Need Brake help please

[erock805]

I recently purchased a 1970 3/4 ton 4x4 pu. The last owner said the rear brakes werent working, even after he replaced the wheel cylinders. Front brakes work fine.

I put on a new master cylinder yesterday evening with a friend and we had trouble getting pressure to the rear brakes. Plus I couldnt hear the shoes actuating when he drepressed the brakes.

So We pulled the line off, and blasted air through the proportion valve and rear lines. Got strong air pressure through the line. I used my vaccum pump to pump fluid through the lines. Didnt build too much pressure but fluid did come out. We attached the line to the drums and proceeded to bleed all the brakes. Front brakes seemed to be working. Strong fluid push out the bleeders. The rear, however, was a weak trickle. I went for a test drive...no rear brakes.

Do proportioning valves go bad? napa, checker nor autozone has them. What am I missing? I need to make sure the wheel cylinders were replaced. Couldnt I connect the rear line to the master cylinder....then I should have strong brake flow? Perhaps thats the way to check the prop valve. Thanks for any help you can through my way.

[workinprogress67]

did you bleed them starting from the furthest point from the master cylinder to the closest? should be rear right, rl, fl, fr. and did u pump the brake before u cracked the bleeder? the cap needs to be closed on the master cyl. another suggestion did u adjust the rear drums using the adjuster hole? put the rear in the air and test it should be one of those if theyre no leaks in the lines. look at the bleeder screws if theyre old and nasty then they werent replaced if theyre are new and shiny they probably were.

[crackerjack70]

Did you bench bleed the master? If you didn't you need to.

[erock805]

Yes bench bled the master. Yes I bled them from farthest out to nearest. I pulled the axles out and removed the drums. the drums barely turned by hand. Had to back them way off to get the to come off. In my experience they were adjusted too tight.

on a side note, finding bearing are a big pain...lotts a diff axles appartently.The outer bearings are fer sure shot so I am trying to replace them. (napa got me a part close...but a hair to narrow for the axle)

I went ahead and replaced the brake cylinders anyway. So, when its back together hopefully I will have some brake pressure back there. If not I will bypass the rear line directly to the master cylinder and see if I get pressure then.

Thanks for the comments guys..brakes are usually pretty dang simple...thats why I was posting for some help.

[A.P.]

I had a similar problem with my brakes in my 72 Chevy pickup. My front brakes would work great but the rear did not assist. at all. It turned out to be my proportioning valve. I took it apart and rust was inside. I did not have the cash to buy a new one, so what I did, was I went to the wrecking yard and I got a used one from a Chevy blazer 4x4. It only cost me about $12 and I had to fabricate one of the small brake line because one of the originals would not align correctly. It is working great now.

[fastwillie 696969]

Slide the tube nut wrench over the brake line at the proportioning valve and orient the wrench so that it will fit over the tube nut that secures the brake line to the proportioning valve.
2


Place a catch pan underneath the brake proportioning valve. Brake fluid will eat through paint, so you will also want to use a rag to help control any brake fluid spray by placing the rag over the brake line to proportioning valve connection.

3


Have an assistant apply steady and firm pressure on the brake pedal.

4


Loosen the brake line with the tube nut wrench by turning the tube nut counterclockwise. Check the connection as you do this. You may or may not notice bubbles forming on the threads of the brake line. Make sure your assistant keeps firm pressure on the brake pedal so that air does not get introduced into the brake line. Loosen the brake line just enough so that any trapped air and brake fluid are allowed to escape, but do not remove the brake line. When the brake pedal falls to the floor, retighten the brake line and have your assistant pump the brakes again to build up more pressure in the lines.




Repeat steps 3 & 4 for all outgoing lines connected to the proportioning valve. The outgoing lines are the lines running to each wheel on the vehicle. Periodically check the brake fluid level in the master cylinder on the driver's side of the vehicle (on the firewall, labeled "brake fluid") and refill the master cylinder to the full line as necessary. Don't let the fluid drop below the lowest mark on the reservoir tank or you may introduce air into the brake lines

[dmack91]

Sometimes the lines get plugged or collapse. If you disconnect the rear line from the prop. valve and try to blow through it, you should be able to tell if it is clear.