UPDATE 2: I have replaced my master cylinders. Note that the factory uses the MC-4A (7.5″) cylinders. I accidentally ordered the MCMC-4s, which are 1/2″ longer. They seem OK, and my brakes are much firmer, but until I’m sure I’d recommend sticking with the ones the factory recommends for now.

UPDATE: Apparently the springs the factory originally recommended for use with the Matco master cylinders scores the shaft/pistons and create air bubbles (which I have noticed in my lines), so I’m planning on replacing those as well. I’ll report back if they fix my bubble issues.

I had been having a small drip from my copilot brake line, which had dripped on the disc. While I was fixing the leak, I thought I’d clean the disc as the brakes had been a bit squishy lately. What I found was that the pads on the backing plate had worn to the rivets, and we were gouging the disk. Ouch. I could probably have these resurfaced, and I might, but I will replace them for now, and if I do resurface, I’ll keep those as spares. Brakes are pretty important on an airplane with a free castoring nose wheel (brake steering), especially one with no rudder propwash.

So, this will be our first brake relining, and I’m still learning how, and what tools to use. I think folks have given this short shrift on other blogs, so I’m going to detail it here – partly for me the next time I need to do it. I will also probably put checking this on my condition inspection sheet. I have an item on there for checking the pads, but honestly, it’s surprising how much pad is left when it’s into the rivet…

So, first off, here are the parts for a Velocity brake. Note you shouldn’t need a disk, a pressure plate, or a backing plate. I have the disc because we gouged it with the rivet. I’m going to spare a pressure plate and backing plate in case I screw up the rivet holes. Basically, though, if you do it right, you buy 8 pads and within an hour you’ve got new brakes for under $100 (buy 2 of the 4 pack), or just over if you need the tool.

I also bought the Rapco RA825 brake tool to remove and set the new rivets, and I’ll report back once I know how that works.

Basically you fix the tool into the vise. There are 3 attachments for it. One is the “anvil” – these are not the real names, which I’m not sure of, but this is for your understanding. You leave it out to remove the old rivets. You place the part in the too with the rivet head facing this bottom hole in the tool, then take the punch that comes with the tool, and a ball-peen hammer, and give it 2-3 good raps until the rivet rockets out of the bottom of the tool. Then get the other rivet out….

Next, get the new pad. It comes with rivets, place the rivet in the pad… head goes towards the disk… Put the anvil in the tool, then get the “setting punch” which has a divet in it, and a curved profile to bend the rivet over. Set the head of the rivet on the anvil, and center the set on the new rivet. Again, 2-3 good raps with the hammer, and check that the pad doesn’t move (much, just enough to get the other rivet in). Now repeat with the second rivet. Voila’. You’re done. Really, if you have the right tool, this is a 5 minute job. Thanks Ray.

Here you can see that my copilot pressure plate pad is worn to the brass rivets. That’s bad.	Here is the disc. It is scratched from the rivet, but my A&P friend tells me that this is acceptable, and that the pad will smooth it back out. There is plenty of metal here.
Various states of pads/linings. Top left is with the pad removed, top right is a worn (but not to the rivets, as it should be) pad, and the bottom is a newly installed pad.	Here is my new brake tool
Here is the new brake disc that I bought	From Mark Riley’s Blog This is the brake rivet tool. The bottom is open so the punch can drive the rivet out. It self-centers in the rivet, which comes out the bottom.
Mark’s guy had a different tool to set the rivet, and screw-down type. Folks like these better since you don’t risk cracking the pad/lining when you set the rivet.	A new brake disc, usually not needed, but Mark had some disc chatter.

Posted By: Brett Ferrell
Saturday January 24th, 2015 at 10:25 PM

Categories: Maintenance
Tags: Brakes Cleveland Maintenance