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Old 12-01-2011, 06:54 PM
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Help with brake problems
Alright guys, I'm at the end of my rope on my rear brakes. This is my last ditch effort for help.

Here's the background: I've got a '95 4runner, SAS, V6 front calipers, FJ60 rotors. 7 years ago, I swapped in a chevy vortec 4.3, when doing that swap, I had to lose the anti lock brake thingy, whatever it was on the front passenger frame rail. Ever since then, no rear brakes.

Replumbed the system without the anti lock box, straight off the rear port of the master cylinder (closest to the firewall). no rear brakes. Swapped out the master cylinder, no luck. Swapped to FJ80 master cylinder, still, no luck. Ditched the LSPV completely, still, no rear brakes. Plumbed a whole new line straight down off the master right to the rear brakes, only a few bends -- yup, no rear brakes, at all, none, what-so-ever.

Used to live in Louisiana, so this was not too much of a big deal. Now I'm in Colorado snow country and it sucks bad. Front brakes lock up almost uselessly in the ice with no stoppage of the rear at all, and in 2 wheel drive, the rear will sit there and spin at stop lights, no matter how hard you're on the brakes. I know the rear brakes are put together right and the e-brake functions perfectly.

I give up, any ideas??? Anything??? I've been dealing with this for 7 YEARS...
I remember the front and rear brakes used to be tied together somehow, I was going to go that route next. Also wondering if there is something special about the rear drum's wheel cylinder, maybe it's a larger size and not getting enough fluid?
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Last edited by black95; 12-01-2011 at 07:47 PM.
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Old 12-01-2011, 07:12 PM
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Disks or drums in the rear?
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Old 12-01-2011, 07:45 PM
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factory drums
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-'88 pickup - Daily driver, AAL's, 285's, ARB bumper, Warn winch, all around cool rig.
-'01 cherokee - 6" Long arm'd, 285's, ARB bumper, custom roof rack, electric locked D30, auto locked 8.8, trussed-plated-fortified.
-'12 Jeep JK - 2" lift, Skid Row skidplates, OR fab bumper

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Old 12-01-2011, 08:38 PM
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snap a pic. drums a super easy.. its either missing parts or both rear cylinders are bad.. could also have bad hose or 3 way.

take the hard line off the cylinder.
have someone pump the pedel one time.
do you have fluid ?
yes = bad wheel cylinders or hardware
no= clog or air in hydraulic line
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Old 12-01-2011, 08:39 PM
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I see no mention of a proportioning valve. Early ABS took the place of the Prop valve and via sensors kept the brake bias in check. Drum brakes inherently require more fluid transfer as the pistons move out to brake and the return springs move the pistons back in when brakes are released. Disks do not move as much fluid as it is only the slight run out in the rotor that moves the piston back when not used. Proportioning valves accommodate this difference in fluid movement thus creating a balance of the brake bias front to rear.
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Old 12-01-2011, 08:43 PM
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is the adjuster installed at the bottem of the brake shoes ? if not your never stop even it it looks and tests perfect
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Old 12-01-2011, 09:38 PM
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The system is bleeding fine, and if you leave the bleeder screws cracked, the fluid drips out on it's own, so I know they're getting fluid without restriction.

The adjusters are in place, on the correct side, and are self adjusting with the E-brake like they are supposed to. It's a real pain to get off my drums because they really need to be changed out and there's a pretty good ridge built up on them.

I think Kevin's on the right track, it's something to do with balancing the system. I know up front, the passenger front brake was somehow tied in to the rear system through a conglomeration of T's and elbows inside the passenger wheel well, before it went into the ABS pump. This has to have something to do with it. It's just so hard to believe that a two piston master cylinder won't work with independent front / rear operation, after all, that was the whole point. even if you lose one circuit, you still have some braking, unlike the old single circuit masters.

There used to be an LSVP (Load Sensing Proportioning Valve) on the rear brakes with dual lines to the rear, one line from the ABS pump to the LSVP, one line back from the LSVP to the passenger wheel well brake line mess. I always thought the second line returning was only needed for the ABS pump to dump extra fluid. This is a '95, so there was only ABS on the rear.

This always gets me down about building your own rig, who the hell do you go to for help with this kind of thing??? I'm so disgusted with these brakes.

I'm going to take a look at the brakes on my '88 pickup tomorrow. Seems like I've done that before, but maybe that will shed some light on the situation. Thought about moving to an FJ60 master cylinder too, since they were made before all this ABS madness.
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-'88 pickup - Daily driver, AAL's, 285's, ARB bumper, Warn winch, all around cool rig.
-'01 cherokee - 6" Long arm'd, 285's, ARB bumper, custom roof rack, electric locked D30, auto locked 8.8, trussed-plated-fortified.
-'12 Jeep JK - 2" lift, Skid Row skidplates, OR fab bumper

KFWD
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Old 12-01-2011, 11:11 PM
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Quote:
Originally Posted by black95 View Post
The system is bleeding fine, and if you leave the bleeder screws cracked, the fluid drips out on it's own, so I know they're getting fluid without restriction.

The adjusters are in place, on the correct side, and are self adjusting with the E-brake like they are supposed to. It's a real pain to get off my drums because they really need to be changed out and there's a pretty good ridge built up on them.

I think Kevin's on the right track, it's something to do with balancing the system. I know up front, the passenger front brake was somehow tied in to the rear system through a conglomeration of T's and elbows inside the passenger wheel well, before it went into the ABS pump. This has to have something to do with it. It's just so hard to believe that a two piston master cylinder won't work with independent front / rear operation, after all, that was the whole point. even if you lose one circuit, you still have some braking, unlike the old single circuit masters.

There used to be an LSVP (Load Sensing Proportioning Valve) on the rear brakes with dual lines to the rear, one line from the ABS pump to the LSVP, one line back from the LSVP to the passenger wheel well brake line mess. I always thought the second line returning was only needed for the ABS pump to dump extra fluid. This is a '95, so there was only ABS on the rear.

This always gets me down about building your own rig, who the hell do you go to for help with this kind of thing??? I'm so disgusted with these brakes.

I'm going to take a look at the brakes on my '88 pickup tomorrow. Seems like I've done that before, but maybe that will shed some light on the situation. Thought about moving to an FJ60 master cylinder too, since they were made before all this ABS madness.


I don't think the problem will go away with swapping MC's! Source out a Proportioning valve from an earlier truck or Cruiser. They are mounted on the lower bolts of the MC. Pretty easy plumbing and I think your rear brake will start to share some of the stopping duties. Right now your MC is doing it's job and one piston is clamping your calipers enough to stop the truck and that's all the peddle you can push.....while the rear piston need to travel further to apply the rear brakes but cant as it's on the common shaft as the front piston. If you tried a adjustable prop valve the results would be the same as you have now.
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Old 12-02-2011, 08:27 AM
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I agree with Uncle Ben, a proportioning valve is definitely worth a shot. You need one especially in a pickup to balance things.

Also, you might look into putting in a residual pressure valve for the rears.... if they have heavy return springs the shoes might just be retracting far enough that a pedal push doesn't bring them back into contact with the drum.


Maybe the Anti lock box served this function in the stock setup and when you removed it you lost the residual pressure valve also. Trying to fix it you went with the 80 MC, but
the 80 MC may not have a residual pressure valve built in since it was on a truck that had disks in the rear.


As an FYI, I am using a T100 MC in the 60 which has runner fronts and stock rear drums and I also kept the stock proportioning valve. I think it has a residual pressure valve built in to the MC because the T100's had stock rear drums. It seems to work well.

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Old 12-02-2011, 09:05 AM
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The box you removed from the frame I think was the actuator. It should have had two brake lines and two power steering lines. The device I think would release pressure from the rear brakes when it detected lock-up and used PS pressure to push the brake fluid back.

When you took off the ABS box, what did you do to block off the brake lines? I believe one of the lines went to the 3-way junction block on the frame and the other to the LSPV in back. When guys remove the ABS they usually remove the actuator and just replace the hard line that ran from the actuator to the LSPV with one from a truck that did not have ABS.

You should not have to re-plumb the junction blocks on the frame by the torsion bar other than for the one line. AFAIK the systems were the same otherwise, same master cylinder, etc.

FWIW, the front port drives the front brakes and the rear port (by the booster) runs the rear. You can put a pressure gauge on the ports to make sure the MC is working, I'd have thought that if you plumbed directly from the rear port to the rear axle junction block that you would have brakes at least.
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