Brakes still randomly build pressure to cause undrivable dragging, everything replace

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71FJ40 said:
Fluid got hot without the truck moving!!?

Can you post a high res pic of the master/booster assembly and another pic of the hard lines going down to the frame?


PS - I still vote for the pedal and plunger not being adjusted correctly. If you disconnect the brake master plunger from the top of the brake pedal does the plunger push itself out past the pedal?
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Pedal and plunger are set as per FSM. No, the plunger does not have pressure on it.

Drove it for a while today. so far so good.

As for pictures, I already moved the brake line. It follwed it down from the top of the manifold all the way down the pipes. The distance awas about an 1" out down about 6"s.
 
Not sure on the location of your hard lines on the front axel, but mine ran across the front axel from the driver side to the pass side. One of the PO's had the cruiser towed for some reason. When the tow truck hooked up to the cruiser, they placed the hooks over the front axel to pull it. When they did this, they crushed the hard line that went across the front axel. Might want to look for that as well..

Shawn
 
Time will tell. Since I can't figure out what would casue fluid to get hot without the wheels turning, I hope I guessed correctly.
 
Hey Slickrock,

I didn't realize how much trouble you were having with this until I read this thread.

I'll try to throw some reasoning out on the table.

It seems you may have had an adjustment problem early on. When you talked about backing off the pushrod, and the brakes unlocked, that would indicate there was a problem with the mechanical side of things (MC, pushrod, etc.).

You replaced one of the lines last month, and the problem was gone for awhile, right? It didn't return until you flexed out the suspension, which would also work the soft lines beyond their daily use. I'm thinking that there is still crud in the system, or those other lines are breaking down, just like the one you already replaced.

The only other thing I had in mind is the booster staying actuated. Let me try to reason through this. The booster has a valve built into it, where the pedal rod pushes it. As soon as that valve is opened, it starts letting vacuum into the booster to assist in applying the brakes. If the valve is held open when it shouldn't be, it can actually apply the brakes harder and harder until they lock up. Things that normally cause this are pedal adjustment or stoplamp switch adjustment. If the stoplamp switch were sticking at times, it could cause an intermittent issue.......Now, as much as I like my own theory, I think you've disproven it when you disconnected the vacuum source to the booster, which should remove all vacuum from the booster. Still, it wouldn't hurt to check that stoplamp switch for smooth operation.

Hope to see the rig in person someday, maybe on the trail.
 
THe stop lamp switch was in issue when first installed (it would not turn off), but once I got the pedal in spec, it worked fine. I drove it for a while again yesterday and all good. But with a random event, it has to happen randomly.
 
Well, I have been driving for a few days in my little 4 stop light town. Haven't had drag yet. Keeping my fingers crossed.
 
It happened again!!!

Bad news. After a few months without any braking issues and driving almost daily over the summer, it did it again Saturday. It was a very hot day (100 degrees) and I drove it about 15 miles away. Started to feel some power loss but thought it was from adjusting my choke incorrectly to lower my idle. Sure enough, after turning it of for 5 minutes, went to drive away and they were locked up (all 4 tires). Apparently it was not my brake lines heating up.

To get it moving again, all I had to do was back off the 4 master to booster mounting bolts until the nuts were almost all the way off so that the master slid forward. I then tightened them back up (not as snug as they were) and the brakes were fine again.

My dang brake pedal is adjusted per FSM so it is some issue between the brake peddle and the push rod. The push rod length is perfect (FSM and with during for 2 months and no issues). The push rod also could not back it self out with vibration because I welded it on.

The only thing I can figure is that maybe something is bent between the brake pedal and push rod / firewall causing the push rod to not go in straight sometimes and bind up. But since this is a random event, I am so at a loss.

Everything is new and or different from the first time this happened except for the brake pedal to firewall hardware. Maybe something is bent but why would letting the master back it self off then tighten it back down cause it to work correctly again?

Maybe shorten the brass prong end of the booster to where it contacts the pedal assembley a bit?
 
The piston inside the master cylinder won't let fluid return to the reservoir if it is not in its free position. By loosening the mounting bolts the piston returned and released pressure from the lines.

One of your two pushrods is too long.
 
THe one in the booster is set to stock measurements and so is the pedal. (the booster rod has been replaced 3 times between boosters 9stock, mini, and now fj60). I cannot back out my foot push rod anymore b/c it will not activate the brake lights.

Anyway to adjust the brake light switch?
 
shortening the push rod between the pedal and the booster should not affect the brake light switching on/off. If you made the pushrod much too short the lights would possibly just stay on. Do you have a return spring on the pedal to return it to the free position? The pin attaching the pushrod to pedal has a machined extension for the return spring.

You should be able to remove/install the pin joining the push rod to pedal with no tension whatsoever from the booster. There should be at least 1/16" clearance from the free position of the pedal to where it contacts the booster, enough that the rod can be wiggled.
 
Flexible brake lines can tear internally and become like check valves, I personally would replace the rear flexible brake line.

If that doesn't work and if your fixed lines will flex far enough swap your front and rear brake lines at the master cylinder. If the problem transfers to the front then you will know that the problem is from the master cylinder back. If the back brakes continue to lock up then you will know that it is in rear brake system somewhere. It won't tell you exactly where the problem is but you have just eliminated half the circuit so you won't waste time chasing phantom problems.
 
I read this a few hours after I sent it out this morning. My typing is like a 5th graders. Sorry about that:

I'lltry to answer the best I can to the last 3 responses
1) my entire syste is replaced except for the cab
2) Yes I have a spring. Maybe I wa thinking about extending out my pedal with the light. Now that you mention it, if I shorten it any more, my brake lights will stay on, not not activate as I said earlier (brain fart). SO to get more wiggle room 1/16, my lighs will not go out. COuld this be that I need to get a stronger spring?
3) brake lines are in geat shape. I checked them all last go around.

I grabbed 2 different size washers to do a temp fix attempt to se how it goe. I am goign to put the thinnest washers in between the master and booster to give more throw. I'll adjust my brakes ot make them a bit more snug to compensate. IF this works, then i know i is a too short rod or i need thicker wsher to make the throw even more.

THat is at least all I can think of at this point.

I want to try to lean towards shortening the bake pedal and figuring oout a way to allow the brake lights to turn off. SInc i shorten it now and it does not return enough to deactivate the brake light switch.
 
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I'm back. So last week they did it again. This time, when they locked up after slowly creating drag, I simply loosened the 4 nuts holding the master on and let it slide forward about 1/2 inch. Once I did this, I bolted it back up and they were fine again. The connection between the master and booster was too tight causing binding.

I figured something has to be wrong with the cab side of things since that is all that is left from the original. I measured the center of the pedal to the front of the tub and it was right on. But I noticed that there was a slight "untrueness" to the peal. Sure enough it was at a slight angle.

After some time, I saw that the firewall had a little bend in it. This bend was causing the booster rod to put pressure at an angle on the pedal. This then put negative pressure on the pedal causing a slight tweak. This tweak might have been from me looking too hard for an issue and it seemed off. Wither way, it might have been the problem.

After putting small washers in font of the booster where it attached to the fire wall to square it and readjusting my pedal, things felt better. Except that I now needed to adjust my push rod a bit since now it went into the booster a bit farther. But since I welded the end of the adjusting nut, this was out. I tried a washer between the booster and master, but it was too much. I only a little bit of brake pressure. I then grabbed some roof flashing and drilled holes in it and cut them to washer size and used those instead. First time the brakes were a bit too much and they locked up at full extension. Since brakes should just almost lock up, I added another row of flashing spacers. This time, only with stomping, will the brakes slightly lock up.

This seems to indicate the brake drums, master, and booster push rod are properly adjusted. Just in case it continues, I cut 8 more flashing washers to add as spacers along with the washers I tried the first time. When the flashing washers are doubled up, they are about half the thickness of the washer. I can at least adjust things a little bit with these.

I drove it for about a half an hour last evening and they seemed to wok very well. But then again, they seemed good last time. Only difference is that the "feel" is better now.
 
good deal

Glad to hear you got it sorted out, I remember reading your thread a while ago. Thanks for posting up the final solution it's nice to know!
 
Old thread revival...

I have a similar issue with brakes dragging. Do you think it is possible that the heat from the engine could cause the push rod from the booster to expand and put pressure on the master? My issue only happens when the truck heats up.
 
SouthBostonFJ said:
Old thread revival...

I have a similar issue with brakes dragging. Do you think it is possible that the heat from the engine could cause the push rod from the booster to expand and put pressure on the master? My issue only happens when the truck heats up.
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Huh? :confused:


So let me get this straight; you start the truck, run the engine and get it to operating temperature and do not drive it and the brakes are dragging?
 
Poser said:
Huh? :confused:


So let me get this straight; you start the truck, run the engine and get it to operating temperature and do not drive it and the brakes are dragging?
Click to expand...

For clarification, I still have drums all around.

No, it happens while driving it. Although, today it is near 90 in Boston and I just went outside and pushed on the brake pedal and it is noticeably firmer and the pedal travel is shorter than when I drove it this morning.

Can heat (from the engine and sun) affect brake pressure?
 
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