Author Topic: Brake bleeding issues  (Read 351 times)

Offline MPlayle

Brake bleeding issues
« on: April 13, 2018, 04:18:04 PM »
Starting a separate thread for this one.

I am having difficulty getting a "firm" brake pedal on the Moke.  It is almost all new everything - the only reused part is the proportioning valve on the rear subframe.  I am using braided lines almost everywhere as well - standard rubber flex lines from the front calipers (7.5" disk brakes in front) to the subframe and over the swing arms in the rear.

The issue:
The first pump of the pedal goes most of the way to the floor - to about 1/2" above the floor.  A second pump about 1 second later stops firm about 1" higher.  If I release and wait 5 seconds, the next pump is soft and low again.  While holding, the pedal does not drop.

What I have done:
I have checked for leaks - none found.

I have adjusted the rears many times and have them set correctly - not too loose.

I have bled the system many times - both with a pressure tank arrangement and the old two-man method.  The last time was the two-man method and we did a combination flush & bleed - making sure fluid ran clean and air-free from all corners.

I have verified the rear shoes are fitted correctly.  They came preinstalled as part of the fully built up new rear subframe.  They came with new Mintex shoes (which do not have the large space at the leading edge).

I figured out how to tell if the Mintex shoes are installed "correctly" based on the different shaped holes in the base plates.  Mine are installed correctly.

Checking with Mike at MiniSport, they have not had reports of issues getting proper pedal feel with the Mintex rear brake shoes.

Dilemma:
Could I be encountering an "expansion" issue with having gone with braided lines everywhere (first pump expands the lines and partially applies brakes, second pump fully applies brakes - long wait allows lines to shrink back)?
Could I still have air in the system?
Are the Mintex shoes made wrong and the insufficient leading edge space not permitting proper adjustment?

I have another set of standard rear brake shoes ordered and due next week to see if it is the leading edges making the difference.

I am beginning to get frustrated as I want to start driving the Moke.

Suggestions?


Offline 94touring

Re: Brake bleeding issues
« Reply #1 on: April 13, 2018, 05:08:34 PM »
Master arm travel?

Offline MiniDave

Re: Brake bleeding issues
« Reply #2 on: April 13, 2018, 05:25:17 PM »
I don't think it's the shoes, and I really don't think it's expansion of the brake lines.

Normally I would say rear brake adjustment, because anytime I've has the symptoms you describe of the first push going down so far and the second push coming up a bunch, that's due to the shoes not being correctly adjusted, and adjusting them fixed it. But you describing the mush after it sits makes me wonder if it's getting air back into the system, and the only logical place that can happen is the master cylinder.

Good luck Michael, I know this is frustrating but it's brakes, so they have to be right.

When I did Stan's car I had noticeable leakage where the hose attached to the calipers....could not get all the air bled out because it would suck it back in again.......after I got that sorted I found the rear shoes weren't adjusted right, so after I did them the pedal came up the way it should. Sometimes you'll get a low pedal like that because the shoes need to bed into the drums, and 100 miles of driving coupled with another brake adjustment takes care of it.

One thing to try, if you pull the handbrake on hard, do you get a higher pedal on the first push? If so that means rear shoes need bedding in, if not then it's something else and you can leave the rears alone.
1989 Cooper Racing Green
2009 Clubman S
1969 Jaguar XK-E FHC
2004 Audi Allroad 2.7 TT

Offline BruceK

Re: Brake bleeding issues
« Reply #3 on: April 13, 2018, 05:39:26 PM »
Is it possibly the master cylinder?   It would sure be whole a bunch of no-fun, but is it possible to swap out the brake MC with the clutch MC to see what happens? 

Or try an old brake MC?
1988 Austin Mini
2002 MINI Cooper S
2007 Triumph Bonneville

Offline MiniDave

Re: Brake bleeding issues
« Reply #4 on: April 13, 2018, 05:49:20 PM »
Brake master has a check valve in it that clutch master doesn't have, they don't interchange.
1989 Cooper Racing Green
2009 Clubman S
1969 Jaguar XK-E FHC
2004 Audi Allroad 2.7 TT

Offline BruceK

Re: Brake bleeding issues
« Reply #5 on: April 13, 2018, 05:52:49 PM »
I know they are different, but could it be done as test to see if a firm pedal can be maintained?
1988 Austin Mini
2002 MINI Cooper S
2007 Triumph Bonneville

Offline 94touring

Re: Brake bleeding issues
« Reply #6 on: April 13, 2018, 06:18:05 PM »
Doesn't take much in arm travel to screw up the pressure.  A worn pin on the pedal will create low pressure.

Offline MPlayle

Re: Brake bleeding issues
« Reply #7 on: April 13, 2018, 09:28:15 PM »
New master cylinders, new clevis pins, new lines, new fronts, new rears, etc.  As stated before, the only thing reused was the proportioning valve on the rear subframe.

I will try Dave's suggestion regarding pedal feel with the handbrake on.

I made sure the master height was also set up to be sure it would have full travel and release pressure properly.

I cannot try the old brake master - it turned out to have a pin-hole leak in the bottom of the reservoir that went undetected due to the gunk and paint it was covered in.  I found the leak when I cleaned it off using a wire wheel.

I've traced the system front to rear looking for any leaks and all is dry.  I did have some leaking at the caliper hose connections to the front subframe, but now have those fixed.

I am going to try bleeding them again tomorrow with a friend's help.


Offline jeff10049

Re: Brake bleeding issues
« Reply #8 on: April 13, 2018, 11:44:34 PM »
sometimes bleeding the rears with the handbrake on can help, I know you said the rears are adjusted right but like Dave said my need to drive it some.
 This really sound like an adjustment issue maybe adjust them too tight, like to where you can just turn the wheel and then bleed them stomp on the pedal a few times after bleeding and see if they are still tight sometimes that helps center the shoes you might think you have the adjustment right but they are actually loose and moving too far causing the low pedal.

Offline BruceK

Re: Brake bleeding issues
« Reply #9 on: April 14, 2018, 12:14:20 PM »
My thoughts keep turning to the brake MC.   I realize it is new, but what if there was a defect or a nick in the rubber seals?  It might behave like you are seeing.

...I cannot try the old brake master - it turned out to have a pin-hole leak in the bottom of the reservoir that went undetected due to the gunk and paint it was covered in.  I found the leak when I cleaned it off using a wire wheel.


If you suspect the new brake MC as the problem, you could simply solder the pinhole in the bottom of the old brake MC and test install it to see if you still have the same problem. 

1988 Austin Mini
2002 MINI Cooper S
2007 Triumph Bonneville

Offline MPlayle

Re: Brake bleeding issues
« Reply #10 on: April 14, 2018, 09:25:50 PM »
I have not done a test drive since working on the brakes a bit today, but static testing it seems a bit improved.

The first test I did was what Dave suggested about trying with the rear set slightly tight and the handbrake engaged.  The pedal was still soft on the first push.  However, upon rechecking the rear adjustments after several rounds of "set the hand brake, push the pedal several times, release the hand brake, push the pedal several times, repeat", the rears were loose again.  So I re-adjusted the rear and repeated Dave's test - still a soft first push.  After a few re-adjust and retest rounds, the rears were staying at the set tightness at the end of a round as the beginning of the round.

Then my friend showed up and we bled the system.  We got some air out of the fronts and that helped a bit.  It is not as soft on the first push, but still softer than I feel they ought to be.

I am suspecting Dave may be correct in needing a bit of drive time on all the new components to bed them in as well as there having been some air still in the system.

I will recheck everything after a bit of driving and post the results.


Offline tsumini

Re: Brake bleeding issues
« Reply #11 on: April 14, 2018, 10:16:50 PM »
I would guess you still have air somewhere. Soft initial pedal suggests air. I helped my son bleed hius race car system seem hunderd times. Invariable soft pedal was either an air bubble or leak. Hissing indicates air in system also.

Offline MPlayle

Re: Brake bleeding issues
« Reply #12 on: April 20, 2018, 12:40:29 PM »
The replacement rear brake shoes came in.  They also have the friction material going all the way to the end of the metal frame on the leading edge instead of having the gap.  A bit of research found that the "budget" shoes are also made by Mintex.

Anyone have an idea of when/why they stopped leaving the gap of the leading edge and went to running the friction material all the way to both ends?

I am debating whether to figure out how to remove some of the friction material at the leading edge to recreate the original style offset and try.


Offline MiniDave

Re: Brake bleeding issues
« Reply #13 on: April 20, 2018, 03:23:54 PM »
Well, you have two sets, why not modify one set and see what happens? take a cut off wheel and cut a groove across the friction material, down to the backing or metal shoe then take a cold chisel and knock the end bit off. Then chamfer the edge where you cut it off to a nice 45* angle.....
1989 Cooper Racing Green
2009 Clubman S
1969 Jaguar XK-E FHC
2004 Audi Allroad 2.7 TT

Offline BruceK

Re: Brake bleeding issues
« Reply #14 on: April 20, 2018, 04:09:58 PM »
Well, you have two sets, why not modify one set and see what happens? take a cut off wheel and cut a groove across the friction material, down to the backing or metal shoe then take a cold chisel and knock the end bit off. Then chamfer the edge where you cut it off to a nice 45* angle.....

Wearing appropriate breathing protection I hope.     
1988 Austin Mini
2002 MINI Cooper S
2007 Triumph Bonneville

Offline MiniDave

Re: Brake bleeding issues
« Reply #15 on: April 20, 2018, 04:15:32 PM »
I didn't think they made them with asbestos anymore?
1989 Cooper Racing Green
2009 Clubman S
1969 Jaguar XK-E FHC
2004 Audi Allroad 2.7 TT

Offline MPlayle

Re: Brake bleeding issues
« Reply #16 on: April 20, 2018, 04:22:37 PM »
I am already going to do that.  I used a coping saw (hand saw) to cut off what seems to be the amount of extra material on the leading edge. 

I still need to taper the cut edges.  Thanks for reminding me to do that.


Offline BruceK

Re: Brake bleeding issues
« Reply #17 on: April 20, 2018, 07:51:48 PM »
I didn't think they made them with asbestos anymore?

Right.  But all the small metallic particles and binding agents released by disturbing the material would be the concern.
1988 Austin Mini
2002 MINI Cooper S
2007 Triumph Bonneville

Offline MPlayle

Re: Brake bleeding issues
« Reply #18 on: April 21, 2018, 08:37:09 PM »
Well, I swapped the brake shoes and checked the pedal.  No real difference after all.  I bled the system and got some more air out of the rears, but that did also did not help much.

I had also made some more adjustment to the carb and took it out for a run to see how the temperature responded and what the plugs looked like.  It was a bit better - did not get quite as hot.  Made a bit more adjustment and the lift-pin test seemed to finally be what it should - slight rev, then plateau.  Second drive test was much better, but still warmer than it should be. Revamping the cooling system should finish that up.

The new radiator arrives Monday.  Then I get to revamp with a new thermostat, the new radiator, new water pump and smaller water pump pulley.



Offline jeff10049

Re: Brake bleeding issues
« Reply #19 on: April 23, 2018, 12:31:21 AM »
what size bore in the master same as the old one?  Mini drums can really kick your ass on adjustment tighten the adjusters until they stop then bleed it one more time if the pedal is good. Then back off the adjusters evenly until it has light drag.

If the pedal is soft with the adjusters cranked up tight either still have air or a bad master is all can think of.

Offline MPlayle

Re: Brake bleeding issues
« Reply #20 on: April 23, 2018, 10:22:11 AM »
The original was a "bean can" single line system.  I went with the plastic reservoir replacement single line master.

I suspect I still have a leak somewhere in both rears as there was a little bit of fluid on the bottom of each back plate when I swapped the shoes.  I had previously check the piston ends of both slaves and they were dry.  I'll scrutinize the hard line attachment and the bleed screws this week.


Offline Jimini II

Re: Brake bleeding issues
« Reply #21 on: April 23, 2018, 01:57:07 PM »
Bleed the whole system again from every connection front to rear starting at the master cylinder preferably with the Moke as high as you can get it in the rear. I had this same issue with my old Moke and it was air in the system. In case you don't know bleed the rears slowly otherwise the valve will block the flow.
I have used the Mintex rears with no issues.