Yeah, hi. I have the 87 IROC and THOUGHT I had the BW 9 bolt but turns out I dont. And after that a guy tells me that if you didnt have that you DEFINATELY have the 12 bolt. I think that is fiction but somebody please tell me he is right. Alright, but let's assume I have th 10 bolt. Im making my first passes this weekend and I was wondering if it would be alright to run my Nitto's on there? It's a basically stock car, I've only added a Flowmaster Muffler, K&N Air Filters, and I removed the sway bar. Tell me what you think. But mind you that it did set up for a year before I bought it, might that weeken it? Alright, that's all i got for ya.

 

If you have a Auto with the 305, you have a 2:73 10-bolt rear. And it will not make any difference what tires you run. Not that much Horsepower or torque with that set up.

 

Fortunately, you can literally COUNT the number of bolts holding the rear cover on and tell for yourself.

9 = 9 bolt, 10 = 10 bolt, 12 = you get the idea.

NO 3rd gen every came from the factory with a 12 bolt. So if you've got one, it's an aftermarket one put in by a previous owner (and can add considerable value to the car- that's a $2000+ upgrade!)

Auto trans cars are VERY easy on the rear end components (trans brake equipped cars nowithstanding). You'll be fine with whatever tire you put back there. I know someone who runs a 10-bolt (with a spool, admittedly, no spider gears to shatter) to 10.75 ETs in a 3rd gen with slicks and ladder bars! I wouldn't recommend this, but they're tougher than you think. 7 out of 10 shattered 10-bolt rears is behind a manual trans, in my expereince.

 

Was just wondering... i have a 84 Sport Coupe, Z28 with a 10 bolt rear and I’m dropping a 350 and new tranny in it.. Will my rear hold up to the 350?? I keep getting mixed stories some say it will be fine some say it wont last what do u guys think

 

The 10-Bolt rear will hold up fine with a mild 350 as long as you do not ABUSE it.

 

Doin 350ci clutch drops with drag radials will tear that 10-bolt apart, but other than that you should be fine.

Also I thought the 9-bolts were only in 88-90 cars.....is that right or wrong? I kinda need to know cuz I'm lookin for one....

 

I think they started using them as early as 85 on the L69 5-speed cars. It was referred to as the Australian rear end.

 

The B-W 9-Bolt rear axles were used as followed:
85-89 305 5sp had the B-W 3:45
87-89 350 auto had the 3:27 & 2:77
The 89 also had the best rear disc brakes, the 11.655 rotors with the Alum PBR calipers.
These rears are getting hard to find, with the most common ones being the 2:77 used with the 350. Parts are available, but are expensive.

 

So the one to look for is the 89 305/T5 rear.....3.45 posi with the alum. caliper rear discs.....

Time so start junkyardin'

 

That would be the B-W 9-bolt to look for, but it will be like hunting
for that White Buffalo. Good luck and I hope you don't need that rear end soon.

 

There has been some rare cases when '90's and even a '91 had a 9 bolt installed, but typically it's 85-89/90 with the 89+ being the best because of the brake upgrade.

PS The parts are not hard to find if you are reading this, but unfortunately, they do cost more than 10 bolt parts.

Miles
Diff Solutions
www.9bolt.com

 

Well I haven't blown my 10-bolt up yet.....but the 2.73 peg-leg doesn't exactly make me happy behind that T-56. Talk about boggin first out

And since I have a blown 383 in mind for the car I need somethin better than a 10-bolt......9 inch is hella expensive though. BW 9-bolt seems the way to go. What I wanna do is find a 3.45 or 3.27 to run till I get the motor built then put a new set of 3.70's and a new posi in it.

BTW Anybody know the RPO's for the 9-bolt rears? Might be hard to crawl under some of these junkyard cars.....