Toyota master cylinder help

Hurdt299

Well-Known Member
Joined
Nov 13, 2006
Location
Asheville, NC
I have an 83 toyota truck. Wouldn't hold pressure on the pedal. Slowly bled down each time I applied the brakes. I changed the master cylinder and now I can't get it to bleed. I've never had this problem before on a MC. I tried to bleed it for about 2 hours the other night. Anybody have any tricks or suggestions? I can't get any pedal to even bleed the brakes. It feels like it has some pedal, then at about half pedal is almost makes a popping and goes to the floor. I bench bled the MC.
 
Bleed the load sensing valve under the truck bed first, then do the pass rear, driver rear, pass front, driver front. That valve is a PITA to bleed.
 
My comanche did the exact some thing when i changed the MC, calipers and wheel cylinders all at once. I bench bled it, but it still took hours worth of bleeding to finally firm it up.. I gave up two or three times, and came back the next day. Not sure if that worked some bubbles out or not. It may have been due to the load sensing valve on my Comanche as well, I didn't see a spot to bleed it.
 
awspence said:
My comanche did the exact some thing when i changed the MC, calipers and wheel cylinders all at once. I bench bled it, but it still took hours worth of bleeding to finally firm it up.. I gave up two or three times, and came back the next day. Not sure if that worked some bubbles out or not. It may have been due to the load sensing valve on my Comanche as well, I didn't see a spot to bleed it.
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I bought a mityvac today so maybe that will save me some time and get all the air out.
 
I wouldn't bypass that valve unless you replace it with an adjustable one. If you eliminate it completely you will have full brake pressure to the rear wheels which could be pretty scary on a wet road.
 
MarsFab said:
I wouldn't bypass that valve unless you replace it with an adjustable one. If you eliminate it completely you will have full brake pressure to the rear wheels which could be pretty scary on a wet road.
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Ok so that is the only proportioning valve on the truck?
 
I'm fairly sure its the only one. I think some of these toyota guys on here will know better than I. There is definitely a possibility that the master cylinder you bought could be bad. Ive seen quite a few with this problem that turned out to be bad off the shelf. Especially Advance auto remans.
 
I bought a reman from NAPA for my 89 Toy. I tried to bleed it for 2 days. I've done many of them so I knew I was doing it right. Come to find out that when they rebuilt it, the piston was wrong(?) When in the rest position it wasn`t far enough to pick up more fluid.

I`ll have to find the pic. but I made a cap to fit on the master cylinder to pressurize it. Made bleeding the rest of the lines a breeze!
 
x2 on the master cylinder. Went through three from advance auto on my dad's truck a few years ago and could not get anything to bleed. Got one from the dealer (surprisingly, was about the same cost) and everything was back to normal.
 
ChrisM said:
x2 on the master cylinder. Went through three from advance auto on my dad's truck a few years ago and could not get anything to bleed. Got one from the dealer (surprisingly, was about the same cost) and everything was back to normal.
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Went through 4 myself from advance, go to NAPA and by a good 1. I think its $90, but it worked the 1st go around
 
I got mine from the local parts store cause I would much rather support my local parts store instead of buying from the big stores. I got the front to bleed today but still can't get the back. I think it's because the load sensing valve isn't working right because of the lift on the truck. I think it's completely shut if that's possible. We have about a foot of snow so I'm not about to try to fix it right now. Front brakes are good enough for the snow since I'm running in 4wd everywhere I go.
 
I dont believe it will close all the way. I've seen quite a few trucks that have just taken the mechanical linkage off which does the same thing as having the bar that pushes on it all the way down. So being lifted alot will lower the bar but cant completely stop the brake pressure. If you open the bleeder on the load sensing valve and press the brake pedal do you get any fluid?
 
Well that sucks. The next best thing would be to bleed it by loosening the line that comes into the valve like you would a bleeder.
 
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