Brakes are locked

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Mainer7

Mainer7

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Joined
Jul 30, 2003
Threads
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Messages
253
Location
Maine
Hello,

(I searched first)
The history: Driving regularly one day, the next morning I go to work and the brakes lock up and screeched when literally touched the brake pedal! Limped it home about 1/4 mile and parked it. (Brakes instantly locked up.)

From what I can tell so far, it's the front brakes (disc.) With the truck running or off, can't push brake pedal down more than maybe an inch. Vacuum hose attached or unattached made no difference. Fluid levels in reserviors had not changes and there were no signs of leakage anywhere. I tried bleeding all wheels and it made no difference. Up until the day before, everything was running just like normal, so it's really confusing this is going on.

Does anyone have any good ideas of what to check?
I've checked the check valve and it's fine. Had occasionally tested the booster over the years, and it seemed fine according to the tests at SOR and the FSM.

My first thought was the original booster had finally shat itself. The MC I put on about a year ago.

Thanks afor any help! Please help.
Jim
 
I don't know any way the booster could go out and make the brakes lock up.

You bled them? Hmmm. Unbolt the MC off the booster and see if they come loose.

I don't know why it would happen suddenly, but it sounds like the booster shaft is holding the brakes on. There are two adjustments, at the pedal, and on the front of the shaft sticking out of the booster. The front adjustment is very fine and critical.

Before you do anything, it would be a good time to make sure your rear brakes are properly adjusted. I had all kinds of problems until I got that right. Pull off a drum and make sure you have some pad left and the springs didn't break, or something.

If nothing else works it's probably some particles of crap stuck in the master cylinder keeping it from releasing. You'll have to take it all apart, blow it out with air, then bench bleed it.
 
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Mainer7 said:
Thanks Fast Eddy. i will do this tonight.
Click to expand...

If you get it done in one night you're about 20 times as good as I am. It took me a couple weeks to get my brakes sorted out, and I thought I'd done it all before.
 
Was it the front or the back that locked up?

How about a loose brake shoe?

Have any lines that have managed to get pinched - steel or rubber?

~j.
 
Fast Eddy said:
If you get it done in one night you're about 20 times as good as I am. It took me a couple weeks to get my brakes sorted out, and I thought I'd done it all before.
Click to expand...

LOL, I only was saying I'll remove the MC from the booster in one night.

Update: It's only the front that are locked up. Rear was fine on both sides, spun freely, no noises, etc. I really don't see how things could become "un-adjusted" just overnight, at least in this severity.

No broken/kinked brake lines either.

I unbolted the master from the booster and that did not unlock things. It allowed the brake pedal to go all the way down. I've got a booster from a 94 toy pickup I wanted to try because I think my booster is on it's way out. (It makes a hiss when pushed down but braking has been fine until the other day.)
I'll try to replace the booster Sunday or Monday.

So the front brakes are locked now and i still would appreciate any suggestions. I'm moving in a month and don't want to tow it 80 miles.

Thanks again:)
 
Update: Both sides are locked and they get less locked up when I unbolt the master. So is the master dead?! I just got it (Aisin) from Toyota Dealership new last year! If my booster was fubar would it maybe have helped to kill the master? Why only the front of the master would die?

Hmmmm...
Thanks Coolerman
 
Oooops! Just read your response again. Do they get all the way unlocked when unbolted from the booster or just partially? If all the way then you need to adjust the push rod clearance between the booster and the master.

If only partially then unbolt the front brake line from the master (Watch it! If it's under pressure you'll get hosed!) Then see if the calipers unlock. If they do pull the master out completely and remove the snap ring from the end. Pull the piston out and see what's going on in there. If it all looks good then put it back together and bench bleed it and put it back on and try it again.
 
I just removed the front brake line from the master and now the front wheels turn as they did when the master was separated (so, partially free. I can spin wheel with 2 hands and it does not keep spinning.) I pushed the pedal a little and it goes down like normal now that the front brake line is disconnected. This evening I will pull out that piston, etc. as you suggested.

Thanks again for this help!
 
Seems to me there's an adjustment on the pushrod between the pedal and the booster. Check it out in Haynes which has the spec and the adjustment. Had a problem with my old Superglide rear hydraulic brake...adjusted the pushrod too tight (not enough freeplay) and when I got on the road and things warmed up it locked up tighter than a drum. I had to drag it off the road, it wouldn't even limp. I know the same thing has happened on Crusiers so check out the free play in your pedal.

Pete
 
Actually, it sounds like the problem you get when the push rod between the master and the booster is misadjusted (too long) so that the pressure does not release when you let up on the pedal. You need about .020 free play between the end of the rod and the MC piston.
 
mainer7 said:
I just got it (Aisin) from Toyota Dealership new last year!Ahhhhhh.
Click to expand...

You didn't mention the new master earlier.

Sounds like it could also be that the master cylinder you installed has a check valve for the front brake line. Drum brake masters have these.

To check: Remove front brake line from master. Remove the large copper fitting on the master into which the front brake line was threaded. Remove the spring and ball hiding behind the fitting. Put back together. Bleed. Drive.

Hydraulics are notoriously mis-supplied. With all due respect, just because it came from the dealership doesn't mean you got the perfect match. JLook at all the threads in this section about "my brakes are adjusted perfectly but I have to pump twice..."
 
if you disconnected the front brake line from the master and the front wheels dont spin freely, then you have a problem with your brake line or your calipers need rebuilding. Have they been rebuilt ever? 30 years is generally a good time to rebuild toyota components...
 
Update...
Front brakes are unlocked, but now do not seem to be "getting the signal" from the MC. (No front brakes.) Also I cannot open the bleeder valve on the pass side caliper and it's pretty much raped now. Can I just crack open the hardline enough to let air escape while bleeding? I tried it and it seemed to work, but...

I looked at the MC internals and they all seemed okay looking. No visible sign of problems and the MC I got new from Toyota Dealer last year! I loosened the small bolt on the side of the MC and the push rod and stuff sort of shot out of it. Is that a big problem or can I just put it all back, push the rod in completely and retighten the bolt?
A local shop told me that if I used my 22re booster/MC setup it would fail prematurely because it was set up for different pressure system. But I thought people on this board had done this successfully. Anyone tried it and had good results?
Thanks again
 
Oh and sorry for the delay! I will also try what Mr. Toad suggested.
Thanks for all these suggestions, I really appreciate the help!

Okay, I did remove the plastic plate and spring (is this the check valve? see pic.) Then I took out the small nut on the side, pushed the pushrod all the way in and put the nut back in place. Then I bled the master and re-installed. I still need to bleed the wheel cylinders, but already the pedal feels like it used to when I push on it.


I'll post up Saturday after the bleed. Hopefully this will be the end of it! (The post, that is.)

:beer:
checkV.webp
 
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Well, I managed to drive it up to the airplane hangar where it rests in winter. Still need to replace on front caliper because I cannot bleed that one side!!!:mad:

It made the hour and a half trip without incident, although I was sort of nervous. Brakes work okay, but the pedal/pressure is really unpredictable...Getting a caliper from the salvage yard Saturday and going up to finish the job.

thanks for all the help
 
Brake woes

Just thought I'd share my experience with my '76 FJ40. Shortly after I got it the brakes became very touchy, locking up too easily. Then the passanger side front brake began dragging so bad it took both hands to hold it straight. The rim was extremely hot as well. What I discovered was the caliper pistons were seizing up on their old o-rings. I had never worked on calipers such as these before (4 pistons each). I ruined two pistons just trying to get them out of the housing (they should have just come out easily). That procedure is a post in itself. Hours of cleaning with scotchbrite pads on the end of my finger(you not supposed to disassemble the caliper) followed by flushing, new o-rings and dust seals, and a couple of new pistons had them functioning correctly.

Leon...
 
Mainer7,

I have exactly the same problem. Just fixed the slave cylinder, took it around the block for a test drive and when I got back in my drive way, the front brakes locked and the pedal became solid. I would like to disconnect the front brake line from the M/C so I can at least park it in a decent spot. Can you please tell me which one it was you disconnected?

Thanks
 
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