I have a few questions on a brake problem, The last 2 weeks I have noticed that when I start the vette I haven't heard the ABS/ASR cycle and as I pull out of the garage the brake pedal is low so I gas it enough to slightly spin the tires to activate the ASR and the pedal comes right up and the brake pedal is fine from there on. This has happened intermitant. Well tonight I was cruising down I-95 at a fairly good clip... now the brakes have been fine all night... I was coming up on a Semi-Tractor pretty quick, I had an SUV on my right and a barrior wall on my left, I assesed at this point that I had no room to go around so I applied the brakes and to my surprise.... NOTHING for about 4 inches of pedal.... I started to look for a place to aim the car so I wouldn't kill anyone, well I made it out of this and headed for the brakedown lane and got out and looked for a leak maybe low fluid... nothing wrong. I got back in the car and still really low pedal so I spun the tires and the pedal came back up. I am figuring there is air getting in the system and the ASR is bleading or pumping up the system for me.


What could be causing this if the fluid is not low and there are no leaks found? There are so many Hydrolic parts on this brake system is there anyone who has had the same or similar concerns.

I have a 1992 auto with the ABS and ASR and the car has 144k miles on it.

Thanks

 

Its been my expierence that the brakes will operate correctly independent of the ABS. You can have a failed ABS system and the brakes will still operate normally. I'd suspect the master cylinder.

Test it. Apply the brakes and slowly push harder if the pedal goes down with pressure it could be the master cyl.
A failed master wouldn't leak it just by passes the fluid and creates less pressure.

Start there.

 

I noticed last night that pumping the brakes several times did nothing to bring the pedal back up only engaging the ASR did. It is quit baffling.
I have been inspecting brake parts all morning and the only thing I can find is that there is a sensor under the master cyl. that appears to be slightly damp with fluid. Last night when the problem happened I checked the fluid and it was full. I am totally baffled because it is not happening today... WHAT GIVES!?!?! You would think that the problem would be here today as well.

 

I also suspect the MC. But before you do that, try bleeding the breaks. Its pretty easy and your fluid might be the problem. If you dont know how, let us know. Use synthetic fluid.

 

Do you mean ...Flush the fluid or just blead the brakes like normal?

 

i would guess the MC too...i just replaced mine because of the same symptoms...although i don't have the ABS to worry about. if your fluid is all brown and gross, flush the sysem and bleed properly...if its newer looking fluid, i would just bleed it to make sure there is no air....but 4 inches of pedal travel is a LONG way for the problem to just be a lil air.

 

Have ever had any sucking sounds coming from brake pedal movement?

The self test should be heard or felt as the vehicle reaches 4 mph. If not, did you get a service abs asr lights at all? If so read the DTC codes. The brake system will still function even if ABS/ASR has failed.

Do the DIC lights come on for 2 seconds then off when you turn the ignition to On then go out?

You should not have any fluid under the master cyclinder. I would start to look at the mechanicals at the master cyclinder and the vacuum boost assist. I think your going to find the problem here.

Moisture causes the fluid to turn dark color (black/brown) that is not an indication of contaimination. Any fluid has moisture in it. Its normal. You can flush the system and load it with fresh new fluid, and within a few days it will start turning dark again.

 

No sucking sounds, the power assit works fine. There is a moist spot(very slight) on the bottom sensor under the master cyl.
The more I read the advise here the more this is pointing to the master cyl. because no matter what happens the ABS or the ASR should not need to pump up the brakes to gain pedal, what is so baffling is the fact that it is not doing it right now and why would a master cyl. have an intermitant concern.... if its broken then its broken I have never seen a intermitant prob with a master cyl. before, once it leaks presure then it usually stays losing presure.

 

Lets look at the master cyclinder. Its split into a front-rear section. The proportioning valve limits outlet pressure to the rear brakes after a predetermined rear iput pressure has been reached. The valve has a by-pass feature which ensures full system pressure to the rear brakes in the event of a front brake system failure. Front pressure is retained in the event of rear failure.

Looking at the diagnostics a leaking internal master cylinder will cause excessive pedal travel. Why might it be intermittent. My guess would be ambient temperatures. We are starting to get some cooler temps here, and this may be causing the seals to swell and contract. Today its warmer, so it may not be showing an indication. But if it gets cooler again over the next day or so, it may show up again.

 

Good point... I will be out cruising it tonight (gently) and we'll see what happens.

 

Ok, we went to diner then drove close to 70 miles total and not one problem. This is not good cause I can't duplicate the problem.

 

be careful drivin that car! driving when the MC finally craps out for good is NOOOOO fun (ask me how i know). brakes are the most important system on the car IMHO, and if its not good, you are really rolling the dice. i still vote for the MC, and if i were you i would replace it ASAP (once you have eliminated all other possibilities)

 

Dude,
what you need to do is bleed the breaks. I am sure that will help. Check your break fluid reservoir. If its not a clear yellowish color, it could probably use. DONT flush. I dont know where you got the idea of flushing, but dont do it. Take excess fluid out of reservoir with a seringe or turkey baster. Add new fluid. Bleed breaks, fill.

 

Master Cylinder

 

I'm gona try bleeding them today, and if it happens again I will replace the master cylinder. You know when it acted up the other night for the first time I was on the tail end of a 70+ mile ride on I-95 doing pretty decent speeds I wonder if a caliper is hanging up causing the brakes to overheat alittle causing the intermitant failure. I don't have any pulls when the brakes are applied though, and I didn't smell brakes burning or heated. I am leaning toward the advise of a master cylinder though. When we went to diner last night I was being very careful always testing the brakes and making sure I had a place to go if the brakes failed. I can deal with a lot of items failing on a car but brakes are not one of them.

Thanks to all for the recomendations I will keep searching and report back with results.

Please keep the advise coming.

 

You know I'm not sure if your ABS will affect the brake pedal or not, I just don't know. It could since its hyrda.
Try running the car in place and put your foot on the brake pedal with a steady pressure and see if it goes down.
If the master is bad or going bad the pedal should go towards the floor.

If the booster is bad the pedal will have a lot of pressure but will not apply enough pressure to really stop the car.
The ABS light should be on in the car if the ABS is bad.

Have you tried locking the brakes? A 4 wheel skid will tell you whats going on with the 4 wheels. Stop as soon as you can and go back and read the marks.

As stated above the brakes are the most important part of any car. If you can't figgure it out tke to a Corvette shop for an estimate.
Good luck.

 

I suspect it is the Master cylinder. The piston inside the m/c is having blow by where the brake fluid is not being pushed by the piston but the fluid is going past the piston. Just a guess but that is what it soulds like.