new/ old brake system troubleshooting lesson learned.. DD-3 & relay valve

[mikelutestanski]

Hello;     
   just a tip when you are troubleshooting your mci brake system.  My 7 has an R-6 relay valve and it leaked out of the bottom  not alot but enough so that i could hear it when walking by the bus in the garage.   SO i found it was an R-6 valve and purchased one from Luke and installed it.. Well much to my surprise the leak was still there.   
   HMMM     poor troubleshooting technique  ..   anyway next I removed the hose to the DD-3 cans one at a time and  the passenger side can had air coming out the service port..
   if you download the bendix service manual and read it the possible culprit is the auxiliary diaphragm.   And sure enough as it happens the  diaphragm had a wear tear on the side.  This particular one was a midland unit and had been is service for ten years . I rebuilt the cans in 99.   SO I happened to have a spare set and changed them out.
   The R-6 valve was a real pain to remove and after 38 years one side of the mounting block was in very sad shape. SO in one sense I am glad to have a new one.   
   SO FWIW make sure you troubleshoot the problem far enough to find the broken or wore out part.
    The manual explains how the system works so i will skip that part , however I do recommend the download SD-02-4600. 
     As far as lubrication the manual is fuzzy but I have it on expert authority to use chassis grease but SPARINGLY...
  (THat means not much) 

regards and happy bussin  mike

[DaveG]

Not to worry Mike. Everyone (usually) learns this lesson. If air is leaking from an exhaust port of an air valve, the valve could be doing it's job...exhausting air! The diagnostic procedure is the same for springbrake, that is that if there is air leaking from the exhaust port of a relay valve with the parking brakes released...set the parking brake and if the leak goes away...look to the springbrake. Your procedure of disconnecting the lines from your brake cans was the correct way to do it. Besides, R-6s are cheap, aren't they?!