Help, Brakes working too good.

[MJBrown777]

After about 20 minutes of driving around town, my brakes start getting tighter until they are locked. I have replaced the Brake Proportioning Valve, and thought that would do it but still happening. As far as I can tell all four wheels are hot to the touch after I stop, so I'm assuming it's all four brakes that are tight.

 

[phxraptor]

Just out of curiosity have you changed the calipers or are they stock originals? If they were changed where did they come from?

 

[pws69]

Have you changed the Master cylinder lately? This can happen with an insufficiently "bench bled" M/C.

 

[MJBrown777]

Thanks for the inputs. I havn't changed the master cylindar yet, so I believe it's still orginal. That is the last thing that could effect all 4 brakes at the same time. It's like it somehow does not realease the pressure and just keeps on building it up.

 

[MJBrown777]

pws69, what do you mean by, "insufficiently "bench bled" M/C.". Because after they changed the valve they had to bleed the whole system...

 

[pws69]

pws69, what do you mean by, "insufficiently "bench bled" M/C.". Because after they changed the valve they had to bleed the whole system...

I have experienced the exact same problems you describe in the past due to 2 different issues.

Once was after I changed the master cylinder and didn't bleed it [enough] on the bench - I should have gone a few more pumps! On yours, although they didn't change the master, it is possible that either someone bumped the brake pedal while the valve was out [causing the master to gulp some air back through the lines] or they didn't bleed the system enough. This is why I now use ONLY a pressure bleeder for the vette.

The other time was when a dealer replaced a master cylinder and they didn't adjust the push rod on the pedal linkage for the new M/C (this was not a vette!). The rod needed to be adjusted "shorter" so what was happening was the master wasn't returning to the "rest" position - the rod was pushing in on the M/C about 1/4" - so it never "came off master" - the result was exactly as you describe your problem.

I suspect yours is a bleeding problem (or a bad M/C.....).

 

[MJBrown777]

Thanks for all the imputs, I'm gonna print the thread out and give it to my machanic that did the work. But I'm afraid it's gonna be the MC... :-( But the ol'girl is still in good shape for having 160K miles...

 

[MaineShark]

Have some hope that it only needs to be bled...

I had some brake trouble a while back, and the mechanic swore up and down that the MC was bad. A buddy and I bled the lines, and it's worked fine ever since.

If I may make a suggestion: mechanics can get very defensive, if they think they are being accused of doing something wrong. If I were in your position, I would make sure to emphasize the "maybe someone bumped the brake pedal" aspect. After all, that is the most likely, since the cockpit is tight, and it's easy for someone with long legs to bump the brake pedal unintentionally.

Joe

 

[Daryllawman]

I had a 77 Vette and it was doing that and I kept on driving and then one day the right rear while cought on fire. I got it out and towed it in........it was the brake caliper that was froze up....

 

[cruisin-davey-g]

After about 20 minutes of driving around town, my brakes start getting tighter until they are locked. I have replaced the Brake Proportioning Valve, and thought that would do it but still happening. As far as I can tell all four wheels are hot to the touch after I stop, so I'm assuming it's all four brakes that are tight.

Hi: Sounds like you've got power booster problems. A bad or faulty power brake booster will lock up all 4 corners as you're describing. Check it out. Could be either a faulty booster, or the vacuum line to the booster (a bad check valve). Good luck & let me know what you discover.


Dave: