ws721 Posted January 25, 2014 Share Posted January 25, 2014 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? Quote Remember if it's got a hood it's no good! Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/ Share on other sites More sharing options...
farmer52 Posted January 25, 2014 Share Posted January 25, 2014 Check your brake pedal and treadle valve to determine if they are sticking.Also, did this just start with cold weather? If so, you might have some moisture. Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-228540 Share on other sites More sharing options...
ws721 Posted January 25, 2014 Author Share Posted January 25, 2014 I oiled the pedal valve. The plunger moves free. Only does it with a trailer on. Doesn't matter what trailer either. Quote Remember if it's got a hood it's no good! Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-228541 Share on other sites More sharing options...
farmer52 Posted January 25, 2014 Share Posted January 25, 2014 Perhaps the trailer supply valve (red knob) or parking valve (yellow knob)? Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-228543 Share on other sites More sharing options...
ws721 Posted January 25, 2014 Author Share Posted January 25, 2014 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 Quote Remember if it's got a hood it's no good! Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-228547 Share on other sites More sharing options...
farmer52 Posted January 25, 2014 Share Posted January 25, 2014 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. Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-228552 Share on other sites More sharing options...
39 Baby Mack Posted January 25, 2014 Share Posted January 25, 2014 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 Quote Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-228556 Share on other sites More sharing options...
doubleclutchinweasel Posted January 29, 2014 Share Posted January 29, 2014 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. Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-229426 Share on other sites More sharing options...
Mack Doctor Jr. Posted January 30, 2014 Share Posted January 30, 2014 Quick release valve that hangs on the front of the rear end. 20 bucks at most Quote Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-229474 Share on other sites More sharing options...
doubleclutchinweasel Posted February 1, 2014 Share Posted February 1, 2014 Find anything yet? Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-229740 Share on other sites More sharing options...
Marcel67 Posted February 1, 2014 Share Posted February 1, 2014 Would love to see he found the issue Quote Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-229741 Share on other sites More sharing options...
doubleclutchinweasel Posted February 1, 2014 Share Posted February 1, 2014 Only thing that confuses me (well...not the ONLY thing!) is he says it only does it with a trailer...any trailer...attached. if not for that, it would pretty much have to be a QR valve. Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-229753 Share on other sites More sharing options...
ws721 Posted February 1, 2014 Author Share Posted February 1, 2014 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. Quote Remember if it's got a hood it's no good! Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-229827 Share on other sites More sharing options...
doubleclutchinweasel Posted February 1, 2014 Share Posted February 1, 2014 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. Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-229841 Share on other sites More sharing options...
ws721 Posted February 2, 2014 Author Share Posted February 2, 2014 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? Quote Remember if it's got a hood it's no good! Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-230176 Share on other sites More sharing options...
doubleclutchinweasel Posted February 2, 2014 Share Posted February 2, 2014 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. Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-230192 Share on other sites More sharing options...
ws721 Posted February 7, 2014 Author Share Posted February 7, 2014 Replaced the treddle valve today. Seems ok bobtailing. Find out for sure when I go retrieve my hay trailer. Quote Remember if it's got a hood it's no good! Link to comment https://www.bigmacktrucks.com/topic/34386-mh-brake-experts/#findComment-231118 Share on other sites More sharing options...
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