peckinpah

I have been having this problem with my '91 2WD on and off for at least a year, but more frequently since the weather cooled down. I'm thinking it's probably time for a new master cylinder, but I'm no rush to fix it if I can get another few months of driving out of the old one.

So my question is, how dangerous is it to drive around like this, what happens when the MC fails, and what kind of time line am I looking at before I'm gonna need to do something?

As it is, I only have the brake pedal go hard maybe one time out of ten, and it still seems to stop the truck OK. Why is it that the problem can come and go like this? Also, it it a difficult or expensive job to fix?

toyotabull

I would check the vacuum line going to it first, second, it is somewhat difficult to replace but not too hard, third, the brakes can fail if the MC fails, but if its a vacuum leak on the MC, which it sounds like ,then it will just be harder to push that brake pedal to the floor. The problem can be a leak in the rubber on the MC in the dash, the vacuum line going to it, or even the rubber boot in the front of the MC.

thook

I've never had a master cylinder go "hard", so to speak. I've always lost brake pedal when they fail. I'd start looking at calipers or wheel cylinders seizing up.

peckinpah

Hmmm. Interesting.

I remember my 78 Corolla doing this a few times back in the day, but I just ignored it and I ended up junking the car before having to deal with whatever was causing the problem.

I assumed that the underlying problem would be fairly easy to diagnose, but it looks like it's gonna be more complicated than I thought, though hopefully cheaper to fix than replacing the master cylinder.

thook

Well, what does the brake fluid look like? Is it dark? When was the last time you flushed the brakes? Do you ever use your parking brake? I've had mine begin to seize up on me causing difficulty with the pedal.

I don't know your budget, but O'Reilly has reman'd Denso units for around $30. I've had good luck with those. In fact, I have one on my '86 right now.

peckinpah

I have never flushed the brake fluid since I bought the truck in 1991. Might be a good idea, once I figure out where the drain plug is.

DupermanDave

How dangerous is it for you? Or for the person you run into? there's 2 important peices on a car. The part that makes you move (the engine) and the part that makes you stop (the brakes). I'd fix it before you drive off a cliff or into a corolla with a baby on board.

I'd definitely just replace the master cylinder and flush the fluid. Try flushing first since that's the most simple procedure.

75k5toy

When you apply pressure to the pedal, does it try to push back? if it does then I think it's the brake booster.

peckinpah

I guess you could describe it as "pushing back". I think I'll flush the brake fluid first and see what happens, but somehow I doubt that alone is gonna help much.

I gotta do some research on how to do this properly, since I don't want to take any chances of causing the brakes to fail due to a bubble in the brake lines or something similar.

Found this thread:

https://www.yotatech.com/forums/f2/o...g-done-149414/

desertcamper67

X2 on the booster.

peckinpah

I'm still not sure i would describe what the brake pedal is doing as "pushing back". Normally when I press the brake pedal, it travels a couple of inches then I feel increasing resistance.

But when it acts up these days, there is almost no travel at all, and it's it impossible to push the pedal more than an inch or so. It stops the truck OK, but it's not exactly confidence-inspiring. Then it goes back to normal after a few stops.

It feel like it's pushing back, but I think that's because the pedal is so hard to press at all.

desertcamper67

Sounds like the same pedal you would have with the engine off. No power brakes.
With the engine off, push and hold the brake pedal down. Now start the truck. the pedal should sink some as the power brake booster starts to assist your effort on the pedal. It probably doesn't. Probably a leaky diaphram inside the booster. The check valve is a way easier fix. Pull it out of the booster with the engine running and make sure you've got lots of vacuum there. You can also spray some carb cleaner around the hose-check valve-booster area to check for vacuum leaks.

peckinpah

OK, so i bought a one man brake bleeding kit and bled all four brakes. I pumped out about 18 ounces of extremely brown brake fluid and replaced it with fresh dot 3 Prestone fluid. Took me about an hour and several wet spots on the driveway.

Braking feels much more confidence-inspiring now, and brake pedal feels normal all the time (so far anyway).

So evidently, my brake fluid needed changing after 200k miles. Go figure. I still have enough fluid left to change out the fluid in the clutch too. I assume that's pretty easy?

theAuthority

done exactly the same way. same nipple also.

Honestly if you're brakes are doing something 'funny' you never just 'ignore' it.

If you hit someone because you 'ignored' failing brakes you'd be in a heep of trouble and guilt.

On the other hand, good job at working brakes (for now)

peckinpah

Yeah well, I can laugh about it now.

And you have to figure that there's always a certain amount of risk in making things worse by trying to fix them. So I was sort of factoring that in, as well as assuming that I could probably sue Toyota if anything too bloody happened out on the road.

theAuthority

see anything wrong with this ? good luck on that suit if it happens

thook

Same way, but not the same nipple. Same kind of nipple....yes. (Nipple....I like that word...)

Anyway, peckinpah.......

Using the same method as flushing the brakes, find the clutch slave cylinder on the passenger side of the tranny bellhousing. You'll see a nipple (there's that word again.....) like the brake cylinders and calipers have on it. Have someone pump the clutch, crack the bleeder, allow the fluid and any air to expel, and keep repeating until the fluid comes clear and air free. Unless you have no one to help you, you really don't need the kit for this. It goes rather quickly. Hell.....since I've never had a bleeder kit, I don't know if it will even work for the clutch. Still.....happy nippling.