Brake Problem

aussieaviator · Post by **aussieaviator** » Fri Nov 14, 2008 3:18 pm

The left side brakes on my M5 are draging causing abnormal wear on the pads. I have removed the calipers and cleaned them, they slide freely but you can't push the pistons back in even using a clamp once they are reinstalled and the lines connected. It appears the the brake fluid is not returning to the master cylinder, almost like there is a one way valve in the line ( of course there isn't). It seems to me that the problen lies within the master cylinder. Has anyone experienced this problem, does anyone have a drawing of the workings of the master cylinder?

aero101 · Post by **aero101** » Sat Nov 15, 2008 12:40 pm

Sounds like you've either got a kinked or deteriorated brake line or the master cylinder overfilled and vent hole blocked solid? I assume that the piston does slide freely prior to hooking up the brake line at the caliper? If you open the bleeder on the caliper will the piston compress? If not the problem is with the caliper, which is most likely? Corrosion or rolled packing on the piston or badly worn housing allowing piston to cock? Good luck!

aussieaviator · Post by **aussieaviator** » Sat Nov 15, 2008 6:04 pm

Hi Jim, thanks for your reply. The vent hole in the master cylinder is clear. The piston in the caliper has been removed, new seals fitted and slides freely until the brake line is connected. Pushing on the piston even using a clamp does not result in any fluid returning to the master cylinder so maybe there is a blockage in that area somewhere. I supose I'm trying to avoid removing the master cylinder.

a64pilot · Post by **a64pilot** » Sat Nov 15, 2008 6:50 pm

Maybe the master cylinder actuation rod isn't returning all of the way?

YELLOWMAULE · Post by **YELLOWMAULE** » Mon Nov 17, 2008 12:40 pm

Do you have dual brakes or single? Might be the shuttle valve if you have the dual.

a64pilot · Post by **a64pilot** » Mon Nov 17, 2008 4:56 pm

YELLOWMAULE wrote:Do you have dual brakes or single? Might be the shuttle valve if you have the dual.

Bet that's it, I've seen it before on a helicopter, but I forgot, it's been a while

aussieaviator · Post by **aussieaviator** » Mon Nov 17, 2008 5:35 pm

Do you mean dual caliper or dual control? I have both. What and where is this shuttle valve? Thanks guys.

UP-M5 · Post by **UP-M5** » Mon Nov 17, 2008 6:06 pm

i had this same problem. it was a bent actuating rod on the master cylinder that would not return all the way. so it always kept slight pressure on the brakes on the left side. my brakes would get really hot taxiing all the way around lake hood, but i could usually reach down and yank on the pedal and it would release- until i used them again.
it finally snapped in half on me while taxiing. new master cylinder, and all is well. its nothing $400 won't fix.
now if that rod had broken on rollout on the strip in the talkeetna mountains that i was landing on.... there wouldn't have been anything left to fix.

a64pilot · Post by **a64pilot** » Tue Nov 18, 2008 8:25 am

aussieaviator wrote:Do you mean dual caliper or dual control? I have both. What and where is this shuttle valve? Thanks guys.

Not sure where it is on a Maule, but there is a valve that will "shuttle" back and forth to allow either set of brakes to apply pressure to the calipers. It's my understanding that without this valve, fluid from one set of master cylinders would simply flow into the other master cylinders instead of applying pressure to the brakes, so this valve has to "shuttle" back and forth to keep the master cylinders separate from each other.
Should be as easy as following the brake lines from the master cylinder to find.

YELLOWMAULE · Post by **YELLOWMAULE** » Tue Nov 18, 2008 12:23 pm

Pull the floor boards and look for the common crossover on the brakelines. It'll be self evident once you get in there and follow the lines.
In order to properly bleed these it helps to have someone with you but if you don't, I use an oil can with a pump like an old fashioned oiler. A long clear plastic hose (3' or so) which I fix to the bleed screw on the bottom of the caliper (double puck Clevelands) this allows me to pump fluid into the bottom of the brake line in a controlled manner and keep my head under the panel to monitor the bleed hole in the top of the master cyl. You'll have to bleed the left brake, left master cyl. Close the bleed screw on the master cyl., push on the right side, left master (pedal) to move the shuttle valve and proceed to bleed that master cyl. go back and forth until you gat all of the air out and the brakes are firm. It'll take some practice but it gets pretty easy after a while. I have to do it twice a year. Stuff a lot of paper towels around the master cylinders to prevent the 5606 from getting all through the belly.
Kurt

aussieaviator · Post by **aussieaviator** » Tue Nov 18, 2008 1:46 pm

Thanks to all for your help and suggestions, guess its time to get my hands dirty.
Brian

MauleMedic · Post by **MauleMedic** » Fri Nov 21, 2008 4:22 pm

One other place to check will be the compensator seal in the master cylinder for that side. I've seen these either get put in wrong and stop working altogether or, as has been mentioned before, the cylinder rod isn't returning completely and allowing that port to open up.

Basically what should happen is that once the rod gets pushed down slightly on the master cylinder the compensator port closes and prevents any new fluid from entering the system from the reservoir (and vice versa, no fluid from the system getting squirted up into the reservoir - the reservoir is usually an integral part of the pilot side master cylinder).

You can test the compensator port by pumping fluid back up the system and making sure that it makes it completely into the reservoir. Then try stepping on the brake and try pumping again - you should not be able to pump any in the second time.

From the description - I would certainly check out the internal compensator ports and seals on the pilot side Cleveland master cylinder. For some reason I can't place where the shuttle valve is, if there even is one on the Maule, but, as has been said, if there is one I'd check there too.

aussieaviator · Post by **aussieaviator** » Thu Dec 04, 2008 10:35 pm

Well, I finally found time to check the master cylinder and found the problem. The cap on the top of the master cylinder is held in by a circlip and has a bronze bush in the center through which the piston rod slides. This bush had come lose in the top cap and was able to drop partly inside the cap thus restricting the up travel of the piston rod and restricting the return of brake fluid to the can. The solution was to refit the bush and crimp it so that it couldn't fall back in again, reassemble and bleed. Problem solved.
Thanks to all who offered suggestions and advice,
Brian

Brake Problem

Brake Problem

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