Re: Still have front brake issues!

steve.nospam.ballantyne@xxxxxxxxx wrote:
Back in December I had opened a dialogue about some rather strange
brake issues I was having, and yesterday I did a bit more work which
didn't really seem to help.

Before I did anything, I replaced the stop plate behind the pedals
because I could see the brake pedal was coming back way too far (and
was probably injecting air!).


Impossible. The master cylinder piston travels all the way to the rear of the cylinder when the pedal is released. Pulling the pedal even further away from the master will do nothing, it is not connected to the master cylinder piston. It only has a push rod, actuating the piston. It cannot pull the piston back. The internal springs inside the master will take care of pushing the pistons back.

That said, the pedal pushrod has to be adjusted so that it FULLY disengages from the master cylinder when the pedal is released. There needs to be about 1mm of free play. It's damn near impossible to measure, but as long as you have some noticeable free play, you are ok.
If there's no free play, it means the pedal (push rod) is preventing the master piston(s) from moving back to their resting position. That is BAD. The piston need free, unobstructed travel to it's fully extended position, in order to open a passage for pressure release/new fluid to go in from the reservoir. If it can't move all the way back, teh brakes will act weird, and probably drag, even lock up when you least want them to.



Then I pulled off the front tires, and pulled off the hubs to inspect
the parts. It looks like the wheel cylinders are working just fine.
I also removed the adjusting stars and greased them up, and then
reinstalled everything. Then - adjusted each star on each tire until
it was just starting to drag on the tire. And then of course, rebled
each tire multiple times.

But ... I still have the same problem.


I see one flaw in your procedure above: You need to adjust all brakes from the stars so the drums no longer turn AT ALL. Before doing the same in the rear, you need to disconnect the handbrake cables from the lever end, making sure the levers at the drums are fully relaxed. Then adjust rear shoes so tight you can't turn the drum at all.

Now bleed.

Then adjust shoes again, so that you hear them scrape maybe 1/2 turn of the drum. Test drive, apply brakes going forward and in reverse, then adjust again in the same way.

If you are happy with the foot brakes, then re-attach the handbrake cables. Adjust handbrake lever so the brakes are fully engaged at 5 (five) clicks.



I know I should be adjusted and bleeding the back brakes as well - but
that is going to mean replacing the wheel cylinders, which would lead
to new lines, which might also mean a new MC. I can't do that right
now, so I am avoiding the rear brakes! But that system has never been
opened. It's only ever been the front brakes that I have been playing
with.

Anyone have any ideas for me? :-)

Do the rears. You should start with the wheel furthest from the master cylinder (right rear) and work your way closer.

You MAY be able to bleed the rears through the brake line fitting if the bleeders are broken or stuck. You'll need two people. Only crack the bleeders or line fittings open when someone is applying pressure to the lines. Open them while there's pressure, and close them quick while there's still pressure left (pedal is still on it's way down).

if you like getting messy, I have had good results with 2 people like this: one pumps the pedal, while the other cracks a bleeder open and covers the tip with his finger. Finger is acting as a valve, allowing high pressure fluid to squirt out (everywhere, uncontrollably), but won't allow air in. All you need to do is keep your finger pressed hard against the bleeder. When done, tighten the bleeder down and remove finger.


Sometimes you can chase small bubbles further down the line by rapidly tapping on the brake pedal several times. Not depressing the pedal much at all, just surface tapping as quick as you can. Then one big pump, open bleeder while pressure is up, and close before the pedal hits floor.

On old, used masters, never let the pedal go all the way to the floor. It may get the master cylinder piston(s) get stuck at the end of their travel, dud to rust inside the cylinder.

Jan
.

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