ydnar417

iTrader: (2)

I've been looking at different options for my rear diff and my head feels like its going to explode. A little background - I have an 86 IROC that was originally a 305/5sp combo. Well all of that is not gone. I tore the car down to the shell and am rebuilding everything. I still have the original diff that I am pulling this weekend. The engine going is is 330hp/380tq, planning on throwing a 6sp from 93-97 behind that. My questions are as follows:

Do I keep the original rear and beef it up? I've read everything from these 7.5/7.625 rears will go with anything over 300hp to guys running 500hp on them at the track every week. Ive priced out 1200 or so in parts.

This is going to be a weekend cruiser, occasional local car shows, that will may hit the track once in a while, maybe.

I've priced out fully built rears from Spohn that range in the 3k area.

Then we have the issue that, even though I am mechanical, I've never rebuilt a rear myself, and would prefer not to on this.

I was debating also heading to a local shop to have them rebuild, and would probably go for a quote this weekend.

big gear head

Your '86 will have the small 26 spline axles. I would not use them. If you have the money then call Moser, Strange or Mark Williams and order a 12 bolt. You will probably break the rear end that you have now if you race it, no matter how well you build it.

ydnar417

iTrader: (2)

I was afraid of hearing that. So far, everything has been in that 3k range. Not too worried about the money, but would like to save anywhere I can. Looks like Im most likely going to end up ordering a 12 bolt.

big gear head

Contact Jim at www.jdrace.com and see if he will give you a good deal on a Moser 12 bolt. He use to be my partner in parts and he has pretty good prices. He goes by monzaz on ebay.


You also might consider a Quick Performance 9 inch.

sofakingdom

iTrader: (1)

That's not enough motor to really stress the rear too bad, especially not with normal street tires and the barest modicum of common sense in how it's driven.

You will HATE HATE HATE any gear lower than 3.73. Your car almost certainly has 3.08 in it now, which will tempt you to open your veins the first time you try to drive it in traffic. To get a good feel for what it will be like, go find ANY halfway peppy stick shift car - GM, Frod, Honduh, Hupmobile, whatever - and take off in 3rd gear from a stop. That's EXACTLY what a T-56 and a 3.08 will feel like.

You need a gear, and while you're doing that, might as well put in a posi, and if you're buying a carrier, might as well be one for 28-spline axles, which means you might as well buy new ones. Which by the time you get done doing that, you might as well learn how to do it yourself, and save yourself about $250; which includes, picking up a new skill along the way, and several HIGHLY USEFUL tools to boot.

jmd

iTrader: (4)

If you have 3.73 gears, run them for a little while.

You know it works. It's paid for. And after driving them with (whatever) T56 you end up with, you will KNOW if you want to keep that ratio or go to 3.90 or 4.30 or some other ratio.

Generally, you'll find the 0.50 sixth gear to be a bit much with 3.73 rear. But if you end up with a 0.57 or 0.63 sixth, you might find it perfect.

Being able to drive a new combination before ordering specific, non-returnable parts can be invaluable.

IIRC, I've driven a T56 with every ratio from 3.23 to 4.30 and with 305, 350, and 400 inch engines. Plus, some guys who (for some crazy reason) like their 4 speeds with a lot of gear find the idea of running a 0.50 sixth with anything less than a 4.88 rear crazy. Me? I like overdrive. So give yourself an opportunity to pick and choose what you want; you'll be the one driving it.

SbFormula

I went overkill and put a Moser 9" with a Motive Gear 3.89 and a Detroit True Trac. This combo was attached to a T56 rated at 450ft/lbs (if I remember correctly), a bigger drive shaft with Spohn torque arm bolted to the frame and dual friction clutch, subrame connectors, etc...

My advise is you have to think driveline as a whole. My T56 is the weak link in the setup so the 383 stroker will have to be around that so I don't destroy the transmission. I could have gone T56 Magnum rated at 700HP but then the weak link would have been the structure. I don't know if you get the idea! Everything as to work as a whole. No sense having a strong rear end if you have a torque arm attached to the tail shaft of the tranny. The more torque the more structure strength you need. And don't forget the tires, they need to stick!

As far as the rear end goes on mine with my set up there are pros and cons. It actually does the job to plant the wheels hard in the pavement even taking off from a corner at WOT. Now the poor 305 feels like a weak engine. However, the Motive Gear are not constructed for cruising but for performance (Motive will tell you!). Mine whines between 45-80mph under load and it is not due to mis-alignment I guarantee. The 3.89 gear combine with the T56 ratios is perfect specially in overdrive. The T-56 # is 1386-000-011 if you want to check the ratios. Everything is full polyurethane bushings so noises and vibrations are transferred to the structure. I also had problems with oil leaks from the rear end that I am still trying to tackle. There were a few manufacturing defects from Moser that were fixed. So don't assume that because it's new out of the box that it is perfect.

By changing the ratios and tranny, your car will experience different harmonics and also different sounds and vibrations. Mine experiences a pulsating vibration that is speed related when the drive shaft and the exhaust sound waves go out of synch. It is very interesting to hear as you put the car in neutral, let in coast around 65mph while revving the engine at 3200rpm. Upon deceleration, the pulsation slows down and goes away just like when you tune guitar cords. Anyhow, all that to say don't expect everything to be 100% perfect as the car was engineered as a whole and you are now modifying it with parts that where engineered individually. There is tons of info on internet about harmonic distortion/vibration. Hurst has a pdf file on it but can't find it!

The more stiffness and strength, the more weight and less comfort but the more torque you can add. My car is now rough and tough but that's the way I like it

Here's a great book

Best of luck!

SbFormula

Found the Hurst document

Also worth mentioning, the rear end installation was done by a supposedly performance shop. The guy had a good reputation but an ego bigger than nature. It was a nightmare afterword trying to fix all the mistakes he had made. I came to the conclusion that he was an expert, but not necessary in restomod. He was an engine builder! He was just not interested in my project and did a half h**ed job.

Ron U.S.M.C.

After a lot of investigation concerning my application I went with this.
Post #45 shows the difference between the 10 Bolt and 9in.
If you have the power to turn the mass of a 9in easily and want to run sticky tires at the track the 9in or 12 bolt is the way to go.
link = https://www.thirdgen.org/forums/tran...de-photos.html

ydnar417

iTrader: (2)

Im going to keep my eye open for possibly a used 12 bolt or 9 inch to drop in, but we'll see. If I can't find one soon enough, I will just purchase a new unit to bolt in.

Night rider327

iTrader: (13)

Keep what you have, until it breaks. Your combo is not that wild and your uses are pretty tame.

Here is my story.. I'll try to keep it short.
1988 camaro RS, 355 V8 swap, th-400, 2800 stall converter..
Daily driver, every weekend dragstrip car.
High Trap speed, but bad 60' and ET.
Kept working little by little to get suspension done and traction there.
I ended up with 116 to 118 mph trap speeds but ETs was in the high 12's.

After about a year, I had an axle bend, so I upgraded rear end parts. Yukon axles, power trax locker, timkin bearings, TA alum. support cover.

More traction aids, and 3 more years of daily driving and weekend track time. I had it running 11.40's @ 118, 1.60's 60' times with Nitto drag radials.

At that point the rear end lasted me maybe another 6 mo. and broke the ring gear.

I had a parts car, so swapped axles, locker, cover over to parts car rear, and put it in my car. Lasted 2 weeks on the street and 1 pass at the track. Broke the pinion gear

Car sat for a year while I saved up for a ford 9"

Point to this though is the rear end lasted almost 5 years behind close to 500 HP engine. It wasn't until I got really good traction that I had a prob.
I put probably on 40-50K miles on the car street duty and can't count the number of 1/8 and 1/4 miles track passes.

The rear end held up fine, but once traction and power was there, it didn't last long.

I would not sink money into the stock rear end. I wasted $1,000 on mine, but I would say drive it, have fun with it. You are not going to break it as soon as you start driving it, and heck it may never break... Depending on what you have in mind for suspension , and launch RPM.

But if you plan to move ahead with your car, engine wise or traction wise above what you listed.. Just start you a 9"/12 bolt/dana 60 fund, throw a few bucks each week into that fund and by the time you need it, you will have the money there to buy it.

Sorry for the long post.

big gear head

330HP+6 speed+track=broken 7.5 10 bolt. If he never takes it to the track it might live, for a while at least. That 6 speed is the breaker here. An automatic would ease the blow (but be a lot less fun).

zz3irocz

I want to upgrade mine too and the only real budget option is a used 3rd or 4th gen rear. Only reason I want to switch is because I have a 2.73 open diff with 700r4 and I can do around 60 mph in first gear which kills acceleration. I have a zz3 crate engine with lt4 hotcam, it makes around 400hp and 420 tq and has been punishing that rear end for the last 20,000 miles and no problems yet.

big gear head

Your automatic transmission is easier on the rear end. Manual transmission shock the rear end harder and usually break parts more often.

beltran89

Speaking off 3.73 gears someone is selling for 100 bucks, should I pick this up for my v6 89 Camaro because everyone tells me I should get a different rear end.

big gear head

You probably need to start a new thread instead of taking this one in another direction.

Ron U.S.M.C.

As the link I posted says and shows in post 9 of this thread, building a 10 Bolt with the best parts I could find works well for a guy like me that only has the one car and uses it as a DD, but wants it to be fun to drive. And have fun I do.
I don't take it to the track because I like my car just how it is and don't want to break it, yet I could not stand the fact it was a 1 wheel peal with 2.73 gears.



When the time comes to build a car for the track that has POWER, as much as I love my Third Gen. Camaro it will most likely be a "69" Chevy Camaro.
Not only are they bad a-- cars but wont fall in the CA smog category that holds me back with my "89".

sofakingdom

iTrader: (1)

Given that a brand-new set of 3.73s can be had for around $200, $100 for used doesn't seem like much of a deal.