jmattiko

Hi All,

From the previous owner, I have Big Reds up fron and 4 piston black calipers in the rear of my 1990 C4. I have not measured or looked for a part numbers, but I assume they are standard later model 964 rear calipers (standard calipers on a 90' C4 werer 2 piston).

I find that the ABS kicks in too early (no tire or road condition related problems) under firm braking.

Short of replacing the rear calipers/rotors, what can be done to correct this?

What about changing the rear brake bias valve to a different bar? If yes, what would be the correct choice for a primary street machine?



Thanks and Best Regards,

Joe.

GG Allin

Wider tires up front might help?

Bill Verburg

At a bare minimum change the rear calipers to the 993 rear 30/34

C4Russ

I find that the ABS kicks in too early (no tire or road condition related problems) under firm braking.

Other C4 owners have found a premature application of ABS due to a dirty or failing accelerometer or perhaps a brake bleed is in order. I would recommend that all basic issues have been reviewed before making any changes to brakes.

There is a current thread on ABS issues in the 964 forum. I can't seem to get the link or URL to show up if you go look, it's titled: 964 Brake Problem!!! Please Help!

Marc Shaw

AFAIK, all C4's had 4 piston calipers and only early C2's had 2 piston calipers rear and later C4's had 4 piston calipers.

All 964's had 4 piston caliper fronts.

Marc

Bill Gregory

That's correct. C2's inherited the C4 rear calipers in 1992. C4's always had 4 piston calipers all the way around.

andy sanborn

Joe:

If my memory serves (I also own a modified 90 c2), there is a proportioning valve just above the ABS unit and i think it cuts 40% of the flow to the back brakes. I removed mine, as did a few other DE/Race guys. (it's easy as it's just a plug in line that can be removed) and after doing so, the total braking system got much better, including a more aggressive abs setting - due to the rear brakes actually helping to stop the car....

andy

Bill Gregory

Several have found that upgrading to the Turbo 60 bias valve makes quite a difference. If you're a PCA member, there was a two part Pano article this summer on brakes, with the July issue focusing on 964 brakes.

andy sanborn

Yea bill, I have heard of that too, but I actually took mine right out and it seems to work great

Bill Verburg

On a 964 w/ big red fronts & stock rears definitely remove the p/v