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ABS Flush

Zixxer

Well-known member
Joined
Dec 30, 2003
Messages
191
Location
Stafford, Virginia
Corvette
1982 Red Coupe
In a prior thread I posted the problem where I'm getting brake dust on the left front and literally nothing on the right. New calipers, rotors, pads, and lines and the problem continues. The right front wheel spins freely while the left front seems to grab a bit but still turns. The suggestion was possible air in the lines still, probably ABS, but I would need the Tech I or equal to do the auto bleed.


Well I found someone with the computer and sure enough there's an auto bleed feature. On the rear calipers the pump was noticeable and fluid poured out of the calipers but on the fronts only a few drops of fluid. While doing this it takes you step by step through the process and the question IS:

Does this help anyone diagnose the problem or is that normal that a lot of fluid flushes from the rear and little or none from the front?

Does this indicate there's a valve problem in the ABS?

All of the valves seemed to pump or at least make the noise while there's a noticeable difference in the rear v. the front.

There were no errors or DICs on the computer while the system performed the auto flush. The guys that had the tool were stumped as they've never used that feature.....long story. Anyways, now I'm bleeding each caliper and I notice the fluid is just nasty so clearly the ABS auto bleed must have cleared out something. I flushed by brakes twice before until they were clear so now I'm repeating the process and I've already gone through a quart of fluid on the front two calipers.
 
Well, ABS leaves me in the dark, but I am interested in the outcome of this situation.

Hopefully we have someone who is learned in the workings of Anti-Lock Braking Systems. Please keep us informed at any rate.
 
There is a bleeder valve on the ABS unit located behind the driver's seat compartment. That must be bled first before doing any of the wheels. What I usually do is use a Mityvac to do this. It's clean and quick.
 
My understanding is the bleeder valve is only present in the J series up the 1995 model. I didn't look for one but I will tomorrow. Where do you get a Mityvac from?
 
Zixxer said:
My understanding is the bleeder valve is only present in the J series up the 1995 model. I didn't look for one but I will tomorrow. Where do you get a Mityvac from?
I got mine at O'Reillys, but Sears has them too.
 
ABS Bleeder valve - 87 Corvette

There is a bleeder valve on the ABS unit located behind the driver's seat compartment. That must be bled first before doing any of the wheels. What I usually do is use a Mityvac to do this. It's clean and quick.

I'm having fits getting firm pedal on my 87 Corvette. I won't go through all i've done but for now I wanted to ask you if there's a bleeder valve on the ABS module and, if so, where is it. Thanks.

More basic: will a probem with the ABS cause too much/no pedal?
 
First, what year car are we talking about?

Second, generally, on autobleed, before you do that, you must bleed the base brake system per the FSM, then autobleed then base brakes, again.

Some ABS units have a bleeder on the modulator valve and some do not. It is suggested earlier to use a vacuum pump to suck the air out of the EBTCM. The FSM advises against that and to manually or pressure bleed the system when bleeding the EBTCM prime pipe..which is what you're doing when bleeding that fitting on the ABS 2S system.
 
First, what year car are we talking about?

Second, generally, on autobleed, before you do that, you must bleed the base brake system per the FSM, then autobleed then base brakes, again.

Some ABS units have a bleeder on the modulator valve and some do not. It is suggested earlier to use a vacuum pump to suck the air out of the EBTCM. The FSM advises against that and to manually or pressure bleed the system when bleeding the EBTCM prime pipe..which is what you're doing when bleeding that fitting on the ABS 2S system.


It's an '87. The reason I asked is that I have looked all over the modulator and see nothing remotely resembing a bleed valve. I know some don't have it and wanted to verify the '87 was one of those. In such a case, though, or even otherwise, can the abs cause the low pedal? The basic problem is little or no pedal without pumping (and sometimes even with). Sounds like the MC. I replaced it once to no avail - still had the problem - took it to two separate auto service places to beed - to no avail. The second shop said it has to be the ABS - but I don't know if that's just becaue the ABS light was on. That's where my confusion is. According to Haynes and people I've talked to, even if the ABS fails entirely, it doesn't affect the hydrauic operation. So, at this point, I've gotten to thinking I got a bad repacment MC (not factory) the first time. So now I have a brand new AC Delco MC an am about to put it in and bleed an flush. And, of course, wanted to bleed the modulator if possible. But even if this doesn't work, can I eliminate the ABS as the problem?
 
An 87 has ABS 2 which does not support autobleed. ABS 2 does not support any scan tool diagnostics, in fact, it has no on-board diagnostics at all other than the ABS Service light. To service ABS2, dealers used a dedicated diagnostic device called an "ABS Tester" (PN J-35890). This device is no longer available from Kent-Moore and since the last Vette that used ABS2 was an 89, the number of dealers which still have one of these devices is limited.

The modulator vave for ABS2 has no bleeders. I suppose it would be possible to "bleed" ABS2 but you'd have to find some way to activate the system and, at the same time, crack the fittings of the modulator's output pipes.

It is true that if the ABS fails, it does not affect the operation of the base brake system.

If the system has little or no pedal unless you pump, the first thing I'd do is bleed the base brakes including bleeding the MC, but...you said that's already been done. The next thing I'd try is replacing the MC. Make sure you bench-bleed the MC before installation.

I'd suggest using the Haynes manual to line your cat box and purchase the factory service manual from Corvette Central.

Lastly, the CAC has an article on C4 ABS service, but the story hasn't yet been posted in the feature articles section. When it goes up, I'd check it out because it has a section on diagnosis of ABS2 without the "ABS Tester".
 
An 87 has ABS 2 which does not support autobleed. ABS 2 does not support any scan tool diagnostics, in fact, it has no on-board diagnostics at all other than the ABS Service light. To service ABS2, dealers used a dedicated diagnostic device called an "ABS Tester" (PN J-35890). This device is no longer available from Kent-Moore and since the last Vette that used ABS2 was an 89, the number of dealers which still have one of these devices is limited.

The modulator vave for ABS2 has no bleeders. I suppose it would be possible to "bleed" ABS2 but you'd have to find some way to activate the system and, at the same time, crack the fittings of the modulator's output pipes.

It is true that if the ABS fails, it does not affect the operation of the base brake system.

If the system has little or no pedal unless you pump, the first thing I'd do is bleed the base brakes including bleeding the MC, but...you said that's already been done. The next thing I'd try is replacing the MC. Make sure you bench-bleed the MC before installation.

I'd suggest using the Haynes manual to line your cat box and purchase the factory service manual from Corvette Central.

Lastly, the CAC has an article on C4 ABS service, but the story hasn't yet been posted in the feature articles section. When it goes up, I'd check it out because it has a section on diagnosis of ABS2 without the "ABS Tester".

Thanks for all the info. I just finished putting in the new MC and flushing and bleeding the lines. My suspicion about a bad replacement MC seems to have been correct. I now have excellent firm brakes.
Thanks also for the info on the 87 ABS.

And, yeah, I know about Haynes' reliability. I use it for the pictures but learned long ago to take things in it with a grain of salt. Hence my wondering if it was correct about the ABS and the hydaulic system.
I didn't even realize the FSM was available. I will get one immedately.
Thanks again.
 

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