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BN2 Master Cylinder

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This has helped me a lot. I have also been bleeding my system, way too much, trying to fix the double pump issue. Then figured it was adjustment rather than air in the system. I don't have to double pump anymore. I do still have a softer pedal than I think it should be, but can live with that for now. After driving it a while I will try a bit more bleeding. Maybe the tilt method will help.
 
kodpkd said:
I think you will succeed.
Spongy pedal = air
Double pump = adjustment.
Click to expand...
Well, just finished doing everything possible to fix this problem so here's where I am - have to double or triple pump to get good brakes.
I have bled this system so many times I have lost count. Tried the "disruptive bleed" system, reverse bleed front wheel cylinders, pressure
bleed with a Motive pressure bleeder, gravity bleed, only thing I haven't bled is me so far ! Pedal is not spongy, just have to pump it
two or three times.

I have adjusted the brakes to the point where you can just hear a shoe/s dragging, think any more aggressive would cause too much
friction and thus heat. Have not changed brake shoes as ones on the car for past several years have plenty of lining left.

Guess I just need to adjust the brakes even more ?
 
Have you fit the shoes to the drums OFF the car to see if the shoes match the curve of the drum? That is the only thing I can think of that is causing the double pump. I thought I had the rear to tight, took it for a test drive, then felt the drums, they were still cool. so they weren't to tight. If you are getting a solid pedal that's a good thing, you don't have air in the system. The double pump is because there is slack somewhere in the mechanics of the system. Is the adjuster on the rears set to the correct 1/4 turn? You can feel as you turn the adjuster when it's at the loose spot every 1/4 turn. The loose spot is correct when it's on the flat.
 
I'll double check the shoes but should be okay as been on the car for some time and no previous problems like not having. So when you turn
that adjuster you can feel it go looser when on the flat and then as you continue to turn it will go tight again. Need to check to make sure I
have them set correctly re the flat spot. The saga continues !!!
 
Don't know if this has been broached before, but have you watched the level in the reservoir as you pump-up the pedal? This is a classic symptom of the fill/return line to the reservoir not getting sealed off when the pedal is pressed.

Roger Moment's new book has a photo of a 100 M/C that's been sliced lengthwise; it's pretty interesting (I'd post a shot here but it's copyrighted).
 
It can if the line isn't properly sealed-off when you press the pedal. The M/C in the 6-cyl cars has a spring-loaded small seal at the front of the cylinder, the 100 M/C has a different mechanism, as far as I can tell the line from the reservoir gets sealed-off by the main piston,
 
So, when I am pumping the brake pedal the brake fluid in the reservoir should be going down and then back up when brakes released? I would need to look as honestly never have when pumping the brake pedal. I did put in a new TRW master cylinder that has been bench bled.
 
Not when 'pumping;' have someone press the brake pedal, somewhat slowly, while you watch the level in the reservoir. If the level rises perceptibly then the M/C isn't sealing off the line to the reservoir and, since the fluid is taking the easy way out it's not expanding the wheel cylinders and engaging the shoes against the drums. When you let up on the brake pedal, heavy springs retract the shoes and cylinders and push some fluid back into the M/C and the piston in the M/C pushes some fluid back into the reservoir.

My understanding, from Roger's book is the piston slides through a fixed (O-ring) seal, unlike the 6-cyl M/Cs where the seal is fixed to the piston. In the retracted (pedal up) position there are two bleed screws that allow some fluid back into the reservoir (but not when applying brakes). There is a weird-looking 'waffle washer,' with raised bumps that allows fluid from the reservoir to be pushed to the wheel cylinders when braking. All-in-all a pretty awkward arrangement; to me, the later-style 'foot valve' is more practical, and certainly easier to understand its functioning. Using a fixed O-ring to make the seal instead of the cup-type seal on the piston doesn't seem like a particularly good design IMO.
 
Latest update on my brake saga ! Checked the MC fluid line as Bob suggested above and virtually no change when pressing on the brake
pedal so believe I am okay there. I have adjusted the rear brakes as tight as I thought possible and after taking out for a drive and using the brakes half a dozen times, minor increase in temp on the drum. Prior to leaving about mid 60's and after returning, about 70 degrees so think that
is reasonable amount of heating up. It's about 55 degrees outside right now.

As to my pedal, if I press down or pump once, marginal pedal, pump twice, good pedal. Guess I will try adjusting the rears even more.

I have also cracked the connection at the front brake cross over line between the two cylinders ( while under pressure) trying to make
sure a bubble is not trapped there. Did not crack any of the other hard brake line connections other than right rear where I replaced
that hard line.
 
I went through the same thing. I thought I was going too tight on the rear adjuster. Make sure when you go tight, so the drum doesn't move, that your adjuster is really at the flat spot. I move the wrench back and forth about 10* until I find the flat spot and see if the drum really is tight, THEN go one flat looser.
I would also do the same adjustment on the fronts, except you don't have 4 flat spots,,,,, you have lots of bumps on the adjuster. Make sure those are also on the little detents.
 
Just came back from a quick run,maybe 10 miles, and obviously got the left rear too tight as all other drums running in the 70's and
that one just over 100 degrees at 102. Thought I could hear it so need to back one down a bit !
 
It kind of depends on how much braking you did. 100* isn't, that, hot, but when not braking you probably shouldn't hear the brakes.
 
Adjusted that left rear and now all drums at about 102 - 104 after a brisk drive with a lot of braking. Unfortunately,
all requiring one pump and then I have decent brakes. I am just dumb founded or maybe should just say dumb as
cannot figure out what is wrong ! Going to call it a day.
 
Looking at the front brakes. Are all four threads on the back of the two cylinders the same? The front cylinder has the main hose from the reservoir and the small hose to the other cylinder,,,,, can you reverse these two hoses. Also,, the rear cylinder has the bleeder and the other end of the small hose. Just looking at how fluid/air runs through the system, it would make sense if these were reversed for bleeding.
I don't think this would fix the double pump but might help for bleeding.
 
Hey Kevin,
I had thought of that idea also but no one has ever recommended trying that and the way the cross over hard pipe between the two brake cylinders is bent, do not believe it would reach anyway. The outlet holes are the same size.

So almost no pedal on first pump but pretty good on second pump. Enough to make an emergency stop as well as typical stops. I haven't tried the front brakes again as far as adjusting even tighter but might do that later today.
Thanks
Mike
 
Depending on how you are bleeding these brakes air can stay stuck in certain parts of the pipes,
when i bleed brakes (two man job) one sits in the car, double pump the pedal and hold the pressure on,
the second guy releases the blead nipple closest to the the master cylinder,
the peadal will go to the floor, first guy shouts down, second guy locks the nipple,
again double pump the peadal to get the pressure up and repeat,
this way you will be forcing, under pressure any stuborn air in the pipes
This will force the air along the pipe, put plenty effort into the pedal.
Then repeat at the next closest and so on until all nipples have been bled.
 
Thought I would post a picture of the right rear brake set up. I have read several times to make sure to have the shoes installed
correctly and believe these are done right but with this on going problem figured might as well post a pic to confirm.

I am going to start trouble shooting the new brake cylinders sourced from Moss to make sure there are no issues with them. That's
when my problems started after replacing the left rear. Shows my wrench used to adjust the brakes
 

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They look good,,,, exactly like mine. I think we talked about this, but you checked the shoes against the drum to be sure the arches match?
 
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