Rocketguy

1967 Oldsmobile A body

Factory 4 wheel non power drum brakes

New master cylinder from ILT

All new wheel cylinders

All new brake lines from ILT

Original proportioning valve

I bench bled the master, installed it, manually pressure bled the system and have good brakes on three wheels; no pressure at the left front wheel.

I am thinking bad proportioning valve?

Thanks for the help, love the Olds community

oldcutlass

A proportioning valve would not effect just 1 wheel. I just did my rear wheel cylinders yesterday and did the old have the wife sit in the drivers seat and pump away method. It took a while to get all the air out and about a pint of fluid bleeding out. Bleed both sides until you have all the air out. Make sure the shoes are adjusted properly.

Fun71

You could try cracking that line at the proportioning valve instead of the wheel cylinder bleeder valve and see if any fluid comes out.

m371961

Follow that sides line back toward the valve loosen fittings and check for fluid as you go. Agree not proportion valve for one wheel. Suspect bad rubber line, or clog/kink in line. Did you blow through lines before install? Remove bleed valve and check for clog. Check adjustment left side.

oldcutlass

Its not the rubber line either if the RR brake is working its from the T to the LR.

steverw

He said no pressure left front wheel, could be the rubber hose, i would disconnect from the valve and wheel cylinder and see if he can blow air through, perhaps take the wheel cylinder apart and check for debris.

oldcutlass

Damn where did I get that from? Maybe because it took a while to bleed my LR yesterday. Sorry Steve and OP.

steverw

No need to apologize, i make more than my share of goof ups

Rocketguy

Thank you guys, I appreciate it.

Yes I did blow through the lines.

If I pump up pressure and hold the pedal I gut just a small amount of fluid at the LF wheel and the pedal does not go down as it usually does when the pressure drops.

It is a '67 so it is a prop valve: not just a T.

I removed the drum and all looks well inside.

I cracked the line open where it meets the hose and same thing; just a small amount of fluid seeps out and the pressure does not drop.

Next I'm going to remove that line back to the valve. The whole thing is awful as brake fluid is just nasty.

joe_padavano

Once again, four wheel drum brake cars do NOT have a "proportioning valve". They simply have a distribution block that also included the differential pressure switch that lights up the BRAKE light if pressure is lost in one half of the system. There is nothing inside the distribution block that can possibly cause one front wheel to get no pressure. The only possible explanation is that there is a blockage someplace. Either there is debris in the system or the rubber hose to the wheel cylinder is bad. Simply disconnect fittings to that wheel sequentially until you find the blockage. I had exactly this problem on a friend's Supreme. We finally found the rust that caused the blockage.

Rocketguy

Thank's Joe. I should have known by taking a good look at the block; a prop valve is an assembly with internal parts and a block only has the switch. I'll post when I've found the blockage.

BTW I bought one of those Eastwood flare tools and its fantastic: highly recommended.

joe_padavano

Yeah, I love mine. You can't get a bad flare anymore (well, you really have to try to get a bad flare... ). The only downside is that you can't use it if you have to flare a line on the car, like when you need to replace only part of the long line that runs down the frame rail. I keep the old flaring tool around for those rare situations.

Professur

You can use it under the car. No where near as easy or convenient as the Mastercool .. but if you grab the square lug on the bottom with a large adjustable you can do it. One of the first things I tried. Would I want to? Hell no. If a line failed along it's length, I'm replacing the whole thing (if possible). But it is doable.

joe_padavano

"If possible" is the key term. The last time I had this come up was on my crewcab dually. Brake line rusted adjacent to the gas tank. Replacement of the entire line was not an option at the time.

m371961

Joe, don't some of the brake valves(switch block) on drum brake cars have a valve that moves and blocks flow to the end that losses pressure?
I know that is not the case here, as only one wheel is affected.
It stops fluid loss from the master. I seem to remember having one stick after replacing a line and could not bleed half the system.

joe_padavano

Yes. The piston that activates the differential pressure switch also moves to block the leaking side of the brake system in the distribution block. As you point out, since only one of the front wheels is not working, that isn't the cause here, however it is often the cause when both wheels on one end of the car won't bleed.

I've previously shown this tool. It screws into the dist block or combo valve, temporarily replacing the differential pressure switch, to lock the piston in the center position and prevent it from moving too far while bleeding brakes.

Professur

I'll mention here (since it came up) newer GM cars don't have that lovely annoying little valve. They're direct plumbed through the ABS solenoid block (even if the car doesn't have ABS, still direct plumbed through a block) The missus's 2005 Malibu was one such. Well, if you have a leak such as a wheel cylinder or a line ... you loose the lot. ABS light on? You're screwed just as hard. Surprise.

Rocketguy

Very cool; I learned something today.


I removed the line at the switch block, gave the pedal a pump and fluid shot out with a vengence. I removed the steel line, blew through it and it was clear.

I removed the rubber line, blue through it and it was clear.

I reinstalled the lines and had pressure to the LF wheel. There must have been a blockage I cleared it but I did not see anything.

Thanks very much to all that helped me out, I sincerely appreciate it.

oldcutlass

Glad you got it.

Army_Vet

I had a similar problem on my 1967 C/S. I replaced the brake booster, master cylinder, installed SS lines from ILT, new distribution block, new brake hoses front and rear and all four wheel cylinders.

When trying to bleed the brakes, I got only a small amount of fluid at R/R wheel no matter how much the pedal was pumped.

I had an extra set of master cylinder lines, so I initially disconnected both master cylinder lines and made the spare lines into bench bleed tubes.

Once I determined I had no air in the lines, I removed the rear tube and reconnected the brake line and the brakes bled just fine. I then removed the front tube and reconnected the brake line and the fronts bled just fine.

This is a whole lot easier than trying to remove the switch on the distribution block.

joe_padavano

If you are bleeding the brakes by pumping the pedal, your method doesn't prevent one from pushing the diff pressure piston all the way to one side. If you have an original cast iron combo valve, rust can cause it to stick there.

Army_Vet

Joe,


My car has the brass distribution block which was replaced with a new brass block. I think my problem was that the front circuit was pumping out with more pressure than the rear. Because of this, it would force the valve to the rear cutting off the supply of brake fluid. By leaving the bleed tube on the front circuit while I bled the rear allowed the rear line to push the valve forward. Once the rear lines had fluid in them and the front line connected, the pressure from the front was met with fluid from the rear. The valve obviously re-centered itself when I was able to bleed the front brakes with little difficulty. While I understand the purpose of the bolt you mention, it is not that accessible with the distribution block in it's stock location.

joe_padavano

Not exactly. The pressure out of the M/C is exactly the same front and rear. The problem is that if there is air in one set of lines, the air will compress, allowing the piston to move. Your solution is the correct way to fix this when it happens.