratio.

[Chief of the 60's]

If the OP had not mentioned bolt in I'd say narrow a Ford 9", put Ford Explorer disc brakes on it and call it a day. Cheap, it will hold up and it will stop.

By the way OP, how did you figure that it is 700 horse? Was it on a dyno?

[Tom Vaught]

Originally Posted by Chief of the 60's

If the OP had not mentioned bolt in I'd say narrow a Ford 9", put Ford Explorer disc brakes on it and call it a day. Cheap, it will hold up and it will stop.

X2 Just what I have under my 64 GTO, Chief of the 60's. Started out as narrow 64 width but then I had it narrowed 2" more for the Disc Brake set-up.
Tom V.

[azbirds]

With the perches moved on the 8.5 it will go right into a first gen. I've used a number of those diffs with good results. The width is the same but the perches are farther apart for the 2nd gen birds.

[Formulajones]

Actually, 2nd gen rearends are 1" wider than first gens. The second gen rearends will take the same axles from a 68-72 A-body, they are the same width. I've done this as my 70 Formula has an original 12 bolt and needed an axle, I pulled one from my 72 chevelle 12 bolt, then bought new aftermarket axles for the chevelle.

If you want a drop in 8.5" 10 bolt for a first gen, the 71-72 Nova's/Ventura's are a direct swap, with the only difference depending on whether you have single or multi leaf setup. They come both ways.

An original first gen 12 bolt is going to set you back $1500 or more depending on condition and codes.

A 9 inch would be an easy retrofit if you can find a good core to start from and you have skills. I've done this as well, in the end though, once setup properly, it ends up costing nearly as much as a brand new complete unit from your favorite supplier. You'll save maybe ~$500 if you can do all the setup and fab work yourself.

Any of the rears mentioned above can be converted to disk if you wish.

Otherwise buying a complete drop in unit new and ready to go is the easiest option with a simple phone call and delivered to your door. I've gone this route at well using Strange. No complaints there either.

[Formulajones]

Originally Posted by mgarblik

Strange Engineering I am almost sure has a drop-in unit for 1st gen F cars. Do not know cost but I can assure you it would be a one time purchase. Bolt it in and move on to some other potential weak link if any. 700 HP is allot to ask of OE parts that were designed for 300-400 HP maximum.

Yes you are correct, they do. A complete 12 bolt ready to go, setup for disc but no disc parts supplied, delivered to my door, was right at $3200

But it's much more than a standard 12 bolt. The casting is extremely beefed around the main cap and pinion area compared to an original so it's much stronger right to start with. It comes with billet caps, I paid extra for a 1350 yoke, a Eaton 33 spline posi unit, 9" ford housing ends welded on, and bolt in 9 inch style 33 spline axles, as well as a support cover. Add oil, toss on my brakes and it's ready to rock. The 9" style housing ends that are welded on can be had with either GM bolt pattern style brakes or ford style brakes, your choice.

Not cheap, but yes, the last rearend you'll ever need to buy, button it up and forget about it.

[RocktimusPryme]

I’ve got an 8.5 out of an xbody that I’m putting into mine. Supposed to be bolt in and a tick narrower end to end.

I paid I think $350 for it? I’ve heard you used to be able to get them cheaper but everyone knows they are the budget first gen swap now. Now I could swap the brakes over and be done with it. $350 upgrades rear.

But I’m putting some cash into mine. It will probably be 13-1500 when I get done with it. 30 spline Detroit and moser axles. Disc brake kit from the right stuff. Still waaaaay cheaper than a bolt in brake to brake 9” from one of the big companies.

[Tom Vaught]

One thing I will say about Moser Axles, THEY ARE EXTREMELY HARD to machine.

I put Explorer Disc Brakes on the 9" for the GTO. It was originally ordered for Ford 11" drums (from Moser with Axles).

So I swapped from the Big Ford Bearing Housing to the Torino Bearing Housing. Same bearing Bore and Bearing but the mounting pattern for the brakes is different. So I had to shorten the axle tubes another inch on the Housing. That was easy enough and was done with a mandrel bar and Donuts.
Deal was now the Moser Axles were 1" too long. So we cut them on a very expensive Lathe at work. The Axles were extremely hard so the cutter had to make very small cuts each depth of cut. About 4 hours later both axles were shortened (on the ends going into the pig).
I do not expect to ever hurt these axles EVER. Even with boost.

I am sure that Strange and Currie make similar parts. Buy the best axles you can afford.

Tom V.

[Scott Roberts]

Ok..i said best bang for the buck..best complete setup for the application. Not cheap..i want to bolt it in and be done. Sorry if my choice of words caused some confusion.. I just know there are several choices and probably smallerr companies I'm not aware of that maybe equally as good as the big names yet less money....best bang for the buck.

[Formulajones]

Originally Posted by RocktimusPryme

I’ve got an 8.5 out of an xbody that I’m putting into mine. Supposed to be bolt in and a tick narrower end to end.

I paid I think $350 for it? I’ve heard you used to be able to get them cheaper but everyone knows they are the budget first gen swap now. Now I could swap the brakes over and be done with it. $350 upgrades rear.

But I’m putting some cash into mine. It will probably be 13-1500 when I get done with it. 30 spline Detroit and moser axles. Disc brake kit from the right stuff. Still waaaaay cheaper than a bolt in brake to brake 9” from one of the big companies.

Yep, that is by far the cheapest way to do it and you end up with a nice piece that will last. As long as someone doesn't mind hunting the interweb and boneyards, the 8.5's are still fairly easy to find. A little time and money spent and it's a good way to go.

The 9 inch way is a bit more spendy. Especially if you have to narrow it because finding the right width is difficult. You have the cost of the rear itself when you find one. Then you have the issue of buying the 3rd member parts. With the HP mentioned, I'd want a Nodular case. Stock cases are weak in the pinion support area, I've taken many apart that were already broken. New N-case from Strange is $400. Then you need a posi (or trac-loc) and the standard clutch style is another $400. More if you want something beefier. You need gears and a setup kit, that will set you back another $300. You'll need fab skills and a welder to set up the spring perches or spend more coin to farm that out. You'll likely want axles, and in most cases the 9 inchers you find cheap will be of the 28 spline variety, While upgrading the 3rd member may as well do the 31 spline setup and spring for new axles, that's another $300-ish. You still have to do brakes. If your resourceful you can save money here, but easier to make a phone call and spend more $$$$ for a brand new bolt on setup ready to go (which is the way I prefer, not a fan of used stuff when it comes to brakes)
So building a 9 inch isn't exactly a cheap way to do it. You'll barely come in under what a brand new piece costs ready to go and shipped to your door.

[Scott Roberts]

Originally Posted by 64speed

Quick performance if you are on a budget and want to use a 9 inch. I paid 2450 minus shipping for what I feel is a really nice differential with a Detroit true trac posi and everything plus they are super nice to work with.

This is what I'm looking for...these type of options..i will call and talk to them..thank you.

[Formulajones]

Originally Posted by Scott Roberts

Ok..i said best bang for the buck..best complete setup for the application. Not cheap..i want to bolt it in and be done. Sorry if my choice of words caused some confusion.. I just know there are several choices and probably smallerr companies I'm not aware of that maybe equally as good as the big names yet less money....best bang for the buck.

If you don't mind a Ford rear in your car (it's pretty much excepted anymore anyway because it's so common) then Quick Performance is highly recommended for price comparison and quality.
If you want a drop in 9" ready to go, that's who I'd be calling.
If you want a drop in 12 bolt, Strange is who I call.

[Chief of the 60's]

Originally Posted by Formulajones

Yes you are correct, they do. A complete 12 bolt ready to go, setup for disc but no disc parts supplied, delivered to my door, was right at $3200

But it's much more than a standard 12 bolt. The casting is extremely beefed around the main cap and pinion area compared to an original so it's much stronger right to start with. It comes with billet caps, I paid extra for a 1350 yoke, a Eaton 33 spline posi unit, 9" ford housing ends welded on, and bolt in 9 inch style 33 spline axles, as well as a support cover. Add oil, toss on my brakes and it's ready to rock. The 9" style housing ends that are welded on can be had with either GM bolt pattern style brakes or ford style brakes, your choice.

Not cheap, but yes, the last rearend you'll ever need to buy, button it up and forget about it.

Then why didn't you just buy a Ford 9"? Cheaper and better.

[Formulajones]

Originally Posted by Chief of the 60's

Then why didn't you just buy a Ford 9"? Cheaper and better.

In this particular car I liked and preferred the 12 bolt option. Too long to explain why but it just depends on what I'm working on.