IBWiglin

I'm having an issue with the brakes on my 91 V6 Pickup and was hoping to get some opinions on it. The problem is with the brakes dragging. So far, they haven't locked up to the point where I can't drive yet. This only seems to happen after the truck has reached normal operating temps (running for 15-20 minutes). My initial thought was that the rubber brake lines were swelling when hot and acting as a one-way valve, but I was unsure because when I would get out and put my hand near each wheel to see which brake was hot, it seemed like they were all a bit hot.

Today, I was driving in traffic and the brakes were dragging pretty badly. Just to try to rule some things out, I cut the engine and then pumped the brakes to release all the vacuum from the booster. When I started the truck again, the brakes had completely released. I would drive for 10 minutes or so, and the pressure would slowly build in the brakes, then I'd cut the engine and pump the pedal, and the brakes would release.

It seems like the problem is almost certainly with the booster, but I can't figure out what mechanism of failure would cause these symptoms. Any ideas? Thanks.

osv

do the rubber brake lines look really old? they can look serviceable on the outside but are rotten and swelled up on the inside, especially if the truck was sitting for a long period of time? it acts the way you describe.

can you verify if it's front or back?

IBWiglin

All I've done thus far in an attempt to figure out which wheel(s) are locking up is pulling over and holding my hand near each wheel to see how hot they are. I'll see if I can get at the brake bleeder screws sometime this week. Unfortunately, I'm living away from home (read without a jack or garage) for the next 3 months. I do have some tools with me, but no jack.

My initial thought was also the rubber brake lines, but pumping the brake pedal while the truck is running doesn't seem to help. Pumping the pedal with the truck off has been very consistently releasing the brakes, though.

Charchee

You might look for any evidence of gear oil seeping out of your rear axle seals into the brake drums. 90W oil between shoes and drum will overheat and make a tar-like sludge that will lock up your rear brakes. This is common on 3rd gen 4runners. I haven't heard of many folks having this issue on your model but it's not too hard to check and rule it out. I just had to replace my seals. At low speeds the brakes would be real sticky and at stop signs on gravel it would actually lock up just as i came to a stop. Tapping the brakes would release them and you could drive through the stick and they would release. Only thing is, if it's not leaking much, the brakes will actually burn away the oil and you won't be able to see a leak onto the ground. You will have to pull the drum off to check it. See if you can get on some fine gravel and try to make a wheel lock up. As soon as it does it, stop and see where you skid mark is.

The brake booster could be a problem or bad lines but I wouldn't run down that rabbit hole until you can verify which brake / brakes are locking up. Your back brakes are completely different than your front in the way they work. I would bet on something mechanical in one brake being the problem like a sticking caliper in the front or rusted linkage in the real as opposed to the hydraulic system. If you had all of your brakes trying to lock up at once, you'd know it and wouldn't want to drive it. You don't have a factory jack? $5 would probably get you one at a scrap yard or just make a new friend and borrow theirs.