How challenging is replacing brake master cylinder?

[Rotten 1]

I wouldn't condemn the master cylinder so fast. And I don't have $.10 confidence in the things on chat gtp . Make sure the rear brakes are adjusted, jack up a front and rear wheel have someone step on the brakes,see if front and rear work. If you have some brakes but not good brakes,I don't suspect the master first .Unless the brake light is on

Ricko

Rear drum brakes adjusted - I can get almost one full spin on them with the truck jacked up and in neutral. Everything I have read and seen suggests this is right - unless I missed something.

Jacked up both drivers side wheels and with the wife pushing the brake pedal the front did not move while there was no change in the rear, it moved the same with and without the brake pedal pressed. With the emergency brake on - the rear does not move at all. It seems like I have some braking ability in front (brake pedal all the way to the floor) but not in the back unless mechanically activated via emergency brake.

I'm not smart enough to know what this diagnosis tells me - it seems to say that there is something preventing the hydraulics from reaching the rear, and in the process reducing front brake effectiveness.

I have a master cylinder coming next week and that will be my next step.

What else am I missing?

thanks everyone

 

[Ricko1966]

Ricko

Rear drum brakes adjusted - I can get almost one full spin on them with the truck jacked up and in neutral. Everything I have read and seen suggests this is right - unless I missed something.

Jacked up both drivers side wheels and with the wife pushing the brake pedal the front did not move while there was no change in the rear, it moved the same with and without the brake pedal pressed. With the emergency brake on - the rear does not move at all. It seems like I have some braking ability in front (brake pedal all the way to the floor) but not in the back unless mechanically activated via emergency brake.

I'm not smart enough to know what this diagnosis tells me - it seems to say that there is something preventing the hydraulics from reaching the rear, and in the process reducing front brake effectiveness.

I have a master cylinder coming next week and that will be my next step.

What else am I missing?

thanks everyone

Is the brake warning light on?

 

[Radiohead]

The biggest challenge I'm having replacing my master cylinder this weekend has been getting the spray paint to dry enough to handle it. Engine paint and low temp/ high humidity is a recipe for a forever dry.

Should have done it in the house when Mrs wasn't around.....

 

[Rotten 1]

Brake Warning Light is not on - I have never seen it on since I have owned the truck. Of course, this could mean that doesn't work either!

 

[Ricko1966]

Brake Warning Light is not on - I have never seen it on since I have owned the truck. Of course, this could mean that doesn't work either!

Well that could be a clue. There is a brake combination valve hidden by the fan shroud. There is a 1 wire electrical sender on it , pull off the wire, clip a 12v test light to battery + touch the switch lead on the combination valve. If the test light lights,the shuttle valve in the combination valve is off center. You will not get the brakes to work correctly until it is centered.Id suggest buying a centering tool to hold it centered while bleeding the brakes. But if it is off center now you can't bleed the brakes properly. I assume your brake light does not work,you would see it come on with the parking brake.

 

[Turbo4whl]

I wanna have a beer with this guy, I bet they have great beer there!!!!!

Or whiskey, they must have some Bourbon from nearby Kentucky!

AI:

Top-rated bourbon is subjective, but according to recent 2024-2025 rankings, Green River was named best in the world, while Four Roses Small Batch and Michter's US1 are widely lauded for quality. Wild Turkey (Rare Breed/Master's Keep) is frequently cited for superior, robust flavor profiles, particularly by enthusiasts.

 

[Rotten 1]

Okay guys = bench bled the new master cylinder and swapped them out. New master cylinder is the stock model from LMC Truck and everything went back together pretty well. I have not yet had a chance to bleed the lines - my neighbor is not available today, so I decided to pull the tires and clean up the rusted lug nuts waiting for him to be available. That's when I noticed my rear wheels are completely locked up. Both wheels. Prior to the swap the drums seemed adjusted so that I could spin them by hand and get about one full rotation. Now, maybe an inch, just a little bit of wiggle.

The front wheels rotate fine

I have not done anything with the proportioning valve yet, is it possible that is the culprit? Otherwise, what did I do wrong?

Thanks

 

[Goldie Driver]

Okay guys = bench bled the new master cylinder and swapped them out. New master cylinder is the stock model from LMC Truck and everything went back together pretty well. I have not yet had a chance to bleed the lines - my neighbor is not available today, so I decided to pull the tires and clean up the rusted lug nuts waiting for him to be available. That's when I noticed my rear wheels are completely locked up. Both wheels. Prior to the swap the drums seemed adjusted so that I could spin them by hand and get about one full rotation. Now, maybe an inch, just a little bit of wiggle.

The front wheels rotate fine

I have not done anything with the proportioning valve yet, is it possible that is the culprit? Otherwise, what did I do wrong?

Thanks

Try loosening the nuts that hold the master cylinder to the booster - don't disconnect brake lines. If the rears free up the new master cylinder is the issue.

 

[Goldie Driver]

Or whiskey, they must have some Bourbon from nearby Kentucky!

AI:

Top-rated bourbon is subjective, but according to recent 2024-2025 rankings, Green River was named best in the world, while Four Roses Small Batch and Michter's US1 are widely lauded for quality. Wild Turkey (Rare Breed/Master's Keep) is frequently cited for superior, robust flavor profiles, particularly by enthusiasts.

I can tell you Wild Turkey 101 is frequently cited for its superior buzzability by yours truly ...

 

[Rotten 1]

I loosened up the bolts to the power booster a bit more than 1/8, no change.
Cracked bleeder valve at the drum, no change
Cracked the brake line off the master cylinder, no change

If I get time tomorrow I’ll crack the nut off the proportioning valve and see what happens.

Anything I should be looking at with the drum itself?

 

[Ricko1966]

I loosened up the bolts to the power booster a bit more than 1/8, no change.
Cracked bleeder valve at the drum, no change
Cracked the brake line off the master cylinder, no change

If I get time tomorrow I’ll crack the nut off the proportioning valve and see what happens.

Anything I should be looking at with the drum itself?

If you cracked the bleeder valve at the drum and still can't turn it. It's a mechanical problem inside the drum
,not a hydraulic problem.

 

[Rotten 1]

If you cracked the bleeder valve at the drum and still can't turn it. It's a mechanical problem inside the drum
,not a hydraulic problem.

That’s my fear, but both at the same time I change the MC? Seems cursed…. What should I be looking at in the drums?

Is there a sweet spot that just needs persuasion from a 3# sledge? Or can I just spray them down with a little Buffalo Trace?

 

[Rotten 1]

Problem solved, I’m an idiot. Sorry guys. Bleeding brakes Monday to hopefully complete the job

 

[Radiohead]

Well, describe the idiocracy. For research purposes only.

I need some comic relief for mine that has the steel lines wanting to turn with the ferrules and not independently. Panther piss soak overnight in progress.

 

[ali_c20]

Problem solved, I’m an idiot. Sorry guys. Bleeding brakes Monday to hopefully complete the job