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/asp...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. 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.

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.

[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