mark kibort

How hard its it to change out the brake bias fitting. what is stock for a 87 and what is stock on an '86 chassis. I think i remember the holbert chassis which was an 86 , having a 11bar bias fitting.

Im going to try a bunch of things to get this braking thing worked out for the race car at laguna. cooling duct work and bias changes are on the agenda

thanks,

Mark

Gary Knox

Mark,

Easy to change, but you may need a special offset wrench to access the lands on the fitting. I always leave the connection AFTER the bias valve slightly loose after I install one, then I push on the brake pedal (or use a power bleeder) to pressurize the system until fluid oozes out of the fitting. THEN I tighten it. By this process, I don't need to bleed the system.

The OE bias valve on the S4's was 18 bar. Most upgrades have the 33 bar valve, but some of us have 45 bar (no longer available, some 964 owners may have one they took off to install the 55 bar valve). I installed the 55 bar and found it provided too much rear braking.

mark kibort

Thanks gary! thats the info i was looking for. anyone have a 33 bar fitting they want to sell?
I think i remember it being right on the ABS module, correct?

MattiasH

The 45 bar bias is available from Porsche, so there is no need to ask around at 964 owners. I bought mine from Roger not that long ago.

https://rennlist.com/forums/11122979-post11.html

/Mattias

Speedtoys

Yup..its right there on the ABS gear, and not hard to replace in-car.

the flyin' scotsman

Roger sells the 33 bar bias valve

mark kibort

thanks. i cant read it that well, but it looks like 11 is imprinted on the side closest to the ABS unit. has a brake line on the back of it. Now, wen you pull this, you dont need to bleed the entire system?
doesnt look like much room to get the line or the bias valve out without unmounting the abs sytem and doing it all through the fender well. anyone got a few tips here??
thanks

RKD in OKC

here is a list of the part numbers...

Brake Bias Valve 60 bar 965 355 305 01
Brake Bias Valve 55 bar 964 355 305 10
Brake Bias Valve 45 bar 964 355 305 00.
Brake Bias Valve 33 bar 928 355 305 02
Brake Bias Valve 18 bar 951 355 305 01

The marking on the valve is a stamp on the wrench flat end... 5/size, example 5/18. Mark is probably mistaking the / for a 1 and the 8 may be worn off.

Tried a 33 on my GT with stock tire sizes and it was not enough so went to the 55 and it seemed to work great.
Because of that experience went straight from 18 to 55 on my GTS with stock fronts and wider rears, and was too much. Is actually more difficult to do a quick stop as the ABS comes on too soon. Discovered it when the Accelerometer came unplugged turning off the ABS and PSD. The rears locked up on braking really easily. Think it's because there is more rubber on the rear of the GTS compared to the GT. Have a 33 to install on next annual brake fluid change.

Rob Edwards

11 mm in front, 19 mm in back. Righty tighty, lefty loosey.

FLYVMO

Sorry to hijack but a quick question regarding the bias valve and front/rear weight: would a 928 that has more than "standard" weight in the back benefit from more rear bias than "standard" front/rear weight distribution? Currently have the 33 bar on my 90GT project but the car will have more weight in the rear than a stock 928. Would I be better off to go to a 45bar? Front tires are 255/18, rear 295/18. GTS front brakes, GT rear brakes.

Cheers!
Carl