A930Rocket

OK. So I finally saw the light at the end of the tunnel and it was a train on the scraper ring/dust seal issue with my S4 calipers. Sorry it took me so long to get it. DOH!

Now that they are finished and installed they have a very front biased set up. The fronts will lock up rather easily. Can I swap out the p/v in the rear for another one that will help balance this or do I remove it all together? Also, where is it?

If I install a manual p/v, do I set it up so that it will reduce the front or open up the rear?

If I install the fronts on the rear, it should have a rear bias if I recall corectly. Then an adj p/v would help here to reduce that correct?

Almost there!

Bill V. Are you out there?

Thanks again,
Jim

Bill Verburg

Somethings wrong in the rear, have you removed the p/v(if so equipped, I can't remember what year the car is), checked rear calipers, lines and pads.

The 993 fronts on the stock 930 rotors is a little front biased but not seriously so.

A930Rocket

Hi Bill,

It's an '87 930.

I have not removed the p/v yet. Not even sure where it's at? All the rear brake parts seem to be OK.

One thing that I thought of was that I have PFC 90's in the rear and used some used pads the PO gave me in the front. Not sure what brand etc. (big question here!) I was going to use them to check out the new S4 calipers for leaks etc. before I installed a new pair of PFC 97's. I was told by PFC they don't make a 90 compound for the S4's to match the rears.

When I first started to drive the car, the pedal had more travel than it used to. More fluid to move I think.

I did some 80 mph to 40 mph stops to bed in the brakes and could smell the brakes after each slow down. It seemed the front brakes got better at stopping when they were warm but would lock up with too much pressure.

Perhaps the issue is the different pad compounds and/or p/v?

Thanks,
Jim

Bill Verburg

The different pads are likely part of the problem, the p/v is a definite problem, follow the lines off the left(facing the rear of the car) side of the booster in the front trunk.

A930Rocket

Great. Thanks Bill.

Hopefully I'll have it done in a few days and I'll post the results.

Jim

RJay

Just had the same problem myself. Pulling the P/v from the booster circuit made a considerable improvement. I believe that the valve is only on the rear so a circuit on that won't help as all you can do is cut pressure to the rear. My mechanic though, however that it might be possible to use the circuit to the front and then be able to dial the fronts back a bit. If I learn anything in the next few days, I post back.

A930Rocket

Well... I went to pull the factory p/v and replace with an adjustable one and guess what.... There wasn't one????

The lines go right from the MC down into the a/c box and from there they are T''d to the front brakes and 90'd to the rear brakes.

I guess now I need to pull that rear brake line off the MC and replace it with two lines and my adj p/v some where convenient.

Any thoughts?

Jim

Bill Gregory

We are having this discussion on another thread....you want to put a brake pressure limiter on the front, so the more you press on the brakes over the limiting value, nothing happens?? Not my first choice. Someone else suggested putting in a dual master cylinder with adjustable front-to-rear bias. Believe Smart Racing, amongst others, sells such a setup. Or install rear brakes with larger pistons, is another option.

Bill Verburg

'87 930 right?

I still suspect a problem w/ the rears, pads may be contributing but check to be sure that all of the rear pistons are fully functioning, that the pads haven't been contaminated or glazed etc.