leweymeister Posted June 20, 2010 Share Posted June 20, 2010 I recently washed my dumptruck, it's an r66, early 80's vintage. When I was done I drove it home, and went to apply the parking brake, and it took forever to come on... the air just hissed out instead of blasting out the unloader like it is supposed to. I took out the unloader relay but couldn't find a number on it. It was all worn out and full of junk, and I have a Bendix r-14 sitting around in my shop. The it has the same ports, but the configuration is slightly different. Does anyone think it will work as long as I put the proper fittings in it? Also... do you think the valve is the problem? Quote Link to comment https://www.bigmacktrucks.com/topic/14460-park-brake-problem/ Share on other sites More sharing options...
Rob Posted June 20, 2010 Share Posted June 20, 2010 I recently washed my dumptruck, it's an r66, early 80's vintage. When I was done I drove it home, and went to apply the parking brake, and it took forever to come on... the air just hissed out instead of blasting out the unloader like it is supposed to. I took out the unloader relay but couldn't find a number on it. It was all worn out and full of junk, and I have a Bendix r-14 sitting around in my shop. The it has the same ports, but the configuration is slightly different. Does anyone think it will work as long as I put the proper fittings in it? Also... do you think the valve is the problem?An R14 relay valve is used to control the application and retraction of the spring parking brakes. They are available in horizontal, and vertical ports. They can also be plumbed to allow for anti compounding of the brakes so you don't warp hot brake drums by applying service brake pressure with spring brake pressure. This eliminates the SR series valves that do the same thing. I'm assuming the "unloader" that you refer to is the "QR" series of valve that is for quick release of the air pressure holding the spring brakes released. These do wear out from time to time but if it is full of trash you probably better check the rest of the air system for fouling and garbage also. You just may have an air compressor needing some attention. Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/14460-park-brake-problem/#findComment-57760 Share on other sites More sharing options...
leweymeister Posted June 23, 2010 Author Share Posted June 23, 2010 I recently washed my dumptruck, it's an r66, early 80's vintage. When I was done I drove it home, and went to apply the parking brake, and it took forever to come on... the air just hissed out instead of blasting out the unloader like it is supposed to. I took out the unloader relay but couldn't find a number on it. It was all worn out and full of junk, and I have a Bendix r-14 sitting around in my shop. The it has the same ports, but the configuration is slightly different. Does anyone think it will work as long as I put the proper fittings in it? Also... do you think the valve is the problem?Well I replaced the relay valve with the R-14 and it still has the same problem. Might it be the dash valve that has issues? I replaced it last winter because the old one was leaking so I didn't think a new valve would be the problem but... Quote Link to comment https://www.bigmacktrucks.com/topic/14460-park-brake-problem/#findComment-58010 Share on other sites More sharing options...
Rob Posted June 23, 2010 Share Posted June 23, 2010 Well I replaced the relay valve with the R-14 and it still has the same problem. Might it be the dash valve that has issues? I replaced it last winter because the old one was leaking so I didn't think a new valve would be the problem but...When you pull either the yellow, or blue handle out from the dash, does the escaping air from the valve itself release immediately, or is a prolonged hiss? If not immediate, the valve has probably gone bad because this valve needs to expunge it's retained air before it can release the air the R14 valve is retaining.On the older systems of your vintage you still could quite possibly have an SR-1 valve in the system. Typically I've seen this valve attached to the rear cab mount xmember. It does sound as if you have a slow reacting valve not dumping it's air pressure fast enough.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/14460-park-brake-problem/#findComment-58012 Share on other sites More sharing options...
leweymeister Posted June 27, 2010 Author Share Posted June 27, 2010 I recently washed my dumptruck, it's an r66, early 80's vintage. When I was done I drove it home, and went to apply the parking brake, and it took forever to come on... the air just hissed out instead of blasting out the unloader like it is supposed to. I took out the unloader relay but couldn't find a number on it. It was all worn out and full of junk, and I have a Bendix r-14 sitting around in my shop. The it has the same ports, but the configuration is slightly different. Does anyone think it will work as long as I put the proper fittings in it? Also... do you think the valve is the problem?Well I figured it out... after I replaced the dash valve and that didn't do anything, I took off the line that was attatched to the exhaust port, and the thing worked like a charm. so I traced the line, and it turns out that the end of it had melted shut, I musta blown it against the exhaust manifold or something when I was washing it. But hey, I learned so much more about my truck. Thanx anyway for the replies. Quote Link to comment https://www.bigmacktrucks.com/topic/14460-park-brake-problem/#findComment-58316 Share on other sites More sharing options...
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