i was under the assumption that GM stopped putting the 9 bolt in f bodies around 88 or 89. anyway, i go to change the rear fluid in my 90 and sure enough, 9 bolt. i thought all 90 iroc's with the L98 G92 combo had 10 bolts and therefore the 3.23 gear ratio....

 

I also have a 9 bolt rear in my Formula 350, but as you stated it is an 89. I was having issues with an gear change the previous owner did and had to do some research prior to repairing the problem. I found out the the 9-bolt was used exclusively with the 350 due to the 9-bolt's strength. Since, GM had not switched the F-bodys over to 12-bolts yet. I would have to guess that they continued to use the Austrailian rear until the 12-bolt was ready.

I hope that helps

 

You're right that in 89 it was the last year of the 9-bolts for the G92. Although the first couple IROC's in '90 got the remaining 9-bolts.

I'm pretty sure you have verified that is a 1990 IROC. When exactly when was it manufactured?

 

MWillie,
Correct me if I am wrong, but even the 93-02 cars only got a 10 Bolt Rear axel...

John

 

No you are correct. I was thinking of all the conversions out there when I started writing the message. Sorry for the confusion.

 

They used what they had left over. Some 90's did get 9-Bolts, I've seen it myself also.

 

so the 9 bolt rear has 9 bolts around the dif. cover? Thats kinda wierd.

 

Yeah but the internal strength is much better than any of the c-clip 10 bolt coporate rear ends.

 

I think just because the carrier size is larger makes it a stronger design. 7.75" vs 7.5" (82-83) or 7.625" (84+ )... I imagine there are other factors in the design that make it better or Stronger tho.

I believe tho GM went strictly to the 7.625" in 93+ cars interestingly.

As for the number of bolts on the back, that is just a cover and there is no strength needed, your wheels have only 5 Lugs, and they take a TON (literally) more abuse than that rear cover... if it seals up and does not leak is all GM was concerned with on the cover.

John

 

it was manufactured in 8/89.

thanks for the info about 90's and the left over 9 bolts. i guess i lucked out...

 

The BW rear was first seen in 1985

According to Hi Performance Pontiac, Dec 84, the Borg-Warner 3.27 axel was a "true posi (as opposed to an Eaton Locker)"


Externaly they are the same as previous axles but inside is 7-3/4 ring gear and 28 spline axels.

The extra duribility comes from a four pin differential, the weak link in rears are the ones with only 2 pinions.

Elimination of the C clips and the use of tappered roller bearings at the wheels are additional strong points.

Is stronger than the chevy 26 spline, 7-5/8 ring gear.

Is stronger than a 8-1/2" Dana 44 !!

Why? The Woodard Schedule......


The Woodward Schedule was a test where Pontiac launched the car by side stepping the clutch at 4000+ RPM and power shifting thru every gear at redline.

They ran about 30 axles through 200 Woodward tests without a single failure.

The Danas broke in this test.

 

Another thing about the 9-bolt is that it is drag legal, due to no clips and the use of axle retainers on the outsides of the axles.

There is not much aftermarket for them, but if your car has one and you want to drag, you won't have to change the rear right away.

 

You can get a 3.70 or was it 3.73 gear set from SLP they also have the transmission speedo gears... For the 9 Bolt... Other than that, there is not much else you can get for it that I am aware of.

John

 

It's a 3.70 gear. www.9bolt.com

 

SLP doesn't list the 3.70 gear set anymore, only the speedo gears. For being a supposedly strong rear end there sure are a handful of blown up BW rears laying around. I've got a 3.45 PBR disc rear out of an 89 Formula that has a tooth ripped off the pinion and a hole in the cover... At least the brakes will get used.

 

"- One of the most common reasons a 9 bolt fails is due to excessive backlash between the ring gear and pinion (usually due to worn out pinion bearings or improper pinion preload) or between the side gear and the pinion gears (usually due to worn out brake (ie posi) cones). "

9bolt.com

 

There are gears available through either Drive Train Direct or Drive Train Specialists. I cannot remember which one has the gears off the top of my head.

 

I have a 1986 Trans Am that I am parting out with a 9 bolt.
I was pretty suprised when I jacked up the rear and counted the bolts.

 

I just got a 9 bolt with 3.73 posi and disc brakes at the junkyard on half off day for $55 and I looked at the ring and pinion and there were no chips or damage but there is a little play in them. Not much just a little. Is that normal?

 

The 9 bolt was never optioned with 3.73 gears. 2.77, 3.27, 3.45, 3.70, yes... 3.73 no.

 

Mabe he THOUGHT it was a 3.73 since there more common than a 3.70. that .03 turn is only a TENTH of a Degree actually = .108°

John

 

I have one 9-bolt on the car with 3.27 gears and one in the garage, that is waiting for me to install the new bearings it needs, with 3.70 gears. The previous owner had the gears changed, but I am guessing that it was not done correctly. Which is why it needs new bearings.

 

A little play is normal for any rear axel, how much is too much? I do not know...

A rear axel should last a LONG time, if they do not blow up.

John

 

Relax. So quick to throw up the BS. You should be in the street racing board. Yes it is a 3.70 I was confused. The point of my post was not asking if the gears were offered in the car. I have a book that lists all the rear ends of every year and their ratios so . . .

OKFOZ - Thanks, the play is minimal but you can hear the ring gear move between the tooth on the pinion a little. I guess the only way to find out is put it in the car? Since I don't want to tear it down and all.

 

Have you opened the rear cover? If so, you can use a dail indicator (with magnetic base) to get an idea of the amount of play. I have a GM service manual that covers the 9-bolt and the specifications for it. I can look it up and give you the numbers if you would like.

But, if you are getting play from the wheels or discs, by moving them back and forth, then that is pretty normal, depending on the amount.

Hope this helps

 

Yeah I opened the cover and I could probably get a dial indicatorif you have the specs, that would be great. Thanks.

 

Drew, The tag on my 85 TA diff says 3.08, and I've heard of a few other 3.08s as well so don't forget them.

 

pontiacZ28

The End Play specifications are:

Axle Shaft - (new bearing) - 0.04mm to 0.048mm (0.0016 - 0.0019 in)
(Used bearing) - 0.076mm (0.003 in)

Runout Specifications are:

Differential case/ ring gear mating surface - 0.05mm (0.002 in)max

Ring gear runout - 0.13mm (0.005 in)

Ring gear backlash - 0.10mm to 0.19mm (0.004 to 0.007 in)

I hope this helps. If not I can copy the page on my scanner and email it directly to you. Let me know.