online170

Im gonna go pick up a BW 9 bolt rear end. Claimed to be out of a 1989 GTA. Disk rear, still has tag on it i beleive.

Ive never seen it before, the guy lives 40 mins away, im getting it for a case of beer cuz its taking up space in his garage,

How do i identify what gear it has in there?

Most of them were 3.27, but my bro used to own a camaro with a 3.90. I really hope its not less than my current 3.42, or else my T-56 will be kinda useless in 6th.

Im gonna pull off the cover to confirm it is a posi. What gear ratio COULD it be? are there numbers or something i can look up rather than turn the axle and count the yoke : disk ratio?

THANKS!

JamesC

iTrader: (5)

The following are for a ten-bolt (stamped on the ring/pinion) but they'll be close:

41 : 15 = 2.73
41 : 14 = 2.93
40 : 13 = 3.08
42 : 13 = 3.23
41 : 12 = 3.42
41 : 11 = 3.73

BTW, the rear should have PBR's.

JamesC

Bullydawg

iTrader: (7)

If it is out of a 350 GTA, it will be 3.27. I would be thankful for a 3 series carrier. They best they came with is a 3.45, so chances are yoy wont be higher than your current 3.42.

AlkyIROC

If it's really from a GTA, it will have 3.27. The PBR calipers mentioned above are the aluminum calipers. The 87/88 9 bolts have steel calipers and smaller rotors.

The most common 9 bolt only had 2.77. The other factory option was 3.45. The 3.70 gear set was available from the GM parts counter and was never offered in a production model.

The 3.27 gears offered in the GTA and Z28 with the 5.7L TPI engines were a good ratio matched with the 700R4's low first gear. The low first gear gave enough torque multiplication to get off the line quickly and the OD in the 700R4 with the 3.27 gears gave a low cruising rpm.

Years ago when I had a 383 SBC under the hood, I was able to get the car into the high 11's at 117 mph with 3.27 gears. It was a slug off the line and I ran out of track before running out of rpm. I was shifting at 7000 rpm.

online170

Thanks, thats very informative. Was it possible to get a 3.90 (from aftermarket)?

My bro's old camaro had a very mild 355 in it, and a carter 650cfm carb. But it chugged gas like guzzler. (in comparison to our other V8's). We figured it was largely in part due to the gear. Plugging in calculations showed, 3.70 and 4.11 werent quite right, but a 3.90 was pretty much bang on. (hopefully im not confusing 3.90 and 3.70 but im sure 4.11 was too high, and 3.45 was too low.)

Im not too concerned with speed at the track, im more concerned with being able to use 6th gear on the highway. RIght now i can go 62mph at 1400 rpm. Which is AMAZING for mileage.

In any case, is the aluminum PBR's a good thing? Will i need anything other than a prop. valve to swap it in place of my 10 bolt?

And finally, can you give me an idea of where these numbers are stamped on the gear? Id imagine along the outer circumference.

online170

Also; Has anyone dealt with this company?

http://www.9bolt.com/gearsets.html

They sell used gear sets (but i think the prices are sorta steep). Says they've been operating since Nov. 2007. They have just about everything you could want though for a 9 bolt.

AlkyIROC

The "old camaro" was probably a second gen which has a 8.5" 10 bolt. There's a lot more gear ratios available for it. I'm not sure if a third gen 7.5" 10 bolt has an aftermarket 3.90 option. The small ring and pinion of the 7.5" 10 bolt doesn't allow a lot of ratio options. The 9 bolt isn't much different with only a slightly larger ring gear.

The ratios I already mentioned were available from GM. The gear sets available on 9bolt.com are what's available from Australia because that's where the diff is made and still used. It's hard to find a North American vendor that sells gears or anything else for the 9 bolt. The only North American cars that used the 9 bolt was the 87-89 third gens and only a handful of those got the 9 bolt. That doesn't leave much of a market demand and it's not much of a performance diff. It's better than the 7.5" 10 bolt but not by much.

I don't know if Miles still operates 9bolt.com. I haven't seen him in the forums for years now. It's possible he sold the company to someone else who's been operating it since 2007.

The aluminum PBR calipers are the preferred factory disk brakes.

online170

Oops, i guess i was a little vague in my description. My bro's "old" camaro was his previous camaro (hes had a few), not old as in generation.

1983 Z28, cloned to an iroc, and had a whole bunch of factory swap parts on it. One of which was the 9 bolt i was talking about in an earlier post. But as i saw on the 9 bolt site, a 3.90 was offered from somewhere.

Im going to go see the rear, HOPE its a 3.45, and if its a 3.27 i dont know. Should i still get it?

To put a new gear in, with seals and stuff will cost about $300 for me. Kind of a hassle... Do those PBR's swap over to a 10 bolt?

JamesC

iTrader: (5)

Yes, with the ten-bolt backing plate, which is available from Ed Miller, IIRC. More about the swap:

https://www.thirdgen.org/forums/faq-...iscs-89-a.html

JamesC

DJP87Z28

I would not get your hopes too high that the 1989 9-bolt is a 3:27 ratio. Unless it was special ordered, in most cases it was a 2:77. But who knows you may luck out,either way it is a good find with the PBR brakes.

online170

No ones gettin their hopes up. Im just trying to cheat into getting a decent posi that suites my combo by getting a used one, instead of investing in a 12 bolt or a 9" moser. We'll see.

Also, i talked to the sales dept on that website (9bolt.com). Its all used parts since they arent reproduced anymore. AND THE PRICES ARE AUD! Thats australian dollars.

So the gearset i was looking at for $220 AUD = $182 CAD = $144 USD. Thats pretty reasonable.

online170

Ok i picked up the 9 bolt today.

Its very very rusty, but still is sealed very good. Turned almost effortlessly if it wasnt for the seized brakes. Popped off the diff cover, and the fluid looked a dark blueish color almost purple.

There were two tags on the diff. Hard to read them, but i could see 3.27 on the smaller tag. After rotating the gears some, i was able to see some sort of date code on the ring gear and it also said 3.27.

Some one metioned that the 9 bolts ONLY came in posi units. Is this true? I turned it all the way around trying to find the springs and clutches, but i didnt see any....

My plans are to clean it up and swap it in as is, and replace the brake items and gaskets. Maybe bearings if they're not too expensive.

But i have a few questions;

1) How do i check if its a posi? When i turned one disc, the other turned the same direction....But i didnt see any springs or clutches.
2) I havent measured the discs yet, but i put a magnet to the calipers and they DID stick... Does that rule out the PBR option?
3) I have some calipers and rotors with wheel bearings from the FRONT of a disc brake of a camaro. They look pretty similar. Can i use those calipers on the rear? What about the rotors?
4) Someone mentioned that the shock "mounts" are different from a 10 bolt to a 9 bolt. Is this true? If so, what would i need to do to put it in the car?

Thanks!

AlkyIROC

I think the 9 bolts used cone type clutches.

The purple oil was probably a synthetic or a posi additive.
Shock mounts should be the same. All the mounting hardware is the same on a 9 bolt, 10 bolt and Dana 44 for a third gen.

PBR brakes were not available until 1989 and the 9 bolt was only available from 87-89 although there's a very small amount of 86 cars with it. If the calipers on the front look like the rears then you don't have PBR rear brakes. I doubt the front calipers would fit. The bolt spacing is probably different and the rear calipers have attachments for the park brake.

The PBR caliper/rotors look like this.

big gear head

The Borg Warner posi that was used in these rear ends is almost completely closed, so you can't see the sping in the center. The case is bolted together with 8 long bolts that go through from the ring gear side. If you hold one axle and can not turn the other axle then it should be a posi. I haven't seen a 9 bolt that wasn't posi, but that doesn't mean that there aren't any.

JamesC

iTrader: (5)

I'm clueless about 9-bolt guts, but this from the FAQ section:

85-90 9 bolt equipped f-bodies were available with either standard open differentials or limited slip versions as well as several different ratios including: 2.77, 3.08, 3.27 (G92 w/auto), 3.45 (G92 w/stick), and a few 3.70 ratio's came in some 85 & 86 Firebird's w/L69, stick & G92=Very Rare!

JamesC

online170

Ok so i definately dont have the PBR's. I was almost certain they werent aluminum by the amount of rust on them... However its good to know the rear end will swap right in.

Ill have to check out that FAQ section James. I couldnt seem to find much of importance when i did a search.