4wheel disk problem

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OK, here is my brake problem. Nov 76' FJ40.

New to me vehicle, PO had rear axle with GM disks set up, but not hooked up.

I ran new lines from front, through a porportion valve and to rear calipers. Bled and set up. They worked good for a week and seemed to stop well although the rears do lock up before the fronts no matter how I had the valve set.

Then I had an issue of the rear callipers tightening and seizing after I drove for about 5 minutes. I could crack the bleeders and let the pressure off and it is good for another 5 minutes if I try and not use brakes. Seems as though if I adjust the valve somewhere in the middle the brakes wont "seize" but the rears do lock up too good with any sharp braking at all, even just approaching a down hill corner faster than a jogging pace.

I am guessing that the fluid is getting past the valve by me applying the pressure at the brake pedal and it is not able to return through the valve??? But when I adjust the valve to allow the pressure to return to the master...It is not restricted enough to soften the rear calipers power.

Any suggestions? Thanks for passing the knowledge.
 
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No I did not...Not aware of what that is. Is it necessary to remove? Is that proper to do when setting up this type rear disks?

Thanks for replying
 
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Hey guys, thanks...So I just pull out the valve for the rear. Bleed the lines at all the wheels, (will I have to bleed the master?), and I assume I will then re-adjust the porportion valve.

Sounds simple enough.
 

FJ40Jim

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Hey guys, thanks...So I just pull out the valve for the rear. Bleed the lines at all the wheels, (will I have to bleed the master?), and I assume I will then re-adjust the porportion valve.
Yes, remove RP valve, then rebleed rear half of system.

That being said, if the brakes are dragging hard enough to slow the truck down or lock the wheels, it's not the RP valve. An RP valve maintains a few PSI in the brake line, between 2 and 8 PSI depending on application. This is enough to cause the disc pads to remain in contact w/ the rotor and get hot, but not enough to cause brake lockup. Lockup require a few hundred PSI.

The next step would be to adjust the MC clearance and pedal freeplay per the FSM, to allow the rear circuit to come off completely.
 

Mace

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The next step would be to adjust the MC clearance and pedal freeplay per the FSM, to allow the rear circuit to come off completely.

Yep...


sounds like the linkage rod is constantly putting pressure on the master.
 
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OK, I darted home at lunch and pulled the rear residual valve. I am planning to bleed when I get home.

They dont exactly "Lock up"...the symptom is that after 5-10min of driving, (with multiple stops), they get pressurized and when I proceed to give it gas it is more or less dragging the truck down and I can only go slow and pull over to relieve the pressure. Then it is fine once I crack the bleeders, so it is like the pressure just builds after a bit and that is when the problem shows. Actually if I park it at that point and let it sit say for a few hours, then run it the problem only occurs after 5-10 minutes more run.

So I believe the pressure just is restricted on the return flow.

Thanks all on the tip on the Residual valve. I will let you all know how it goes.
 

Bossman

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Yep...


sounds like the linkage rod is constantly putting pressure on the master.

Mace / FJ40Jim - tell me more about this procedure. I don't have an FSM to follow but recently started having the same sort of problem with my disc 14bolt rear. The stock 77FJ40 master (with the residual valve removed) has been working well for me for about a year but on the Katemcy ride I started to experience serious drag problems with the drivers side rear (not so much on the passenger side for some reason) I could crack the bleader screw and be good to go again for a while. Also, it seemed to only happen at the end of the day when things warmed up. Still sound like linkage rod adjustment to you folks? Thanks in advance.
 
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Mace / FJ40Jim - tell me more about this procedure. I don't have an FSM to follow but recently started having the same sort of problem with my disc 14bolt rear. The stock 77FJ40 master (with the residual valve removed) has been working well for me for about a year but on the Katemcy ride I started to experience serious drag problems with the drivers side rear (not so much on the passenger side for some reason) I could crack the bleader screw and be good to go again for a while. Also, it seemed to only happen at the end of the day when things warmed up. Still sound like linkage rod adjustment to you folks? Thanks in advance.


That sounds like a sticking caliper since it is only affecting one wheel.
JMO

Ed
 
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Mine is both wheels, (whole rear).

One more question for you all...The Porportioning valve say turn to "Decrease" and turn to "Increase". Would turning it to fully decrease, give the rear less power from the pedal?

Just checking cause' sometimes if you decrease the "flow" of some things...it in turn "increases" the pressure...That is what may have me confused.
 
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Mine is both wheels, (whole rear).

One more question for you all...The Porportioning valve say turn to "Decrease" and turn to "Increase". Would turning it to fully decrease, give the rear less power from the pedal?

Just checking cause' sometimes if you decrease the "flow" of some things...it in turn "increases" the pressure...That is what may have me confused.


Screwed all the way out, as in lefty loosey, gives maximum restriction to the rear. Kinda the opposite that you would expect.

ED

EDIT: I was addressing Wannabe's problem as he has just one that drags in the rear. Sorry for the confusion.
 
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It is all cool...

FYI, I pulled the valve and bled em' after work. Drove about 15 minutes and all seems good!!

I'm gonna go out and test it some more. Thanks all...
 
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Hey thanks for the help with this fix everyone.

I drove it last PM and all feels good. That valve made a big difference. Bled em' good and got a good amount of pedal. The brakes seem to stop a lot more evenly. Also they feel smooth, like it should.

I Put the porportion valve at all the way out, (decreased), and tested the brakes on a dirt road. Fronts and rears appear to lock up at same time. Probably if I had at least some amount of weight in the back end it would be even better. Anyways I am satisfied that they are working good.

I am driving it about 160miles tomorrow, first long drive since I picked it up about a month or so ago.
 
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Thanks for the thread links on the speedbleeders. I think I'll try them. I rarely have help on this stuff. The wife is good to come out when she is not busy with other things.
 

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