skrez

So after driving my 96 4runner for awhile the brakes seem to be engaging on its own. It isn't that they aren't releasing rather that they are applying on there own. I checked the calipers and the pistons are fine. Re-lubed the caliper pins as well as the break pad slides. The car is manual so as I shift (release my gas pedal) I can feel the breaks hit. It all began when I started to feel my stearing wheel shake and then the brake pedal would be tight, this happened on the freeway. Now it happens on side streets doing 35-40. Cant drive for more than 10-15 minutes with out this happening. Any ideas? I have heard things about the master cylinder or brake booster. Anybody have any ideas? I need help ASAP!!! Thanks.

bigpoppa

Does it feel like it is just in the front, or just on one side or all of the brakes? I have never heard of brakes applying on their own.

Is it at all possible that it is not the brakes? Could it possibly be something else like a binding CV joint or wheel bearing that makes it feel like the brakes?

skrez

It is definatley the brakes. The pedal gets firmer as this starts to occur. It's both front brakes. There was smoke pouring out of the wheel well the other day.

SuperSixOne

idk.... full break lock up like that sounds like a fluid problem.... IE: Master Brake cylinder. But engaging on their own? Depending on the year of the truck, it could be drive by wire where the computer actually controls the cylinder through an electrical connection and not mechanical right from the break pedal. Although im not so sure that a 96 had that system. I thought it was much later.

bigpoppa

I'm not very knowledgable in how ABS works but from what I understand, there is a pump in the ABS controller to reapply pressure to a particular wheel if the pressure is released by the system. I wonder if this is malfunctioning and the ABS is what is applying pressure to your system.

You may want to do some research and see if you can disable the ABS, I think you can do it by pulling a relay but please research this yourself. Then take it for a drive and see if the problem goes away.

I will add another disclaimer. I think that you can disable the ABS and take it for a drive and you will simply not have ABS, but still have brakes. But please confirm this before you try it.

SuperSixOne

Disabling your ABS system will not disable your normal break function. Assuming everything is working properly, pulling the ABS relay from the engine compartment of the truck will shut that system down.

dannomite

I had a volvo that stated doing that but only when I was in traffic and it was warm. It turned out to be the seals in the master cylinder were bypassing and when the fluid heated up it would apply the brake. Although it did not apply them hard enough to make smoke come out from the wheel.

mtbdick1

Did you figure out what was engaging your brakes?

I have a similar problem on my '96, but just with the rear. I start out with the rear wheels turning freely and with plenty of parking brake clicks, but after 10 minutes of highway driving something starts to apply the rear brakes. I start to feel shuddering and when I feel the parking brake (with button pressed), it's clear that it is engaging right from the very bottom of the travel. By the time I get to work, I can smell burning brakes and the rear drums are *very* hot.

I just checked (after everything is cooled down) and the parking brake is not over-adjusted. Perhaps it's related to the ABS/master cylinder, like the Volvo above? Or a rear apportioning valve? Any idea how to tell which component is the culprit (master cyl. or rear apportioning valve)?

I just changed the rear diff seals, wheel bearings, shoes and up until now, had assumed the problem was related to that job, but now I'm starting to think it's unrelated and maybe I'm only noticing it because I now have dry drums.

A couple years or so ago, I replaced the master cylinder. Went through heck trying bleed it on the bench, and it never seemed to stop the car as well as I thought it should, though there was no apparent air in the system. I wonder if that crappy master cylinder is acting up??

If I do have to repeat the exercise (noooooooo!!!!!), anyone know of a reputable source for a master cyclinder? The one I put in was from Cardone and it's still under warranty ... but I don't want to do this again.

Thanks,

Dick