Hey guys,
brake issue here - brakes have been working fine for ages, but the past couple of days, it seems like the pedal travels much further, and after a couple of full braking tests, I think I may have a problem.

the pedal goes almost all the way to the floor, and the truck feels like it's very slow to stop. I thought it might have been leaking or gotten air in the system, but there's no fluid leaks that I can see.

it does feel a little spongy, I guess, which would indicate air in the system right? but how would I get air in all of a sudden without losing fluid?

definitely a lot of travel with little result.

I cannot lock up the wheels even on wet pavement. it's kinda sketchy!

what do you think?

I would say bleed the brakes as a start just to rule that out.
If the fluid level gets low enough in the reservoir to get air in up there, then you'll essentially need to do a full fluid replacement to get all the air out.
It is possible to get air into the system without loosing fluid by boiling the fluid. Easy to do if you have a stuck caliper and not know it.
While you're bleeding the brakes, you can do a visual on them and see if you need to replace pads/shoes.

Todd

Brake master cylinder.

thanks fellas, I'll give everything the good once over and post back with my findings.

Another thing you might check is the adjustment of the rear brakes. I am assuming you have drums on the back.

My son was working on our old 4Runner a couple of months back and having similar issues. He had ordered the new master cylinder but was still trying to prove to himself that it was needed. (he is a mechanic)

It turned out that the rear brakes were out of adjustment - too loose. Once he tightened them up, it was back to normal.

Randy

Hey fellas, just wanted a report back with my brake issue.
I ended up bleeding the system as recommended, and it seemed to fix the pedal issue for the most part, though it still seemed a little squishy.

With that, I decided to pull a front wheel real quick to check the condition of the pads, not that I suspected them to be the culprit, since the system should operate with relatively the same feel regardless of the wear condition of the pads, assuming nothing ridiculously low or worn. Well, it turns out that the pads *were* pretty worn down, surprisingly. They weren't metal on metal, but they were almost down to the wear indicator split. I would say that what was left was a little less than half the thickness of that of a new set of pads. There was more than 1/8" but less than 1/4" left on the pads. At $20 from the local parts store, I decided to replace them.

Things feel much better now, more back to normal. I didn't do anything with the rotors, as they seemed okay. Took a few miles for the new pads to seat a bit, but brakes are working pretty well again, and feel much more responsive than that sketchiness before.

Randy, this was a good idea. I hadn't gotten around to checking the rear, as I'd just replaced them recently, and this problem seemed to come on all of a sudden, so I never even considered that the rear shoes may be out of adjustment. I will probably give this a closer look the next time I do an oil change and chassis lube. I may just give the parking brake a few good pulls to "tighten" the clearance a bit, but the parking brake is working pretty well, so I figure the shoes have to be somewhat reasonably positioned.

If you have a bit of sponge left it might be air from the proportioning valve. I've had shops bleed my brakes and ignore that valve. It's left me with a little sponge.

How often are you topping off the fluid? If you are at all, it has a leak somewhere, brake fluid doesn't evaporate <img src="/forums/images/graemlins/kewl.gif" alt="" />

Try checking where the pushrod connects to the pedal inside the cab. If it is damp, there is at least one of the leaks. I've rebuilt many master/slave cylinders over the years, only costs a couple bux <img src="/forums/images/graemlins/cheers.gif" alt="" />

good call.
I was just hopping back on to report that the pedal went kinda flat and spongy again. I ended up breaking out the vacuum bleeder kit I picked up from Harbor Freight several years ago and pulled fluid through all the lines until it was all fresh, including the LSPV.

wherever it was, there definitely seemed to be air in the system somewhere. it holding pretty solid now.


I wasn't topping off any fluid at all, except when vacuum bleeding the system, and that was just to make sure I wasn't draining the reservoir.

I have had a leak before where you mention, in fact, that's how I came to replace the master cylinder a little over a year ago.

so you've had good luck with rebuilds? I've never tried one before. guess you have to have the small cylinder hone? isn't that pretty much all there is to it?

I've never had to hone them out, it's usually the seal that goes bad. The piston is made of a soft material so it usually takes on most of the wear and is usually included with the kit.

Glad to hear that bleeding them worked for ya <img src="/forums/images/graemlins/cheers.gif" alt="" />

Josh