Brake Confusion

[Eggo]

I recently swapped over the master cylinder on my '73 Satellite. Had just done this on my '76 C10 so didnt look into how to do it because assumed it'd be the same so didn't consider the proportioning valve and the brake light has been on ever since. The brakes bled fine when I did the swap and the brakes felt really good until yesterday when the pedal went spongey and felt like there was air in the system. Checked the fluid and in the half for the fronts it was so full and spilling out when I took the reservoir lid off and the half for the rears was empty. Tried bleeding the rears and the rear passenger side bled fine but the rear drivers side would not bleed at all. Super confused what the problem is here, is it likely it's the proportioning valve and I need a new one?

 

[493 Mike]

I recently swapped over the master cylinder on my '73 Satellite. Had just done this on my '76 C10 so didnt look into how to do it because assumed it'd be the same so didn't consider the proportioning valve and the brake light has been on ever since. The brakes bled fine when I did the swap and the brakes felt really good until yesterday when the pedal went spongey and felt like there was air in the system. Checked the fluid and in the half for the fronts it was so full and spilling out when I took the reservoir lid off and the half for the rears was empty. Tried bleeding the rears and the rear passenger side bled fine but the rear drivers side would not bleed at all. Super confused what the problem is here, is it likely it's the proportioning valve and I need a new one?

Did you pull the bleeder screw out and check for plugging? I assumed you bench bled the master?
Mike

 

[Eggo]

Did you pull the bleeder screw out and check for plugging? I assumed you bench bled the master?
Mike

I haven't pulled anything out, what is plugging? Yeah bench bled it. The brakes felt great until yesterday which is confusing me more

 

[chescharger]

Rubber hoses

 

[70bigblockdodge]

I would lean towards bad master cylinder since the fluid moved on you. Q.C. at its finest.

 

[Ron H]

Brake conversions can be a bee-itch, I know. Could be any of a ton of things. It can be difficult to toss over advice telling you what you have already done like bench bleed. Rubber hoses? The rear line if it’s aged could be a problem collapsing under pressure. On occasion, the t-block on the rear housing can be clogged, rear brakes (drum?) need to be adjusted if not done. My case, one time was the drums were maxed out getting new ones. Other, is pedal ratio that can be tricky. Needs to be adjusted so the home position has a tidbit of free play, not binding against the brake light switch. Power brakes? If so more on that, with booster rod gap to MC. With a partner, check the action of the brakes/pads to be sure there’s no binding/sticking going on. A system flush to remove all old fluid from the lines is another thing if the fluid is old. Tossing out things you may already know – hope it might be useful. Yeah…there’s more. Lol.

 

[Cranky]

I haven't pulled anything out, what is plugging? Yeah bench bled it. The brakes felt great until yesterday which is confusing me more

When you opened the bleeder, nothing came out, right? If the other side did fine (rear brakes), the bleeder where nothing came out could be plugged up with something. Take it all the way out and see if fluid comes out of the wheel cylinder. If nothing happens and the bleeder looks good, you need to replace the cylinder or unplug the blockage in it. But, it's kind of strange your master emptied half and over flowed the other half. Keep in mind that the front half feeds the rear brakes.

 

[Eggo]

Rubber hoses

checked them and they seemed fine and didnt seem to be leaking but will check again when i get home from work just in case

 

[Eggo]

I would lean towards bad master cylinder since the fluid moved on you. Q.C. at its finest.

thats what i was thinking but im confused if maybe thats not the issue if the back drivers side wasnt bleeding. the brakes were working so well as well up until yesterday evening & i drive it daily

 

[Eggo]

Brake conversions can be a bee-itch, I know. Could be any of a ton of things. It can be difficult to toss over advice telling you what you have already done like bench bleed. Rubber hoses? The rear line if it’s aged could be a problem collapsing under pressure. On occasion, the t-block on the rear housing can be clogged, rear brakes (drum?) need to be adjusted if not done. My case, one time was the drums were maxed out getting new ones. Other, is pedal ratio that can be tricky. Needs to be adjusted so the home position has a tidbit of free play, not binding against the brake light switch. Power brakes? If so more on that, with booster rod gap to MC. With a partner, check the action of the brakes/pads to be sure there’s no binding/sticking going on. A system flush to remove all old fluid from the lines is another thing if the fluid is old. Tossing out things you may already know – hope it might be useful. Yeah…there’s more. Lol.

I think the hoses are fine but will double check. What would I do to unblock them if they're blocked? Will research into how to do the positioning. The fluid was fresh when I swapped over the cylinder

 

[Eggo]

When you opened the bleeder, nothing came out, right? If the other side did fine (rear brakes), the bleeder where nothing came out could be plugged up with something. Take it all the way out and see if fluid comes out of the wheel cylinder. If nothing happens and the bleeder looks good, you need to replace the cylinder or unplug the blockage in it. But, it's kind of strange your master emptied half and over flowed the other half. Keep in mind that the front half feeds the rear brakes.

Nothing came out, thought there was a bit that dribbled out but not sure if that was from the one man brake bleed kit i was using. Not sure what would have caused a blockage because I bled all the old fluid out when I swapped over the cylinder, is there a chance I've done something wrong doing that and it's caused a blockage?

 

[Dave6T4]

I would go with it being a bad master cylinder. Brake fluid should NEVER migrate from one reservoir to the other.

 

[Eggo]

I would go with it being a bad master cylinder. Brake fluid should NEVER migrate from one reservoir to the other.

how would it have migrated from one side to the other? bit confused about how that's possible even though it seems as though that is what's happened

 

[Cranky]

I would go with it being a bad master cylinder. Brake fluid should NEVER migrate from one reservoir to the other.

If he had pressure going to one rear wheel, he should have pressure to the other rear wheel too. Sounds like there's a problem with the master and that one rear cylinder.....

 

[Cranky]

how would it have migrated from one side to the other? bit confused about how that's possible even though it seems as though that is what's happened

Sounds like something is wrong with the internals of the master....one of the pistons has a hole or cut?

 

[Eggo]

If he had pressure going to one rear wheel, he should have pressure to the other rear wheel too. Sounds like there's a problem with the master and that one rear cylinder.....

*she & you think maybe is both that's the problem instead of just one thing? So weird they'd both go at the same time, the brakes up until yesterday felt great like wasn't pulling to either side when braking or anything like that

 

[Eggo]

Sounds like something is wrong with the internals of the master....one of the pistons has a hole or cut?

thinking maybe it's worth getting another one, it wouldn't be anything to do with the proportioning valve not being reset would it?

 

[Cranky]

thinking maybe it's worth getting another one, it wouldn't be anything to do with the proportioning valve not being reset would it?

If it was the PV, it would be a first that I've ever heard of one doing that

 

[Dave6T4]

Fluid moved from one reservoir to another, resulting in emptying of one side and overfilling of the other. The only way this can happen is internal failure of the master cylinder. Has nothing to do with prop valve.

 

[70bigblockdodge]

Not building any pressure on the rear brake system because the fluid is moving to the front brake reservoir this is what is turning the light on.