Yesterday someone offered to sell me a 3:27 posi disk from a firebird. According to RPO code in my car it has 2.73, and I'm assuming it hasn't been changed. I hadn't really looked into swapping a new diff or going to disks but it got me interested. It seems like the only problem I would run into is adjusting the speedometer to read correctly. (Although, if someone could tell me any other problems/disadvantages that would be great)

I've done some searching, and it looks like I can either change the gears in the VSS so match the new ratio, or I can get this electronic module that changes the signal. It looks like the module is about $150, but I though switching the gears would be cheaper and easier...I just can't find where to get them.

Anyone have any idea? Thanks!

You might pursue the link below for general info about the swap (combination valve, parking brake cables, speedo gears, etc.):

https://www.thirdgen.org/forums/tran...-10-bolts.html

You don't mention what type of trans you're running, but you might find what you're looking for from the following company:

http://www.transmissioncenter.net/sp...n_______va.htm

JamesC

Did you search at all? Because there are threads about changing from drum to disc on the brake board, and there are more then a few speedometer gear threads too.

You can get the gears from GM, or aftermarket suppliers like http://www.transmissioncenter.net/sp...0gear%20driven

3.27 is a Borg Warner ratio. Which would mean it's a 85-89 rear end. Which brings up the question of the 85-88 disc brakes. Long story short, unless that rear is out of an 89 with PBR discs, it's not worth the trouble to swap over. A short search will tell you why...

Thanks for the links. I did already read over the first one, and had ben to the second as well but somehow missed that particular section. I wasn't sure if the VSS gears were different between cable-driven and electronic speedo cars...

As far as I know it has the stock trans for a 92 tbi.

I did a few hours of searching last night. I didn't look into switching drum to disk because if I'm putting in an axle that's already assembled with disk breaks I didn't think there would be that much to it, besides possible swapping that thing below the master cylinder whos name is evading me right now...

Like I said above, I wasn't sure if the VSS gears were different between cable and electric vss, and didn't find anything specifically addressing that.

In the picture he sent it did look like the calipers were mounted on opposite sides, which, according to the link JamesC posted above, would mean that it would have the older style breaks. However, I wasn't really looking at it for the disk factor, I was more interested in posi. Are the 82-88 disks worse than my 92 drums?

Thanks for the help, like I said I did search a lot and found a lot of information it was really the specific question about the VSS that I couldn't find an answer to.

Different, at least for the T-5 manual trans:

https://www.thirdgen.org/forums/tran...ve-driven.html

Many members will maintain that drums are better--especially since the Delco-Moraines have a tainted reputation here on TGO. That said, with the recall kit in place and with the parking brake used with regularity, I personally never experienced any problems with them. Frankly, I upgraded to PBR's because I had the time and money. Glad that I did? Sure.

JamesC

Doh, should have specified it was an automatic.

Yea, I don't really mind the drums at all...do you think that the posi would be worth going to those disks?

Stock drums are better then the Delco discs. Under ideal conditions the iron caliper discs work as well as properly functioning drums, but they aren't really an upgrade. It speaks volumes that GM went to PBR for a rear disc setup that actually works. The expense of changing the prop valve, and the E brake cables is reason enough not to swap to the old discs. IMHO.

Changing the speedometer gears is easy. The hardest part is determining which gear you actually need.

If, and that's a big IF, the limited slip in that Borg Warner rear still works, it'd probably be a worthwhile upgrade for the improved gearing and posi. BUT if you ever have to service that rear, parts are hard to come by and expensive.

Personally, I would have to think long and hard before spending the money to switch from a 10 bolt to a 9 bolt. Even if you get a really smokin' good deal on the used parts, the unexpected expenses are going to make it an expensive upgrade for the actual improvement. If it were a 10 bolt with good gears, a functioning limited slip, and PBR discs it's a much clearer upgrade. Depending on the situation, I'd consider upgrading the rear you have now, before swapping to a junkyard/used rear.

According to the guy it was from a '90 Formula. I attached the pictures he sent me.

The last year for the BW rear was 1989, which was also the first year for PBR disc brakes. That rear might have just been removed from a 1990 Formula, but it didn't come in that car from the factory. That's an 85-88 rear axle.

That's what I suspected, thanks for confirming. I really appreciate the advice.

1990 was the last year for the BW rear.

89 was the last year for the 9-bolt.

JamesC

check out "Everything I know about 9-Bolt Rearends!" and then come see the 9 bolt on my '90 formula with 33K miles.

I'd suggest that the rear is an 89 'left over.' The following thread might prove to be interesting reading.

https://www.thirdgen.org/forums/hist...c-l98-g92.html

JamesC

Left over suggestion or not, my car and many other 90's were built with the rear. I worked at the GM plant in Wilmington for 30 years and back in the old days, when things weren't delivered "just in time" like modern auto manufacturing, the supply of rears ( and many other parts) would be abundant at the plant and used until exhausted. The only time that wouldn't happen is, say, a different trim color or option that was new to the model year, then the old parts would be scrapped or shipped back to become service parts. So we can go back and forth all you want but the fact is that the BW rear survived into the 1990 model year.