Brakes need help.

[pontus]

Hello:

I could use some help/member experience. I have a 76 F model. The mechanic advised the brakes were soft and needed to be bled. After bleeding they were still soft. He then rebuilt the masters and the calipers and the park brake seals and new pads.  The brakes would not hold for run-up. He suggested change the masters to new models.  We did, the brakes are better but not great. He seemed to take a long time bleeding because of the orientation of the masters. Lots of places for air to hide. The right brake is still a little soft but does work. Should I expect the brakes to be super firm or not? Should the park break hold for run-up? Is this common for Mooney’s to be difficult to bleed and have soft brakes? Is there something else I can try?  

[clh]

How old are your brake hoses?  Mechanic should have already looked at that.  My brakes are pretty firm.

[jax88]

The brakes on my 75 F hold just fine, including the parking brake.

[Piloto]

My experience with the brakes is that if it holds on run-up don't fix it, leave it alone until it leaks or need to pump the pedal. Best way to bleed them is to pump a 1/2 pint of the fluid from the caliper while draining the excess at the reservour. Don't bother with pedal pumping to bleed because it will always be spongee.

Jose

 

[KSMooniac]

Were they bled from the bottom-up as Piloto advised?  

[pontus]

They were bled from the caliper nipple up. The hoses were checked. The masters are horizontal and that is one of the problems according the mechanic. Does anyone know of a procedure to follow concernng this model?

Thanks for your suggestions.

[M20G]

If you can disconnect one end of the master cylinders (from the pedal or where it is connected to the airframe ) then you might be able to angle the horizontal master cylinder upwards a bit so that the air will travel up and escape while being pressure blead from the bottom. I will be looking at mine today and know more then. Pat

[N601RX]

Jacking up the front of the plane might help also.  If it has hydraulic flaps they are fed from the same line that comes from the fluid resevor.  There could air in that line getting back into the line that goes to the brakes.

[Dingo]

G’day

Just read your query and I might have the solution if the same has happened to you as it did to me when I first bought my E model 15 years ago, I found the brakes poor and would go to the floor, but if I pumped them fast the brake come up hard and responsive, after a bit of looking around, in a previous bit of work someone had left out the wave washers on the master cylinders ( allowing a little pressure on the cup and not allowing a slow bypass of pressure when the brakes were applied, fast reaction would hold these in place, slow action would allow a slow bypass) found a couple of washers and they’ve been perfect ever since

I’ve always pressure bleed my brakes from the calliper with an oil can. Never any problems

Hope this is helpful, let me know

Cheers

Darren

[scottfromiowa]

Good luck with your brakes.  I had a poor functioning left brake and at annual had tires, brake linings, flexible brake lines and all rubber gaskets in masters replaced at annual...first flight prior to start I notice that my LEFT brake is now perfect...and my right brake is NOT functioning.  My mechanic says that he noticed a little washer (I will call it also a wave washer) was broken...and he didn't replace it.  I phone the Mooney service center (Wilmer) and the mechanic sends me two (2)...they cost $1 dollar a piece...He describes POOR brake function without these in masters and functional.

Waiting for decent weather to take plane over to A&P for install in the right brake....

Make sure these are NOT broken and functioning.  If brakes are realy mushy this might be the problem...

[pontus]

Thanks for the great help;

I have contacted the mechanic and advised him of the suggestions. I also contacted LASAR and their advise was to keep bleeding until its right. I will have the nose tilted up and bleed again. About the washers the masters are new. I will tell him to look at them. I went up 2 days ago and I am certainly not happy with the brakes, especialy after the investment I made in them.By the way this plane is wicked fast.

 

[Alan Fox]

I bleed as follows , Bleed the air from the calipers at the bleeders , than I remove the calipers and pads and leave them hanging from the lines , (do this one caliper at a time) , Have some one in the plane pump the brake until the caliper piston moves out almost to the O ring , Than with a clamp or pliers push the piston all the way back in and repeat about 5 or 6 times....  This will force all the air in the system back out the masters.... Works every time ... Even on pipers!!!