Porker928

Hi

Can anyone here confirm that I can bolt GTS rear brake calipers [928.352.421.03 & 928.352.422.03] onto my S2 rear hubs?

I also want to use S4 rotors with this set up.

Will I face any alignment problems.?

Thanks.

Cheburator

You can bolt the GTS rear calipers to S2 hubs. You will need to add washers between the caliper and the mounting surface so that the caliper is correctly aligned relative to your original S2 brake disk.

With the risk of stating the obvious - I hope you are fitting S4/GTS calipers at the front of the car too...

AO

To build on Cheb's stating of the obvious, IIRC the stock bias valve is 18% - meaning that 82% of the braking force is done by the fronts and 18% by the rears.

Porker928

Thanks guys.

I am currently fitting S4 brakes and suspension to the front which is why I haven't even had time to look at any potential rear brake set-up problems yet - which is why I asked the question.

Andrew -

Will it be OK to have 82/18% brake bias with S4 front brakes and GTS rear brakes? - Why did you post this?

Thanks.

Mrmerlin

the rear proportioning valve can be changed

could you please list the year and model of your car

Cheburator

I have the same set-up on my 1984 S2, which received S4/GT hubs in order to make the mounting of the front S4 brakes less painful. It stops well, I don't think you will have any problems with your current set-up. You can change the bias valve if you want to get an even better braking by making the rears work harder, but for a street car in the UK the stock set-up is good enough IMHO.

HTH,

Alex

Porker928

My 928 is the same as Alex'es - a 1984 S2 Manual. Now with front S4 Brakes and suspension. Where can the brake bias / proportioning valve be found?

AO

The reason I pointed it out was to let you know that unless you are changing the fronts, you won't get much benefit out of the GTS rear brakes.

hacker-pschorr

I thought the brake bias changed with the introduction of ABS?
The early cars have more rear brake bias from the factory. A few people have installed the early valve on S4's to increase rear bias.

Cheburator

Hacker, the UK early-ish cars - S2 (4.7 twin dizzy 310bhp) came with ABS as standard in 1984...

Porker928

Am I to understand that my brake bias cannot be adjusted due to the ABS system?

Thanks.

dr bob

You can change the bias valve to give you more rear participation, and it will help right up to the point where the ABS needs to help you with a slipping wheel. IIRC, the ABS affects -both- rear wheels if it determines that -either- is slipping. So don't go overboard on the rear bias, especially if you regularly drive on less-than-perfect surfaces like rain-slicked roadways.

Porker928

Done about 5000 miles now with this set up and it looks like the rear brakes are definitely taking more punishment than the fronts.

Not that this is a problem but I think the next time I replace the brake fluid I will switch to the 18BAR S4 limiter to put more bias to the fronts - just to see what happens over time. - Will report back.