Soft Brakes

[johnggreen]

The brakes on my Bravo have never been what I would call "strong", but recently they seem to be getting weaker. The first time I apply them after start up, they take a couple of seconds to seem to activate and then only with an undue amount of pedal pressure. Even after being used during taxi, same feeling that they lag in operation. They don't bleed down with pressure but it takes more pedal travel than I think is appropriate and more pedal pressure.

I have asked my mechanic to read up in the service/maintenance manual and then let's tackle the issue. His first guess is that both master cylinders simply need new O rings.

Surely, someone has experienced this before. Any "been there", "done that" insight would be appreciated.

Jgreen

[KSMooniac]

I think your mechanic is likely correct. Not sure it is O-ring or not, but Maxwell told me about some sort of washer/seal thing inside the master cylinders that gets old and passes fluid, leading to spongy brakes. I'm living with mine for now b/c R&R is a PITA.

[johnggreen]

KS,

Thanks. Kevin, the mechanic says that the brakes will get spongy without having to be "pumped up" which goes along with what you say. PITA or not, I want brakes! Honestly, I suspect that it takes three plus inches of pedal travel to get any braking action. Anymore "slack" and I'm going to have to run into something to stop.

Jgreen

[29-0363]

My reply is based on the assumption you have inner gear doors. On my previous Ovation, my mechanic, his sidekick and I spent 2 full days troubleshooting including bleeding multiple times, removing cylinders and replacing seals etc, until I actually got down and watched the movement of the caliper and found the cause (the problem appeared at the end of an Annual inspection).

Has there been any recent maintenance on the U/C recently, particularly removal of the gear doors? It is possible to refit the inner gear door in a way that interferes with the disc caliper. The door pressure against the caliper will increase the clearance between the disk and the brake pads, requiring a number of applications to get the correct pedal "height".

Check the gaps between the disc and brake pad - the clearance should be minimal either side of the disc, and if that's what you have, look elsewhere, but if you do see a gap on one side and no gap on the other, operate the brakes with an observer. With the brakes hard on, release and watch the brake pads relax. If a gap reappears, look to find out what is causing it - in my case it was the improperly fitted inner gear door.

[Awful_Charlie]

Have you flushed the brake fluid recently? There is a FAQ on the Mooney site http://www.mooney.com/service-support/faq.html (last entry at the bottom of the page) about the fluid getting thick. At each annual I make the point of putting a couple of pumps from each toe brake through with the bleed nipple open to draw some fresh from the resovoir, and then top up. It doesn't take long (if there are two of you)

[johnggreen]

All good points. I should add that one brake went soft and we had to add fluid about three weeks ago on that one side. Don't have a clue as to where the fluid went. Once filled, we were back to two "soft" brakes.

Jgreen

[John Pleisse]

KS,

Thanks. Kevin, the mechanic says that the brakes will get spongy without having to be "pumped up" which goes along with what you say. PITA or not, I want brakes! Honestly, I suspect that it takes three plus inches of pedal travel to get any braking action. Anymore "slack" and I'm going to have to run into something to stop.

Jgreen

[John Pleisse]

Wait....3 inches of travel? That's a lot.

[N601RX]

I have a couple of late model Master Cylinders if a new seal kit doesn't fix yours.

[Seth]

When I test flew a different Mooney Missile than the one I purchased I was amazed how much pressure I had to generate to stop the aircraft on landing and during runup. I was worried that it was indicative of the power of the aircraft not matching up with the brakes. I was incorrect. My Missile does not have this problem and I let the owner (now former owner) of the other aircraft know as well as the mechanics that took care of it so that they could look into the matter.

It sounds VERY similar to yours - not that there is no braking action, but that you have to REALLY squeeze those brakes with a lot of pressure to get proper stopping action.

So I have heard of this similar issue before, but I do not have a fix. I would defer to the others that have made reccomendations.

Take care,

-Seth

[johnggreen]

Soft Brakes Solution,

Took the Bravo to the shop Monday. My mechanic said he would check everything, but would first flush the lines. He had seen one other instance of congealed brake fluid in a Mooney. Checked the fluid and it looked good so he rebuilt the master cylinders. When he put it back together the brakes were still "sluggish" and slow in releasing so he flushed the lines. PROBLEM SOLVED. There was a section he said in the metal lines where the fluid was like jello. He has only seen this in his 20 years on another Mooney and a Cessna 206 that sat under a shed for 20 years; that's another story but the family finally sold it, 800TT, for $30m.

Anyway, the congealed fluid might have been the only real problem. From now on, every second annual, we are flushing the Bravo's brake lines.

Jgreen

[fantom]

Thanks for the update, John.

I've been told this a somewhat common issue in newer Mooney's with dual brakes, especially J's. I've had the same problem and now flush the brakes every second or third annual. No more problems.

Sorry I didn't read your earlier post.

[thinwing]

My Bravos braking ,though shows no softness ,spongyness or excessive pedal travel are from the start of my ownership are frankly not the greatest...i have assumed as gross weight increased these brakes are at there maximum compared to a 4 puck cleveland found on a Baron for example...those you could really lockup...not on my Bravo...k

[johnggreen]

Thinwing,

I will agree. Even after rebuilding the master cylinders and completely flushing the system, the braking action is marginal at best.

But then, I'm not using this airplane for STOL work, thank goodness. I've got a good amount of legitimate soft, short and rough field experience with everything from Cubs to Helio Couriers so I'm certainly not a virgin to that environment. I have never flown anything but the long body Mooneys, Ovations and Bravos, but these airplanes have no business on anything approaching an "unimproved" runway. A couple of months ago, I flew into a small paved airport in Arkansas and didn't notice a drop off on the taxiway to the tie down area. When it "dropped off", about a four inch change of elevation in the taxiway, the only thing that prevented damage to the tail was the rear tie down which took the energy of the impact.

Jgreen

[AndyFromCB]

Soft Brakes Solution,

Took the Bravo to the shop Monday. My mechanic said he would check everything, but would first flush the lines. He had seen one other instance of congealed brake fluid in a Mooney. Checked the fluid and it looked good so he rebuilt the master cylinders. When he put it back together the brakes were still "sluggish" and slow in releasing so he flushed the lines. PROBLEM SOLVED. There was a section he said in the metal lines where the fluid was like jello. He has only seen this in his 20 years on another Mooney and a Cessna 206 that sat under a shed for 20 years; that's another story but the family finally sold it, 800TT, for $30m.

Anyway, the congealed fluid might have been the only real problem. From now on, every second annual, we are flushing the Bravo's brake lines.

Jgreen

Same thing here. Here is quote from my MSC mechanic doing my annual:

When we went to reseal the right brake caliper we found heavy sludge, almost like syrup oozing from the right brake line, we feel we need to reseal the right master cylinder and do a system flush of the right side to complete this repair properly. Please advise with approval at your convenience.

[fantom]

A word to the wise....it's a common problem especially if you have brakes on the passenger side.

Flush your brakes every two or three years.