That isnt that terrible of an old truck, the jar your talking about sounds like a water dump valve of somekind maybe??? is the rubber thing like a check valve like a one way valve on a boat drain? if its pressurized? or could it be a place to add alcohol to the sytem maybe.??? Dunno just try it without it... You cant feel air brakes the way you do with hydraulic, First off air compresses...and also the pressure your applyin from the pedal isnt direct to anything that you would feel like hydraulics are to cylinders.....and as far as manuals and instructions they will tell ya anything that isnt necassarily true... Any manual will tell ya not to ride the brakes downhill for any length of time..... But due to the fact you cant feel air brakes the same way...they would probably tell you that cuz..you couldnt feel if they were getting hot and fading like you could with hydraulic... dunno....
Ohhhhhhh i see after rereadin ur last post...yeah that little jar is just a water trap...the push thing is the drain for it...(its a schradervalve type thing in the rubber) you can see water in it to drain.. its not hurting anything where its at...or it wont hurt to remove it...and if i remember right...the second tank is just a reserve air tank,,, it has a check valve in it if the first tank is drained,,,it could also be the trailer supply tank, as the other guy said to charge the trailer brakes. most systems have two tanks anyway with one as a reserve....or emergency tank, as in you stated if ya loose air you still have a second tank to try to get stopped.....those air brake systems can get pretty complicated. Also one last thing,,, the slow buidup..??? uhhhhhh it takes abit to build air..and yeah it dont last long without it running to pump air... belt driven compressors arent any worse than gear driven ones. Id say if i remember right, from no air to a full 120lbs would take about 3 minutes or so at least at high idle.... there are specs for it... Same with bleed down... You hold down the pedal and shouldnt drop so low , in so many minutes but i cant remember how long?
