Sorry, don't have much other info, but did just edit my above post and add 'dual diaphram' where appropriate -- which does speak somewhat to internal capacity (and correct year on one entry).

 

.....to "read" or "activate" the "internals" in an 88's abs, etc, would a tech 1 or tech 2 be needed?......whom usually manufactures these items?..names?..tnx!

 

***i remember now...the abs did kick in because i remember it sounded like someone hammering on the frame...i went back to the spot and found no broken pavement or anything like that......this ammends posts 71 and 72....

 

has anyone tried the brembo brake pads? are they any good as fronts for a c-4? better then the stock pads?

 

Amazing this issue hasn't generated a class action suit against GM by now. Somebody must have bought the farm as a result of these crappy, inadequate brakes sometime ago.

 

based on what i have read, i'd say the same thing too as i suffer from the exact same symptoms too and did pretty much what mailman did and others. i deceided to get an upgraded ft pad in desparation and try that. ya know anything about brembo pads?

 

Had basically these same problems on my 1987 non Z51, replaced the ABS modulator (this is about a $600-$700 part, but got used at Vette2Vette for $225) and relays and now it is like a new car. Can't really explain it, but it brakes like a new on now. The old modulator was probably not porting the proper amount of fluid.

 

all you did is change the abs unit? another guy here did the same thing and it did nothing for him at all. i reworked my ft brakes today by putting on a set of brembo pads thinking that it would make some difference, it did not. changed the computer the other day, no difference either. good brake fluid quantity and stream and still bad brakes. the abs only comes into play during a "slide" and cannot increase pressure.

 

Can I read the codes on an 89? I was under the impression I could not.

 

not through the diagnostic link. that year doesn't store codes.

 

Well, I'm going to hang in here until someone unravles this mystery. Got to be something wrong with something. Isn't there some brake specialty shop that knows what's up? I know, they will recommend an upgrade!

 

Im not 1000% positive but Im pretty sure the pre LT1 cars did not need a tech anything to activate the ABS. Wouldnt a simple scanner be able to read if there was a trouble code for ABS in a OBD 1 car?

 

Just an FYI for all interested:
To clear the DTC (Codes) from the EBTCM (ABS/ASR computer) memory one can do it via the CCM:

Ignition "off"
Connect jumper from DLC term "A" to "G"
Ignition "on"
Press "Trip Reset" until you see 9.0
Press "Trip ODO" twice to change the display to 9.7 (It's a sub menu)
Hold ENG/MET until "---" appears in the speedometer area (this actually clears the system codes)
Ignition "off"
Remove jumper

Hank

 

mailman, have you done any more with your brakes?

 

If the piston in the abs modulator is seized the brake pedal will be hard and brake performance will be bad.

 

how did or do you make that determination that it is "seized" and not some other underlying problem?

 

thanks

 

I am one of the ones who replaced it all to including the ABS pump with no real difference in braking operation. I did the J55 up grade but would like to know the answer also to the mystery.

As a point of information, if the ABS is deactivated by you manually, or if a problem exists in its operation, it will shut down the ABS operation and should become a passive unit. Meaning that the brakes in theory should have the same braking effect but just with no anti-lock operation (ABS).

Older ABS units, 91 and back have been having clogging problems usually with one of the lines which usually means no braking to one of the wheels. This is usually a straight forward problem but is not related to the poor braking problem being discussed.

Brake fluid does not flow much. You really transmitting pressure from the M/C to the calipers. Any blockage would constitute no pressure to a wheel or maybe no release of the caliper.

There are valves in the ABS units which when activated by the brake computer and with the aid of the pump, restrict some of the brake pressure to that one wheel, and pulses the pedal thus not letting that wheel lock up. Kind of lets it spin.

The last part I tried before I installed the J55s was the ABS unit. My theory was that there might have been a weakness or something in the ABS pump unit that was absorbing the brake pressure and not putting full pressure at the calipers. Kind of like a spring or ballast that was not letting the M/C produce full pressure in the lines. So less pressure, poor braking. (Before installation I did check for any blockage, both OK)

But unless I installed a defective ABS unit, there was the exact same effect. I did not install a new unit and would hate to think this one had the exact same symptom. The ABS action and function of both pump units worked the same and normal.

 

Coming in here a tad late, but since my 87 Vette meets the "poor" braking requirements, thought I would add some info:

1. 2nd owner, Z-52 auto trans, purchased in 1991 @ 23K miles. Brakes never "touch" by dealer, etc. Now have 105K miles.

2. From the getgo, brakes not up to my standards, with poor distance to stop. Pedal always "good" firm, not spongy. Both my 62 Vette with non-OEM front disc brakes (70's era big Chevy calipers with stock 62 drums in rear) and my Dodge Hemi Magnum stop much better! The 87 ABS has always preformed correctly (hammering ABS when trying to stop on ice slick road - Chicago area, not FL). ABS function is not an issue with this Vette - it does what it should, but not "often" now that we are here in FL.

3. Replaced all pads (rotors in great shape, so no change), no essential change in stopping distance. Several different pads tried over the years. Never wore a pad out, just want to try the next best, greatest pad to see if they might just be the answer - Nope!

4. Also change to the "upgrade" bias spring, although it was identical to the one I removed (coil wire dia., number of coils, etc.), and made no difference.

5. Replaced front rotors and calipers with J55 parts. Braking much improved, but still not "great". Note that some of the J55 braking improvement is due to increased leverage of rotor dia. increase, and some due to 2 piston calipers increasing effecting clamping force. Also "think" that the J55 is a stiffer caliper. Stiffer in the sense that it does not bow outward from clamping force at a lower pressure like the original caliper. Have witnessed clamping force deformation on calipers, which is the limit to how much total force the caliper can exert on a rotor until it starts to deflect. Once deflection begins, you cannot exert any more on the rotor - all you are doing is trying to bend the caliper.

6. I have recently changed rear brake pads (again) to Hawks, and have seen no effective change in braking (fronts are currently Raybestos "premium" pads, but have a set of Hawks that I was going to try next). Have used several different pad sets with the J55 upgrade, including Praise pads. Essentially no real difference was ever seen including the OEM pads that were on the Vette originally. Only the J55 front upgrade made any significant difference. And they still are not as good as I want.

7. Have also witnessed the rear rotors' poor stopping power, when jacked up and supported at the rear spindles, auto trans in gear at idle, it takes a great amount of foot pressure to stop the rears from turning. This is not as it should be, and I feel is most of the issue. Simply it is a very small rear brake caliper on a small rotor that cannot even stop the wheels from turning, let alone help stop the vehicle.

My next "test" is to do a pressure check on both front and rear calipers, to verify that the correct brake pressure is reaching the calipers. Have done this before on other vehicles, and it can be enlightening (will tell if ABS is bypass some pressure due to a fault, or ?).

I have read "somewhere" that is was possible to change the rear calipers by installing the original 12" front caliper onto the rear brackets. Have never seen this done, or heard about it again. So I ask if anyone knows if it is possible. With or without a bracket change, adapting a larger caliper to the rears should help increase the rear braking. I understand the limits and reason for forward biasing of brake systems, but rear brakes that cannot even stop the rear wheels from turning is almost biased at 5% at best, when it should be closer to 30%. If I find that the rears are too effective, I can always add an adjustable proportioning valve.

Thanks,
Plasticman

 

1994 - 115,000
Agree with your whole post. We have paralleled many efforts and feel like I’m looking in a mirror.

As for the rear brakes, always felt they were ineffective. The emergency brake is a joke in regard to stopping the car in any kind of emergency, just no power at all. I know its a parking brake, but compare to other cars.

But I pose some questions for thought. How could these cars have been sold with brakes as poor as they are. And, if the brakes were good when sold what could have changed over the years.

I believe the J55s are a stiffer caliper which I do think helps. But the 12 inch system has the same piston diameter as the 13 inch system calipers. Bigger pads might help also to take advantage of the increased surface area.

I also think the increased diameter and leverage is a major factor in the increased performance of the J55 system. But the kicker is, my Datson 1979 280ZX has 10.5 inch rotors and the brakes will put you thru the windshield.

It was pointed out in a few previous posts about part substitution over the years. I don’t think the parts of today are inferior to the past. I have been buying the basic brakes parts pads, rotors, m/c rebuild kits from Autozone and the rest for 25 years for the Datson and no matter what I do the brakes are always great, I can’t screw it up. The brake system just works.