Brake help...

[CATCHALLBLUE]

I put in a new master cylinder today (already bench bled) and began to bleed my rear brakes. At first some break fluid began coming through the bleeder line (very little actually) and then nothing. So i try the other rear break and again very little comes out then nothing.

I move to the front brakes and they move fine no problems.

The fluid isnt moving at all in the rear reservoir. Whats going on here?

Its a 69 1 ton with a booster and drum brakes

[alsriv2]

I had the exact thing happen on my '69. Here is what I found:

1. My bench bleed was not successful due to the lines I used initially had plastic nuts that would not seal around the threads of the master cylinder and allowed air into the fluid path. Purchased a quality set of bleed lines from NAPA, bench bleed problem solved.

2. I had a small clump of rust on the fluid line that ran between the frame and one of the rear crossmembers on the passenger side. My frame was rust and corrosion free, however there was a little clump of dirt that built up over the years where the line ran through the crossmember/frame location and completely rusted the line shut.

In my circumstance, there was no fluid leak showing. It was only when I was looking for a kink or damage on the line did I find the clumped dirt/rust spot. Just as soon as I cleaned the hard dirt clump out and moved the line a bit, the line broke at that small spot and I found the rust had penetrated into the inner part of the line and shut off the fluid flow completely.

I replaced the line and the bleeding process was easy after the repair.

I would never have suspected a rusty brake line to cause my problems as I had a clean, rust free frame, but after a detailed inspection, I had found the problem described above.

Be suspicious of the bench bleed process that was used. ALL air needs to be removed. With 2 persons, the bench bleed can actually be done while the master cylinder is installed in the truck before the brake lines are attached.

Let us know what you find out.

[CATCHALLBLUE]

Thank you for the detailed response. I used the cheap plastic nuts also and the rear reservoir nut didnt seem to make a tight fit.

Before posting i made a quick glance of the rear lines and didnt see any damage. I'll do a more thorough examination tomorrow. Shes been sitting for awhile so it wouldnt surprise me if it had a rusty line. My initial thought was a clogged line but where was the mystery.

Hoping i dont have to replace the entire rear lines.
.

[CATCHALLBLUE]

checked the lines and while there is rust along 95% on the surface how can i tell if the rust has penetrated? hmmmm

I guess the best way to know is just replace all the lines.

[ERASER5]

The porportioning valve has a stop slide in it. The rear brakes could be cut off. Check the FAQ section for brake work. A lot of guys use a clamp the force the valve back to center. The BRAKE light on the dash should be on if this is the case, assuming the light works.

[LSUMurse]

Try disconnecting the rear brake line at the tee. With your reservoir cap off, see if it flows out (by gravity) easily. If it does, that should at least narrow down your possible problem areas. I thought I had rusted shut lines to my right rear, turned out to be a bad wheel cylinder. I did have an accumulation of gunk into that wheel cylinder that I had to use a drill bit to clean out.

[68gmsee]

After you try the above (disconnecting at the T) remove the rubber brake line on the rear and check internally. You can't tell by looking at it but they collapse internally restricting fluid flow. Happened many years ago on my 69.

If it's never been replaced, I would replace all of them anyway. Cheap insurance.

[cdowns]

read up the factory service manual has excellent instructions on how to properly bleed the brakes

[cdowns]

Originally Posted by ERASER5

The porportioning valve has a stop slide in it. The rear brakes could be cut off. Check the FAQ section for brake work. A lot of guys use a clamp the force the valve back to center. The BRAKE light on the dash should be on if this is the case, assuming the light works.

you need to read this about 6x till you understand what is written then proceed

[CATCHALLBLUE]

ok disconnected at the T. The fluid didnt flow with gravity but did come out after pumping the brakes. Not sure of the pressure that the fluid comes out (it was more of a steady drip/stream, wasnt spraying out. After that i tried to bleed the driver rear again and it started flowing slowly out then it stopped. The rear passenger got no flow at all.

Could it be internal in the drums or is it looking like the rubber passagways are the culprit? As i said it flowed from the T although it had to be pumped.

Didnt take off the rubber line but If i can get to the auto store I'll just buy a new one as you say cheap insurance.

[CATCHALLBLUE]

What exactly does the proportioning valve sensor do? Mines been disconnected, looks like the rubber connector melted.

[68gmsee]

Originally Posted by CATCHALLBLUE

What exactly does the proportioning valve sensor do? Mines been disconnected, looks like the rubber connector melted.

Senses unequal pressure between front and rear and warns you. Normally, you would immediately know if the rear or front brakes failed. The light is just an added feature.

I've had master cylinders new defective before. I had to return two of them once and finally told them to return my money. Went to another parts store that sold a different manufacturer brand and did not have any more problems.

[CATCHALLBLUE]

Originally Posted by 68gmsee

Senses unequal pressure between front and rear and warns you. Normally, you would immediately know if the rear or front brakes failed. The light is just an added feature.

I've had master cylinders new defective before. I had to return two of them once and finally told them to return my money. Went to another parts store that sold a different manufacturer brand and did not have any more problems.

ok cool. Im not even sure i have a light on my dash. Bare bones dash.
Defective in what way?

Thinking now my rear cylinders are gunked up. Should i buy new cylinders or....

How difficult a job is it to clean up the cylinders? Do i need the wheel and adjuster parts?

[davepl]

So if the pistons are bunched together and the light's on, someone want to throw the instructions on how to reset the prop valve in here? I know it's on another thread, but sometimes having the answer at the end is nice...

[truckdude239]

Hsd the same problem mine wss the rubber hose gone bad

[davepl]

I was bench bleeding mine (with tubes looped back into the reservoir rather than plugs, just the way I happen to have been taught, right or wrong.

After a while I noticed not much going on in the rearmost bore. So I think I rammed the two pistons together.

[68gmsee]

Originally Posted by davepl

I was bench bleeding mine (with tubes looped back into the reservoir rather than plugs, just the way I happen to have been taught, right or wrong. After a while I noticed not much going on in the rearmost bore. So I think I rammed the two pistons together.

That's the way I do it on a new m.c. and IIRC the instructions say to use short strokes until all the bubbles disappear. If you push the pistons in all the way until they stop, it's possible to damage the seals.

From Cardone site:
6.Using a blunt tool or dowel (brake pedal if mounted in vehicle), SLOWLY press in and release the master cylinder piston using short strokes of 3/4” to 1”. NEVER STROKE PISTON MORE THAN 1”. Repeat this step until resistance to piston movement is firm and less than 1/8”.

[mgchevyparts]

That is not a proportioning valve, it is a distribution block with a low pressure warning switch. While bleeding the brakes it is very possible for the shuttle valve in the low pressure switch to move and block off the front or rear system. To reset just open a front and a rear bleeder(at the same time) and pump the pedal, the pressure will equalize and reset the valve.. Close the bleeders and resume proper bleeding technique. Buy a suction type air bleeder, much easier then trying to bleed by depressing the pedal. Don't pump pedal fast.

[CATCHALLBLUE]

Originally Posted by mgchevyparts

That is not a proportioning valve, it is a distribution block with a low pressure warning switch. While bleeding the brakes it is very possible for the shuttle valve in the low pressure switch to move and block off the front or rear system. To reset just open a front and a rear bleeder(at the same time) and pump the pedal, the pressure will equalize and reset the valve.. Close the bleeders and resume proper bleeding technique. Buy a suction type air bleeder, much easier then trying to bleed by depressing the pedal. Don't pump pedal fast.

Thank you. Will get a suction and try this.

[CATCHALLBLUE]

Ok im narrowing it down to a few problems...

1. Used plastic bench bleed nuts. The rear resevior bleeder nut (rear brakes are the issue) wont airtight seal. Noticed this after installed the MC. So I didnt get all the air out in bench bleeding.

2. When i removed the lines connected to the MC the front drips freely while the rear would not drip at all.

Is my MC faulty? Is it clogged? Not sure how it would be clogged, maybe some rust got in there. The rear fluid moves when depressing the brake however thats for sure. BUT im not getting anything out of the rear bleeders. Checked the rear T and fluid came through.

[CATCHALLBLUE]

Used a vacuum bleeder on the rears and it got a lot of gunk and bits of rust out then nothing again. Took the bleeder nuts out to inspect and sure enough they are full of gunk and rust. Cleaned those and put them back in, vacuumed some more and still nothing.

Now I think if my rubber line wasnt collapsed before it is now after using the vacuum. Going to just change the rear line first as the fronts were ok. Might be a couple days to get the part.........

[mgchevyparts]

Sounds like a lot of junk in your lines, should replace them.

[davepl]

Originally Posted by mgchevyparts

Sounds like a lot of junk in your lines, should replace them.

Indeed. At a very minimum you need to clean them out but I vote for new lines including rubber. Since you can order a brake line kit for a half-ton cheap and easy, shouldn't be much pain or price involved.

Proper brakes are cheap life insurance. Safe money elsewhere.

[CATCHALLBLUE]

Originally Posted by davepl

Indeed. At a very minimum you need to clean them out but I vote for new lines including rubber. Since you can order a brake line kit for a half-ton cheap and easy, shouldn't be much pain or price involved.

Proper brakes are cheap life insurance. Safe money elsewhere.

Have a good source for brake lines? Ill probably just change the rears for now if i can purchase them separately. My truck is a 1 ton by the way. Thanks.

I should also mention the rear resevior barely moved during all the latest bleeding. Wondering if my MC is bad.

[davepl]

I'd price ship inline tube, classic tube, and the LMC-style vendors. If its not a show truck just get the cheapest mild steel ones.

I have my old set but it's a long way to Catchall.