jackb61sx Posted June 1, 2014 Share Posted June 1, 2014 Was using my 89 Superliner today and went to park it and found out the maxi's are not working. There is no are leak, brakes where working fine, but now in the cab I have the tractor, trailer maxi's button's ( for lack of better word) and my Blue maxi that has no air to it does nothing, no feel to it at all. Trailer maxi works when hooked to trailer. So I figure it's a valve but which one. Any help in shortening my elimination process a help.Jack Quote Link to comment Share on other sites More sharing options...
Gmerrill0516 Posted June 1, 2014 Share Posted June 1, 2014 Somewhat limited knowledge here but if the service brakes work, then setting the parking brakes should work as they do escentially the same thing but through the use of springs rather than the air on the diaphram. Are you sure your brakes are working all around? If the front brakes (service brakes only) are doing all of the work and you are not hauling heavy then that might be hiding a problem. Have you inspected the adjustment of all the slack adjusters all around yet? That is the prudent spot to start. I guess in theory if the maxis were not releasing air when you set the parking brake, then that would be another possible solution and a valve problem as you suggest. I'd look everything over asap. Get a friend to see if all the cans set visibly when you set the parking brake or not. There is typically a dump valve that opens when setting maxis too and perhapse that has failed in some way. You could chock the wheels, and dump most of the air by fanning the brakes (engine off) and see once the valves blow due to low pressure, you should set the parking brakes automatically....this could indicate if it is a control problem or a problem at the brakes themselves. If they still don't set with no air pressure in the system, you have more than valve issues.Good luck...hope this makes sense and helps a bit.Greg 1 Quote Link to comment Share on other sites More sharing options...
jackb61sx Posted June 1, 2014 Author Share Posted June 1, 2014 I am at where you described, you apply brakes and the cans hardly move slack adjusters, so some thing changed from the time I took it out to the time we parked it, do believe its a valve issue just need to figure out, thx for help. Quote Link to comment Share on other sites More sharing options...
gearhead204 Posted June 1, 2014 Share Posted June 1, 2014 will the truck roll? or is it stuck (brakes applied) and wont release the parking brake? also did anyone adjust the brakes? if adjusted backwards it will do as described in prior posting. if I remember right the blue knob will be dead if red knob is pulled and yellow knob is shoved in. to check the control trace the air lines from the emg. port on the air can to the relay valve then find the control port, usually at or near the top remove the control line and then shove in yel. and blue knob should have air in control line if so re attach line and remove one at air can do same thing again and line should have air in line if not relay valve or relay valve air supply faulty. if truck don't move when brake dash valves are in you may have failed a air can (maxi) and the air to release the big spring is by passing in one chamber and applying the service brake. to check remove a air can air line from the sev. port, push in dash valve you should hear no air if you hear air, do this to each can and then condemn the can with air coming from svc. port. if you have never changed a maxi DO NOT TOUCH! it can kill you find a guy who does!!!! Quote Link to comment Share on other sites More sharing options...
39 Baby Mack Posted June 1, 2014 Share Posted June 1, 2014 If this is a three button system like the "MH"'s had the three buttons are as follows:Yellow button-system park, this valve supplies air to the other two valves, and can be used to park everything with just the one button.Blue button-supplies air to the spring brakes on the tractor(if the yellow button isn't in the blue button will have no air going to it and will do nothing)Red button- supplies air to the tractor protection valve(to release spring brakes and supply air to the trailer)There is probably only one axle on the tractor equipped with spring brakes and my guess is that both spring brake chambers have gone bad.They both wouldn't go bad at one time but there is a good possibility that only one has been working for some time and second one has finally went bad!Ron 1 Quote Link to comment Share on other sites More sharing options...
jackb61sx Posted June 1, 2014 Author Share Posted June 1, 2014 No when maxi's applied truck will roll freely, they have not been adjusted recently truck has been only driven 3 times since December when they where last adjusted and things where fine previous, hear no air leaks but will take all advice and look at Monday,,,,,,,,,,thx Jack Quote Link to comment Share on other sites More sharing options...
39 Baby Mack Posted June 2, 2014 Share Posted June 2, 2014 If the springs are broken in the parking brake side of the chamber it will roll, the springs are what keep the brakes applied.Ron 1 Quote Link to comment Share on other sites More sharing options...
gearhead204 Posted June 2, 2014 Share Posted June 2, 2014 Baby Mack: thanks for the correction, I knew id probably get it wrong with out going out to the truck and checking. Jack: block wheels and release tractor brakes then back off the slacks on the maxi axles, mark the push rods and then apply the park brake you should have more than 2" of rod travel. if less than 2" with loose slackadjuster clevis pins either spring in can is broke or dirt and sand is built up in the can behind the push rod. 1 Quote Link to comment Share on other sites More sharing options...
thomastractorsvc Posted June 17, 2014 Share Posted June 17, 2014 My guess is the blue knob got pulled out and is not releasing the brakes, normally if you don't mess with the blue knob the yellow one will work like a two knob truck, sometimes the blue knob will get pulled out and until it has air will not stay/lock in. I find it hard to believe that both chambers went bad and no air is leaking, also make sure that you re adjust all 4 of the slack adjusters the same if you messed with them. Quote Robert"I reject your reality and substitute my own." Link to comment Share on other sites More sharing options...
jackb61sx Posted June 17, 2014 Author Share Posted June 17, 2014 Thanks for the info, they are all fixed picked up 4 new slack adjusters for it and all is well in my world, they are adjusted right, jacked up each wheel to do the adjusting and it stops better than before, also replaced a broken self adjusting one on the right front side.Jack Quote Link to comment Share on other sites More sharing options...
Gmerrill0516 Posted June 17, 2014 Share Posted June 17, 2014 So broken springs? What was the final verdict?Greg Quote Link to comment Share on other sites More sharing options...
jackb61sx Posted June 17, 2014 Author Share Posted June 17, 2014 Just worn out the pins where oblonged where they meet the shackle to the can and adjusted to where they should be, lesson learned jack each wheel off the ground spin wheel as you adjust because each side adjusts opposite the other. The front slack adjuster was stripped out on the spline so that was junk but all are fixed now and it stops just fine already drove it down 495 in pm rush hour from Hopkinton to Wilmington and that is nothing but stop and go,,,lol 1 Quote Link to comment Share on other sites More sharing options...
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