Sysgen

I know that the brake ratio between front and rear is around 70-80% front and 20-30% rear but I have a feeling that my rear brakes are not working at all. My front pads are maybe 30% left and the rears look brand new.

I also have a problem on the track where it seems I'm always running out of brakes, I have to put Hawk Blues in the front, if not I get an incredible vibration from the front wheels as soon as they get a little hot.

So my guess is that I have brakes only in the front and the rears do nothing.

I bled the system and aside from a few bubbles they seem to be fine. I am getting oil flow in the rear when bleeding.

So the question. How do you test if the rear brakes are actually doing anything?

AlpharettaRK

Perform a few hard stops and jump out at hit the rotors and calipers with an infrared temp gun. I can't give you a number but they should be hot. Brake bias can be adjusted with your pads and Hawk Blues are pretty aggressive, so it may be that for a given amount of pedal pressure you are not getting your rear pads to do proportionate work. Hawk Blues in the rear as well would be one suggestion. Good luck!
Cheers
Randy

MAGK944

Jack the rear, spin the wheels and apply the brakes. Do you have a stock brake bias on the master cylinder? This could be faulty though I have never heard of them failing.

Sysgen

Good idea with the temp gun! I would need a reference to compare though. It might get hot just from the bearing and rotation.

How do you adjust the brake bias? dont you need a brake bias valve which I think is not stock

Sysgen

I don't think I would get a good result, they are too easy to stop when free rolling but it's worth a try.

Did S2's have a brake bias valve?

pontifex4

I believe that it's the 5/18, like the Turbo. The 944S had a 5/33, if I recall correctly.

MAGK944

I think S2's must have them, my turbo has one and the S2 has the same brakes. Take a look, it's a small metal cylinder attached where your brake pipe goes into the master cylinder. There are two versions giving different bias front to rear.

Can't see how it could fail but there is always a first time.

Sysgen

I'll look again even though I did take a look last week and didn't see anything but now I'll be looking with a different perspective

MAGK944

If you have help (someone to depress the brake pedal), jack all 4 wheels, apply the brake in stages and measure (by feel) the resistance on all the wheels.

You will find a point when you cannot turn one set of wheels by hand and just about be able to turn the other set. At least with the brake pedal fully depressed you can see if all your wheels are locked and you will know that you have rear brakes.

Paulyy

we put the car on a hoist took the wheels off and jammed a very long bar between the studs and tryed to spin the disk while someone is pushing the break. thats how we tested them to see if they work or not

Sysgen

That's a good idea! without bending the studs of course. Having something to attach to the 5 studs would be perfect and the put a big torque wrench on it, all the things I do not have

I'll try the with a long bar.

AlpharettaRK

As far as temp compare to the front wheels, bearings won't heat it up any more in the back than in the front. I'd think you'll see 400-450 degrees F on the front and 350-400 on the rears, but those are guesstimates.

Sysgen

Good, that's some good numbers I can compare. I'll try to borrow a temp gun and give it a try.

Thanks everyone !

Van

On a lift, or jack stands, start the car, put it in gear and see if you can stall the engine by stepping on the brakes. If that works, give it some gas while you step on the brakes with your left foot...

Oddjob

S2s will have the 18 bar stock. S2s have ABS, so the prop. valve is on the ABS pump in the p-side fender, not on the master cylinder. There are around a half dozen different prop valve ratios available from porsche for various different cars/models.

What pads are you using on the rear? Why not blues back there too?

By the way - its normal to go thru all of two to three sets of front pads before killing off a set of rears, even w/ a higher pressure rear bias/proportioning valve.