Brake help

[Jerome Simmons]

I just purchased a 77 k5 blazer. Replaced the master cylinder, bleed the brakes (no air in the lines). Brake pedal won't come all the way back up? It's barely enough that it leaves the brake lights on. This was the only issue with the k5 when I bought it and thought replacing the old rust cylinder would fix the problem. Thank you.

 

[rampage]

How did you bleed the master cylinder? What method did you use to bleed the brakes and in what order?

 

[Jerome Simmons]

Left rear tire then right rear tire, front left tire then front right tire. By releasing the valve on each tire while a friend pumped the brakes between each release. Took about two hours until no air was being released from each valve

 

[rampage]

And how did you bleed the master cylinder?
Bleeding order is farthest from MC to closest, so that would be pass. rear, driver rear, PF, DF. And I'd suggest making a pressure bleeder out of a gallon spray bottle (garden sprayer) for $20. Can do all 4 corners in about 20 mins by yourself and better too. Do a google search for "homemade pressure brake bleeder". No need to fill the sprayer with fluid, just use air pressure from it and make sure the MC stays full.

 

[Jerome Simmons]

I bled the master cylinder first with kit that came with new cylinder. I will try your steps now. Thank you

 

[diesel4me]

The pedal should return regardless of whether there is air in the system or not--some had a return assist spring on the pedal linkage under the dash,or on the pedal cluster pivot,some didn't--there is a spring inside the master cylinder that should return the piston in it back "up" and the pedal also..
I'm not sure if the power brake booster has a return assist spring or not..if something internal is wrong with the booster it might prevent the pedal from coming back up fully..

At any rate,if the pedal will not return all the way.,I'd guess something is amiss inside the master cylinder,if the pedals seem OK--the fact it was so hard to bleed also makes me suspicious that it was put together correctly inside,or has other defects like a torn seal on the piston .

Most of my GM trucks I have bled by just opening the bleeders one at a time and let gravity do it--usually if the rubber brake hoses are OK and no crud is in the steel lines,it'll gravity bleed itself most of the time without any pedal pumping..

--if one is stubborn I use a vacuum hose off a running gas engine along with a jar hooked in line with the hose,that has a metal lid with two 3/16" brake tubes soldered into it--one tube protrudes almost to the bottom,the other only 1" or so from the lid..

I connect the hose from the jar lid with the longer tube,to the bleeder,and watch the fluid get sucked into the jar (I used clear hose)--you can watch the air bubbles be sucked out,when you see clear fluid with no bubbles--shut the bleeder,then on on to the next wheel..you can bleed brakes with this setup alone in like 10 minutes,with minimum fluid loss..

 

[Jerome Simmons]

The pedal should return regardless of whether there is air in the system or not--some had a return assist spring on the pedal linkage under the dash,or on the pedal cluster pivot,some didn't--there is a spring inside the master cylinder that should return the piston in it back "up" and the pedal also..
I'm not sure if the power brake booster has a return assist spring or not..if something internal is wrong with the booster it might prevent the pedal from coming back up fully..

At any rate,if the pedal will not return all the way.,I'd guess something is amiss inside the master cylinder,if the pedals seem OK--the fact it was so hard to bleed also makes me suspicious that it was put together correctly inside,or has other defects like a torn seal on the piston .

Most of my GM trucks I have bled by just opening the bleeders one at a time and let gravity do it--usually if the rubber brake hoses are OK and no crud is in the steel lines,it'll gravity bleed itself most of the time without any pedal pumping..

--if one is stubborn I use a vacuum hose off a running gas engine along with a jar hooked in line with the hose,that has a metal lid with two 3/16" brake tubes soldered into it--one tube protrudes almost to the bottom,the other only 1" or so from the lid..

I connect the hose from the jar lid with the longer tube,to the bleeder,and watch the fluid get sucked into the jar (I used clear hose)--you can watch the air bubbles be sucked out,when you see clear fluid with no bubbles--shut the bleeder,then on on to the next wheel..you can bleed brakes with this setup alone in like 10 minutes,with

 

[Jerome Simmons]

Thank you, there is no return spring under the dash. I re-bled the brakes as advised above. This did not fix my problem? Let me state that amount rust on this rig is substantial (inside and out) I don't know it that would effect the pedal at all? I purchased this k5 to restore and get it back to factory condition. I feel like a return spring would fix this issue but there is no where to attach a spring?

 

[diesel4me]

It's possible if the rubber brake hoses were not new,the old ones are likely hardened up and possibly deteriorating inside--they can plug up solid,or act like a one way check valve--let fluid go TO a caliper or wheel cylinder,then "hold" pressure,like your foot is still applying the brakes,and not let the pedal return..

Last fall I replaced the rear "main" brake line on my '81 G-10 van,the 1/4" line that runs from the front junction to the rear axle's rubber brake hose..
I tried everything,the brakes just refused to bleed,and if I ever got a brake pedal,after frantic pumping,if I stopped pumping the pedal and waited a few seconds,it'd go right to the floor with zero resistance on the next pump!...also no fluid to the rear wheel cylinders...

Thinking the master cylinder was junk from sitting 10 years,(and was "stuck" the first time I tried applying the brakes,and it broke free and loosened up,that led me to think the seals in it ripped,etc,and it could not pump fluid to the rear brakes-- I bought a new master cylinder,and bench bled it-)-only to find it did the same dam thing! .

...then I had the thought to unscrew the new brake line at the rear rubber hose,and fluid came gushing out--so it was getting THAT far.....took off the 2 steel lines on the rubber hose going to the wheel cylinders,zero fluid..!.that rubber hose had actually sealed itself shut inside SO well,125 psi from my air compressor could not blow through it..

I had a used "good" brake hose to swap on in its place--presto--brakes bled perfectly in 5 minutes !..probably the old master cylinder would have "lived"and wasn't junk "yet" ,but I felt a new one for 20 bucks was well worth it for peace of mind..I came close to returning it thinking it too was bad !.....
Also-back in the 90's when this van was my daily driver--I had issues with the front calipers failing to release--bought 2 rebuilts and new pads,installed them--next day the front brakes were smoking,still dragging...2 new rubber brake hoses "fixed" it...not the calipers fault!..

 

[blazer74]

Master cylinder has a pretty good spring in it, should return the pedal.

Last time I had a non returning pedal it was in an 07 chevy cobalt. No matter how much I bled it, even with a pressure bleeder.
It was the new master cylinder.

Start over, do the master cylinder bleed with the kit again and see if that corrects the problem with the rest of the system disconnected.

Right rear, left rear ,right front ,left front.

 

[Jerome Simmons]

So after all was said and done. There is a brake return spring under the steering colum above the break pedal that needed to be replaced. Problem solved.