Dragging Brakes

[AJcolorado]

Update:

I put on the 'new' caliper and the problem is still the same. If I apply extra pressure to the breaks when the car is running, the caliper locks and only opening the bleeder valve releases it. If I apply extra pressure to the breaks when the car is off, then the wheel turns normally after releasing the break.

[xirdneh]

i wonder if the power assist could have something to to with it
like it is hanging up somehow
seems if it did it would affect both front brakes

[Petros]

that is really odd, never heard of such a problem. the only thing that is different when the engine is running is the power booster is engergized with vacuum. It is possible the power booster is bad? it does not seem that could cause that, it should affect all of the brakes, not just one. There is a check valve in the master that can hang up, but again that would affect all the brakes, not just one. that would only leave the propositioning valve and the flex hose to that caliper (didn't you replace the flex hose already?). If you have a new flex hose than try replacing the propotioning valve, though it might be possible the new flex hose is bad (but I have never seen that before, only old ones). if you have your old flex hose you might swap that old one back in just to check before you buy a new proportioning valve.

BTW, just to clarify; do your brakes have breaks, or are the brakes broken? It is breaks you do not want on your brakes, broken brakes are not good to have, but break the breaks in your brakes and the brakes should work again properly. You do want good brakes, without breaks, so the brakes will work again.

[dlb]

and it's just that one corner, hey? i think my money is on the proportioning valve than. if it was all of them, or at least both fronts or both rears, i would bet master cylinder first. keep us posted.

[AJcolorado]

Yeah, its just the front left. I'll move on to the proportioning valve. I was thinking of changing the hose again, just in case... it is new but seems like it could cause a similar issue?

[marlinh]

Have you jacked up all four wheels to see what is happening on all four brakes? Usually if the proportioning valve has switched it is due to a loss of hydraulics (blown line or wheel cylinder) and you get braking on one front and the opposite rear wheel. It shouldn't lock on. Very strange problem.

[AJcolorado]

I haven't jacked up all four, sounds like I should just to check...

[AJcolorado]

While break line is on order, I jacked up all four wheels and the right rear seems to drag while the left rear doesn't. The drag happens more in one section of the rotation, so it spins okay for about half a turn, then drags.

I can't find the proportioning valve in my Tercel manual. Can anyone point me to where it is located?

Thanks.

[marlinh]

Underneath the master cylinder mounted on the inner fender.

Now that you have all four wheels off the ground I am curious if any other wheel locks up when the left front does.

[Petros]

slight drag is normal, intermittent dragging as it rotates means rotor or drum is warped (not a big deal unless it affects braking power). neither will cause it to lock up as you describe. Sounds like the lock up problem is isolated to the one front brake caliper, or possibly the proportioning valve.

[AJcolorado]

Neither of the back breaks lock in the same way as the front left. It's not a full 'lock' either, with strong effort the wheel will turn but returns to normal when the bleeder is opened.

[Petros]

that should not be the case, the hydraulic system on that one caliper is staying engaged, and it should not behave theat way. have you tried replacing the flex hose? even if putting the old one back in as a test, it is possible the new one was defective and swapping that out will eliminate that possibility.

[AJcolorado]

Okay, the new 'new' flex hose came in and I have replaced it, but still the problem remains. I'm heading to the salvage yard to pull a proportioning valve and see if that fixes it.

[AJcolorado]

The replacement proportioning valve didn't fix it. But now the sticky break issue seems to be the same on both front wheels. When I start it and pump the breaks they both stick and drag a lot until I open the bleeder valve. Seems like it has to be the master cylinder or booster now.

[dlb]

man, this has turned into a real odyssey. good for you for sticking with it though, and for documenting it so well here. it will be useful to many people in the years to come, i'm sure.

that does seem to point to the master cylinder now. a few people on the forum have had problems with remanufactured ones but i bought a reman off of rock auto earlier this year and it worked well. you just never know with reman stuff so keep your receipts if you do go that route.