Brakes still randomly build pressure to cause undrivable dragging, everything replace (1 Viewer)

[slickrock]

1973 FJ40 Drum to drum

Please don't say I need disks. I stop faster and straighter than other disk braked rigs and I stop totally straight without my hands needing to be on the wheel.

I keep having a repeating break issue and I am totally at a loss at this point. I have replaced the entire system (except for the rear cylinders but they are in good shape) and still it does this . . . .

After driving for a week or two or on really long trips, my brakes tend to slowly build pressure until they finally start to drag on the breaks and I have to pull over and pop the master off and turn the push rod down. This is totally random. I can drive for 300 miles or 3, it totally seems to be random.

Before you say that my push rod needs to be turned down it has been turned down, out, and repalced (the rod is adjusted to where I have to fully slam on the pedal to just about lock up my brakes and this happens even after many different adjustments).

Here is what I have done in the past to fix this problem.

1. new brake master
2. new brake booster – same issue starts up
3. mini-truck booster – same issue starts up
4. now an FJ 60 booster which stops much better but it started up again last night.
5. new calipers in the front
6. brakes adjust per FSM (adjusted to where wheel stops after hard rotation and backed off the required number of clicks)
7. bled and more bleeding of brake line.
8. Nothing is original with the braking system except rear calipers.

I thought I finally had the issue taken care of. I have a new brake master and 60 series booster. It normally stops perfectly and was happier than can be to have a drum brake cruiser that would stop totally straight and stop me when I needed to stop. But a few weeks ago, this new set up started to bind a bit again, in the same manner as before slowly replacing everything. I thought I might need to only back my push rod off a bit so I did. When I put it back together, I had no brakes. So I kept extending out my push rod. I finally extended it out about 2 full turns and my brakes were spot on again.

I did notice that once, right after start up from sitting for a few days, I had a soft pedal and pumped the pedal once and the brakes were good. But yesterday, the same old thing started happening (not as bad), but when I pulled into my driveway and took my foot of the brake and put it in neutral, the rig did not roll back. I went inside for a few hours and came back out to put it into the garage. I started it up, pulled the parking brake and it started rolling back. Obviously the pressure let up.

What is going on here? Remember, front has new cylinders, rear or original but I took them apart and they are in great shape with no leaks or anything that would indicate blow by or leakage. When I have my foot on the brakes and turn off the rig, I get a good amount of pressure push back in the pedal.

There is also no signs of caliper leakage in any of the drums. I pulled them and totally dry.

Are my break pads just adjusted too tight and as heat builds, they expand and start the drag?

Might there possobly be a small hole in the brake line allowing air to enter the system?

Is it a vacuum related issue?

Is there air trapped in my lines that I can’t get gravity bleeding?

Do I need to simply take it to a shop that can use a pressure bleeder since this might be as simple as air in the system?

 

[Gundy]

Old brake lines? I've had them cause sticking brakes before.
The rubber sections are particularly prone to rotting inside.

 

[Blue77FJ40]

Don't forget to check the basics, per the FSM. The pedal height, the freeplay of the pedal (don't forget to also check the adjustable rod that goes into the back of the mc - may be adjusted too long), and the freeplay of the slave.

 

[BC40]

Before you say that my push rod needs to be turned down it has been turned down, out, and repalced (the rod is adjusted to where I have to fully slam on the pedal to just about lock up my brakes and this happens even after many different adjustments).

Not sure what you mean by this? The push rod should not need re-adjusting once it is set correctly.

Are both ends dragging or is it just the front, or back? When it is dragging and you crack a bleeder valve on one of the wheel cylinders how much pressure is there? If the drag is only at one end of the truck it could be a collapsed brake hose as was suggested.

But I still find the push rod comment strange. There should be a little bit of free play, not as much as the clutch pedal, but enough that the cylinder returns to its free position.

Good luck.

 

[slickrock]

Not sure what you mean by this? The push rod should not need re-adjusting once it is set correctly.

Are both ends dragging or is it just the front, or back? When it is dragging and you crack a bleeder valve on one of the wheel cylinders how much pressure is there? If the drag is only at one end of the truck it could be a collapsed brake hose as was suggested.

But I still find the push rod comment strange. There should be a little bit of free play, not as much as the clutch pedal, but enough that the cylinder returns to its free position.

Good luck.

Every different set up (new baster and booster) I have had to either adjust the push rod in the booster in or out.

This last time and with this particular set up, I thought I had the push rod at the correct lenght to have a bit of room in the pedal until the brakes started to grab.

to respond to the question about which brakes start to grab, I think it is the rear first, then it goes to the front. (rears start to drag first).

Still looking for issues. I do recal that since the brakes work off vac pressure, could this be a engine issue?

 

[dgangle]

dimes to dollars....adjust the pushrod...between the booster and the mastercyclinder. If it won't adjust then you may have to grind to shorten or weld to lengthen.

 

[FJROSS]

I just got done going over the brakes (disc/drum) and it started with the same problem of front disc lock up. I don't believe that a booster pushrod could ever go out of adjustment on it's own. There a P.I.A. to adjust on the bench. Did you flush your brake lines before installing the new master. I believe my problem was with crap inside the master not letting the residual valve equalize pressure. In time, mine would release on there own also. If the drum brake master have residual valves, check to see if you may have debris stuck in the valve that might be letting pressure build up and relieve over time. Air in the lines would just give you a soft pedal or a pedal that would pump up.

 

[Downey]

My guess is one of two things:
(1) I agree that the adjustment between booster and mst. cyl. is critical, and if adjusted improperly could leave the brakes applied all the time.
(2) One of my rigs had a bad booster (never did find out what defect was) and it would not piss off pressure, kept the brakes applied even when pedal not pressed. I simply installed a new booster.

 

[Fast Eddy]

Your pushrod needs to be adjusted, for sure, but...

I had exactly the problem you're describing.

I believe my new (Toyota OEM) master was shipped with a drum-brake residual valve in the front circuit. Once I removed it, they have worked great. I would probably try out a 2lb valve in my front circuit if I had one when I had it apart next time.

 

[slickrock]

OK let me review:
New master, 3rd booster, and push rod adjusted so many times I cannot count
Remember the brakes work fine with where the push rod is adjusted. Over totally random periods, the brakes would build pressure, to only release after th rig sits for som time or I physically mess with the push rod. The rod is adjusted correctly. I wouldn't be able to stop or move forward at all if it wasn't adjusted properly to begin with.

Maybe it is something in the brake lines (crud) that isn't comming out.

 

[billmc]

I've usually seen this when the soft lines get old and swell on the inside. You can push fluid out but return pressure at the cylinder is not strong enough to push it back. But you say you replaced everything so that can't be it. Maybe you have a slight kink in a hard line which is collecting crud.

Bill

 

[slickrock]

I've usually seen this when the soft lines get old and swell on the inside. You can push fluid out but return pressure at the cylinder is not strong enough to push it back. But you say you replaced everything so that can't be it. Maybe you have a slight kink in a hard line which is collecting crud.

Bill

I think I am going to check my front soft line. Before I started to replacing everything, I was drivng about 90 miles from home and my front lines locked up (this was the beginning of the saga). I had to use some vice grips to lock off pressure to the front lines so I could limp home with only rear brakes. (this was not fun, but now after typeing this, know i is my front lines casueing the trouble). I DO NOT RECOMEND DRIVING WITH ONLY REAR BRAKES, NOT FUN.


Anyone got a spare front soft line?

 

[Fast Eddy]

I had to use some vice grips to lock off pressure to the front lines

IMO, that would kill the soft lines after only doing it once.

 

[FJROSS]

If your rig is not pulling to one side or the other, that would mean that both soft brake lines would be bad. There's also the line that goes from the frame to the axle that could be changed. If your going to do this I would also flush the system a few times and dissasemble the master and clean. Sounds like debris is obstructing an orifice and but letting pressure eventually equalize.

 

[slickrock]

You migh tbe right. I am picking up a new soft line tomorrow for the front and will disconnect that line and bleed without it connected. THen do a brake bleed floowing FSM. Idon't think anything is in the master since it is new.

 

[Gundy]

I'd soak those line fittings with PB Blaster or some such a day ahead.
If you don't have a flare wrench, get one.

 

[billmc]

Don't just do one, you ought to replace all the soft lines at the same time.

Bill

 

[Quazii]

I had the same problem. For two years I struggled with this. I replaced the master and all slave cylinders and thats when it began. never consistant. Sometimes the brakes were good other times I had to pump. Quarter turn clockwise on the pushrod and the brakes would build exactly as you describe Quarter turn counter-clockwise and pump everytime. Impossible to find a middle ground. REplaced master twice more. then I talked to Mark Algazy of Marksoffroad.net

SOLUTION!!!
Your pushrod is adjusted out too long. This is not allowing the fluid to completley return to master cylinder. Your wheel cylinders are not adjusted out enough. Sounds impossible I know.
Back the push rod off a bit so brakes will not build till seizure.(This may mean the pedal goes to the floor and has to be pumped to get brakes)
*Adjust each wheel cylinder till each wheel slightly drags. After doing all 8 back down your drive and pull back up again dragging the brakes.
Adjust all 8 wheel cylinders again. Back down drive again
Again
Again
Tedious but will solve your problem.
Repeat this * procedure untill you have the brakes you are looking for.
THis could take a few hours

Good luck
Chris

 

[slickrock]

I had the same problem. For two years I struggled with this. I replaced the master and all slave cylinders and thats when it began. never consistant. Sometimes the brakes were good other times I had to pump. Quarter turn clockwise on the pushrod and the brakes would build exactly as you describe Quarter turn counter-clockwise and pump everytime. Impossible to find a middle ground. REplaced master twice more. then I talked to Mark Algazy of Marksoffroad.net

SOLUTION!!!
Your pushrod is adjusted out too long. This is not allowing the fluid to completley return to master cylinder. Your wheel cylinders are not adjusted out enough. Sounds impossible I know.
Back the push rod off a bit so brakes will not build till seizure.(This may mean the pedal goes to the floor and has to be pumped to get brakes)
*Adjust each wheel cylinder till each wheel slightly drags. After doing all 8 back down your drive and pull back up again dragging the brakes.
Adjust all 8 wheel cylinders again. Back down drive again
Again
Again
Tedious but will solve your problem.
Repeat this * procedure untill you have the brakes you are looking for.
THis could take a few hours

Good luck
Chris

OK. sounds like you had thesame issue. so your saying that the rod is way to far out right now? why then when backed off do I not get pressure? it would seem that it should be backed out more.


Check this with me...
YOu think I need to back it in a whole bunch until they do not have pressure unless really pumped. Tighten all cylinders until drag,
roll down drive with brakes dragging
adjust all wheel cylindars until it doesn't drag or drag?

 

[Quazii]

The push rod is only slightly too long. Should have between 0.12in and 0.23in freeplay ( distance between where pedal rests normally to where it touches the push rod, measured at the foot pad). Hard to explain but the FSM should show it as my Haynes does. Otherwise just back it off a quarter turn or so. Your brakes are not seizing quickly so it's not off by much. If you can set per factory spec. it would be best as you would eliminate it from the equation. You may or may not have to pump them at this point. Mine was pretty off so when I backed the push rod to where it needed to be pumping for me became necessary. If you back off to far pumping will always be necessary even after proper wheel cylinder adjustment

Now it's time to adjust the wheel cylinders. After you back up and pull forward again (slightly applying the brakes) they will need readjusting. Dragging them helps center the shoes. Basically what happens after the first few adjustments is the dragging you hear while adjusting is only from one side of the shoe. As you center the shoe the side that was dragging slightly moves away from the wheel (now it's not dragging) and the side not initially dragging has moved closer to the wheel. eventually these distances become even and the shoe has a tight tolerance and will function properly. Did I mention it's tedious? The bright side is it will get there.

I hope this clears it up a bit. I remember how frustrated I was till talking to Mark. My brakes havn't seized since.

Remember: adjust then back up/pull forward
repeat
repeat...be patient...continue till it gets there
Keep in mind it's just one small master cylinder trying to feed eight wheel cylinders. That makes for tight tolerances.

Hope this helps
Chris