Brake help! Exhausted ideas...

[Ride The Snake!]

I'd like to bleed the whole system again and see what happens, and then worry about the distribution block. Not risking munched bleed screws; I'll get the proper offset wrench. Will post update. Thanks for the information.

[Getter-Done]

Just a suggestion.
Have you tried bleeding the wheel cylinders
at the line instead of the bleeder screw to see if the wheel cylinder is full of (Crud)?


Over time these line nuts get rounded when care is not taken to loosen them or someone grabs a pair of vice grips to loosen it.
Most auto stores have brake line wrenchs.

Here is a link.
Link:https://shop.advanceautoparts.com/p/...h+Set+standard







.

[RichardJ]

>>Some dist blocks have a reset. Some you remove the switch and centre the valve.<<
BULL SIT. NO distribution block, NO pressure differential switch and NO combination valve has a RESET BUTTON.
There is no such thing as a RESET button.

The pin sticking out the front of a COMBINATION VALVE is part of the Metering Valve. It has absolutely NOTHING to do with the Pressure Differential Switch. They are NOT connected and the operation of each is completely independent of the operation of the other.
The Metering Valve Pin doesn't reset ****.

A combination valve is simply three independent valves combined into ONE unit to save space, plumbing and costs.

The picture below is typical of what was used on 1st Gen Camaro and some other Chevys. Top left is a Pressure Diff Switch, same as used on drum/drum. Top right is the Proportioning Valve. Bottom is a Metering Valve. The pin under the rubber cap is used when bleeding the brakes It has no other purpose.

The Metering Valve is such a simple devise, but it causes an alarming amount of confusion. Even Jeg's call it a proportioning valve. I don't know if they are stupid or just going with the flow.

>>Or remove the outlet line from the dist block to the front brakes and see if the piston can be moved that way.<<

That is completely ASS BACKWARDS.
The PISTON inside the Pressure Differential Switch is normally CENTERED, because the pressure on the front lines is the same as the pressure on the rear lines.
IE, if you push on the brake pedal and generate 200 psi of hydraulic pressure, you will have 200 psi on the front brake line and front of the pressure differential switch, YOU WILL ALSO HAVE 200 psi on the rear brake lines and the rear of the pressure differential switch piston. 200 psi on both end of the pressure switch keeps the pressure dif switch piston CENTERED.
Press the pedal harder and you have 800 psi front and rear and the piston stays CENTERED.

If there is a failure as in this case, the side with the higher pressure pushes the piston to the other side.
The rear brakes are locking up, there is little or no pressure to the front, the rear pressure will have pushed the piston to the front.
If you open the rear system, either with loosening the bleeder or loosening a rear fitting, you can apply the brakes and use the front pressure to move the piston toward the rear.

THAT'S HOW YOU CENTER THE FRICKEN PISTON.

Going back. First things first. You need to find out why the brakes are not bleeding properly....

In many cases, considering all the parts you have replaced, the problem can be traced back to inadequate brake shoe adjustment.

The piston on this Pressure Differential Switch doesn't completely block the flow for bleeding purposes when the piston is pushed to one end. Fluid flows around the springs. Don't be confused in thinking the two springs keep the piston centered. The "O" rings on the piston prevent an electrical ground path for the switch. The springs provide the ground path.

I have a second type of switch, center bottom that is self contained with its own ground path.

[Ride The Snake!]

Sir, you just dropped some knowledge on my head.

[LockDoc]

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On the drum brakes, one thing I found on mine is when you put everything back together and adjust the brake shoes you can’t just adjust them out until they start rubbing and quit. You have to adjust them out as far as they will go and you cannot turn the wheel or drum at all. This centers the whole assembly in the drum. (I even tap around the drum as I tighten them to help them center themselves) Then you back them off until the wheel/drum just turns, and stop. If you only adjust them out until they start rubbing and quit, the first time you press on the brake pedal the brake shoe assemblies will center themselves and you will have too much clearance between the shoes and the brake drum. I also put three lug nuts on backwards to hold the drum tight against the axle on the rear when adjusting them.

I know it is a pain in the butt to try and hold the self adjusters off of the adjuster wheel while you back them off, but this is the only way I could get my drum brake shoes adjusted correctly.

LockDoc

[Ride The Snake!]

Originally Posted by LockDoc

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I know it is a pain in the butt to try and hold the self adjusters off of the adjuster wheel while you back them off, but this is the only way I could get my drum brake shoes adjusted correctly.

LockDoc

Without doing this properly were you getting zero braking from the affected side? I guess I'll follow this procedure too.

[LockDoc]

Originally Posted by Ride The Snake!

Without doing this properly were you getting zero braking from the affected side? I guess I'll follow this procedure too.

Not zero but the pedal was really low because the brake shoes had to travel too far before they contacted the drum, and it ran out of wheel cylinder movement.

LockDoc

[Ride The Snake!]

Originally Posted by LockDoc

Not zero but the pedal was really low because the brake shoes had to travel too far before they contacted the drum, and it ran out of wheel cylinder movement.

LockDoc

My pedal feels good. Just checked and right rear will bleed a bit initially, then the pedal firms up and wont push more fluid. I'm definitely replacing the section of rubber hose over the diff.

[LockDoc]

Originally Posted by Ride The Snake!

My pedal feels good. Just checked and right rear will bleed a bit initially, then the pedal firms up and wont push more fluid. I'm definitely replacing the section of rubber hose over the diff.

That may just take care of it. I thought you had already replaced it.

LockDoc

[Ride The Snake!]

So I replaced the hose to the rear, bled all four wheels successfully, have a firm pedal, and still no grabbing from the front brakes. But it's obviously not for lack of pressure at the wheel cylinders.

Going to pull the drums off next and look at the adjustment of the calipers.
I don't know if it's just because the front brakes aren't grabbing at all and this being a front-heavy, unladen pickup, but the rears will lock ridiculously easily.

Removing the brake line's flare nut to the hose's female end was not fun. Two days soaking in penetrating oil, slightly munched nut threads, then a stuck on line wrench after getting the fitting apart. Lucky to get it off, and be able to re-tighten with a downsized metric open wrench (11mm).

[dmjlambert]

Are you having a helper try to turn the front wheel by hand when you are holding the brake pedal down, and it's spinning freely? Is that how you're checking? Or are you just noticing skid marks on the road only from rear wheels when testing an emergency stop?

Is the parking brake working ok, and disengaging OK?

[Ride The Snake!]

Originally Posted by dmjlambert

Are you having a helper try to turn the front wheel by hand when you are holding the brake pedal down, and it's spinning freely? Is that how you're checking? Or are you just noticing skid marks on the road only from rear wheels when testing an emergency stop?

Is the parking brake working ok, and disengaging OK?

I'm just noticing skid marks from the rears, and I can feel quite obviously that the truck isn't dipping/diving in the front when brakes are actuated. Yes, the parking brake is engaging, disengaging normally.

[dmjlambert]

Looking at it from a physics point of view, it seems logical to me the back tires have less pressure pressing them to the road because there is less weight back there. Therefore less friction between the tire and road in the back. If you put the same amount of friction between the drum and brake shoes in front and back (which you do), the back wheels should stop turning while the front wheels are still being forced to turn due to the better grip the front tires have on the road. I don't know if there is a true test. I suppose put a 1/2 ton load in the bed and secure it, then repeat the emergency stop and see what you get for skid marks.

[jkeady]

Adjust your front brakes to where you think they ought to be. Get yourself an infrared thermometer (there’s cheapies at Harbor Freight and it’s a tool you’ll use often). Go out on some empty road and do a few hard stops from, like, 45 mph where you don’t lock up the brakes. Just hard, quick stops. On the last one, throw it in park and measure the temp of the front drums. They should be pretty hot. If they are sub 100 degrees then they probably aren’t doing much.

[jkeady]

And for what it’s worth, my truck unloaded and on OEM-sized tires will lock the rears very easily.

[dmjlambert]

Originally Posted by jkeady

Adjust your front brakes to where you think they ought to be. Get yourself an infrared thermometer (there’s cheapies at Harbor Freight and it’s a tool you’ll use often). Go out on some empty road and do a few hard stops from, like, 45 mph where you don’t lock up the brakes. Just hard, quick stops. On the last one, throw it in park and measure the temp of the front drums. They should be pretty hot. If they are sub 100 degrees then they probably aren’t doing much.

That is a fantastic idea. The function of the brakes is to convert the kinetic energy of the moving vehicle into heat energy. You should be able to measure the stopping power just by measuring that heat.

[Ride The Snake!]

That is a great idea. But I need to get them actually working first. Heading outside momentarily to adjust them.

[Ride The Snake!]

Update: passenger wheel cylinder leaked out of the piston seal and one of the shoes is pretty contaminated. All these wheel cylinders are maybe 3 years old and the truck has been sitting outside and in a garage for most of that time. Could I have blown the seal early because the brake was not initially adjusted snugly enough? That seems far-fetched but I don't understand how else this happened.

I've read claims of success in cleaning brake fluid-contaminated pads by boiling in water and a bit of dish soap for 20 or 30 minutes. I don't trust that the brake cleaner I already used is able to penetrate much into the material, what with its low flash point. I know it's a gamble and the brakes may chatter even after the cleaning, but the shoes are barely used.

Opinions?

[Stocker]

Well, it's only my opinion, but at this point I would bite the bullet and get new parts. New wheel cylinders aren't expensive and neither are new shoes.
Make sure they are adjusted before bleeding and hopefully there won't be any leakage this time.

There may be ways to salvage what you have, but that's what I would do.

[Steeveedee]

The brake cleaner is more volatile than brake fluid and will remove the fluid. We used to dip brake shoes in the hot tank when we replaced the rear axle seals and they were greasy, especially if they had a lot of lining left. Never had a problem. As far as the wheel cylinder exploding because of over travel, I doubt it. If they were new, the adjuster wouldn't be out that far, yet. So that shouldn't be the problem. Some of these new parts made in China have an incredibly short life. It's annoying. I never believed in the term "planned obsolescence" but the Chinese made stuff is cheaply enough that it may as well be the case.

[Ride The Snake!]

I don't mean to necro the thread if that's bad form here, but I just wanted to mention it was my right wheel cylinder blown. Since they were all new a few years ago and with no more than a thousand miles driven on them, I just replaced the failed one instead of the front pair. Bingo, brakes work.

The truck seems to pull to the right under medium to heavy braking a bit, but it's progress.

[dmjlambert]

It is good to hear about how things worked out. No, that's not bad form. If you put some miles on the truck I wonder if the pulling to the right will diminish. So, what all did you do, did you boil the shoes like you mentioned earlier? New shoes?

[Ride The Snake!]

I hit the shoes with some brake cleaner, then later on a propane torch for a couple minutes. The mild stain that was on there seemed to disappear.

I could probably stand to fiddle with the pre-adjustment on the shoes on both sides of the front. Although it's pulling to the right, yet the front left drum is the one that feels a little snug--go figure. As you said, perhaps driving a bit will diminish the imbalance as the assembly seats more. I could also try to grease the backing plate on the left; I had only done the right since that's the only one I wanted to disassemble.