I have spent about 3 hours searching this forum and I have found some great info on the swap on which i am ready to perform, but need a little more help/guidance. 1992 firebird with recent 305tbi to 350tbi ultimate swap/mods (approx 375 horse). Just finished (UMI Performance) subframe connectors, steering subframe connectors, new lower control arms, torque arm, etc. Now it's time to beef up the rear end. Swapping stock 2.73 limited slip rear end/drum break with a late 80's 3.27 posi rear end with disc breaks. Simple swap right? Possible proportioning valve replacement, but other than that a quick and easy swap? I will upgrade the rotors, pads, etc while i am in the process. Thanks so much!!!!

Prop valve should be the only thing as far as I know. I had a 9-bolt 3.27 laying in the basement and pondered the swap for a long time before I sold it off. In my research I only found that the prop valve needed to be changed to support the rear disks.

Cool! That is what I thought. Get the valve for the make, model and year of the vehicle that the rear end came out of?

Don't forget the speedo gears. I did the same swap but from a 3.73 drum 10 bolt to a 2.77 9 bolt disc. I've now got a 3.27 9 bolt ready to go together and be swapped in it's place. Get the valve for your year model car, not the car the donor rear came from.

The proportioning valve for my car will be sufficient enough? As far as I know my year, make and model never came with rear disc breaks.. just drum.

what do you mean by "dont forget the speedo gears"?

You'll need the prop valve only if you've got the cast iron saginaw brakes, which is pretty likely as only a few of the nine bolts are rumored to have come with the later PBRs. There's also a recall kit available from GMParts Direct for those brakes. It comes with everything needed for a standard re-build and fixes some known issues with them.

http://www.thirdgen.org/techboard/br...ght=kit+recall (Just acquired a rear disc axle)
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You'll also have to replace your speedo gears in the tranny OR multiply your mph by 2.73/3.27 in your head while driving.

Speedo gears are cheap ... you can order from any GM parts counter for a few bucks each. I had a shop install mine in the tranny when I swapped out my 2.73s for 3.42s. There is a thread on here somewhere that has a table showing which drive gear and driven gear have the correct number of teeth (in combination) to make your speedo right (or at least close to right) for your gear ratio. It takes tire size & wheel size into account when you calculate, so have those numbers handy. And you have an electric speedo, so you can re-use your old part that the driven gear attaches to (can't think of the name of it). If you don't change the speedo gears, I'm going to guess that your speedometer will be off by about 9 mph with that gear ratio change.

Awesome. Thanks for the advice

SOOooo, if his speedometer is registering 9 mph he'll actually be going 0 miles per hour?
The speedo will be off the exact ratio of the gear change (assuming it was correct to start with) So when you're registering 50 mph you'll actually be going 50 x 2.73/3.27 or 41.74 mph. At 25 mph registered you'll actually be going 20.87 mph. I know, , but I had a few minutes to spare.

So i need to know the tooth count on the output shaft and the tooth count on the "driven" gear?

So i remove the speed sensor and the drive shaft and...???

Help? LOL

http://www.transmissioncenter.net/sp...__va.htm#700r4

This is the link for everyone. I just need to figure out what i have.

http://www.700r4.com/speedoCalc/speedocalc.shtml

Another link...