road racing/autocross??

[SicMonte]

I have the $$ now to buy a rear end for my 88 monte carlo ss....that is set up for road racing and autocrosses. I have a bone stock rear in there now (3.73, posi, 7 5/8" 10 bolt) and I want to get something that is stronger and ideal for road racing. I was thinking either a 9" or a 12 bolt...but have no idea whih is better. any suggestions? personal experiance?

[Randy67]

Either the 9" or 12 bolt would work in this application. Look here for a 9" rear end http://www.speedwaymotors.com/xq/aspx/paging.yes/dept_id.91/display_id.4856/qx/Product.htm
Pretty good price for a bolt in 9" with full floater hubs. Just add a center section with gears and diff and you are ready to go. :drive1: Places like Moser have bolt in 12-bolts if you prefer a GM rear end.

[SicMonte]

im not sure what to get....is there any benefit from one to the other?

[big gear head]

The Moser 12 bolt would be a good choice. You will want the Truetrac differential for road racing because it is smoother than the Eaton or other differentilas. This will help with traction when turning. You will also want the tapered roller bearings because they handle side loads better. These are 9 inch Ford axle bearings which will eliminate the c clips. The Moser housing ends are designed to accept Chevy brakes, or you can spec Ford housing ends and use Ford brakes. You can get a 1310 or 1350 yoke on the Moser 12 bolt. I can install the 3R yoke (which is what your drive shaft uses), but Moser doesn't do that. I don't recommend the aluminum cover for the Moser rear end because the bearing caps are so much larger and the bolts are larger. It just doesn't need the aluminum cover. A rear end set up like this would run around $2270 plus shipping. The 12 bolt is lighter than the 9 inch and takes a little less power to turn, so your car will be a little faster with the 12 bolt.

[SicMonte]

would that have disc brakes on the rear? I can get a 9" with explorer disc brakes for around $2100.

[white79bu]

I have a 69 chevelle rearend in my 79 malibu. I took it to my chassis guy and told him I wanted everything cut down to the stock 7.5 measurments. It works great. But I did it almost 7 years ago and I had around $1200 with a new four series Brute strength posi, 4:10 gear, moser axles, c-clip eliminaters and housing. I have drag raced, autocrossed and beat the snot out of it and never had a problem. Andy

[big gear head]

The Moser rear end doesn't have brakes on it for that price. You can use the Explorer brakes if you get the Torino housing ends on it. What does the 9 inch have in it for that price?

[SicMonte]

33 spline moser ales, US Gear posi unit

[slowcamaro]

9" Strange aluminum center and a detroit true-trac diff

[big gear head]

Is the US Gear unit the Traction Lock with the steel side cover?

[SicMonte]

dude i have no idea. a buddy of mine got it in his monte carlo...and he is out of town to get all this kind of info.

im not sure what to get. Everyone has a different opinion. From what im getting..people are saying get the 12 bolt b/c 1) it is a lil bit lighter 2) has less parasitic drag (b/c the pinion gear is 3/4" closer or something)...thats all i know. I want to get the 9" b/c...well its a 9"...and the ones ive found come with disc brakes already on that set up....but i guess if i get a 12 bolt with the 9" hubs...i could get the same type of brakes.

do you sell rears or something?

[chicane67]

Exploder brakes... are a complete friggin joke. Solid rotors are a "no-no". Can we all say 'waste-o-money' ?? I knew ya could...

And FWIW, Freddy's recommendations are something you can take to the bank. :slap:

But if it were me however, Id call Mark Williams and have them whip you up a nice little 12 bolt. The cost difference isnt that much considering that you get what you pay for from MW. If you were to look at a few other, like sites, you will see that the majority of the differentials with problems are from Strange and Moser. I'd say it would be alright to purchase your stuff from either of them, but dont have them assemble it.

[SicMonte]

so it looks like a 12 bolt huh? i will contact mark williams on monday...anything else i should look up?

[vintageracer]

A 9 inch Ford and 12 bolt Chevy rearends are HEAVY! In road racing you do not put near the initial stress/shock loading on the rearend you do in drag racing. There are LOTS of Mustang road racers running 8 inch Ford rearends because they hold up and are lighter. Just put good axles in whatever rearend you run.

I would look for an 8.5 inch 10 bolt or an 8.5 rearend from a G body like a Grand National. With good axles, fresh bearings, some oil control washers installed in the axle tubes and synthetic gear oil, you will be just fine.

No sense in spending large $'s for a heavy 12 bolt or custom made 9 inch. I personally think everyone here has to much of a drag race mentality rather than road racing knowlege. Bigger, heavier and stronger is nice but not necessarily needed!

[hectore3]

An 8.5 inch 10 bolt with a T/A products cover and Torsen T2R ($600.00) style rear differential would be ideal. This is the way I am going with my build.

The Torsen unit is worm gear based and not friction based like Eaton or Auburn's. And while there will be a degradation of the the friction based carriers as you put miles on. The Torsen T2 and more aggressive T2R will be at the same performance at 100 miles and 100,000 miles.

Think about it.

[SicMonte]

what about a 8.5 with a true trac diff? a buddy of mine has 4 8.5's sitting around his house...im sure i can get one for cheap.

[slowcamaro]

8.5 10 bolts are supposed to be a decent rear. and the t2r IS a killer diff. If you can do the swap cheap it'll be a worthwhile upgrade.

[big gear head]

The 8.5 has 28 spline axles, but can be easily upgraded to 30 spline axles. The problem is that the only G bodys that had them were the GN and T type Buicks (and a few Olds 442s). They are rare and most of the time they are expensive. Then you still need to upgrade the axles and differential. How much heavier is a 12 bolt than the 8.5? I doubt that it's much. The 8.5 is a very good rear end if built right, and parts are usually a little cheaper. The 8.5 needs the axle tubes fully welded because the factory plug welds are pure crap. The axle tubes will spin in the center casting if much torque and traction are applied.

[chicane67]

An 8.5 GM, a 12 bolt GM and an 8.8 Ford are very close to being the same in weight. The 9 inch is on a whole'nother scale all together.....

I am very, very critical on weight myself as most of us road race/land speed record types are. The weight and efficiency of the 12 bolt was the hands down winner over anything else. 8.8's are not too bad either, but I have fixed and/or repaired more 8.8's than all other differentials combined..... I still and always will state that it comes down to the assembly and who assembles it that makes the biggest difference overall.

[SicMonte]

ok it loooks like i will be going with a GM 8.5" 10 bolt. Now I need to know what to get for it.....and what to do to it.

[big gear head]

Get a 30 spline Torsen or Truetrac and a set of 30 spline Moser axles. The gear ratio is up to you and you will need a good installation kit with quality parts in it (say no to Ratech). The housing will need to be narrowed and brackets will need to be cut off and others welded on, unless you find one of the GN or T Type rear ends. You will need the 3R yoke to mate with your drive shaft. 8.5 rear ends from '76 and up will have this yoke. Then it needs to be assembled by someone who knows how to set the pinion depth, bearing preload, backlash and can read the contact pattern.

[Kenova]

An 8.5 GM, a 12 bolt GM and an 8.8 Ford are very close to being the same in weight. The 9 inch is on a whole'nother scale all together.....

How much weight can be saved buy using an aluminum centre for the 9" ? Both 9" and 12 bolt centres are available for 9" housings.
Ken

[SicMonte]

looks like im gonna get a 8.5 out of a regal.

[6'9"Witha69]

8.8's are not too bad either, but I have fixed and/or repaired more 8.8's than all other differentials combinedI will second this about the 8.8. The biggest issue I heve with them is the bearing seals going bad (rather quickly) and burning the bearings.

[SicMonte]

to get 30 spline axles in a gm 8.5"...all i need to do is get a new center section?? would they still have c clips??

[big gear head]

Yes, a new 30 spline Eaton posi and a set of 30 spline Moser axles with c clips.

[SicMonte]

i heard that c clips arent that good for a road raceing car? any opinions?? it wont see the track all that much...mostlly street, but on occasion it will get thrashed!!

[big gear head]

The only good option is a set of Moser housing ends welded to your housing with the 9 inch Ford tapered axle bearings. This requires a special set of axles and a housing fixture to weld on the housing ends. Do not use c clip eliminators for road racing. They are designed to go in a straight line and are not designed to handle side loads from cornering. C clips usually work pretty well for cornering because the differential bearings are what handle the side loads.

[SicMonte]

update......

a buddy of mine has a 8.2 or an 8.5 (notsure) out of an early 70's cutlass he gave me...for free!!! it has a 12 bolt cover but a 10 bolt carrier. will this fit in my car?? any opinions welcome..and basic info on this rear.

big gear head...you have a pm!!!

[big gear head]

If this rear end has the 12 bolt cover and 10 bolt ring gear then it is the "O" axle. The ring gear diameter is 8.5, but it is not the same as the corporate 8.5 10 bolt. If this rear end is from a '68 to '72 Cutlass then it won't easily fit into your '88 Monte Carlo. There were some controll arm kits that would allow the earlier rear ends to be bolted into the G body cars. I'm not sure who still makes them.

[John S]

I've been looking for a decent 8.5 GN rear for months without any luck in this area so if you could snag one at a decent price I would do it. Now though I decided to go with a Moser or Currie 12 bolt because I can have custom length tubes with GM flanges. This will allow me to run my rear without the 2.5" spaces I need for the offset of the ZO6 rims and I can swap my Baer rear discs right onto it.
If anyone has contact information for someone else that can buold the G Body rear like this let me know, I would'nt mind an alternative to Moser or Currie.

[SicMonte]

john....you need to contact "big gear head". he has answered a lot of my questions about rear ends. He knows his stuff!!!

[Skip Fix]

Not a rear end swap expert but there were a few years of coporate 8.5s in Cultasses and maybe some Buicks, early to mid 70s I think. So that might be something to look for, alot easier than a GN find! I would assume they would nee the modified control arms used to fit those early rears like 12 bolts in G bodies. If you find one the 30 spline "truck" Eaton fits in with 30 spline 12 bolt type axles. There were no passenger car 30 spline 10bolt axles, only truck or passenger car 12 bolts.

There are ALOT of circle track parts for G bodies. They are generally cheaper than the equivalent part for roadrace or drag source.

[big gear head]

The '73 to '77 Monte Carlo, Cutlass, Regal and Le Mans rear ends are way too wide for the later cars. The controll arm brackets are also wrong. You are right about the 30 spline truck diff fitting into the car housing, but the trucks used the Governor Lock, which is too weak for a performance car. The 12 bolt axles can be used in a 8.5 rear end, but the c clip button on the end must be reduced from .312 to .250 to fit. The '90 to '96 Caprice and Impala had the 8.5 with 30 spline axles. Also too wide for the G body cars.

As soon as I get my hands on some of the '73 to '77 rear ends I'm going to narrow them and change the brackets so that they will fit the G bodys. Build them with 30 spline Eaton posi and Moser axles. That is when I get time. I've been planning this for a few years and it hasn't happened yet. I've had a lot of interest in this, I just can't get caught up enough to do it.

[SicMonte]

hmmm....if i supply you with one....would you do all that for me?? I can be a guinee pig for ya.....


would that be the same rear end that Im getting for free...the "o" axle one? 10bolt with a 12 bolt cover

[big gear head]

The '73 to '77 cars had the corporate 8.5 10 bolt. The O axle was only used for about 3 years, '68 to '70 I think. I could build one for you, but I don't know how long it would take to get to it. I need to do some experimenting with it first to be sure that the upper controll arm eyes are in the ringt place. I have one bought already, I just have to go get it.

[SicMonte]

well....what would you charge to build up an 8.5? 30 spline...detroit true trac...the works....

[big gear head]

You have mail.

[SicMonte]

i didnt get any mail yet....

[big gear head]

I tried again. See if you get this one.

[SicMonte]

nothing yet....just pm me.

[Skip Fix]

Those Gov Locks look pretty scarey can't imagine they are that much cheaper for Gm to build over a real posi!
Use the taper bearing ends and get no C clip axles would be a good thing too.