What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

RV6A brakes

dvalle

Well Known Member
Been having fits with a friends RV6A brakes. After couple weeks of bleeding to make sure no air, the crossover lines get air in them preventing co-pilot braking. My last time I cleared the lines and tightening all fittings, it happened again but this time upon landing and with even braking it pulls hard to the left. So, this time I replaced all the brake lines and the fittings for the nylon crossover lines (NSR tubing and fittings), disassembled, cleaned and rebuilt the calipers, installed new pads, the discs look good. Test flew yesterday, still pulled to the left, not sure about the air in the crossover lines, too soon to tell. The only thing left is the master cylinder?? Any expert input would be appreciated....
 
Suggestions

Are the master cylinders Cleveland or Matco? If Matco, the return springs are not as strong, and some builders modify with extra springs.
Also check if the brake pedals are binding at the pivot bolts. This may be a problem if the pedals don't have the mod which uses a single long bolt instead of the standard, which is a separate bolt at each pivot.
 
I strongly suggest pressure bleading from the calipers up, and not trying to blead them by pumping the breaks.
 
There are several rubber parts in the Matco MC's. Over time, these break down and they allow air to enter the MC and migrate into the fluid supply lines. I have had this happen on two older planes/kits. If the MC's are over 10 years old, I suggest rebuilding the Pilot side MC's. The rebuild kit only costs $12.

Not enough info to speculate why it is pulling left.

Larry
 
Thanks for your input. They are Cleveland brakes and I always bleed them from the caliper. Need to admit, it is VERY challenging compared to what I'm used to, Cessna, Beech, Mooney, Piper. For probably the same reason as the issue, I have trouble as it takes more pressure to fill. I'm starting to believe it must be something in the master cylinders....??
 
If it takes much pressure to bleed, the master cylinder is not fully extended. Disconnect the master cylinder upper attachment point and pul on the rod to make sure it is fully extended. Ask me how I know. The extension springs can end up loosing their tension over time and not fully extend the rod. There is a spring in a valve internally that has to be overcome to open the bypass when the rod is fully extended.
 
Dan

Thanks for that one, I will check. Do you think that could have something to do with it pulling to the left (maybe the right is not working correctly)?
 
cy

I too have struggled with small air bubbles in the cross over lines.

One culprit that I found is that if I did not cycle the first few pumps back in to the reservoir can before attaching the hose to the brake bleeder there would be very very small bubbles in the lines. Fortunately I used very clear tubing from the hand pump to the bleeder so I could watch for those very small bubbles as I was pumping. I also learned to pump very slow. I learned that if I pumped too fast, the bubbles would have a tendency to appear suspended in the fluid.

There was more than one occasion that those almost microscopic bubbles would float up to the high point in the cross over tubes after a day or two after pumping.

Just some tips to watch for.
 
How to deal with mixing brake fluid types

I am in the process of getting set up to bleed my RV7A brakes up from the bottom. I have ordered Royco 782 Brake fluid [MIL PRF 83282] but, since I just bought my aircraft in July I do not know what type of fluid is currently in the aircraft. Is there a problem with mixing the brake fluid types?
 
I am in the process of getting set up to bleed my RV7A brakes up from the bottom. I have ordered Royco 782 Brake fluid [MIL PRF 83282] but, since I just bought my aircraft in July I do not know what type of fluid is currently in the aircraft. Is there a problem with mixing the brake fluid types?

If it is red 5606, they are compatible, but you lose some of the higher flash point of the synthetic fluid. You can thread a fitting into the top of the reservoir and run a tube into a container. If you bleed enough, you'll replace all the fluid. You'd need to do both sides to get all the old fluid changed out. It's really not necessary though unless you are convinced you need the higher flashpoint. I use the ATS brake bleeder which moves a lot of fluid quickly. I've made a few bleeders using pump up garden sprayers. It's a bit hard to adapt tubing that will fit the bleeder fittings and won't blow off. The ATS unit is pricey but works very well.

Ed Holyoke
 
Back
Top