Soft Brakes

[Rookie]

My right brake does not hold the plane when doing the run up!

If the caliper was not holding the pressure created by the master cylinder, you would have an external leak? Rite?

It there anyone that knows a Pressure the master cylinder should make?

Do they make a master cylinder rebuild kit?

 

Thanks,

[carusoam]

Air bubbles in the line have a tendency to compress and make the brakes less effective.

If the bubble is in one line and not the other, an imbalance in braking might occur...

 

If this is the source of your issue, there are threads here that talk about how to remove old jelled brake fluid, and how to bleed the brakes.

How does that sound?

PP thoughts only, not a mechanic....

Best regards,

-a-

[Shadrach]

As Anthony says, likely air in the line. If there is no hydraulic fluid leaking in the system, then there must be air in the line. Try reverse bleeding from the caliper (pushing fluid into the system) if unable to clear the system.

[Skates97]

The guy I bought my plane from was having problems with soft brakes. He tried many different things and was still getting air in the system. Finally ended up replacing the lines above the calipers. They weren't leaking fluid, but they were letting air into the line. That was a couple years ago, the brakes are still working great today.

 

[peevee]

29 minutes ago, Shadrach said:

As Anthony says, likely air in the line. If there is no hydraulic fluid leaking in the system, then there must be air in the line. Try reverse bleeding from the caliper (pushing fluid into the system) if unable to clear the system.

I've been meaning to try this. Our right brake goes soft and has to be pumped a few times on final to get pedal pressure back. I have also assumed air in the lines.

[Rookie]

I've not tried to pump them, I'll try that. Then bleed them.

Brake fluid looks good.

[rgpilot]

It's best to bleed Mooney brakes from the bottom by pumping fluid into the caliper and opening the reservoir at the top. First drain some fluid out of the bottom to purge calipers of old fluid.

[neilpilot]

Any idea when, if ever, the hydraulic fluid was flushed?  Old brake fluid, especially near the brake caliper, can become very viscous with time.  I cured weak brakes on my 64E with new fluid and bleeding, and no mechanical work done to the calipers or master cylinder.  This concurs with rgpilot's suggestion

[Rookie]

29 minutes ago, neilpilot said:

Any idea when, if ever, the hydraulic fluid was flushed?  Old brake fluid, especially near the brake caliper, can become very viscous with time.  I cured weak brakes on my 64E with new fluid and bleeding, and no mechanical work done to the calipers or master cylinder.  This concurs with rgpilot's suggestion

I'll try to flush and bleed this week. 

[Yetti]

Start with the basics...  How are your pads?  How is the brake fluid level?  A leak of the master cylinder would be under the Pilots feet.  To bleed get an ole timy pump oil can and pump about 30 times from the caliper bleed screw.   watch the reservoir level. watch for bubbles. A turkey baster or one of those Flavor injector syringes works for pulling the fluid out of the reservoir.

[MooneyMitch]

My suggestion, which follows along with others, replace brake fluid and do that from calipers up to reservoir.

At some point (2 years ?), the fluid begins to become less effective.

i experienced soft braking action on my former Mooney, changed fluid and oh my, problem solved.

Best to you 

[75_M20F]

Removed all my old fluid out of the resavoir with a turkey baster... refilled with new, bled brakes till all old was gone..... brakes worked a lot better 

[Rookie]

6 hours ago, neilpilot said:

Any idea when, if ever, the hydraulic fluid was flushed?  Old brake fluid, especially near the brake caliper, can become very viscous with time.  I cured weak brakes on my 64E with new fluid and bleeding, and no mechanical work done to the calipers or master cylinder.  This concurs with rgpilot's suggestion

Yea the '13 annual it says the fluid was replaced and bled.

 

[neilpilot]

46 minutes ago, Rookie said:

Yea the '13 annual it says the fluid was replaced and bled.

 

Well if the fluid is only 3-4 years old, and the flush included the lines through the calipers, then your fluid should not be causing any issues.

[Bartman]

Had mine serviced a few years ago.  Same complaint as Rookie.  Shop bled the entire system, including he parking brake which did not work right, and said the old fluid was very very thick.  May have been the original fluid from 1977 as far as I know, but has worked fine the past 8 years or so including the parking brake which I almost never use except to check operation occasionally.

[N201MKTurbo]

If your brakes are soft, pump them when you are at altitude (you don't have anything else to do) it will often stiffen them up. It is free, what do you have to lose?

[Rookie]

So when I tried to pump up the right brake there was nothing. Pedal goes all the way to the stop.

So I opened the bleed valve. Brake fluid dripped out. It was a little darker than normal.

Closed bleed off tried to pump brakes, nothing. 

My A&P pushed some fluid from caliper up.

I was watching reservoir and the air bubble came out.

Full break peddle, no more turning left!

Thanks Everyone for Ya'll help!!

 

 

[peevee]

tried to bleed ours, I used to have a mightyvac that could pressure and vacuum, bought another one. Guess the new ones only suck, plus with the inner gear doors and lack of access it just wasn't happening. I'll get someone to do it.