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ws721
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I started using my MH. Brakes don't always release when I take my foot off the pedal. Doesn't happen all the just most of the time. I replaced the Tractor Protection valve. What next? The treddle valve?

Remember if it's got a hood it's no good!

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Only happens when I use the brake pedal. And not all the time. I was told there is another relay valve in the system under the cab. I haven't found it yet. As my "garage" is my driveway and it colder than zippe doo I haven't been as patient as I should be. They say we're in for a heat wave today, maybe as high as 25. I'll try some more today

Remember if it's got a hood it's no good!

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I looked in the Air and Brake System Service Manual. The only other valve in the system (other than Trailer Air Supply and Tractor Protection) is the trolley valve.

Doing some additional reading..there is a Tractor Protection Manifold that contains two (2) dual check valves. I do not know where it is located nor do I see it in the parts book. I will keep looking.

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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If it is a twin screw there probably is a relay valve mounted on the frame towards the rear end of the tractor.

Ken the single axle short wheelbase tractors like the ones we're used to don't have them.

This may be a long shot but could the trolley valve be bypassing a little air?

Ron

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The treadle valve COULD cause this. But, it is highly unlikely it would cause problems only when a trailer was connected.

Leaking trolley valve can definitely do it. Might be able to unhook the service line to the trailer and listen for some air leaking?

Of course, I've been wrong (uhhh...twice) today already.

"Eagles may soar, but weasels don't get sucked into jet engines."

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I am going to Mack this am to get a treddle valve. The pedal kicks back at you sometimes as well as has full brake with very little foot pressure. See what happens next.

Well, that could definitely be something worth looking into! Let us know how that works out for you.

"Eagles may soar, but weasels don't get sucked into jet engines."

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OK, now were going to test your, MH knowledge. I've been told that there was a recall on the 85 MH's about a brake problem. The same problem I have. The brakes SOMETIMES stay on after you take your foot off the pedal. It takes 30 to 50 seconds for them to relase completely. The notice says to reaplace the check valve with an updated or bigger bore check valve. Where is the check valve and has anybody else heard of this?

Remember if it's got a hood it's no good!

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OK, now were going to test your, MH knowledge. I've been told that there was a recall on the 85 MH's about a brake problem. The same problem I have. The brakes SOMETIMES stay on after you take your foot off the pedal. It takes 30 to 50 seconds for them to relase completely. The notice says to reaplace the check valve with an updated or bigger bore check valve. Where is the check valve and has anybody else heard of this?

Would this be the double check valve which feeds the trailer brakes? It is supposed to port air to the trailer brakes, regardless of whether you operate the foot valve or the trolley valve, but prevent air going to the tractor brakes if you operate the trolley valve.

On my R, it is attached to the treadle valve and incorporates the stop light switch.

"Eagles may soar, but weasels don't get sucked into jet engines."

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