Very stiff brakes - First time bleeding

TCONROY · #1 02-23-2015, 03:20 PM

I just bled my Matco brake system from the bottom up with the commonly used HF oiler and some tubing. Worked very well and was easy to do. Pumped until fluid was coming out of the reservoir and then repeated on the other side.

I thought I had a problem because it seemed my brake pedals were not moving much at all. I called Matco and talked to tech support. He thought maybe my reservoir wasn't vented so I removed the inverted check valve I had installed. Same issue...very stiff brake pedals. I also double checked to make sure the calipers were not compressed...they were not. I could spin the tire. Lastly, I verified the shafts were completely extended on each master cylinder.

Following Matco's suggestion I found someone to sit in the plane and depress the brake pedals. Sure enough the calipers compressed as they should. The crazy thing is, the toe of the brake pedals don't move more than 1/4" for the brakes to fully apply...is this right??? Seems like a couple inches of travel would be nominal. Anyone else had this issue on a brand new set of master cylinders and calipers? Maybe things loosen up over time or after following the brake "brake-in" procedure?

krw5927 · #2 02-23-2015, 03:45 PM

You don't want it to loosen up. In fact it sounds like your filling procedure went exactly as planned and there's no air trapped in the lines.

You don't want them to be at all "mushy" or have any give. Brake fluid is incompressible, and the pedal is supposed to be hard to depress.

Sounds like everything is as it should be. Carry on!

lr172 · #3 02-23-2015, 05:12 PM

I just bled mine and get just a bit more travel than you. The caliper pistons are much smaller than an auto and that accounts for the limited travel, relative to what you experience in your car.

TCONROY · #4 02-23-2015, 05:14 PM

Very interesting. I have flown a lot of different single/multi-engine piston airplanes and several jets and have never seen a brake pedal that deflects so little. Guess we will see what happens with taxi tests.
Thanks!

flightlogic · #5 02-23-2015, 05:58 PM

I suspect the small travel will be just fine. Do some taxi test and see how the behavior is.
Mine hardly move at all.

TCONROY · #6 02-23-2015, 08:01 PM

Quote:

Originally Posted by flightlogic

I suspect the small travel will be just fine. Do some taxi test and see how the behavior is.
Mine hardly move at all.

Glad to hear I am not experiencing anything abnormal.

aerhed · #7 02-23-2015, 09:55 PM

Trevor, I'd bet all the planes you speak of either had air or worn/sloppy pedal linkage or both. Now you have a new frame of reference.

BillL · #8 02-24-2015, 06:54 AM

Good Job Trevor - perfect result.

RV3bpilot · #9 02-24-2015, 09:22 AM

I found this very thing when I bled my breaks for the first time. I used my hand on the break pedal and with my foot on the tire and I noticed that the pedals moved very little before the brakes locked up the tire. It was the same on both sides.
Now I have over 140 hours on the plane and still not much movement of the pedal is required make the brakes work. It took a little to get used to but now I like it.
No excess wear, no hot breaks, they always work, aircraft rolls very good when not applied.

Smilin' Jack · #10 02-25-2015, 04:55 AM

Trevor,
They are working like they should. I too have hardly any pedal movement but they work well, when you get it running make sure you do burn the brakes in per Matco instructions... The brakes are great.
Jack