liv2soar

After driving a few miles down the road, my brake pedal gets harder and harder. Then it progressively gets so hard that the brakes are sticking and it slows me down. After about 20 total brakes presses, the brakes are locked up.

In an effort to fix this problem, I have installed:
-new master cylinder
-new front calipers
-new brake pads
-new brake hoses
-bled the brakes multiple times

The brakes are only sticking on the front, the back works fine.


Any suggestions?

eutu1984

It may be a problem with your parking brake sticking, ether the cable or the mechanism on the caliber that apply s pressure to the pads depending on what year you have.

65GGvert

I don't have an answer, but I don't see how the parking brake could make the front brakes stick. It sounds like a problem I've seen on older cars where there is a block in the brake hose that allows fluid to pass through when the brake was pressed, but not let it back through to release the brake. Usually changing the hoses would fix that, but sounds like you have already tried that.

65GGvert

By the way, there is no mention of the year of your car in the question and nothing filled out in your profile. That might make a difference in getting the proper help with your problem.

speedycat3

Most likely you have air still in the lines.
Have you changed all the fluid? If not, air in the lines coupled with moisture in the fluid will boil the fluid in the calipers and bind them.
I don't see what year your Vette is (I am on my phone), but I would recommend carefully bleeding the system using the recommended sequence. If you suspect air in the ABS (Mine had lots of air in it when I finally bled the ABS yesterday) bleed the ABS first until clear, bubble free fluid flows out. Then bleed the farthest wheel from the ABS (Right front then Right rear, then left front and finally left rear until you see clear, bubble free fluid from all of them. If you have speed bleeders it is easier, if you have regular bleeders, wrap the threads in one, thin wrap of teflon tape in the thread. Do not open the bleeder a lot, just enough to get fluid flowing.
I had most of the symptoms you describe after upgrading my 93 to J55 in front, and it took me a while to get the brakes to a firm pedal and good braking.

eutu1984

Sorry misread about it being the front brakes.

liv2soar

The Vette is a '92. Can you expand more on how to bled the ABS?

Also, the girl sat up for 8 years without moving. I'm breathing the life back into her, thanks to you all.

speedycat3

I simply connected a bleeding (clear) line to the bleeder port in the ABS, and pumped the pedal. Like I said, on the first pump I could hear the air, and as I looked back to the ABS and bleeding line, I could see all the bubbles in it. Just pump enough fluid through it until you see it clear and no bubbles. Make sure that you do not bleed the MC dry. Same as bleeding the calipers. Once done with it, just continue with the calipers in the sequence described, starting by the caliper farthest from the ABS and continuing on the the nearest one.

92ragtop

I was planning on doing this as well, but after lifting the ABS compartment lid, I don't see how you could even get to the bleeder since the ABS unit is mostly forward of the opening. What's the trick for access?

65GGvert

Please post a follow up to what you find. I am interested whether air in the lines can cause the pedal to get harder and harder and then lock the brakes. It should be just the opposite, the pedal should feel soft on first press and if you pump them to firm, get soft again if you hold them. I think the fluid is getting trapped in the caliper due to a line blockage somewhere and causing the brakes to be already on when you press the next time, making the pedal feel hard and brakes stay on. I am willing to learn and would like to know how you finally resolve it.

You may be able to tell by having someone pump the brake and hold, open the bleeder and see if a free stream comes out. Close the bleeder again and pump the brake up again and release it. Then open the bleeder again and it should not be under pressure with the brake pedal not pressed. If it is, you have a blockage somewhere in the line trapping the fluid after the pressure of the pedal forces it past the blockage.

speedycat3

Not sure in your 92 Vert but in my 93 coupe I could actually reach into the compartment enough to put the wrench in, connect the air line and losen the bleeder. There is certainle less space in the vert. You could take the seat off so that you have better access and reach in there with ease I guess.

eutu1984

I'm interested to here what happens to, I rebuilt my brakes over the winter and was not able to vacume bleed them so i used speed bleeders, that made a big difference. i still have problems with abs and on a 1990 there is no bleed screw on the abs unit. win it self test it pushes the brake peddle up, i am going top have to have someone pump the brake peddle and just loosen the lines.

speedycat3

Air in the brake line, with cold brakes, will feel like a very loose pedal with too much travel. Once you start driving, the air will heat up really quick and will create vapor that will heat up the moisture in the lines very quick. The vapor will not allow the fluid to flow freely back to the reservoir. If you wait long enough for the brakes to cool down, the fluid will flow back and the calipers will not grab anymore. Air, moisture and brake fluid all heat up and boil at different temperatures. Changing all fluid with new fluid (from a sealed container, not one that was used to refill the master cylinder and then left to sit), and bleeding until clear fluid with no bubbles has come out from all bleeding points is the key to eliminate air and moisture.

Tom400CFI

^No^. None of that is right.No! That is not right at all and it has started the OP on a wild goose chase. Neither air, nor water will cause the system to behave as you've described.



Yes. When you installed the new Master Cylinder, you were supposed to check/adjust the MC pushrod length. It is adjustable. What is happening, I believe, is that w/the new part (MC) your pushrod length is too long. The piston in the MC is not retracting far enough to uncover the "compensating port" which is what allows fluid to flow back into the MC reservoir when you release the brakes (and allows the calipers to retract). You're pumping fluid into the caliper, and as it heats, it expands, applying the brakes. Check your pushrod length.

speedycat3

Do one caliper at a time, and follow the recommended sequence fir your car, based on proximity to the ABS unit. In my old C3 the sequence was right rear, left rear, right front, left front, since It has no ABS. I only realized of the difference with ABS once I read more about it. the FSM shows the correct sequence for bleeding.

mtnmanut

Just curious as to what event took place that started this problem. Did this problem start after doing certain repairs to the car,or did this start slowly or one drive fine then the next drive it started doing this. We can speculate as to the cause all day long. You can replace parts all day long. Yes i can see a caliper with rusted pistons causing this or brake lines soft causing this,but not to the point of locking up the brakes.I would be looking into the abs. ask yourself how does an abs work.What tells the abs what to do. Read up in your fsm about abs.I can agree with tom400cfi. If the problem started only after replacing the M/C . But, we still need to know what event started the problem. just my 2 cents.

speedycat3

How can you be so sure? Did you work on my car? The OP was asking for suggestions on what the problem might be. I showed him my experience chasing the same gremlin for the past 3 weeks, and finally finding the air bubbles stored in the ABS. My calipers did bind after driving for a while, and released after cooling down, it did that twice, even after I thought I had bled them correctly. I changed 2 sets of J55, after thinking that one of the sets was defective, brake flex lines, and bled the system twice. I did not touch the MC even though some here are quick to recommend getting a new master cylinder. I am giving my honest to goodness opinion on a very similar problem that I just so happened to solve yesterday.
The one thing that the OP has not mentioned and I have not asked is whether the MC was bench bled before connecting it to the downstream lines. If it was not, then the bleeding process needs to start there.

Tom400CFI

His problem is not related to bleeding.

Tom400CFI

I can be sure b/c I know how cars WORK...even yours. 20+ years of doing this, (+auto schooling) does that. If the MC pushrod is adjusted properly, no amount of air or water, should cause the brakes to engage themselves. The expansions caused by air or water boiling is simply pushed back up into the reservoir!

Read HERE, pay attention to page #15.

IDK why your symptoms were (seemingly) caused by air in the ABS, but I'd guess that is was coincidence. I'd have to look at a hydraulic schematic of the ABS unit for a rational explanation of what you observed.

speedycat3

I guess my 25 years working on similar ( albeit a little more complicated) hydraulics systems in Boeing aircraft ( yes, with Boeing schooling) have not taught me well about how air and moisture affect hydraulics.
Carry on, I do not claim being a master mechanic because I am not. I have only worked in every single one of my cars for the past 35 years as an hobbyist that does all his maintenance. And yes, boiling moisture trapped in the caliper will cause vapor lock in a line and will not allow it to release.

The mention of air in the ABS was related to soft pedal and long travel. The mention of air trapped in the calipers was done because of the calipers locking up. The OP had all kinds of lines disconnected, lending help to the idea of air entering the lines. As soon as the air starts to heat up, it will travel along the lines and heat up the rest of the fluid and boiling up any air pockets in its travel.
Finally, the OP mentioned that the car sat for several years. As we all know, air tends to travel upstream with time. Since the ABS is midways between the calipers and the MC, the previously existing air in the lines could have moved up and got trapped in the ABS.