Smooothie119

Some of you may remember me posting back in December about my '87 IROC with the blown rear. Here's a quick recap, it has an LB9 with a gutted air box, air foil, Fast Chip Stage 2, T5 tranny, 3" cat-back exhaust into a Flowmaster (80 series I believe) muffler with 2-1/2" outlets, and 9-bolt 3.45:1 rear (until it was blown of course). Anyhow, I didn't have any luck finding any used rears and needed my car back desperately, so I had to settle with 3.73's for my 9-bolt. I was a little weary because I had been told by many that 3.73's would be terrible because of the characteristics of the engine and how 3.45's were a much better fit. Since I've had my car back for about 4 months now, I must say I'm quite pleased. The rpms are a tad higher on the freeway but not too bad, and I can still maintain the 18-20mpg I enjoyed with the old rear with careful driving. One of the biggest differences that became very apparent is the feeling that the car just always wants to go, as if its always in its sweet spot in terms of rpms. But, like I said, it just feels that way. I haven't had a chance to actually test out the car against others to see if I actually gained anything or actually made it slower. I've what babied the car ever since I got it back, until the past few weeks when I began driving a tad more aggressive after putting about 600+ miles on the new gears. Till this day I'm kinda weary about cruising along and just deciding to downshift a gear and just hammer on it like I'ved done in the past, seeing as how thats how the first rear went and it wasn't a wonderful experience. I guess after all this rambling, I'm just interested in hearing some opinions from you all in terms of my new rear and such. Did I actually make it slower, etc? Another ?, seeing that my speedo is also off, what do u all think my top speed has been cut down to? With the 3.45's the car hit 145mph.

Smooothie119

anyone?

Z28SORR

You probably haven't gotten any responces because you've already answered your own question.
You should still be able to hit 145, maybe faster?

Smooothie119

oh, I wasn't necessarily answering my own questions, I was just stating my observations. I just thought that maybe there would be some people with similar experiences that could shed some light on this topic. I mean, I understand there's a difference between how these cars feel and how fast they actually are in reality. Since the gear change, the car feels somewhat faster, it seems to pull harder after 3,000rpm as compared to before. However, it also seems as though the car has slightly lost its lowend power, or at least it feels that way, especially in 1st and part of 2nd gear. I dunno if this makes sense to anyone. Also, I have a question about shifting......is it ok to downshift more than 1 gear as long as 1) you dont downshift into 1st (I'd never dare do that) and 2) the gear you downshift into doesn't put the engine near redline??

I was just wondering cuz when I busted the original rear, I was cruising along and decided to go from 4th to 2nd (which I've done plenty of times in the past) and as soon as I let the clutch out, I heard the most high-pitched god-awful noise. The mechanic that rebuilt it for me said that the original gears must have had a weak tooth because one of the teeth on the ring gear was broke.

TheGreatJ

That has to be a casting flaw. For one thing: when a gearset goes it usually doesn't just break one tooth. It breaks like half of them. For another thing: a 9-bolt rear should be able to handle a lot more power than a T-5. I've seen guys running over 500hp through 9-bolt rears, and other guys blowing up T-5's with under 300hp.

I have a 6-speed in front of my 9-bolt and I up- and down-shift multiple gears all the time. When I'm driving in traffic I often shift 1-3-5 (to reduce leg-work) and if I'm on the interstate and a ricer tries to pass me I'll kick it from 6th to 4th and just walk away from him. I never even had a problem with my 10-bolt, much less my 9-bolt.

Smooothie119

If there's one thing I've been hearing consistently, it's the fact that 9-bolts are pretty damn strong rears. I'm pretty happy I decided to have it rebuilt instead of searching around for the more common 10-bolts that some people were suggesting that I find. I even had a few sources tell me that GM must've switched from 9 to 10-bolts for a good reason.

Anyhow, I thought that was pretty interesting after hearing that a single tooth broke off of one of the gears of a stock gear set that had about 106,000 miles on them. It does make more sense that if the gears were weak, more pieces would've broken off. I don't know too much about rears but isn't there some sort of bearings or shims (I'm probably not using the correct terminology) that keep the gears properly aligned? I wonder if something else was off in there? The rear had a little whine to it, but it wasn't much louder than the normal whine or hum that rears have and it only occurred between 2500 and about 3200rpm or so. Who knows, maybe that was my warning sign and I refused to pay any attention to it.

irocz8957

where did you find a set of 3:73's for a 9 bolt, i thought the only ratio that high was a 3:70 for a 9 bolt?

Smooothie119

If I remember correctly, my mechanic said he got them from US Gear. I went to their website, but I dont see anything listed for 9-bolt rears.............I too thought it was strange when he told me that he could only get 3.73s for the rear. I dont suppose there's much of a difference between 3.70s and 3.73s........

88 427 Camaro

9 bolt ratios to 4.10 are now available for the borg warner 9 bolt at www.9bolt.com Also, new posi units and lots of other stuff too.

Miles
Diff Solutions
www.9bolt.com

TheGreatJ

GM's "good reason" was cost. The 9-bolt was imported from Australia (hence the nickname "aussie rear") and therefore cost a LOT more than a 10-bolt. In fact the only reason GM used the 9-bolt at all was because they didn't think the 10-bolt would stand up to the torque of the TPI motor. Once they realized it could handle it they stopped paying more for the better rear.

[QUOTE]Originally posted by Smooothie119
I don't know too much about rears but isn't there some sort of bearings or shims...that keep the gears properly aligned?[/q]

Yes there are shims and bearings on both sides of the carrier and on the pinion shaft, but if they had worn down or broken then the rear would have chewed up all the teeth instead of just breaking one off.


Also there is no 3.73 gearing for the 9-bolt. That's a 10-bolt gearing. I don't know how long you've been going to your mechanic or how knowledgable he is, but that's basic information that he should know if he's rebuilding rearends for a living. Also if he ordered new gears there's no reason for them to only come in one ratio, and a non-existent ratio at that. I find myself wondering if he got a set of used gears and just charged you for new ones. Did he show you the old parts, or did you see the rear partially assembled or anything? I myself am a mechanic and the whole thing just doesn't sound right to me.

88 427 Camaro

That is not true anymore!! Diff Solutions www.diffsolutions.com currently has the following brand new ratios for the 9 bolt available (yes, these are the correct ratios and yes, these are for 9 bolts): 3.23, 3.45, 3.73, 3.91, 4.10 along with lots of other stuff for 9 bolts.

The only reason GM stopped using the 9 bolt was cost.

Miles
Diff Solutions
www.9bolt.com