Two pumps to make front brakes work?? (1 Viewer)

[amaurer]

I'm having an odd problem; I've been troubleshooting it for a month now with no end in sight. Disk front, late model drums in the rear.

My front brakes don't work unless I double pump the pedal. Rears work great but if you've ever driven without front brakes you'll know the truck stops for s*** on just the rears (which also lock up easily). After a double pump they work properly for a short time (30 seconds? I dunno).

I've readjusted the rears, bleed the brakes, eventually replaced the master. Now the symptom is still there, but at least its consistent; the fronts ALWAYS need 2 pumps.

Today I thought that it HAD to be air in the front circuit, no matter how many times I bled it. So I got a Power Bleeder and REALLY bled the fronts; not a single bubble. And, of course, same symptoms.



Is it possible the calipers are bad?

 

[Glacierskier]

Check for bulging lines maybe

 

[bikersmurf]

What shape are the rotors in? Are they warped?

If you double pump them to get them working, do they stay working if you're not driving? Ho
How's the pedal feel?

If the residual valve in the rear circuit isn't working, you can have the rears locking... How do they work if the rears are backed off a bit?

Any signs of fluid leakage around the pistons of the front calipers? Are they dry under the dust seals?

 

[amaurer]

What shape are the rotors in? Are they warped?

Fine. Which is to say they're not new, but they look fine and historically I've had no problems like pulsing, etc.

If you double pump them to get them working, do they stay working if you're not driving?

Hard to say, I have difficulty telling when the phenomenon is occurring if the truck is stopped.

How's the pedal feel?

Odd. It doesn't feel squishy, instead it drops most of the way down with little resistance at all and then becomes very firm. Pressing on it after it becomes firm works the rears normally. After a double pump it feels good, firm, proper travel... for a short time.

If the residual valve in the rear circuit isn't working, you can have the rears locking... How do they work if the rears are backed off a bit?

When I say the rears "lock", I mean that the wheels lock up when I attempt to stop in a reasonable distance and with reasonable pedal pressure. As far as I can tell everything about the rear works properly.

Any signs of fluid leakage around the pistons of the front calipers? Are they dry under the dust seals?

None that I can see, but I haven't taken the wheels off in a while.


My layman's opinion is that it behaves like the calipers are retracting too far... maybe a residual/check valve problem?

 

[CRZR45]

Did you bench bleed the Master when you put it in? My vote is for air in the system(front) . Take the front tires off and spin the rotor, is there any slight drag(normal) or are the pads far away from the rotor when the brakes are "relaxed". Try looking at them before you have to do the pump trick and see the distance from the rotors are(both pads each side) then start it up to get vacuume and pump the brakes til they feel good then check the pad clearence.. My 2cents..

 

[amaurer]

Did you bench bleed the Master when you put it in?

Absolutely. Extensively.

My vote is for air in the system(front) . Take the front tires off and spin the rotor, is there any slight drag(normal) or are the pads far away from the rotor when the brakes are "relaxed". Try looking at them before you have to do the pump trick and see the distance from the rotors are(both pads each side) then start it up to get vacuume and pump the brakes til they feel good then check the pad clearence.. My 2cents..

K, will take the wheels off next and see what I can see.

 

[brian]

the rears control pedal pressure.
the way it sounds you mixed and matched brake parts? sounds like something is out of whack.

 

[CRZR45]

Agreed on the rear.. Confirm they are adjusted correctly..

 

[Pighead]

I assume you removed the residual valve in the front circuit...do you still have a residual valve in the rear circuit?

 

[amaurer]

The setup is stock, I have whatever valves came with the truck.

 

[Pin_Head]

Some things aren't worth trying to figure out what is wrong if you value your time above minimum wage. Just replace all the front parts like the master, calipers and hoses and your problem will probably go away.

 

[lcwizard]

X2 with pinhead. I've gotten a lot of brand new masters that just don't work right. Start with that. Buy Aisin
or Toyota to be safe

 

[tornadoalleycruiser]

What year master and have u replaced flex lines?

 

[bikersmurf]

Fine. Which is to say they're not new, but they look fine and historically I've had no problems like pulsing, etc.



Hard to say, I have difficulty telling when the phenomenon is occurring if the truck is stopped.



Odd. It doesn't feel squishy, instead it drops most of the way down with little resistance at all and then becomes very firm. Pressing on it after it becomes firm works the rears normally. After a double pump it feels good, firm, proper travel... for a short time.



When I say the rears "lock", I mean that the wheels lock up when I attempt to stop in a reasonable distance and with reasonable pedal pressure. As far as I can tell everything about the rear works properly.



None that I can see, but I haven't taken the wheels off in a while.


My layman's opinion is that it behaves like the calipers are retracting too far... maybe a residual/check valve problem?

Unlike drum brakes, there isn't anything to make the disc calipers retract. I've been running for 18 years without any residual valve, so I don't think that's the source of your problem.

I tend to agree with Pinhead, if uncertain of your front calipers, I'd replace them and the flex lines. Although you've bled them to death, is sounds like air in the system...

Or perhaps the brake proportioning valve in the rear circuit. I'd also double check the adjustment of the rears.,. Dang I hate drum brakes. I don't miss adjusting brakes one bit...

 

[zebrabeefj40]

How well adjusted are the front wheel bearings? If they are a little loose the pads can be knocked far enough off the rotors to need a couple pumps to get back to the discs to work right...

Have you parked the truck overnight on a hill to help dislodge air in the lines? I've had issue with FJ40 brakes that needed to sit overnight to bleed out all the air.

How about the pushrod on the booster? Is that adjusted to spec? I doubt that's the issue but ya never know. I'd hate to throw money and parts at the problem without checking all the free stuff first.


Nick

 

[lcwizard]

residual pressure valves are supposed to be built into the master cylinders . That has been standard for many years. It's usually as simple as a rubber disc under the the large brass nut that has the hard line fitting. I can't see a caliper or soft line creating this occurence. Improper pushrod adjustment usually results in a brake not releasing rather than not holding adequate pressure in the line. This is more common with the rears than the fronts to have improper residual pressures since the rears since drums require about 10 psi vs 2 for disc. If you don't want to swap masters you can try a 2 psi inline residual pressure valve. Summit or Jegs would have them. I haven't found one with a 10mm 1.0 fittings so it would require flaring with 3/8 inv flare ends.... It's probably easier to try a new master

 

[amaurer]

Some things aren't worth trying to figure out what is wrong if you value your time above minimum wage. Just replace all the front parts like the master, calipers and hoses and your problem will probably go away.

X2 with pinhead. I've gotten a lot of brand new masters that just don't work right. Start with that. Buy Aisin
or Toyota to be safe

I tend to agree with Pinhead, if uncertain of your front calipers, I'd replace them and the flex lines. Although you've bled them to death, is sounds like air in the system...

Sigh. New calipers and lines will be here Wed.

 

[Fast Eddy]

Sigh. New calipers and lines will be here Wed.

Wait a minute...

residual pressure valves are supposed to be built into the master cylinders . That has been standard for many years. It's usually as simple as a rubber disc under the the large brass nut that has the hard line fitting. I can't see a caliper or soft line creating this occurence. .... It's probably easier to try a new master

100% agree. Did this start all at once, or what?

What you are describing is either misadjusted drum brakes, or a bad residual valve. How the problem started and progressed will determine the best course to take to solve it.

A residual valve is about $1.

 

[amaurer]

The problem started gradually... it was intermittent and then grew worse until it was almost always present.

Then I changed to a new master and the problem persisted.

The rears are absolutely, 100%, adjusted properly.

 

[Pighead]

The rears are absolutely, 100%, adjusted properly.

Please to define "properly".
Properly as in the FSM or properly as we have learned it should be done ( a lot tighter than in the FSM)?