LITTLEJOE_MACK Posted May 3, 2006 Share Posted May 3, 2006 HELLO EVERYONE, I AM NEW TO THE SITE AND HAVE SOME QUESTIONS I HOPE SOMEONE CAN ANSWER.I JUST BOUGHT A 86' MACK MIDLINER MEDIUM DUTY SINGLE WHEEL RIG.IT HAS THE RENUALT TURBO DIESEL, SIBGLE 5 SPEED AND A DAY CAB.I BOUGHT IT WITH IT ALREADY HAVING BRAKE TROUBLE.IN FACT, IT HAS NO BRAKES WHATSOEVER.THE QUESTION IS, AIR OVER HYDRAULIC MEANS WHAT ??THE PROBLEM WITH MINE IS THERE IS A POD MISSING ON THE PASSENGER REAR WHEEL. I HAVE BEEN TOLD THAT THIS IS JUST A PARKING BRAKE AND IF I BLOCK THE AIR LINE GOING TO IT AND SCREW IT DOWN I CAN STILL DRIVE THE RIG I JUST WON'T HAVE A PARKING BRAKE.HERE IS WHERE I AM AT RIGHT NOW. I TOOK A SHOP AIR COMPRESSOR AND FILLED THE AIR TANKS UNDER THE DRIVERS DOOR. ONCE THEY GET A GOOD AMOUNT OF PRESSURE BUILT UP THE LINE THAT GOES TO THE POD STARTS LEAKING. I HAVE FOUND THAT MUCH OUT.BUT THEN HERE IS ANOTHER ISSUE. THE COMPRESSOR FOR THE TRUCK DOESN'T SEEM TO BE WORKING EITHER. I PULLED THE HEAD AND INSPECTED WHAT I COULD OF IT. THE REED VALVE, OR AT LEAST THAT IS WHAT IT LOOKS LIKE TO ME, SEEMS TO BE FINE WITH NO RESTRICTIONS FROM WHAT I CAN TELL.WHEN RUNNING THE TRUCK DOESN'T SEEM TO BUILD PRESSURE TO RELEASE THE ONE POD THAT IS STILL FUNCTIONAL IN THE REAR. I BASICALLY AM AT A STOPPING POINT BECAUSE I DON'T UNDERSTAND THE AIR OVER HYDRO SYSTEM.IN SHORT, NO BRAKES, ONE MISSING POD ON THE REAR, COMPRESSOR THAT RUNS BUT DOESN'T BUILD PRESSURE, AND NO HELP FROM THE LOCAL "MECHANICS" SO FAR.PLEASE ASSIST OR STEER ME TOWARD A POSSIBLE HITCH IN MY GIDDY UP ! ! IS THERE A CHECK VALVE OR SOMETHING THAT IS OPEN IN THE SYSTEM THAT I AM MISSING ? ? IT IS VERY HARD TO HEAR A AIR LEAK WITH A RUMBLING DIESEL .THANKS GUYS, MARCEL Quote Link to comment https://www.bigmacktrucks.com/topic/1084-good-brakes-gone-bad/ Share on other sites More sharing options...
Barry Posted May 3, 2006 Share Posted May 3, 2006 There should be a governer valve in line between the compressor and air tank...check that first! They seem to cause alot of air building problems. Beware...all fittings and airlines are metric!! Quote Barry - Watt's Truck Center Parts Manager and BMT Webmaster...1-888-304-MACK Link to comment https://www.bigmacktrucks.com/topic/1084-good-brakes-gone-bad/#findComment-5632 Share on other sites More sharing options...
ThaddeusW Posted May 3, 2006 Share Posted May 3, 2006 Air over hydraulic is simple to understand. Imagine two master cylinders one for the front and one for the rear. Instead of having the foot pedal directly actuate the cylinder there is a piston similar to a brake chamber that operates the master cylinder (that thing is called an air hydraulic intensifier). Its a full air system up until you get to the air hydraulic intensifires. then its just normal hydraulic brakes on the axles. Some mid liners had air over hydraulic on the front axle and regular air s-cam or air disc on the rear. The parking brake I think has a spring chamber on each rear wheel and works like a wedge brake to park it. With no air in the system the compressor should immediatly start to fill the tanks as there iis no air pressure in the unloader line. Disconnect any lines to the compressor and see if air starts blowing out of one of them while the engine is running. No air means the compressor valves might be bad, or the unloader valve in the compressor is stuck open. I am not 100% sure but the govenor might be mounted to the air dryer. Also check the delivery line from the compressor and the air dryer for clogs. The euro brake systems are different as they have no wet tank, all accessories are back fed from the primary and secondary brake tanks as well as the trailer supply tank if its a tractor (yup they have a tank just for trailer air and tractor spring brakes). There is a valve manifold mounted to the dryer and it cuts the accessories off once the pressure drops below a set level in the tanks. also the govenor is usually mounted on the air dryer in most newer euro brake systems. Quote -Thad What America needs is less bull and more Bulldog! Link to comment https://www.bigmacktrucks.com/topic/1084-good-brakes-gone-bad/#findComment-5641 Share on other sites More sharing options...
fullfuel01 Posted May 3, 2006 Share Posted May 3, 2006 the compressor never stop pumping on these Mack, that's why this nice sound.. the signal from the governor goes thrue the exhaust of the air dryer... Quote Link to comment https://www.bigmacktrucks.com/topic/1084-good-brakes-gone-bad/#findComment-5642 Share on other sites More sharing options...
LITTLEJOE_MACK Posted May 4, 2006 Author Share Posted May 4, 2006 THANKS GUYS, I THOUGHT THAT THERE WAS SOME KIND OF "VALVE" THAT BLEW OFF THE EXCESS. THAT IS WHY YOU HEAR THE "CHOO" NOISE WHEN YOU ARE SITTING BESIDE ON AT A LIGHT OR GOING DOWN THE ROAD. I DIDN'T KNOW THE NAME OF IT UNTIL NOW.I WILL CHECK IT FIRST THEN MOVE ONTO CHECKING OUT THE REST OF THE SYSTEM.I KNEW THIS WAS THE RIGHT SITE TO JOIN. YOU GUYS DEFINITELY KNOW YOUR STUFF AND I THANK YOU FOR THE SCHOOLING.I AM HOPING TO GET THE MIDLINER ROAD WORTHY AND THEN LIST IT ON EBAY.I AM GOING OVER TO POST A QUESTION ABOUT SOME TIRES .SEE IF ANYONE CAN HELP.THANKS TO ALL AGAIN, MARCEL Quote Link to comment https://www.bigmacktrucks.com/topic/1084-good-brakes-gone-bad/#findComment-5650 Share on other sites More sharing options...
ThaddeusW Posted May 4, 2006 Share Posted May 4, 2006 One thing you can do to trace a leak is get some dish soap mix it with water and put it in a spray or squirt bottle. Then spray it all over the air lines and look for bubbles. Now you dont have to worry bout the engine running, you can see the leak. Quote -Thad What America needs is less bull and more Bulldog! Link to comment https://www.bigmacktrucks.com/topic/1084-good-brakes-gone-bad/#findComment-5652 Share on other sites More sharing options...
MackMan96 Posted May 4, 2006 Share Posted May 4, 2006 HELLO EVERYONE, I AM NEW TO THE SITE AND HAVE SOME QUESTIONS I HOPE SOMEONE CAN ANSWER.I JUST BOUGHT A 86' MACK MIDLINER MEDIUM DUTY SINGLE WHEEL RIG.IT HAS THE RENUALT TURBO DIESEL, SIBGLE 5 SPEED AND A DAY CAB.I BOUGHT IT WITH IT ALREADY HAVING BRAKE TROUBLE.IN FACT, IT HAS NO BRAKES WHATSOEVER.THE QUESTION IS, AIR OVER HYDRAULIC MEANS WHAT ??THE PROBLEM WITH MINE IS THERE IS A POD MISSING ON THE PASSENGER REAR WHEEL. I HAVE BEEN TOLD THAT THIS IS JUST A PARKING BRAKE AND IF I BLOCK THE AIR LINE GOING TO IT AND SCREW IT DOWN I CAN STILL DRIVE THE RIG I JUST WON'T HAVE A PARKING BRAKE. This pod is used for both parking and service brakes, definately needed.HERE IS WHERE I AM AT RIGHT NOW. I TOOK A SHOP AIR COMPRESSOR AND FILLED THE AIR TANKS UNDER THE DRIVERS DOOR. ONCE THEY GET A GOOD AMOUNT OF PRESSURE BUILT UP THE LINE THAT GOES TO THE POD STARTS LEAKING. I HAVE FOUND THAT MUCH OUT.BUT THEN HERE IS ANOTHER ISSUE. THE COMPRESSOR FOR THE TRUCK DOESN'T SEEM TO BE WORKING EITHER. I PULLED THE HEAD AND INSPECTED WHAT I COULD OF IT. THE REED VALVE, OR AT LEAST THAT IS WHAT IT LOOKS LIKE TO ME, SEEMS TO BE FINE WITH NO RESTRICTIONS FROM WHAT I CAN TELL.WHEN RUNNING THE TRUCK DOESN'T SEEM TO BUILD PRESSURE TO RELEASE THE ONE POD THAT IS STILL FUNCTIONAL IN THE REAR. I BASICALLY AM AT A STOPPING POINT BECAUSE I DON'T UNDERSTAND THE AIR OVER HYDRO SYSTEM.IN SHORT, NO BRAKES, ONE MISSING POD ON THE REAR, COMPRESSOR THAT RUNS BUT DOESN'T BUILD PRESSURE, AND NO HELP FROM THE LOCAL "MECHANICS" SO FAR.PLEASE ASSIST OR STEER ME TOWARD A POSSIBLE HITCH IN MY GIDDY UP ! ! IS THERE A CHECK VALVE OR SOMETHING THAT IS OPEN IN THE SYSTEM THAT I AM MISSING ? ? IT IS VERY HARD TO HEAR A AIR LEAK WITH A RUMBLING DIESEL .THANKS GUYS, MARCEL Quote Link to comment https://www.bigmacktrucks.com/topic/1084-good-brakes-gone-bad/#findComment-5662 Share on other sites More sharing options...
POWERBRAKEBOB Posted July 13, 2007 Share Posted July 13, 2007 WE MAY BE ABLE TO HELP YOU. I DO REBUILD THOSE UNITS, BUT OUR FAVORITE IS TO CONVERT THE AIR/HYD TO A NEWER SYSTEM. Quote Link to comment https://www.bigmacktrucks.com/topic/1084-good-brakes-gone-bad/#findComment-12974 Share on other sites More sharing options...
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