Brake Master Cylinder Issue? (1 Viewer)

[ron1]

New information.

When the pedal is first depressed and goes to the floor, the fluid level in the reservoir does not drop. After I release the pedal and depress it to it's firm spot, I noticed the fluid level does drop a little. Does this offer any clues?

Have not had a chance to rebleed the system yet.

 

[peesalot]

Yes, there is an air bubble in the master or elsewhere, try clamping the soft lines dropping to axles and check pedal, that will tell you if air is in wheel cyl.'s or in master, maybe both. If you get a firm pedal with lines clamped then you need to bleed the wheel cyl. Gravity bleed all at same time, have someone dumping fluid in as nec. and rig a piece of vacum tube on each bleeder to a water bottle so you dont make a mess, let it run, in some cases we have vibrated the wheel cyl to burp air especially where the cross over tube is. Another point to mention is if you are adjusting the shoes to drum with wheels bolted on ? I realize they are run tight for test purposes but when you get it solved you want the wheels mounted for final adjustment.

 

[ron1]

Bled the master again, bled 1/2 litre of brake fluid thru the system, very minute air bubble at start, then solid fluid at all bleeders. Gained about 1/4 inch travel from floor on first application.

Noticed the fluid in the reservoir "burps" when the pedal is depressed, the clutch fluid does not, very stable. Seems like fluid is bypassing the piston.

Ordering a master rebuild kit.

 

[B y r o n]

Sorry, what does the clutch have to due with the brakes?

 

[ron1]

Nothing to do with the brakes. As I stated, I noticed the fluid in the clutch reservoir stays "calm" and just drops when the pedal is depressed. When the brake pedal is depressed, the fluid burps up.

Similar master cylinders, very different behaviour.

 

[Pighead]

How do you bleed your master?
I use a piece of brake line from the outlet(s) back to the reservoir

 

[ron1]

Yes, I do it the same method.

 

[ron1]

OK, here it goes:

Rebuild kit installed, issue of pedal going to he floor once resolved. But pedal travel is excessive, almost to the floor.

Pinching the rubber hoses to ensure the master is OK. Did that and the pedal wouldn't move at all.
So I adjusted the pedal push rod longer, brake issue resolved.

When I disassembled the vehicle, I did not take note of the pushrod length, just cleaned the threads. When I reinstalled it, I made sure the piston returned all the way rearward to the snap ring, apparently it doesn't need to be.

Pressing the brakes, then releasing, all wheels turn fine, no drag.

What a mess, but I think it's good, will recheck tomorrow.

 

[65swb45]

If the piston does not fully retract, you WILL build residual pressure as you drive. Made the same mistake on my first rebuild…35 years ago.

 

[ron1]

Will recheck, but if I let the piston fully retract, the pedal travel is excessive, even with the brakes adjusted very tight.

Will verify if the piston is retracting, or staying forward a little. Other than that, not sure where to go from here.

 

[B y r o n]

OK, here it goes:

Rebuild kit installed, issue of pedal going to he floor once resolved. But pedal travel is excessive, almost to the floor.

Pinching the rubber hoses to ensure the master is OK. Did that and the pedal wouldn't move at all.
So I adjusted the pedal push rod longer, brake issue resolved.

When I disassembled the vehicle, I did not take note of the pushrod length, just cleaned the threads. When I reinstalled it, I made sure the piston returned all the way rearward to the snap ring, apparently it doesn't need to be.

Pressing the brakes, then releasing, all wheels turn fine, no drag.

What a mess, but I think it's good, will recheck tomorrow.

Download a copy of the Field Service Manual. It will cover rod length setting procedure as well as factory pedal height measurement.

 

[ron1]

Looked at manual.

It states to adjust shoes one adjuster at a time.

So, do I adjust just one until the adjuster and drum won't turn, back off 4-5 notches, then repeat on the other shoe? Or do I adjust both adjusters until they won't turn, then back off both 4-5 notches?

Going to verify the pedal measurements today.

 

[65swb45]

The first thing you need to do is just adjust them all tight. Period.

Get pedal.

Establish a baseline.

 

[ron1]

Thanks, did that. The rod was about 1/4 inch too long, piston returns to snapring/washer, and slight gap between the piston and rod.

With the wheels adjusted so the drums turn, and the pedal adjusted per the manual, when depressed and wheels/brakes lock the drums, the pedal is approximately 3-3 1/5 inch from the forward angled up floor board. Still plenty of travel remaining.

Wondering if I'm expecting too much from an old system like this, hence the pedal traveling more than my other vehicles?

 

[B y r o n]

"Wondering if I'm expecting too much from an old system like this, hence the pedal traveling more than my other vehicles?"

Maybe so. When I got my Ram truck it took me awhile to get used to the feel of the brakes. It was the first vehicle I've owned that had a hydroboost brake system. The brakes worked great but simply felt different and it took me awhile to get used to their feel.

 

[Pighead]

So, do I adjust just one until the adjuster and drum won't turn, back off 4-5 notches, then repeat on the other shoe? Or do I adjust both adjusters until they won't turn, then back off both 4-5 notches?

I found that the manuals 4-5 notches was too many.
I adjusted 1 wheel cylinder tight then backed off until i could just turn the wheel with 1 hand and backed off of that 2 or 3 clicks. Adjust the other cylinder until tight then until you can just turn with 1 hand. Back it off those same 2 or 3 clicks. Then adjust each cylinder in 1 click, 1 at a time. Balancing the drag equally between the 2 shoes, then matching that on the other wheels. You'll click in and out many times to find the correct setting. You need to find the feel of how much dragging is right for you and your pedal travel. Some drag is good, it'll self clear.

 

[ron1]

I readjusted the wheels, everything feels good.

Compared to a couple of my '50's vintage vehicles with single master cylinder, they feels very similar.

 

[StephaniesFJ]

I am chasing down a similar problem.... by chance does your idle go up when you let off the brake?

 

[ron1]

Sorry, still assembling the vehicle, not running.

But, the brake is a manual, no booster, so I would assume idle would not be affected.

 

[reade69fj]

I share your pain. My brake pedal went to the floor a month ago. No leaks in system lines. I have replaced all shoes (drum brakes), replaced all wheel cylinders (adjusters on 2 where frozen-up; 2 were wet under the rubber boot so I replaced them all, and replaced the MC (bench bled), and bled the system. Still, pedal goes to floor…so frustrating. From reading the above, I will try adjusting shoes out until wheels lock (they are just scraping now), then see what the pedal does.

11/8 Update: Worked each wheel adjusting until both cylinders were equally tight - to the point I could not turn the wheel by hand. Then pressed the brake pedal - got firm resistance/stop - did not go to the floor.
Then worked each wheel again backing off equally (cylinders) until I could rotate the wheel with one hand - leaving some friction when turning. Pedal still firm, brakes work great. Thanks for the help in this thread. Nice day, went for a long drive.