07-12-2004 Ask Mike! Archive
Dynamic brake relays

Hi Mike,

I am an A&P doing an annual on my 1958 BE-95 Travel Air which I have owned over 20 years. Never any problems in the past, but I suspect I may have a bad dynamic brake relay in the landing gear system. Uplock cable tensions were tight and would not maintain proper tension after adjustment at cable ends, changed after each retraction test. More importantly, I have always had the 1/8 to 1/4 turn of handcrank travel before hitting the internal stops after gear extension or retraction tests. Now have very little if any handcrank travel after test. Checked switches and required to much adjustment of screw for up travel or tab bend for down travel. Manual for 1958 travel only says replace dynamic brake relay or adjust switches to correct problem. I understand there is a test procedure in later model Beech manuals for the Bonanza or Baron to test the dynamic brake relay. Could you elaborate or suggest anything before I order a new relay.

Any information or advise would be greatly appreciated. I am trying to get a copy of a later manual or would like to know where the procedure can be found.

Thank you!

Best Regards,
Carl


Carl;

If the cables will not maintain tension, they are coming apart, only a matter of time before they snap. Pull back the tygon tubing from the end of the cable in the gear well, this is where they will typically start fraying, causing the loss of tension.

As for the overtravel issue, don't jump into replacing the dynamic brake relay just yet. My experience has shown (99% of the time) the seal in the end of the gear motor has gone away, there is now some grease inside the motor which allows it to skid, instead of stopping, when the reverse current is applied to the leads from the relay. Pull the top brush out (easy to get to) and inspect, any sign of grease or moisture, as well as worn out brush, should be cause for removal and overhaul of the motor.

Gear Green,
Mike