Julie Bergman

I just picked up a '91 Formula WS6, TPI and five speed. Surprisingly this car has a drum brake year end! I thought RPO GU6 got you four wheel discs? Anyone know if it was possible to get a WS6 LB9 TPI car without four wheel discs? I am wondering if they took out the stock rear end and threw something else in before I bought the car.

TAdan

Their was a rear disk brake shortage in 91. Drums were used as substitutes.

Julie Bergman

Thank you Dan, that is really interesting! I have ordered the PHS documentation for this car, wonder what it will say if anything about that! I wonder if they reimbursed folks that ordered them?

twobirds

Do you have the code in the console for the car? That should tell you, but I asume you don't. Thought I'd ask.

Conrad

Julie Bergman

Hi Conrad, I do have the codes, the sticker is in the rear locked compartment lid. I heard that was a mid year change Either I overlooked it or I could not find the code for drums in back. I also ordered the PHS packet for the car, looking forward to seeing it all decoded.
I have a book that decoded most of it.

ForzaAzzurri

I have the same car a 91 formula lb9 5 speed with 3:42 posi drum rear.
Like they said some how GM ran out of rear disks

GTA Jim

FWIW, J41 is the RPO for rear drum brakes.. The RPO for rear disk brakes is J65

Colin91Z

My 91 Z28, which has G92, has rear drum also. I have seen alot of other 91s like this too so there must be some truth to the "great rear disc brake shortage of '91"

okfoz

Correct me if I am wrong, but I thought that most years disk brakes were an option, as was the performance rear axel. Therefore you could order one without the other.

Early T/A's for example with the WS6 got the disk brakes, and WS7 cars were the same suspension but with drum brakes. That changed when the RPO sheet was introduced in 84, then each component got its specific RPO.

I know that for some engine combos, specifically the 350 auto cars, the Disk brakes were manditory, less the times when there was a shortage such as 1991, then you got the Aluminum drums, which are probably as good as Disk brakes for a normal street car.

But I have never heard of a manditory rear disk brake with the 305 TPI 5 speed cars and the performance rear axel, although most of them got it.

John

Colin91Z

To my knowledge, when the G92 package was ordered on a camaro (not so sure how it worked on firebirds) from 89 to 92 you got an engine oil cooler, dual cat exaust, rear disc brakes, performance rear axle ratio (3.23 for autos 3.42 for M5s) and the 145mph speedo. I know the L98 required G92 (on 90-92 at least) but G92 was an option on TPI 305 5-speed cars. Oh yeah, and my drums are not aluminum, and I'm almost positive they are the originals. Also my car has all the other G92 options except the disc brakes.

injdinjn

82-85 WS6 came with rear discs.
86-89 WS6 the discs were optional or part of another package.
I dont know about 90-92.

okfoz

same for 90-92...

Colin91Z, I guess I should admit that the aluminum drums is what I was told here on the boards, when you got the 350 in the shortage time.

John

Colin91Z

Well, I know that I have iron ones right now, but i guess its possible that they were replaced before i owned the car, but they do appear to be the originals. Maybe someone will chime in that knows for sure...

FrankieRider2

Julie, the 1991 Pontiac Firebird Car Order Worksheet says:

"UPC LB9 - 5.0L FI V8 Standard Trans Am - NA Firebird - Optional Formula - (Credit GTA Option)

Requires G80 Limited Slip Differential - Requires R6P Performance Enhancment Group (Engine Oil Cooler, Dual Converter Exhaust, Front Disc - Rear Drum Brakes and 3.42 Axle Ratio) on Formula and GTA with 5-Speed Transmission"

I don't know about the disc brake shortage and I've always heard there was one, but this order sheet was printed in 7/90.... and it already says that all TPI Formulas would get the drum rear brakes, so....?

It also lists the drum brakes for the 5.7L TPI cars.... apparently if your car was built with the R6P group, then you got the rear drum brakes, regardless of the engine used. There is no mention of a GU6 RPO on any of the order sheets from 1987-1992, whereas the R6P group is shown as required with any TPI engine in both '91 and '92.

The 1992 order worksheet shows a reversion back to four-wheel-disc brakes for both TPI engines with the R6P group.

Just an FYI.

Julie Bergman

Thanks everyone for all the useful and interesting input! My first mod to the car is a Pro 5.0 shifter. I am liking the LS1 brake conversion idea also....

okfoz

I got the Baer Brake$, expen$ive, but well worth it. I used to be afraid to drive my car hard, in fear of stopping... not any more

If you want to retain your stock wheels, the you need the 12" on all four corners. The 13's will fit up front ,but you will need to grind down the fins on the calipers, as they rub. I chose to go with 12's.

John