71 fj40 front brakes locking up

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rugerberetta

rugerberetta

10 Year
Joined
Apr 6, 2011
Threads
43
Messages
189
Location
Defiance Missouri
I have a 1971 FJ40 Drum brakes all new cylinders, shoes and drums. It also has new brake booster and master cylinder. It was fine for the first 20 miles then I drove it to get inspected it passed but they said my brake pedal was really hard with vey little play. When I got in the car to drive home they were right the pedal had lost all the play. I stopped to get gas after about 10 miles and when I went to pull out my front brakes were locked almost solid. I had to wait about 15 minutes for them to release so I could limp home. I have adjusted the rod between the booster and the master several times but they keep locking up if I drive more than a few miles. Hitting the brake does not seem to have anything to do with it, is seems to be based on how long the drive is. I replaced the rear brake lines and have ordered new flex lines to replace the original rubber ones up front. If this does not work any suggestions? and how sensitive is the adjustment of the rod between the booster and the master? can a one turn either way to much cause this? :confused::confused:
 
Have you tried backing the shoe adjustment off a click or two? I suspect you have the shoes a little tight, and the friction heat is causing the brake fluid to heat, expand, and pressurize your cylinders.
 
Pin_Head said:
It is usually because the booster push rod adjustment is too long. Back it off until there is about .015 gap. You can check it with some plumbers putty or clay.
Click to expand...

So I place they clay between the booster push rod and the cylinder piston then re-attach and see it the booster push rod remains about .015 away from the back of the cylinder piston when at rest. I will give it a try if I still have issues after I install the new lines. Thanks
 
Have you jacked the front up to see if it's one or both wheels that are dragging? If it's both it's probably the pushrod. If it's one, it might be that a rubber brake line is failing and not releasing the pressure on the cylinders.
 
It is both, have new braided lines on order, should have been here today bu no show. I also adjusted the pushrod per previous post. Hopefully I get my new lines tomorrow and can test to see if one of these changes fixes my issue. I just got my inspection and it passed but they did say my brakes seemed real tight. I thought it was because everything was new until they locked up on the way home and I had to sit for 15 minutes until they cooled and release enough to get the rest of the way home.
 
Alright, New booster, new master all new lines and still brakes locking up. I have adjusted the booster push rod 100 different times and still front brake dragging not as bad but still not drive able for extended distances. Does anyone have any other suggestions beside converting to front disc?
 
just found out I have my shoes in wrong. My year does not have retainer pins and clips so the springs must be on the back side. I have the front spring on the back side but the rear spring is on the front. I think this might be some of the issue although the rears are the same and haven had any issues. I guess I will be putting shoes on tomorrow. I hate messing with the springs.
 
Have your drums turned. it might help get you get a little space, and will guarantee your drums are round.
 
I would have them turned, if they were mine, but that's just me. Rotors, no...but drums, I would. But if you are running tight in your drums, and the shoes are adjusted all the way in, then turning them would get you a little more space. The plus side to this, is you can turn them for about $20...and that's a lot less than a disc conversion...You asked for suggestions...
 
Is the master cylinder japanese mfg or some other eastern rim. I've only seen this once in hundreds of master cylinder replacements but I had one master where the relief port was literally not drilled. The port that the brake fluid returns to the fluid cups when the pedal is released was not drilled . There was a dimple in the casting but no hole. After about five miles driving the front would lock up and start smoking.
I drilled the ports and the brakes worked fine. Since then I try to buy Aisin parts
 
The master is not an Aisin. Where is this port so I can check? Also when you adjust the booster push rod is this done by adjusting the brake pedal or by removing the master and actually adjusting the length of the rod. i have been removing the master each time. I did save the old factory master I did rebuilt it but it had been setting in a field for 10 years so I opted for a cheap replacement.
 
How about the hard lines (as in the one that bridges the wheel cylinders). Also, I assume you adjusted the brakes with the front off the ground by doing the friction test?

I almost installed my wheel cylinders in opposite swapped positions ( thus I would have tightened instead of loosened.

I am gonna go check my Toyota service manual


Edit... Manual says possibly a faulty booster, no free travel in pedal, faulty master, or bad/ distorted brake shoe
 
Last edited:
lcwizard said:
Is the master cylinder japanese mfg or some other eastern rim. I've only seen this once in hundreds of master cylinder replacements but I had one master where the relief port was literally not drilled. The port that the brake fluid returns to the fluid cups when the pedal is released was not drilled . There was a dimple in the casting but no hole. After about five miles driving the front would lock up and start smoking.
I drilled the ports and the brakes worked fine. Since then I try to buy Aisin parts
Click to expand...
I checked the old master against the new master and the old has a small hole drilled in the very front of the cylinder the new one does not so if this is the relief port then this is my issue I purchased from coolcruisers so I will call them and ask. Thanks
 
I keep telling the noobs not to buy brake parts from ccot...but do they ever listen? Noooo...
 
after taking the OEM apart the does not seem to be any difference between it and the aftermarket. I still must have an adjustment issue with the booster push rod. I will keep working at it.
 
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