Weird results bleading brakes

[sgaylord]

Trying to bleed the rear drum brakes. After having my wife pump the brakes and hold, sometimes I hardly get any fluid out the bleeder. Sometimes it squrts like normal. I noticed that when I get no fluid, if I press the pedal really hard, it will seem to fix the issue and it will squrt/bleed like normal.

Does this mean I may have an issue with my mastercylinder or possibly a clog in my line? Or is this somehow normal.

This is on my 69 burb with power brakes.

Thanks,
Steve

[Blue'72]

I would vote maybe a crudded up slave cylinder or crud in the line..

[Longhorn321]

Try opening the front bleeders while bleeding the rear. Just put a vacuum hose on the bleed screws and run them into a plastic coke bottle to keep from making a mess and keep an eye on the level in the M/C.

[cdowns]

do you have the pin on the combination valve clamped to keep it centered?

[sgaylord]

Thanks everyone for the replies.

CDOWNS,

Can you walk me through what to check? I dont know what the combination valve is.

Thanks,
Steve

[steelhorse]

Sometime the combination valve will get "one sided" and opening the front or pressing the pin will usually center things up.

[sgaylord]

Thanks everyone for the help. It's times like this that remind me that I dont know as much as I thought I did....

Here are some pics of my setup. I found the combination valve on the frame below the radiator, not under the master cylinder like it is on my 70 c-10.

There is a button on the end. What is that for?

Thanks,
Steve

[cdowns]

from the master cyl the short brake lines attach to the combination valve(many people wrongly call it the prportioning valve) at the front of the valve is a pin thats sometimes covered by a rubber bubble/that pin needs to be clamped in the in position in order to bleed the brakes properly

[Longhorn321]

Originally Posted by sgaylord

There is a button on the end. What is that for?

Thanks,
Steve

Don't push that button!! It's the "Self Destruct" button!

[ChevLoRay]

I was taught to go to the wheel fartherest from the master cylinder and bleed it first, then work your way back to the closest one. So, that would be right rrear, left rear, right front, and finally the left front.

I had a power bleeder that I actually picked up at our city dump, still containing brake fluid and still holding air pressure. I carted that thing from house to house for 30 years before I gave it to my mechanic cousin. Nope, never used it. Didn't have the plate that attached to the top of the master cylinder. Crazy thing is my cousin had never used one. They always use two people at their shop.

[sgaylord]

I pushed the button. My burb turned into a pinto..........


Thanks for the advice guys, I will try to clamp the button down when I bleed the rear brakes. Never done that before, makes me wonder how I have bled these things before without doing that.

Thanks,
Steve

[Huck]

Shop manual refers to a special tool for the combination valve to hold that pin in place. Basically the pin is attached to a sliding piston. This piston ensures braking should a leak occur in either the front or rear brakes and if it is a multi purpose (combination-proportioning valve) it also ensures proper pressure to the front and rear (ie disc-drum). Just a thought--the furthest brake away from the master cylinder is actually the drivers side rear. The measurement is not "as the crow files distance" but in distance via the brake lines. Our trucks run the rear brake lines down the pass side then split at the rear axle with the drivers side wheel cylinder the furtherest from the master cylinder. Huck

[sgaylord]

Thanks Huck


This is why I like this site soooooooooooo much.

Steve

[MikeN]

I had a similar problem on a 69 Chevelle, and it turned out the short piece of rubber brake line over the rear end housing was corroded from the inside and blocked. New hose (readily available at NAPA) solved the problem. It would be pretty easy to remove the hose and see if it's blocked.

[ChevLoRay]

Thanks for the update, Huck. When I learned to bleed brakes, we had a single master cylinder and only foreign cars had discs.

...showin' my age, huh?

[72lb4x4]

I asked at the local nondenominational service place to do it for me after replacing a wheel cylinder and cut (why?) line on the rear. They said about $50 to flush and that bleeding was obviously included with flushing.

Of course when I came back they tried to charge for both.

Money well spent since I kept emptying the MC while doing it myself...

[Zappafan]

I use a vacuum bleeder and find that it makes the job way easier. You can do a complete flush in no time. It was only about $60. I've used it on my motorcycles as well.

[chris71]

what did you do to warrant a bleeding of the rear brakes? if you replaced brake lines, than it will take several pump/hold/bleed sessions to get the fluid back to the wheel cylinders and all the air out, so how many pump /hold/bleeds did you do? if you are not getting a solid jet of fluid then there is air in the system. you may have a leak somewhere that when you pump, air is drawn into the system, check all connections that you have messed with for any leaks, those will need to be tightened up or fixed. i dont think it is the MC here unless a connection is loose, leaking, and drawing in air

heres for giv'n the wife calves of steel!! i know mine does!

[chris71]

oh, forgot to mention that you when you bleed you need to perodically make sure that the MC is full, if she gets empty on you, start everything all over again, because that will pull air into the system.