Brake help needed

[Dan LeBlanc]

I know this isn't Cadillac related, but the advice I've got here has been so far so good and hopefully folks here are willing to help out another Cadillac guy trying to do something good for someone else.

My wife's grandparents want to put their 1979 GMC camper van back on the road.  In the past two years, it's been driven about 200 miles, but, specifically, in the past year, it was driven around the yard once.  Their in their 80's and on a fixed income, so I told them I would help get it on the road as long as they supplied parts (fair deal I think).

We got it going on Saturday really easily but I had to hook my truck on it to move it - stuck brakes.  Once everything broke loose, the first time someone hit the brake pedal, they got the warning light (no surprise, it's been outside for two years and hardly moved).  So far, here's what's been done:

1. Replaced leaking steel lines
2. Replaced rear wheel cylinders (stuck)
3. Replaced calipers (stuck), rotors (rusted beyond servicability), pads.
4. Adjusted rear shoes
5. Flushed brake fluid and bled the brakes (hose in a jar method).

The pedal almost as firm as my Grand Marquis and F-150, however the warning light is still on, the back brakes, well, when I was bleeding them, I had nowhere near the volume of fluid I did with the front brakes and they're barely grabbing.  The front brakes are pulling hard left when applied.  If I stomp the pedal however I can lock up the front wheels.  I did find it odd, however, that I could not bleed the brakes without the engine running (no fluid at all at the bleeder screws without it running

I'm left with the following four possibilities unless there's something I can't think of.

1. I didn't bleed enough
2. Three collapsed flex hoses
3. Master cylinder is toast
4. Proportioning valve is corroded and stuck.

Any advice on what the next most likely candidate is?  Since their in their 80's, I don't want them to spend money on parts they don't need.

Hopefully this doesn't get me kicked out of the group, either.

[Otto Skorzeny]

I would spend the money on 3 new rubber brake hoses. When those go, you often can't tell by looking at them. Since the two front ones are probably less than $20 each and the back one might be $30, I'd consider that pretty cheap insurance.

I just replaced the hoses on my '79 F100 a week ago. The brakes worked fine but I can tell a big difference now.

When brakes pull to one side, it's often the opposite side that is the problem. The grabby side is working but the other side isn't. You might have to check the front pistons for rust which may be causing the right side to hang up.

I'm not specifically familiar with a '79GMC but I've never seen a vehicle that required the engine to be running in order to bleed the brakes.

[DinoBob]

Replace those hoses. Re-bleed as well. Invest in a vacuum bleeder (Mightyvacs are cheap and effective) and pull that fluid until it's all clean and free of air. And make sure everything is tight when you sung the lines, bleeders, etc...down.

[Dan LeBlanc]

Pretty much start with the simplest first, I take it.  More than likely collapsed hoses inside?

I was thinking of doing what this guy did by making his own vacuum bleeder except I'd use a hand vacuum pump instead.

http://www.crankshaftcoalition.com/wiki/How_to_Make_a_Vacuum_Power_Brake_Bleeder

[Otto Skorzeny]

I would follow the procedure in the shop manual to bleed the brakes. It's a pretty uncomplicated system and I don't think you'll gain anything by making a power bleeder or whatever. Just get someone to help you and start with the wheel farthest from the master cylinder and work your way to the closest.

[Dan LeBlanc]

The part I found really odd was needing the power from the brake booster to be able to get fluid though the bleeder screws.  I've never had to run a car before either to get that - my 62 Caddy didn't, nor did my Grand Marquis when I busted a front brake line.

[The Tassie Devil(le)]

If you have to run the engine in order to bleed the brakes, then there is something wrong with either the Master Cylinder, Proportioning Valve, or any line between the Master Cylinder, and the Wheel Cylinder you are trying to bleed.

One way to isolate the problem area is to start "Cracking" each joint, starting from the Master Cylinder, and move towards the Wheel Cylinder, Bleeding as you go.   

This way, you will eventually find the spot where you can't get any fluid from, and you will narrow down the area to fix, repair or replace.

The way to get the Warning Light to go out is to undo the sender switch at the Front/Rear Junction Block, which sometimes is incorporated into the Proportioning Valve, remove it, and replace.   This action allows the central piston to "Centre" itself, and the plunger will seat home, waiting for the time when something goes wrong again.

Bruce.

[Guidematic]

There is definitely a problem with the hydraulics. Bruce's suggestion will locate a restriction, if any.

The typical method of bleeding brakes is to start from the farthest wheel from the master cylinder, and work your way to the closest. Right rear wheel, left rear wheel, right front wheel then left front wheel. It's a tried and true method. You don't need any fancy equipment to bleed the brakes. I have found that more often than not, they actually create more work.

You can try to gravity bleed the brakes first, as well. Fill the master cylinder and leave the lid loose. Then go around and open all the bleeders and just let the fluid flow. You'll find that it works well for the front (often this is the only method I use) and that after time, you'll flush most if not all the air from the rear.

Something to keep in mind here, is that the parking brake switch is on the same circuit as the switch in the proportioning valve. So make sure that is not keeping the light on.

Mike

[harvey b]

Hi All,another thing is this truck may have the hydraulic brake booster on it,it runs off of the power steering pump,this system would need the motor running to work.you cannot push the pedal down hard enough to get the brakes to apply when it isnt running,if this isnt what it has then i am stumped too,another thing would be to get a mechanic buddy to take a look at it,myself i hate brake work,especially if it is acting up,and you dont want to take a chance on something like this.HTH Harvey B

[Guidematic]

 That's possible if it's a 1 ton chassis. I don't recall seeing Hydra-Boost on 1/2 or 3/4 ton chassis.

So, what series is this thing? G-10, G-20 or G-30?

Mike

[Dan LeBlanc]

It is a 1/2 ton chassis with the vacuum booster.  The old grandfather thought the brakes would still be good as he had them done in 1989 . . . LOL.

[Guidematic]

Yeah, I know as you get older, time goes faster.

So, with the vacuum booster you do not need to run the engine to bleed the brakes.

Mike

[Dave Shepherd]

Find the proportioning valve should be under the m/c, there should be a " button" on the end of the valve, this should be pulled outward when bleeding the rear brakes.

[Dan LeBlanc]

Really?  I never noticed that.  I'll give it a look see.

[The Tassie Devil(le)]

Find the proportioning valve should be under the m/c, there should be a " button" on the end of the valve, this should be pulled outward when bleeding the rear brakes.

That is a new one on me.

I wonder what valuable information I have had squeezed from my brain to allow this new bit of information to enter?

Bruce.

[Ohio57-62Sedan]

I wonder what valuable information I have had squeezed from my brain to allow this new bit of information to enter?

Bruce.

I doubt it... Har....Har....Har....  you oopend the door.....

[Dan LeBlanc]

We have brakes.  As it turns out, I underbled and was not pushing the pedal hard enough when the van was not running to force the fluid out.  Today, however, I got help from mother nature and did the gravity feed method with a hose in a bottle.  Let it run until no bubbles.  Worked like a charm.

Thanks everyone!

[Guidematic]

Glad to hear it worked for you. It's a method I have used for years since often there is no one around to help me. I find it really effective, and always go the route first.

Mike

[Dan LeBlanc]

It was awesome.  I could see the fluid going down in the master cylinder.  I've never had brakes bleed so easily before.

I also fixed the old grandfather's fix on the parking brake light - instead of a rubber band on the lever to keep it tight to keep the light off, I adjusted the brake cables.  Now instead of 12" of pedal travel, I have 4 and can't budge the van.

[Guidematic]

Cool! Now it's coming together.

The gravity bleed just proves that you don't need all that fancy equipment to do the job. Just remember, KISS. Often folks revert to the fancy stuff because they don't grasp the basics of what they are doing.

Mike