Night Stalker

I have a 1987 IROC-Z 350 with a posi rear and 3.42 gears. I want to upgrade to 3.73 gears but I have the 9 bolt rear end. Do I just buy gears for a 10 bolt 7.5" rear or do I need special gears? Thanks

AlkyIROC

Your 87 IROC with a 350 should have come from the factory with 3.27 gears. The 305 model came with 3.45 gears. 3.42 is a 10 bolt ratio.

9 bolt gears are 9 bolt gears. Trying to put 7.5" 10 bolt gears into a 9 bolt diff is as easy as trying to fit Ford 9" gears into it.

The only thing the 9 bolt and 10 bolt have in common is that they have the same external mounts to install into a third gen. Other than that, they're 2 completely different diffs.

Parts for the 9 bolt can be found at www.9bolt.com

Night Stalker

Thanks, is there anywhere else to get gears for this rear, I rather get new ones if possable. Also, where can I get an install kit? I didn't see one listed on 9bolt.com.

jb3829

iTrader: (1)

I dont know what kind of skills you have....but installing gears is better left to the pros. They have the proper tools and experience.

Night Stalker

Thats what I'm going to do....but I still need an install kit for the shims and gaskets and I also want to replace the bearings while it's being done...

AlkyIROC

That's the bad thing about the 9 bolt. Because it's an Australian made diff, there's little if any aftermarket parts for it in North America. It's easier to just yank it out and put in a 10 bolt so you have something that can be worked on.

Here's a listing on Summit for 9 bolt stuff

http://store.summitracing.com/egnsea...115+4294894011

big gear head

I can get you a new set of 3.70 gears for $180. I'll have to check the price of the installation kit. All of the 3.70 gears have a little noise in them, so don't be supprised when you drive it for the first time and it whines.

Night Stalker

How loud do they whine? Will I have to turn the radio up extra loud so I can hear it? Do all the numerically higher gears whine?

The problem is that right now my rearend whines really bad. I think someone before I got the car changed the gears to 3.42's because at 60mph in 3rd gear my RPM's are just under 3000 with a 25.65" tire. I have not gotten under the car to do the spin the driveshaft test because it really didn't matter to me what gears were in it because I was going to upgrade to 3.73's or whatever.

But, my main intension is to quiet down the whine. So if 3.27's don't whine then maybe that would be my better option.

Is there a phone number I can contact you at? Thanks

big gear head

Factory installed gears will be quiet if they are set up right. The after market gears sometimes make noise, and all of the 9 bolt 3.70 gears make noise. It isn't too bad if they are set up right. It is usually just within a 5 MPH range, around 50 MPH usually. Send me an email at biggearhead@bellsouth.net