Brake Master Cylinder Issue? (2 Viewers)

[ron1]

Cleaned and honed all the brake cylinders and master. Bled the system, no leaks at any fittings nor cylinders.

The pedal is firm, but after it is released for a few seconds, and pressed again, the pedal goes to the floor for the first stroke. Then repeated pressing, it is firm and will not go the the floor. After released for a few seconds, it repeats and goes to the floor once.

I checked all of the master components, looks correct per the manual, shortened the pedal push rod, bled the master. Cannot resolve the pedal going to the floor on the first application.

I am stumped, and will probably order a rebuild kit?

Anyone experienced this and have a suggestion?

 

[jembourbe]

If you have drum brakes, adjust them.

Edit: I didn't mean to sound snitty. You might be having to pump the MC multiple times to fill the wheel cylinders enough that they extend the shoes all the way to the inner surface of the drum. If you adjust the shoes properly, they'll be closer to the drum and you won't have to pump them full from the MC

 

[ron1]

After I rebuilt the wheel cylinders, I did adjust them per the manual.

After the pedal goes firm, it only travels about 1/3rd to 1/2 the distance. But I will recheck the adjustment as suggested.

 

[ron1]

Just checked the wheels cylinder adjustment, all is good.

Forced a stick from the seat to the brake pedal to keep it held about half way down. Did not loose its position, I.E no leakdown, and no leaks at the fittings nor wheel cylinders for over 10 minutes.

Stumped, will probably get a rebuild kit unless more suggestions?

 

[Pighead]

Adjusting per the FSM? Some people, like me, adjusted them a bit tighter.
Try, just for fun, adjusting the shoes a bit closer to the drums, like to the point you can barely turn the wheel by hand. Then try your pedal and see if it's better. If so, problem solved. If not. You've at least ruled out adjustment...

 

[B y r o n]

Did you bench bleed the master cylinder before the install? It's possible that you have air in the master which requires the pump to build pressure.

 

[ron1]

I did adjust a bit tight, no change.

I did bleed the master on the bench, plugged the end and the next day could barely push the piston in. Also bled the master on the vehicle as well.

I am stumped.

 

[B y r o n]

I didn't notice which year/master cylinder you are working with. Don't know if it will help but maybe it will.

 

[-MaTTi-]

I did adjust a bit tight, no change.
I am stumped.

Continue, the brake shoes are too far. Try to tighten them to lock and try after that. I’m pretty sure you have firm pedal. Then a little bit back.

 

[Pighead]

Do you still have the residual valves in the MC?

 

[ron1]

The master and wheel cyls are original 1968.

Not sure what you mean by residual valves?

The rubber check valve at the end of the return spring and the reed type valves on the piston and cup seals are all in good condition.

Will also try putting the shoes tight, tomorrow.

 

[Pighead]

Oh. '68.
So, a single-circuit set up?
No idea if they even had a residual valve, which sits in the MC where the brake lines thread in and keeps a littl pressure in the lines and keeps the shoes closer to the drums.

 

[ron1]

Yes, single cylinder. Only check valves I found was a rubber cup at the end of the spring and the reed type valves on the end of the piston.

So, adjusted all of the cylinders to where I could not turn the drum or adjuster. Did one at a time to be sure I didn't tighten the drum from just one allowing the other piston to move excessively. Same issue, except when the pedal is hard, it is higher.

When manual bleeding, I.E. pressing the pedal, after the air was expelled, no bubbles at all, solid fluid. But I find it confusing when I use a vacuum pump on the bleeder screw, it is not solid fluid, has air in it, even put oil around the bleeder screw to be sure I have a good seal.

Rechecked lines and wheel cylinders, no visible leaks.

 

[Pighead]

Stumped, will probably get a rebuild kit unless more suggestions?

If you only honed the cylinders, and re-used the old cups, then I would put a rebuild kit in it.

 

[Skreddy]

Did you get the cylinders back in right? Bleeders up? I would guess there’s still air in there, especially with the single reservoir system, it can be a lot to get them bled.

 

[65swb45]

Lock all four drums up at the same time and report.

 

[ron1]

All four drums are locked tight, cannot rotate drums nor adjusters.

Did not remove the cylinders, honed in place. Previous owner replaced all the seals before I purchased, they all look great. I honed to clean rust film from sitting.

 

[B y r o n]

So with the brakes locked against the drums do you still have the same problem with the pedal going to the floor on the first press? If so there is air in the system somewhere if there are no fluid leaks.

 

[65swb45]

Drum brake help

I just went completely through the brakes (4 wheel drum) on my 74 fj40. Replaced everything, including the master cylinder. Bench bled the master, and all of the wheel cylinders, adjusted the shoes and I still have to double pump and stand on the pedal. I understand that a reasonable amount of...

forum.ih8mud.com

 

[ron1]

Yes, the pedal goes almost all the way down, will try to rebleed tomorrow.