I have posted this on the Socata forum 3 days ago but not one comment after more than 100 views. Support can be very selective there. Maybe here someone has a clue, unfortunately, it is very Socata specific.
“I have a problem with my left break. When I use the break a couple of times the left brake starts to block on its own when taxiing. The breaking power increases the longer I taxi until I have to get out and have to open the relief valve. It has happend 3 times now and only intermittently. There is no corrosion in the breaking piston, the fluid lines, at least the visible ones, look fine. Somehow the fluid cannot return, what could be the cause?”
Thanks Placido
What I have found is that many maintenance shops never bleed the brakes. One shop told me the system never needs bleeding and the fluid is perfect after 30 years…!! You may have debris in there. So I would start by getting a proper service by a new shop.
There is nothing special about the Socata brakes. Like most GA wheels and brakes, they are made by Cleveland. The master cylinders are made by an obscure French company here which makes bits for homebuilts and Socata certify them under their 145.
If you can open a valve and it stops dragging, then it sounds like the pistons definitely aren’t sticking, but there’s a blockage in the system working as a one-way valve (or perhaps a fault in the master cylinder).
I find it amazing a shop can think a brake can go 30 years without maintenance (at least disassembling the calipers, cleaning, new O-rings, new fluid). So much for “approved organizations”!
The only thing even slightly unusual about TB brakes is the hydraulic lock for the parking brake, although one would suspect if that were blocked then both brakes would drag.
I would agree you should check for debris acting as a non return valve.
We changed the left brake actuator on the pilot side but that didn’t cure the problem. The next thing on the list is the park brake valve. Where could we look for debries? Do we have to check all fluid lines. The visible ones from the outside seem ok.
Hello Placido,
When your left brake is blocked, if you apply and release on the left pedal from the right hand side seat, does this release the brake pressure?
Tom
Tom, we tried but it didn’t. My mechanic suggested to do this. If it would have released the brake then apparently it would have been the park brake valve. It didn’t work but it still does not exclude the park brake being the culprit. You have to exchange the whole assey as there is no part number for the o rings
Or it could have been the piston of the master cylinder that doesn’t move back freely.
I think you can have a standard exchange directly from Socata.
Peter wrote:
What I have found is that many maintenance shops never bleed the brakes. One shop told me the system never needs bleeding and the fluid is perfect after 30 years…!!
This is rubbish, This is for sure not the general idea at maintenance shops. Fluid replacement is at a 3 year interval at Socata TB21. Other items are at 5 and 10 years, so pratically it should be 3 years and then 2 years, if you stick to the Socata suggested maintenance intervals.
I would start catching up with the maintenance program, if you outside these figures. It is quite a simple system and it is all very detailed in the maintenance manuals, including suggested time limits.
While there is strong movement to absolute bare legal minimum, this is in my opinion, not a good solution, and for sure will not be the most economical on the long run. Again I am really amazed when people neglect maintenance suggtions or fail to understand that proper maintenance is time consuming. If you think these shops are expensive, ask them why they are, any good shop will be able to tell you what they will do.
Jesse wrote:
Fluid replacement is at a 3 year interval
…and you can see it; recently I had cause to drain and bleed the brake on one side of mine, and the new brake fluid was a visibly different colour to the fluid in the other side (which has now also been changed). So it’s evident that there is some kind of degradation to the fluid going on over time.
