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I have been having long duration issues with my 1976 AA5B Tiger brakes. After studying the manuals and looking at the system, I strongly suspect that my symptoms are due to the parking brake. I encounter a symptom whereby one brake (typically the left) does not release. This happens while taxi-ing into run-up area. It sometimes requires me to make a 360 degree turn while pumping both brakes and jockeying the pedals back and forth in order to get both brakes to release. My A&P made some adjustments to master cylinder in the hope of ensuring that parking brake would release easily, but we still have the symptom. We do not ever use the parking brake. I understand that it is not a legal fix to simply disconnect the chain system. My questions:
1.) I understand that later models (after 1976) had a re-designed parking brake mechanism. Can anyone tell me how it works, can it be retrofitted into 1976 model?
2.) I have seen pictures of improved parking brake using a valve in the brake lines (AuCountry Aviation web site). Can something like this be installed without an STC? Anybody have the STC or experience with improved design?
3.) I looked very carefully at the chain system as attached to wire used to actuate parking brake. This looks like poor mechanical design, it would make more sense to have a pulley or something round so that chain tension would always be uniform on both master cylinders. The standard part looks like it can hang up one brake. Anybody made an improved part or STC?
4.) Any other ideas or experience with the Tiger parking brake?
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Here is what I now understand after a conversation with a guru (Thanks, Roscoe!):
A design change was made in the 1978 model year to replace the chain system with a valve located on the firewall. This is not perfect or ideal either due to the need to replace o-rings. The new design can be retrofitted into earlier year planes without an STC, but form 337 is required since it is a change to hydraulic system. Approval from FAA should be a routine matter since design was approved already.
Based on talking to other experts:
The general consensus is to avoid use of parking brake unless absolutely needed. The only time I can think of where it would be important is if you were flying solo and needed to hold the plane in place for a few moments until you could apply chocks.
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I finally did a simple thing: removed chains connecting the cable to brake pedals. Parking brake is now plackarded “inop” and everything has been working fine. I wish I had done this much sooner rather than spending so much time thinking about it and trying to figure out other solutions.
Thanks for the people that helped me sort this out by phone and email. I appreciate it!
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One other thing that I have recently figured out regarding my brake issues. There was a bad O-ring within one of the master cylinders. It was causing intermittent issue where pedal would go straight to the floor with no braking action. It was rarely encountered, but it made troubleshooting complicated because there were actually two separate issues in my brakes. The parking brake hanging up, and bad O-ring that caused brake not to work at all. One thing we learned when taking master cylinder apart is that the actual part does not match the drawing in manual. It is not that complicated, but we had to take the master cylinder completely out of the plane to dis-assemble and inspect it on bench.
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I recently engaged the parking brake out of curiosity. Bad move. My 77 Tiger became a merry-go-round. I was able to pry the break pad off the rotor a little bit enough to break it free and push it back into the hangar, but does anyone know how to disengage a frozen parking brake correctly? Based on a rough visual inspection, it seems to just use the existing brake caliper.
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