Z4Ccoupe

I have a 96 SS. I'm fairly certain that this used to be someone's drag car in a previous life. I went to get an inspection sticker and it failed because the parking brake does not work at all. Spent a day trying to figure out why the be parking brake wouldn't work. It is a fairly simple system, after all. No joy. But while we were working on it, a friend who was helping noticed that the regular brakes were not stopping the rear wheels all the time. I would really have to stand on the brakes to get both wheels to stop the rear axle while the car was jacked up. Is there something that a previous owner could have done to reduce the braking force of the rear brakes? We bleed brakes, etc. to try to get them to work better but no joy there either. And all of the normal ABS hardware is still there.

Injuneer

Does the “ABS INOP” light come on for a few seconds when you turn the key to "run"? May have had a problem and they removed the bulb. Any sign of a line lock solenoid on the front brake line? That can cause ABS codes/INOP light. Pulling the bulb would eliminate the annoyance.

Mechanically, check for frozen pistons in rear calipers, or corroded slider bolts.

Z4Ccoupe

I haven't noticed any ABS INOP light, but I usually don't pay attention to any light that doesn't stay on during the start cycle. I have noticed that when I brake slightly harder than normal, I feel the growl(?) that I would normally associate with ABS intervening, even though I'm not stopping that hard. And if I really get down on the brakes, the car seems to stop normally, even though the rear brakes probably aren't doing a whole lot. I don't know where a line lock would normally be located, but I have been all over/under/around the front end and haven't seen anything unusual. Rear pistons are not frozen and slider bolts are OK. I installed a new right rear caliper before I figured out that the only problem with the original was that the parking brake actuator arm had over traveled and the pin had just popped out of place.

Injuneer

Line lock solenoid would be in the front brake line, between the master and the combination valve.

ABS INOP light is at the bottom of the instrument panel, right below the “0” for the tach. If it doesn’t come on for a few seconds when you turn the key to “run”, either the bulb is burned out, has been removed or the wire cut.


If the ABS is activating, it should turn on the LOW TRAC light. That's just to the left of the “3” on the tach. CHECK GAGES above it and BRAKE below it. If there's a problem with the front/rear differential pressure switch in the combination valve, the BRAKE light would be on.

Z4Ccoupe

Thanks. I'll look at that.

Z4Ccoupe

I finally made myself pay attention to the lights on start up instead of being on auto pilot and not paying attention. I do have an ABS INOP light and a LOW TRAC light on start up. And there isn't a line lock solenoid on the front brake line.

Injuneer

One last “light” question..... when you pull up the e-brake, does the “BRAKE” light come on? That light is also connected to the switch on the side of the ABS unit that checks for unequal hydraulic pressure in the front and rear systems.

With all the lights working and none of them coming on, the problem would appear to be mechanical, not electronic. That would indicate the “growl” is not the ABS, since ABS operation turns on the “LOW TRAC” light.

Does the car have “ASR” (traction control)? Would have a black box for the throttle servo, sitting on the driver side valve cover, with the throttle cable attached to it. Again, when that operates the “LOW TRAC” light would come on. Trying to rule out all these systems as the source of the problem.

Z4Ccoupe

No sir. No "BRAKE" light when the parking brake is applied. The car does not have traction control. I'm thinking that the growl I am feeling must be from the slotted and cross drilled brake rotors. Not ABS.

Injuneer

Then the BRAKE light probably isn’t working. If there was a loss of rear braking, due to low pressure (leak, air, low fluid, etc.) the light wouldn’t come on to let you know. I have Baer slotted/drilled rear rotors, and no “growl”. Don’t have them in front though. Stock front brakes and Baer rears pull the car down from ~130 MPH trap speeds no problem.