scj

iTrader: (89)

Like the tittle says I'm looking for some feedback on what rear and differential to go with for a Fbody set up for a road course. Currently car has stock 10bolt with aurburn diff ,fays 2 watts link, and a UMI full length adjustable torque arm. I'm looking for a beefer rear that will handle more abuse than the 10bolt and still be able to retain the watts link, stock driveshaft length, and UMI ta. From my research the strange 12 bolt seems like the best way to go. My only concern going this route is the the differential selection. My buddy who road races and autox's his s2000 and ls swapped Miata soon tells me a Torsen diff but strange doesn't offer that. The closest thing I can find is a eaton Trutrac, but I'm not sure that's even available in a strange 12 bolt. Any advice/ help or recommendations please.

BiGcamo

In my M6 3.90s and new bearings in the 10 bolt work very well for road racing or autox.....im pretty sure i have the torsen not the auburn though

FASTFATBOY

iTrader: (23)

Wasting money on a rear end for a auto X or road race car. Simply not needed.

My 10 bolt with a Detroit TruTrac is very good.

R Myers

iTrader: (7)

Yep nothing wrong with what you have in car now. Run it till you break it then replace it with what you want.

scj

iTrader: (89)

Car should make 500rwhp though. From my research the 10bolt is good for under 400rwhp.

I'm definitely one to "do it once, do it right"

And id rather spend $2500 on a bullet proof rear than put $1500 into the 10 bolt and break it and have to spend more money fixing it or the $2500 replacing it after the fact.

If you're all saying a 10bolt is still good enough I should just put a trutrac in it with some stronger axles and new bearings and seals and be done?

FASTFATBOY

iTrader: (23)

As long as you don't ****** the car around, drop the clutch on drag radials and such the stock rear is fine for road course and auot X duty.

Leave the stock axles in the car, they are the best. Buy decent axle bearings if you run Rcomp tires.

1981TA

iTrader: (7)

OP: the underlying message here is that Road Race / Auto X driving does not torture the rear end anywhere near as bad as drag race. If what you have is still in good condition, go ahead and use. When it dies *then* get the bulletproof rear end, but as FFB alludes, I wouldn't bother doing swapping it out early just because. Just do the normal maintenance and make sure bearings are good quality,

scj

iTrader: (89)

Currently it is a 160k mile 97' ten bolt that leaks, has one bad wheel bearing that's already worn grooves into the axle shaft, and has an original auburn diff in it. If I was going to use this rear it would need axles, a different diff, and a complete bearing/ seal rebuild. It's not a situation of "use it till it beaks" because imo it's already broken. I don't know if sinking money into it would be worth it compared to getting a strange 12 bolt and not having to worry about it. From my research on frrax it seems people are killing 10 bolts pretty easily on the road course too. Granted I may not be beating this car nearly as bad as some guys do around the track, I'd rather spend the money the right way the first time, and in my eyes putting $1500 into a 10bolt knowing its a pretty weak link only to have the possibility that it will break compared to a 12 bolt at $2500 and have a good peice of mind.

79_T/A

iTrader: (1)

The only reason mine blew up was because it had an auburn racers diff that I let wear too far. It slipped for a while and I continued to beat on it. Rebuilt it with a fresh diff and bearings, and its been great since. I drive the car hard. Really hard. I feel bad for it sometimes. I put 100 miles on the fresh rear and drove it straight to a 2-day autocross event and made around 50 laps that weekend.

A clutch limited slip is a wear item, and in a 7.5 rear, the clutches get pretty small. That's where most people have their issues, including me. A gear limited slip doesnt have the same issues.

Keep in mind, that 12 bolt is goddamn heavy, and its un-sprung weight. I thought long and hard and the only piece I would swap the 10 bolt for is a fab9 equal in weight to the factory piece. If you want the 12, make sure to have really good shocks to control that weight.

scj

iTrader: (89)

The car is sitting on KW coilovers and will likely get some stiffer springs than what comes with the kw's. As far as weight goes a 12bolt should only add 15-23lbs over the ten bolt, which is less than I added putting in the roll cage and subframe connectors. Being in the rear it should also help balance the weight of the car too. I'm not overly concerned with adding a bit of weight anyways as it's going to be a "have fun" car, not full out competition car. It has mostly full interior and is fully sound deadened. It's not like I'm adding 40-50lbs putting a 1 ton s60 rear. Hell, I weigh 125lbs. that's reduced driver weight from most people in sure. Haha

FASTFATBOY

iTrader: (23)

You came on here and asked for advice, you didn't take it.

With that said, you really don't know about weight and how it works when a car turns.

50lbs of unsprung weight is a HUGE difference. There is a reason why road course cars keep the stock rear.

From the sticky in the gears and axles section:

GM 10 bolt 4 channel out of a 2001 SS fluid drained;
-complete with rotors,backing plates+dust shields-178 lbs.
-less rotors,backing plates+dust shields-140 lbs.
-less axles,but with carrier+gears-105 lbs.



I pulled the rear end out of my car the other day and weighed it.

Strange 12-bolt, 4.11's, posi unit, complete brakes, 3qts fluid. - 228lbs


My 12 bolt Moser with Trutrack was about 50 lbs heavier


As you were, carry on. Need the number to order that 12 bolt?

1981TA

iTrader: (7)

So, let's talk weight.

Pound-for-pound, unsprung weight (tires, brakes, etc - stuff that moves around when you hit a bump) has a much more pronounced effect on a car's handling than sprung weight (in a nutshell, anything that isn't a moving suspension part). Case in point, look at my car. It's old 60 and 70s tech. The original brakes and suspension stuff was mostly heavy cast iron and the springs were soft, sinking pieces of crap.

Their more modern replacements are not only stronger, they knocked 25 pounds off each corner. This greatly improved handling by the simple virtue of reducing suspension inertia. The car can more quickly and effectively respond to road changes. This is in street, highway, cruising, auto-x or road race driving - it doesn't matter where. This also results in reduced suspension and bushing wear.

At the same time, I've been on a relentless quest to reduce the total weight in my car. It currently tips the scales around 3000 pounds (stock weight was 3500). Of that reduction, the suspension weight has done the most. I would much rather live with the extra 400 pounds in the "sprung" portion of the car, than the 100 pounds taken out of the suspension.

I would avoid adding unsprung weight to a car (12-bolt, S60) unless there are obvious benefits that would offset the handling penalty. For instance, maybe you tow a camper with your car, or maybe you drag race. That heavier rear axle makes a lot of sense in those cases. But, as mentioned by 79 TA, there are fabricated 9" options that are just as strong, while weighing about the same as your stock 7.5".

Here's another suspension change that people commonly do that adds unsprung weight: bigger rotors.

Some do it for looks, some for increased brake performance. Both are perfectly valid reasons and factor into each person's project differently. I obviously am not concerned about appearance. My car is a track beast, with occasional street and cruise use, and I take great pleasure in embarrassing people in expensive cars with what appears to be a backyard reject. However, in order to do this, the car need brakes that can absorb and shed a tremendous amount of heat without fade or cracking.

I had perfectly good 12" Wilwood rotors on the car until this year. For street and auto-x, they were WAY better than I needed. They also weighed 5 pounds per corner less than my current brake setup (30 less than stock), and the car handled slightly better with them (and much better than stock).

Unfortunately, the rotors lacked the mass to effectively soak/shed heat generated by slowing down repeatedly from 140 MPH. So I got 13.4" C6 Z51 rotors, bigger Wilwood calipers and put in 3" cooling ducts. Heat is no longer an issue. Handling took a slight hit - shocks are set a click or two harder on the front, but this was more than made up by the ability to hit the brakes later on corners. I have higher sustained speed. So, factoring up the variables in my particular project, adding the weight made perfect sense.

By the way, I think a 12-bolt adds 12-23 pounds when compared to a 8.5" 10-bolt (which I have). It is quite a bit heavier than the 7.5" 10-bolt in your car and will definitely impact your handling (street, track... anywhere).

Jeff Smith

iTrader: (44)

Get extra axle for back up..I have 3 axles (10 bolts)..

Boss002

I have used the Torsen T2R (easiest to drive on) and now the detroit Tru Trac when it felt like that was having problems (not as simple to drive on, but still works great and cheaper). This is for autocross not road racing, but the tru trac has been in a few high prepped autocross cars and I like it other than it's tendency to induce over-steer pretty fast, but then if your on it, it's great.

People will tell you this is not a competitive diff, but hey I got FTD on East course at nationals with it with no practice except West course, and beat the other camaro because.... his auburn was burnt up

smitty2919

Boss002, you think the oversteer tendency of the TruTrac could be taken out by tuning the rear swaybar/spring combo? Having a 3 way adjustable rear bar along with a 7way adjustable Watts Link I would THINK one could tune out the oversteer of the diff. This is on Strano 150lb springs.

I'm still up in the air what direction I want to go. TruTrac has an appealing price vs Auburn Race Diff though.

DAlgozine

My opinion:
Stock 10 bolt and 500 HP with sticky tires on a road course, driven hard is not going to last, especially with taller gears. I have personally seen many 10 bolts break in a road course racing environment with far less HP.
Racing with less then 300 hp (per class rules - NASA Camaro Mustang Challenge) I installed a 9" . Bullet proof, especially during those inevitable times when you wheel hop. Yes its heavy, and maybe not ideal selection for everyone, but falling out of a race because of broken parts sucks and in the end cost a lot of time and money. Plus the 9" has some great diff options compared to the 12 bolt.

79_T/A

iTrader: (1)

I wouldn't worry about oversteer. Any functioning diff will cause oversteer compared to a clapped out stocker. If you want to remove oversteer, drop the watts link down a couple holes and it will disappear. Just don't go too far because those springs are too soft for a really low roll center. You will get nothing but push after a certain point. Luckily it's one of those things that is quickly and easily changed.

smitty2919

Thanks for the reply 79 T/A I figured I had enough adjustment between the sway bar and watts link to make up for it.

Aside from getting my first car trailer in a week...I can't WAIT to upgrade the diff.

scj

iTrader: (89)

I asked for opinions as well as experience and recommendations.
im not disagreeing with you or trying to be a dick, but it sounds like you're opinion/ recommendation may not the the only one in the world.

I know the number to stange and have discussed this with them also, but like and like any company, they're selling parts, not advice or experience.

This is the kind of comment that distracts me away from the 10bolt, and there's a few other threads I've found on frrax that suggest the same thing.

I'll weigh my options... Cost/weight/ durability and decide that way I suppose. There's no point in keeping spare rear ends if that's the route id be taking with the ten bolt even if it adds a little weight and effects the handling characteristics going with the 12 bolt. I'll just dial the suspension setup to accommodate the extra weight better. I wanna be driving the car, not working on it all the time.

Racerx's ls3 firebird build by blainefab making 650rwhp is running a strange 12 bolt, must handle like a big pile of **** then.

79_T/A

iTrader: (1)

Even Alan would say the 12 bolt has drawbacks. I believe it's been in the car since its street days. It's also needed a few rebuilds now that the car makes so much power. Also, the cars suspension has been finely tuned over the years to compensate for the extra weight.

Keep in mind even though you have a powerful motor, you won't be driving it nearly as hard as these guys do in a wheel to wheel race. Your car is beautiful, it's going to be hard to push the cars limits after all the painstaking work you put in it. There's a huge difference between lapping at an HPDE, and competing wheel to wheel.

All in all, if you have the means to upgrade, do it. I don't think it's necessary for you at this point but since you have to assemble the car, might be the best time to do it. I do, however, think there are much better choices than the 12 bolt. A 9inch is a much better option in my opinion. The diff selection is much better, and a fab9 can keep the weight down. The downside is cost.