matco master cylinder sucking air?

Lan Vinh Do · #1 03-31-2017, 04:18 AM

is it possible that my matco cylinder is sucking air in my system

This annual, i rebuilt the right brake pilot side on my rv-10 because it was leaking,

I bleed the brake after and i notice that i had air in my left brake line pilot side. It was in the feeding line I bleed the brake again 3 time from bottom up and from up to bottom. ( almost a liter last time to be sure that no bubble was there. ) Everything look fine but as soon as i touch the brake on the left side , i see bubble going up on the feeding side. The brake are not soft but i see air bubble on the feeding line coming from the cylinder.

Is it possible that the cylinder introduce air in my brake line ( feeding side) ? There is no fluid leak

TS Flightlines · #2 03-31-2017, 05:25 AM

Lan, maybe not inducing air, but possibly the o'ring s are not sealing and the pressure isnt building, giving you a spongy pedal. Back in the car days, if we had to overhaul one hydraulic cylinder, we'd do them all. We figured the weakest link in the chain would be the next cylinder that you didnt fix.
In your case, I assume that all the cylinders have the same amount of service time, so instead of leaking externally, its leaking internally, giving you the spongy pedal.

Tom

Lan Vinh Do · #3 03-31-2017, 05:38 AM

The brake are not spongy at all. I only see bubble coming up after i depress the brake ( when it spring back) and coming up the feed line.

MikeT · #4 03-31-2017, 05:49 AM

I assume you are talking about the master cylinder at the brake pedal. There are two seals in the cylinder. One for the piston, and one around the shaft. The one around the shaft is to stop air from coming in when you depress the brake. That area goes negative pressure and sucks in fresh brake fluid. If the seal is damaged, it can suck in air.

Lan Vinh Do · #5 03-31-2017, 06:14 AM

Thank you. That is what i was looking for. Just want to be sure i wasn't crazy

guccidude1 · #6 03-31-2017, 08:42 AM

I had a similar, if not the same problem. RV-9A, brakes both sides, pilot's left brake would induce air into the plastic line to the reservoir. When the air bubble got large enough the brake became spongy. Rebuilt it twice, no joy, replaced with new and problem solved. Matco folks say they never heard of such a thing. Oh well, Dan from Reno