All ABS experts inside!

[cuisinartvette]

I have the spongy brake syndrome on my 90. Everything is new, bled, rebled and bled some more. It was like that when I bought it and after all this work its still the same. I dont think Ive ever seen the ABS light come on upon startup or definitely never heard it do the self check once you start rolling.

I took it up to about 75 and leaned on the brakes

It sucks, dont stop for beans.

Im not a real techie type guy, where can I start? Couldnt get the ABS to enact. Everything else on the car is great now, except it stops like an old truck..

Where do I start?


Edit: Upon backing out of the driveway this afternoon I thought I heard the ABS check. Never heard it in forward motion or seen an ABS light on the dash.

[gbrtng]

What do you mean by everything is new ? Does that include new front calipers ? What kind of pads ? Condition of the rotors ?
My 91 always had a slightly spongy pedal but I can hit ABS at will. Look in
the compartment behind the driver's seat to see if the heavy red wire is
connected to the ABS unit. If it's not connected, somebody has removed
the check ABS light, and you probably have a bad controller.

[cuisinartvette]

I will check it tomorrow and check for codes (A and H??).

Rotors are new, performance friction pads, calipers cant tell but they are dry. . Booster and master are both good. Seems (from pedal feel when bleeding) that the rears arent getting all their due pressure for some reason. Pedal feel improved some from bleeding fronts. Unless its old school brakes, Im lost. Dont know what a brake solenoid or controller would look like if it hit me in the face.
Thanks for your suggestion

[tomtom72]

I'm no brake expert either but my 90 has had the same issue.... the brakes just didn't seem up to it, yea spongy I guess. To me I was remembering the brakes on my 72. Ya know those old iron FIXED 4 PISTON calipers w/ large pads.

Anyway enough of the old school stuff. I had the dealer check my abs against the shop SBDSytem & the abs got a clean bill of health. To get my abs to work I have to go way beyond controlled effort on the pedal...but it does work. I don't speak abs either.

Here is what I've done so far and they are better: s/s lines, DRM bias spring, rebuilt the fr calipers & rears will wait till winter, really soft street pads Brut Stop by raybestos, new hardware for the pads, ya know clips & pins & speed bleeders & Valvoline D3 syn fluid.

Now they work much better but still not what I call "stop on a dime & give nine cents change". They work but they feel like they are not. I guess they don't telegraph much back to the driver. If I unload the inside wheel a bunch in a corner & do a bit of braking I can feel the abs react to that unloaded wheel....so I'm confident it works as intended. I grew up on old stuff & pride myself in having learned brake modulation....I ain't no race car driver but I have some learned habits w/brakes pre-abs.

Oh, I did rebuild the M/C when I did the DRM spring...ya know "while we're here" rule. I even bought a new set of stock lines & may try that this winter. OH, yea, another thing if ya think ya got all the old fluid out with 3 qts of bleeding by foot...think again. My fr calipers still had some crap hiding in them. Not that that means anything, just thought I mention it. Oh, yea reason on trying the stock lines again is they have a larger I.D. than my Earl's s/s lines...more fluid movement but less pressure but ya can at least fill the rear reservior of the M/C to the fill line without it spitting fluid out under hard use....not much, very little but it spits some out...even before the DRM spring.

Sorry Ron for rambling & giving ya no exact answer. I just figured if ya had some more info ya might tumble on to something for your situation.


Tom

[8upZR1]

Something I always do when I am checking brakes/ABS is to pull the fuse for the ABS and take a test drive. With ABS completely disabled the brakes feel totally different and you will realize just how much the ABS system is or isn't doing for you. It is simple and surprisingly insightful.

The brakes on my 90 are awful. The system is functioning properly but there is just not enough bite. For the amount of tire and suspension these cars have the brakes should be able to do there job extremely well. I think a large rotor & caliper upgrade is the only option if you want excellent braking on your ZR1. 14" and 6 or 8 piston monobolcks should get the job done. I rode in an LT1 C4 with 13.5" rotors and 6 piston Brembos. It would put my car to shame. Cost is the only problem as big brakes require big wheels & rubber. Goodluck with the brakes.

[gbrtng]

Originally Posted by 8upZR1

Something I always do when I am checking brakes/ABS is to pull the fuse for the ABS and take a test drive. With ABS completely disabled the brakes feel totally different and you will realize just how much the ABS system is or isn't doing for you. It is simple and surprisingly insightful.

The brakes on my 90 are awful. The system is functioning properly but there is just not enough bite. For the amount of tire and suspension these cars have the brakes should be able to do there job extremely well. I think a large rotor & caliper upgrade is the only option if you want excellent braking on your ZR1. 14" and 6 or 8 piston monobolcks should get the job done. I rode in an LT1 C4 with 13.5" rotors and 6 piston Brembos. It would put my car to shame. Cost is the only problem as big brakes require big wheels & rubber. Goodluck with the brakes.

Pulling the ABS fuse to disable the controller should NOT make any
difference in braking under normal conditions because the ABS is not
being actuated until the system senses wheel slippage. If pulling the
ABS fuse makes a difference with normal stops there is something
wrong with the system that I have never seen.

[gbrtng]

Originally Posted by cuisinartvette

I will check it tomorrow and check for codes (A and H??).

Rotors are new, performance friction pads, calipers cant tell but they are dry. . Booster and master are both good. Seems (from pedal feel when bleeding) that the rears arent getting all their due pressure for some reason. Pedal feel improved some from bleeding fronts. Unless its old school brakes, Im lost. Dont know what a brake solenoid or controller would look like if it hit me in the face.
Thanks for your suggestion

Has the car been like this for as long as you have owned it ?
What Performance Friction compound pads are you using ?
What makes you suspect the rears are not getting all their due pressure ?

My guess about the spongy pedal is that there is one or more fatigued
or cracked calipers - let me explain - under really extreme continued use
on track I have seen stock front calipers spread open so that the pistons
are no longer parallel. If you replaced the front pads you can inspect them
to see if there is a normal wear pattern, i.e., the friction surface should be
parallel to the backing plate. If not, you have this problem. The stock
calipers are made of die-cast zinc, aluminum, or some alloy which
creeps unter stress. It is rumored that the 1996 GS calipers were
reinforced, but I've compared them with stock and can't see any difference.

Please PM me with your phone number and a good time to call; this
needs more investigation.

Glenn

[John Boothby]

One item I have not heard mentioned here is the vacuum power assist. The diaphram in these do go bad and greatly affect the feel of the brakes. When you rebuilt the M/C was this checked? Just my two cents.

[cuisinartvette]

The M/C appears to have been replaced before I got it. I pulled it out to see if there was an adjustment to "unslack" the pedal but there isnt. Ive seen others who throw parts at this same situation to no avail..

If I have my foot on the brake pedal it does not sink as if the master was bad.

However with the car off if I pump the pedal up it doesnt get hard like any other car would.

Now that the car has good shocks and can handle I just want it to stop, would love to try a road course, especailly if I can make it to Vegas gathering. Otherwise whats the use....

Keep the feedback coming, anything is helpfull.

[cuisinartvette]

Ok with the key in the "ON" position I shorted the A and H terminals, no codes. On the other forum I had seen posted that pumping the brake pedal 40 times with the key off resets a modulator valve (under the car???) releasing full pressure in teh rear brakes, anyone ever heard of this?

Id like to get it fixed, otherwise this will be me on the road course this fall (about 30 sec in)

http://www.youtube.com/watch?v=9ZF7DJPN-5M