So, it's been a week or so since I've had to work on my truck and I think she was feeling neglected.

My brakes have never been all that great, but I bled and flushed them a while back and that seemed to help a bit.

Well, the reason I bled/flushed them was every now and again I get such a stiff pedal that I can't even push them down.

Today it's back with a ferver.

If I pump them up it gets even stiffer.

If I stand on it, it will stop the truck.

It's also wet out today, not sure if that would have anything to do with it.

Grrr.

Any ideas?

PS - Plenty of vac at the nipple on the booster (for the heater controls)

PSS - My brake light has been on since my ebrake cable broke and the ebrake pedal went to the floor.

 

It seems like the obvious would be a bad booster and a good place to start...Mark

 

Ok, I'll go check. I have the following procedures I dug up:

I'm putting my money on the booster...been there, done that.

Here is the diagnostic procedure from the '92 FSM:

Master cylinder/booster test

1. Start engine and check booster vacuum hose connections. Hissing noise indicates a vacuum leak. Correct any leaks before proceeding.

2. Stop engine and shift transmission into neutral.

3. Pump brake pedal until all vacuum reserve in booster is depleted.

4. Press and hold brake pedal under light foot pressure.

a. If pedal holds firm, proceed to step (5).
b. If pedal does not hold firm and falls away, master cylinder is faulty (internal leakage).

5. Start engine and note pedal action.

a. If pedal falls away slightly under light foot pressure then holds firm, proceed to step (6).
b. If pedal effort is high, or no pedal action is discernible, power booster or vacuum check valve is faulty. Install known good check valve and repeat steps (2) through (5).
c. On diesel models, vacuum pump hose or pump component may have malfunctioned. Check pump output with vacuum gauge and repair as necessary.

6. Rebuild booster vacuum reserve as follows: Release brake pedal. Increase engine speed to 1500 RPM, close throttle and immediately turn off engine.

7. Wait a minimum of 90 seconds and try brake action again. Booster should provide two or more vacuum assisted pedal applications. If vacuum assist is not provided, perform booster and check valve vacuum tests. Also check vacuum output on diesel models.

Power booster check valve test

1. Disconnect vacuum hose from check valve.

2. Remove check valve and valve seal from booster.

3. Using hand operated vacuum pump, apply 15-20 inches vacuum at large end of check valve.

4. Vacuum should hold steady. If gague on pump indicates any vacuum loss, valve is faulty and must be replaced.

Power booster vacuum test

1. Connect a vacuum gauge to the booster check valve with a short length of hose and a T-fitting.

2. Start and run engine at idle speed for one minute.

3. Clamp hose shut between vacuum source and check valve.

4. Stop engine and observe vacuum gauge.

5. If vacuum drops more than one inch vacuum within 15 seconds, either booster diaphram or check valve are faulty.

 

So, my printer is out of ink, and I couldn't print out the above, but instead went to the fsm (duh) and went through the troubleshooting section on the brakes.

Problem: Pedal is terribly stiff. If I really stand on it they work, but I drove with the transmission most of the way home.

The FSM says it's either watersoaked linings or a booster related issue.

Well, I pulled the front wheels and looked at the brakes and they didn't look bad (without taking them apart). Plenty of meat and no ugly grooves. Don't really know what they'd look like if they were water soaked, so it's hard to say if me looking is the end all/be all.

While I was down there I hooked up my little reservoir and bled both sides, just for good measure.

Then I ran through the booster/check valve/vac pump tests with my hand operated vacuum pump (typical) (according to the fsm. ) Didn't seem to turn up any issues there either, other than my vac seemed to stay up at the top range of acceptable (around 25ish most of the time). Never getting even close to the lower range of 8.

So, I don't really know. I haven't pulled anything off the back, but the back seem to lock up pretty easy...at least when the brakes work.

Now that I think about it, I've never even seen an ABS light, nor felt the operation of the ABS system.

But I guess that's neither here nor there.

Any thoughts?

 

Buy a new brake booster or see about a rebuild kit. Bet it solves it.

 

I'm with the consensus on this one, sounds like the booster ...

unless the vacuum line has holes or cracks in it somewhere. (scratch this since you said you have vac for heater controls)

 

check the rwal valve on drivers side frame under bed. mine did the exact same. was stiff pedal with nothing there. got rid of it and have been fine since

 

I had same...Bought loaded booster/master for $100. Fixed.

I had a vacuum reading of 20. Rigged it up w/ gauge in cab, hit pedal and it dove down to 5.

 

Well, huh.

I just went through my emails, and the booster/cylinder are about 1.5 years old at this point. Wouldn't think they'd be shot just yet.

Of course, the brakes have never been the best in the whole time I've had the truck.

Guess I should check out that valve out back before I go dropping $150 on relatively new parts.

Grrr...not the time of year for this shiz!

 

My vote is also with checking and/or deleting the RWAL valve.
You mentioned an e-brake cable breaking.
How and why did this happen?

You also mentioned that the rear wheels will lock up before the fronts.
Is it possible someone went through the rear brakes and installed smaller diameter wheel cylinders?
This could explain the much stiffer pedal.

Mark.

 

Well, the stiff pedal is a relatively new thing. The PO was a real stickler for things being factory correct, so if he replaced something, it'd be OEM.

The cable didn't really break, the end of the cable bent the connection to the pedal a bit and it came out...just haven't taken the time to fix it. It's on my to do list, though, as an e brake REALLY makes backing my boat into the water a lot easier.

I'll check the RWAL as soon as I possibly can and report back.

 

I had one booster do what yours does. I put a used one on and then if I even thought about touching the brakes it would lock all the brakes. If I tapped the brakes it would actually pull the pedal away from my foot and suck it to the floor. nice.

 

If the rear brakes are locking up too easily you need to look for a leak in the axle seal. If you get differential fluid on the brake pads they will become VERY grabby and lock at the though of touching the brake pedal.

I also have issues that I think are booster related. Mine seems to lose vacuum at longer red lights while I'm on the brake.

 

Oil contaminated brakes only lock the one side up that's contaminated.
In severe contamination cases it locks up the DRY side.

As I read it, he's locking up BOTH rears.

Mark.

 

Hey guys,

Not sure what the issue was, but I found out that the PO had deleted the RWAL system. I bled all the brakes and found when I bled them last time I didn't quite get one bleeder closed. DOH! Think that was the most recent problem.

While I was back there I also adjusted the rear brakes.

Seems to stop better than it has since I've owned it. Hopefully it lasts for a while. I had to turn the rear adjusters quite a bit to snug them up.