Building 8.5 for my G-Body please HELP!!

[sschevyss]

Hello all,

I am trying to finish up the rear end for my 1986 Monte Carlo SS before I get the body work started. What I have is a 8.5 from a Grand National. I plan on mini-tubbing the car to fit 18's maybe 19's. I have not made the wheel purchase yet but I am not satisfied with the 17" black torque thrusts I currently have on the vehicle.

My problem is choosing the proper differential carrier to best fit my driving. I am not famaliar with the different brands and their performance so maybe someone can help.

My question to you guys is since you all deal with the whole pro-touring type of modified vehicles (This is the style I am trying to build) which differential carrier and axle setup should I use. The car is currently powered by a mildly built 350 with a th350 trans but I will be swapping a mildly built LS2 with a 4l80e trans come summer. Car is lowered approx. 4-1/2" in the front and 3" in the rear. I will be driving the car to and from work maybe once a week but will be out on the streets highway driving on weekends. I plan to hit a road course a few times and complete a long haul in the 2012 Hot Rod Power Tour. Can any one recommend and give me some detail on the variations of differential carriers available.

I was told by one gentleman at summit racing tech support that the Eaton Detroit Tru-trac differential would be my best bet.

All opinions and comments are welcome.

Thanks guys.

[SicMonte]

Tru-Trac is the only way to go...just get that one and you will never look back.

[sschevyss]

Thank you sir. Hearing it from a fellow Monte Carlo enthusiast makes me feel far more convinced. Let me ask you a question I do know a guy that has a curry g-body 9in housing only. Do you think I should stick with the 8.5 or purchase the 9in?

[SicMonte]

Depends on what you want to do with the car. The 9" will handle more power but would be more expensive to buiild. The 8.5 can handle some power and is fairlly cheap to build. I have the stock 7.5" 10 bolt in my car...and its just fine with about 400hp to it.

[Crossupbill]

Personally I like the Eaton style posi carriers, I used an 88 and up GM carrier with 30 spline moser axles in my malibu. Works pretty good for me.

[RomsMotors]

I have moser 12-bolt w/ eaton posi units, richmon gears, and moser axle. With the type of build you are doing it would be wish to upgrade axle from stock it a the little added insurance. With the upgrades of posi unit and axle should give you a good rear end that will handle the power. A 9 in would be a good choice but, will cost a little more to set up since you have buy housing, center section, posi unit, axles, gears and brake kit.

[sschevyss]

Thanks a lot guys. I see that the majority of you run moser axles. With what I am doing is there a true benefit for 30 spline axles over 28 spline axles?

[Crossupbill]

Extra spline equates to a larger diameter axle and ultimately a stronger axle shaft. Also adds a bit more rotating mass but in this application it will be unnoticed. It depends on how it will be used and what kind of power you are making. I am sure the stock 28s would be fine for most practical applications but I have been known to abuse parts so the choice was easy for me.

[sschevyss]

I heard that lol. I am only 22 just now getting ready to graduate college here in May but since I bought the car when I was 16 I have always learned the hard way it seems so spending the extra money for the long run is definatly something I always take into consideration. Looks like Moser 30 splines.

Edit: I just looked on summits web site and they only show a listing for the 28 spline. Guess I will have to call moser.

[SicMonte]

When I had my stock rear re-built this summer I opted out on the better axles. I did this b/c I knew I was going to get a better rear within the year. When I do get a rear I am going with an overkill Fab 9. If you decide to keep the 8.5 and beef it up then I would definately get better axles! Moser makes them, just give them a call.

My buddy has a 8.5 in his olds cutlass and runs low 11's at the track all day long...and the rear is fine.

[Nothingface5384]

tru trac diff, with wither dse or ta performance diff cover

either u.s gears r/p yukon, or motive performance
hit up jdrace.com

30 spline mosers 3/16 retaining plates timkin bearing and all that good stuff

[Nothingface5384]

only thing i dont like about the corporate rear is that it uses c-clips and 2 5/8 axle tubes where as a 71-72 buick skylark/olds cutlass uses 3in tubes and bolt-in axles
not a big deal though

[sschevyss]

Thanks bro.

[sschevyss]

Okay so I now pose the question to all of your good and or bad experiences with Clutch-type Posi vs. Cone-type Posi vs. Detroit Lockers. Which do you like best, dislike, recommend etc. Just want to see what you all think.

[MonzaRacer]

Take the 8.5, use Moser 30 splines, an true trac and c slip eliminator kit and a preload rear cover.
To anyone who says 8.5 wont live is a fool. Bob Joysey used drag these rearends in 10.5 wide dragracing and they stood their Camaro up on the bumper for years.
My buddy has had a built 12 bolt (8 7/8 ring gear) in his Super Pro car(18deg 280 in sbc, pg, 16/33/15 slicks low 5s high 4s in 1/8th and NEVER broke it and it ran first 5 years with only Comp Engineering billet caps.
As for a 9in it sucks up a lot of power, in a Gbody the upgrade is the 73-77 Abody rearend, and several companies sell control arms to install them.
also I have used many gears sets over the years and so far my best luck has been calling Mike Maddox at West Coast Differentials 18003099342 ext 110. Sierra gear ring and pinion have held up much better than Motive for me. Motive has given me noise issues in past, especially if the user doesnt follow break in procedures.

[roanokejim]

I'm also asking for the same question. I hope that we can find answers here. :D