There have been several interesting e-mail list threads about Cleveland brakes in the last few months. I have been meaning to post a note to inform builders for quite a while, but I got distracted. Anyway, here here goes with a few brake gotchas:
- Improperly assembled calipers delivered from factory.
- Rough finish inside caliper.
- O-ring damage due over-heating.
Read on for information on each of these issues.
Issue 1 - Improperly assembled calipers delivered from factory. First posted on the RV-List by Sam Buchanan
We have had a couple of cases here in the Tennessee Valley RV Builders Group of brake caliper pistons popping out of the caliper bore when the brake pads have worn to some degree. This has been both a puzzle and a source of concern because two of the instances occurred at fly-ins a long way from home and caused considerable aggravation due to having to the repair the brakes at a distant airport.
The solution we immediately grasped was to replace the pads at every condition inspection so the pads would never wear to the point that the o-ring on the piston could exit the piston bore. We also considered fabricating a shim that would prevent piston over-travel but the design of the caliper thwarted our efforts.
It turns out that the REAL problem is improper caliper assembly at the Cleveland factory! The o-ring on the piston is located near one face of the piston. On each of the pistons that "popped", the o-ring was located near the face of the piston closest to the pad. Matter of fact, this is the way the brand spankin' new caliper I borrowed from RV builder Marty Emrath was assembled. Once the o-ring reaches the outside edge of the bore, the fluid gets dumped next time the brakes are applied. In the latest case of popped piston in our group, the pads had not worn very close to the rivets.
After further consideration of this matter, RV-8 pilot Robin Hunt found the Cleveland manual for the 30-9 caliper used on RVs and the manual clearly shows the piston inserted in the caliper with the o-ring on the OPPOSITE end from the pad. Robin's suspicions were first aroused when he found each piston on his RV-8 installed differently.
Apparently some calipers have been shipped from Cleveland with the pistons installed the wrong way. We have urged each TVRVBG member to check the orientation of the brake pistons at the next opportunity in order to avoid the possibility of losing the brakes at an inconvenient time. A slight amount of air pressure at the caliper inlet is sufficient to pop the piston out of the bore so you can insure that the o-ring is located near the face of the piston farthest from the pads. The aggravation of having to rebleed the brakes is minor compared to losing a brake on rollout following a landing, especially in an -A model.
Sam Buchanan (RV-6)
http://thervjournal.com
There was a long discussion of the list, and then Sam posted:
After thinking about this a little, it should be easy to check for proper installation with completely disassembling the caliper, even on an operational RV. Just remove the wheel and pads, hold you fingers tightly on the piston face, and have a helper VERY GENTLY apply the brakes enough to push the piston out enough to verify the o-ring is not located near the open end of the piston bore. If the piston protrudes at least 1/8" without the o-ring being visible, then the piston is installed correctly.
If installed incorrectly, you will probably get a face full of brake fluid..... ;-)
And finally, Bill Dube posted an even better idea:
I'm no expert, but I would think that if you substituted a flat plate for the disk that was, say, 1/8" thinner than the disk, you could check the calipers quickly and easily. Couldn't you slip the caliper off the disk and slip in the spacer, then have someone step on the brake? Afterwards, you could gently push the piston back into the original position with a C-clamp or one of those nifty plastic cam-action caliper tools. If the o-rings don't pop out, slip it back on the disk, bolt it up, and you are all set.
Issue 2 - Rough finish inside caliper. Posted on the Yahoo RV-8 List by Danny King:
I went to the hanger one day a few months back and found a puddle of brake fluid under and around the Doll's right wheel. I pulled the offending caliper and found the same thing you did. The O-ring was worn out! The reason for the failure with less than 300 hours was the caliper's cylinders that the piston moves in had a course finish. They had not been polished at all. The rough sandpaper like surface simply ate up the O-ring. I pulled the left caliper and found the same thing. I purchased four new O-ring from a local vendor. I installed them and now I have a pair in reserve. I took fine emery cloth and did a good polish job on the cylinder walls before I reinstalled the pistons. The replacement O-rings will probably last a long time. I though that my calipers must have been built on a Monday or something and did not think it was an ongoing quality control problem. I should have reported it to the listers. Sorry! So listers consider yourself informed. The O-rings are cheap, and it only takes about an hour a side to remove the pants, wheel, caliper and do the rework. It would be advisable for everyone to check this in the next few hours. A brake failure at the wrong time could ruin your whole year!
Danny King
Beautiful Doll 80434
Issue 3 - O-ring damage due over-heating.
Scott Jordan posted a message indicating that he had managed to over heat his brakes, causing the O-rings to become soft. The brake fluid leaked, and he had a brake failure. So, any brake over heating incidents probably justify disassembling them for inspection.
