Is my master cylinder shot?

[mtrdrms]

Hey guys. I just put a webber carb on my 1f 71 fj40. I also put on new rear wheel cylinders. Now I have no brakes. When I initially hit the brakes the pedal goes to the floor but if I pump them they will grab and work but after a few seconds of driving the pressure drops again and I have to pump them to stop. The system is power assist (I believe?) and has a vacuum line going to the intake manifold.

Now before you blast me, I did bleed the hell out of the brakes (front and rear) twice. I also adjusted the shoes twice. What else should I check? The reason I mentioned the carb is because when I hit the brakes the idle gets rough. Don't know if that has something to do with it.

Thanks

Andy

 

[dgangle]

sounds like you have one or more possibilities. such a common subject it reappears often and most certainly covered in the FAQ.

Assuming your MC is good, readjust your rear brakes. Then readjust your rear brakes again. No seriously, readjust your rear brakes. Get the idea?

re-bleed if necessary

as far as the idle issue, sounds like your booster may be bad. Do the test outlined elsewhere (eng off, foot on brakes, start engine, pedal should go down some then be firm). And/or use a vac gun/gage to pull a vacuum on the booster and see if it leaks off/stays steady.

did it do this before? did you change the wheel cylinders and carb at the same time? If so you don't know what is causing what. Whenever possible I always try to do only one thing at a time so I'm not chasing my tail. Can you put your other carb back on to isolate the rough idle issue when depressing the brakes? other????

 

[mtrdrms]

Thanks man. I will readjust tonight. I did do the carb and brakes at the same time but now I am wishing I hadn't but hindsight is always 20/20. I'm off to the FAQ...

 

[lostmarbles]

Your master probably isn't shot (as a guess).

Bleeding the brakes can be a pain in the butt when you have had major components out (like you have).

My guess is that you still do have air in there.

There are a few threads relating to the extreme difficulty some people have had getting air out of CCOT wheel cylinders for instance.

And pumping the brakes like that will affect the idle because the way the vacuum-assist is connected ton the inlet manifold.

 

[fj404life]

Any fluid leaking out the end of the master under the dash?
I had 2 new aftermarket masters leak on me there within days of installing.
Had same symptoms you have to the T. Then the masters started leaking.
New OEM master solved issue....good luck I have been there. Adjusting drums 20 freakin times SUCKS!!!! LOL

 

[Poser]

Any fluid leaking out the end of the master under the dash?

His truck has a brake booster...It would have to leak A LOT of brake fluid into the booster, in order to get fluid onto the inside of the cab.


Now a non-boosted brake master cylinder is a different issue...they will leak inside the cab when they fail.

 

[lostmarbles]

His truck has a brake booster...It would have to leak A LOT of brake fluid into the booster, in order to get fluid onto the inside of the cab...... Now a non-boosted brake master cylinder is a different issue...they will leak inside the cab when they fail......

My OEM booster has a "drain groove" indentation to ensure there is no seal between the master and booster at the bottom. I would expect this to ensure any leaking fluid enters the engine bay rather than getting sucked inside the vacuum system:



Don't they all have these grooves or do these grooves just get clogged up Steve?



(I've heard a number of people say that their brake fluid ends up inside their boosters and its puzzled me.)

 

[Poser]

My OEM booster has a "drain groove" indentation to ensure there is no seal between the master and booster at the bottom. I would expect this to ensure any leaking fluid enters the engine bay rather than getting sucked inside the vacuum system:

View attachment 305414

Don't they all have these grooves or do these grooves just get clogged up Steve?



(I've heard a number of people say that their brake fluid ends up inside their boosters and its puzzled me.)

Is there not a seal around the outside of the nose on the master cylinder where it seats into the booster? If that were the case, then how would fluid leak past that seal and out the 'drain groove'?

 

[lostmarbles]

Is there not a seal around the outside of the nose on the master cylinder where it seats into the booster? If that were the case, then how would fluid leak past that seal and out the 'drain groove'?

Man I am S-T-U-P-I-D!

Now that you meantion it, I went through this exact same learning curve about a year ago when did up my booster. (How could I forget something so recent?)

You're right! The nose of the master does have a seal on it where it enters the booster. And here is a picture of that seal on my master:



The seal does have a "notch" cut out of it - but that notch is at the top so it won't stop the leaking fluid from entering the booster around the booster's input-rod seal.

 

[mtrdrms]

No fluid leaking from the master. I have bled the system 3 times and adjusted the drums 3 times. Still the pedal goes to the floor. When I pump it up however they work well. Any tricks on how to bleed more effectively? I am using a mightyvac and 3 quarts of brake fluid...

Thanks for the info guys,

Andy

 

[dgangle]

I have Mitivac like this



http://www.mityvac.com/hq_images/MV7430.jpg

and find it usefull for flushes but for whatever reason it will not evacuate all air from the system like one must do when replacing a caliper, MC, brake line, etc. In this instance I revert back to the 2 person method.

If the brakes are adjusted properly and a manual re-bleed doesn't solve your dilema, then I would suspect the MC.

 

[skintunes]

Don't know why people are more concerned with getting blasted than the answers. If it has your master -you would never get a pedal nor hold it- this is most likely an adjust prob- drums/shoes cut?/New? When off the pedal springs/shoes send whl cyl to there relaxed state and you need to pump all over again
Check shoe clearance at backing plate lips -can cause hang up of direct shoe/drum contact - Wheelcyliders are requiring multi pumps to make shoes completely contact- or you do have a bad wheel cyl or 2

 

[dgangle]

Don't know why people are more concerned with getting blasted than the answers...

Wow. Not sure where that came from. Nobody is blasting anyone. He's got a problem and a few of us are trying to help him. He's said 100X he has adjusted the wheel cylinders so at some point one must assume he's done it and move onto the next possible issue. Lighten up.

 

[mtrdrms]

No worries. I appreciate everyone on here trying to help me. I did adjust the brakes again and it got a bit better.

Like Ringo said: "Peace and love, peace and love."

 

[Poser]

I did adjust the brakes again and it got a bit better.

Please describe how you are adjusting your brakes.




Then,



Please elaborate on what got better.

 

[mtrdrms]

Ok.
So I drove for a bit and used the brakes often. when I got back and put the truck on the lift and spun the tires. I then used a small flat-head screwdriver to turn the adjusters on the cylinders until shoes touched the drums and the tire would not spin. I then backed the adjuster off 3 clicks.

Once that was done to all 4 tires, I took it out for a spin. the brakes don't NEED to be pumped but it still goes just about to the floor before I get any pressure. Its not exactly confidence-inspiring but its better. So I will try this again to see what happens.

 

[rockcrawler]

when I hit the brakes the idle gets rough.

I'll agree with dgangle - Brake booster, though of course there may be other issues with the brake system as well.

 

[Poser]

I then used a small flat-head screwdriver to turn the adjusters on the cylinders until shoes touched the drums and the tire would not spin. I then backed the adjuster off 3 clicks.

Don’t back the adjuster off that much. Back them off only enough to allow the wheel to rotate.

 

[mtrdrms]

Don’t back the adjuster off that much. Back them off only enough to allow the wheel to rotate.

Got it. It should'nt rotate freely should it? It should only rotate one turn with a good spin of the tire, right?

 

[skintunes]

Yes -a slight drag should me there-before you back off any clicks ch ck your pedal-shoes will shift there seating as you drive . Read his original post Dgango-
things are pretty light here