Air leak help . . .

[Steve102C3]

On my 102c3, there is a leak in the treadle valve (I think that's the name). It's under the driver's seat in the compartment with the accessory tank.

When the air system is at 120 psi, this valve leaks at the bottom where there is a rubber flap.

Would it be better to replace this valve, or is there a rebuild kit for it.

Thanks in advance.

Steve

[Highway Yacht]

Steve.. My MC-9 also leaks air through the brake application valve located under the drivers seat in the spare tire compartment, but only when the park brakes is applied. If I scotch the wheels and release the park brakes then the air stops leaking. My air leak is caused by a bad park brake diaphragm on the drive axle. Does your air pressure leak down very fast after shutting down the engine??? If so, try shutting down the engine with the park brake released and the wheels scotched and see if that slows the pressure drop. If so, you also probably have a bad park brake diaphragm.

Jimmy

[Joe Camper]

When you step on the brake the air that is coming out of that treadle is not the air going to the pancakes. It is just signal air going to R12 valves (brake relay valves) that are always located directly or close to the axle. When the signal coming from the pedal hits the R-12 it opens and feeds brake tank air directly to those chambers.

This is done to eliminate possible fade or delay.

Sometimes when the r12 valves leak it will bleed thru the exhaust valve on the treadle when not in use.

Most of the leaks I have seen like this are not a bad brake pedal its the R-12. Not always buy usually.

[Steve102C3]

Thanks Jimmy and Joe. That's good info.
I'll try shutting down the engine w/o the park brake applied and see what happens. I'll also c/o the r12 valve to see if if might be the culprit.
Steve

[eagle19952]

This will help confirm what's been said and help you to be confident in your decision, read away.Especially page 4.

http://www.meritorwabco.com/MeritorWABCO_document/tp0569.pdf

[buswarrior]

There are more diagnostic checks you may do before resorting to parts changing,

however, it serves a busnut well to work their way through the brake system and replace all the valving so that they are all of known vintage.

Commercial operations are not rebuilding valves, they just put new ones, the kits plus labour cost more. For us, how do you know under what conditions whether to condemn the core or not?

In my opinion, you have lots of other things to spend time on rather than trying to rebuild air brake valves.

Call it preventive maintenance and enjoy many years of trouble free reliability.

happy coaching!
buswarrior