I've Got No Brakes!

[Matador]

Alright-

I was greeted to a little surprise today. I have a 1987 R10 (305/700R4). The brakes always pulled a little to the left, but it wasn't that noticeable. The truck has been sitting for about a month.

I turned it on today, and shifted to Reverse. The Red Brake Warning light on the bottom of the fuel gauge came on. I moved the truck backwards, at about 5-10 MPH. I hit the brakes, and really had to push them for the truck to stop. I then carefully drove down a road stretching on our property. I reached about 15-20 MPH, and then went to stop. The pedal gave me no resistance until I hit the end of the pedal travel. Then, the truck started slowing. It wasn't slowing as much as it should, though. I've made panic stops in that truck before- mashing the brake will lock the tires every time. This time, though, the stopping seemed leisurely at best.

Any ideas where to start? I've never done brakes before, but it looks like I need to now!

Thanks for the Help!

[mongoose]

does it have brake fluid?

[Matador]

There was some fluid in the master cylinder. It was very badly colored, though (Looked like motor oil). The fluid was at the Minimum lines in both "chambers" of the master cylinder.

I heard a kind of a hiss noise for about 1/2 second when I shifted from Drive to Reverse (My truck always has a clunk when shifted, but no hiss).

[rudey737]

Plus one on break fluid and then a good old brake system bleed might help with that pedal travel. If that doesn't work, then you might want to check the system for leaks or breaks in the line. After that, you'll have to talk to someone with a higher pay grade than me.

[cleansquare]

If the light is on then that mean the proportioning valve is tripped. Its usually under the fan shroud on the frame drivers side. There are two lines going from the master cylinder to the prop valve. Follow them to find it. One line is bigger, that's te rear brakes. The smaller line is front.

If the light is on it means probably you've lost fluid to the front or back brakes.

What the prop valve does is, when you lose fluid say to the rear brakes due to say a bad wheel cylinder, then the valve cycles and cuts off the supply to that rear system, which allows you to still have front brakes.

You need to look for leaks everywhere. Check calipers, all hoses and hard lines, pull drums and check wheel cylinders, check master cylinder for leaks underneath, etc.

Fill up both chambers in the master cylinder. Then crack each bleeder at all four corners on the wheels. Let the truck gravity bleed for awhile and always keep master full. If nothing comes out of the rear, unscrew the bleeder all the way and stick a coat hanger in there or something to break the rust and crud barrier it may have. After you've at least got a trickle or drip of fluid from all 4 corners, close all the bleeders.

Go up to the prop valve and there is a little pin that sticks out of the side, it has a rubber cover on it. Push that pin in. Thats supposed to reset the valve. IF IT DOESNT:

Have some one pump up and hold your brakes. You need to identify which system you lost, feont or back.Bleed the rear brakes first, pass rear and then drivers rear. Alternate between them. If yiu want, go on up to the front and bleed them then, pass front and then drivers front. You should know by now which one are bad. The front bleeders should have enough pressure to squirt fluid up to the inner fenders. The rear will have a good amount.

If the rear has fluid but no pressure, theres your problem. Same with front. If the rear is the problem, CLOSE front bleeders, and leave rear bleeders open. Make sure the master cyl is full and covered. Get in and punch the pedal hard. This may cycle thr valve open.

Vice versa if the front is thr problem. Open front bleeders and close rear. Stomp on pedal and then bleed normally till you have nice pressure at all 4 corners.

If those methods don't work to unstick the valve, then close all bleeders, fill up and cover master cyl and drive truck. STOMP on brakes in forward and reverse. This is another method that sometimes works.

If none of that works you'll need a new proportioning valve.

But, first, look for leaks in your system. Fluid had to go somewhere.

If you need help message me. I'm on a few times a day.

On the left is where the little pin is. "Metering valve"

[Matador]

Thanks @cleansquare!

I just looked at the truck after sitting for about 5 hours. The front chamber of the Master Cylinder is now mostly empty- there's a little fluid in the bottom of the tank, but I can see into the hole clearly. The rear chamber looks about the same as it did before.

I found the Proportioning Valve, but haven't done anything with it.

I think I found the leak with a visual check. It's at the Passenger Rear tire. On the drum backing plate, roughly underneath the leaves, the brake line enters the drum backing plate if my terminology is correct. Both rear insides of the drums are caked with mud. This is a picture of a different truck (obviously- mine is totally stock), but it's roughly my vantage point:


both rear drums have some mud on them, but the dirt on the Passenger Rear drum is wet. The truck was sitting, so I assume it has to be a brake fluid leak.

I think this has to be the problem, but I don't know where to go next. I've done pads and rotors on a 2000 Impala, but I've never serviced drums before.

Thanks for the help!

[Slammed84]

Drums can be tricky, but not too bad. I would suggest if you do end up working on them, go ahead and change the wheel cylinders, shoes and at least have the drums re-surfaced. Just do one side at a time so you have a reference.

There is hella videos on YouTube to show you how.

[cleansquare]

^^^what he said.

One side at a time so you can use the other side for reference how it all goes back together. And yeah bring the drums in to oreillys or somewhere and have them turn them very lightly unless they check out real bad, in that case either turn them lots or replace them.

Probably wheel cylinder that's leaking. Youll see it when you slide the drum off. Little thing at top cylinder.

. If you replace brake shoes as well, and turn the rotors, you'll want to adjust the rear brakes to get them working optimal. Pretty easy to do. There should be a small hole in thr bottom of the drum backing plate.hold the little tab out with your finger while you crank on the sprocket at bottom of drum until you can barely slide the drum on. Then once the drum is in and good and tight (the idea is to get the pads adjusted out to where they don't have to travel far to reach drum when brakes are applied) then back them off a few turns till the drum rotates moderately freely on the pads.

[Keith Seymore]

Agree with everything said up to this point - except:

I'd start looking for leaks in the front system.

If the front reservoir was "empty" (or low) - and that's the big chamber - then it feeds the front brake system.

That would also account for why the truck seemed to be stopping in a lazy fashion - you were stopping with the rear brakes only. Most of the braking is done with the fronts; If the rears were out and you were stopping with the front brakes only you might not have even noticed a difference.

K

[cleansquare]

^^true, but he needs to determine what chamber feeds what system. My original and reman master cyls were.opposite.

The bigger line off the master cyl feeds the rear brakes. The smaller the front. Thatll tell you which system is empty by looking at which one is dry

[Keith Seymore]

Originally Posted by cleansquare

The bigger line off the master cyl feeds the rear brakes. The smaller the front. Thatll tell you which system is empty by looking at which one is dry

Other way around. Big = front; small = rear. The bigger line/reservoir feeds the discs, because it takes more volume to move the piston in the caliper than it does to move the wheel cylinders in the drum.

But - agree - he'll need to look and see if his front system is in the front of the master cylinder, or if the front of the master feeds the rear.

K

[Matador]

I'll have to check the lines tonight, but I can remember that the larger reservoir on the master cylinder was the one closest to the firewall. The front chamber was about 1/2 the size.

By the wheel cylinder, do you mean this part?:


If so, I wouldn't be surprised. It's always a $5 part that causes the problem!

[cleansquare]

I remember on my stock cast master cyl, the rear chamber was very small and fed the rear brakes.

On my new plastic one, the front chamber feeds the rear brakes.

Yes that's the wheel cyl we are talking about

[Keith Seymore]

Originally Posted by cleansquare

I remember on my stock cast master cyl, the rear chamber was very small and fed the rear brakes.

On my new plastic one, the front chamber feeds the rear brakes.

I've had a similar experience on my Chevelle: stock cast iron m/c the front fed the front and rear the rear. I replaced it with an aluminum m/c (plastic reservoir) and reservoir/feed was swapped.

K

[Matador]

I have the drum off, and the wheel cylinder has a leak.

I'm not in front of the truck now, but does anyone know the size of the tubing wrench I'll need to remove the old cylinder?

Thanks