The International Cessna 170 Association

cessna170bdriver wrote:Each brake pedal on the new-to-us 170B occasionally goes to the floor then pumps right back up. This particular airplane has McCauley brakes, but there is no leakage at the wheel cylinders. I’m assuming I need new piston o-rings and lock-o-seals in the master cylinders. I was looking on Aircraft Spruce and they have a kit that includes 3 o-rings, a lock-o-seal, and a “tube fitting gasket”. The illustrations in both the 170B IPC and the 100 series service manual only show a piston o-ring and lock-o-seal. Are the other parts just to make the kit cover more models, or is there something I’m missing on the illustrations?

Also, is there a better source than ACS?

Bruce Fenstermacher wrote:Can’t answer your question but it is your lock-o-seal that is not sealing to allow the cylinder to build pressure. I fixed mine ordering just the oil ring and lock-o-seal from the IPC.

edbooth wrote:...

Sometime ago I had a right brake pedal that would go to the floor, usually at a most inopportune time. Finally replaced the lock-O-Seal..... No more problems. Was easy fix, just unscrew the top cap and pull the guts out, replace parts and slide back in.

cessna170bdriver wrote:

edbooth wrote:...

Sometime ago I had a right brake pedal that would go to the floor, usually at a most inopportune time. Finally replaced the lock-O-Seal..... No more problems. Was easy fix, just unscrew the top cap and pull the guts out, replace parts and slide back in.

Thanks Ed, That’s pretty much what I guessed from looking at the IPC and service manual. It looks like the hardest part will be working behind the pedal to remove and replace the cotter pin at the top of the piston rod.

edbooth wrote:

cessna170bdriver wrote:

edbooth wrote:...

Sometime ago I had a right brake pedal that would go to the floor, usually at a most inopportune time. Finally replaced the lock-O-Seal..... No more problems. Was easy fix, just unscrew the top cap and pull the guts out, replace parts and slide back in.

Thanks Ed, That’s pretty much what I guessed from looking at the IPC and service manual. It looks like the hardest part will be working behind the pedal to remove and replace the cotter pin at the top of the piston rod.

I think that was the hardest part Miles. To make it a little easier, took out the front seat so I could lay on my stomach and get to everything.

gahorn wrote:Ed’s idea of laying on one’s stomach is the hard part for me.

edbooth wrote:Dave, you don't have to take the lower attach point loose for this. Just take the shaft loose from the rudder/brake pedal, unscrew the assembly from the top of the cylinder and pull it out. If you still have that dorky parking brake, this should be disconnected for ease of repair. Install the new repair parts and slide it back in. (Put a rag around the cylinder so brake fluid don't run down where you don't want it)

DaveF wrote:

edbooth wrote:Dave, you don't have to take the lower attach point loose for this. Just take the shaft loose from the rudder/brake pedal, unscrew the assembly from the top of the cylinder and pull it out. If you still have that dorky parking brake, this should be disconnected for ease of repair. Install the new repair parts and slide it back in. (Put a rag around the cylinder so brake fluid don't run down where you don't want it)

Ed, sorry, I didn't mean to suggest removing the cylinder for the work under discussion. I was just remembering the difficulty of removing the cotter pin on the clevis at the bottom attach point. I pulled it to replace the hoses and repair the brake cylinder attach bracket.

gahorn wrote:When disassembling any items,...COUNT the number of turns (threads) being disassembled so that you can return them to the same position during reassembly.