BACKinMACK Posted January 12, 2022 Share Posted January 12, 2022 (edited) Hello, I am replacing the treadle valve in my 1999 MACK RD688S dump truck. I believe it is original. The air line fittings are a mix of push to fit and compression. The two larger 1/2" lines are compression, the balance being five 3/8"lines, and one 1/4"line are push to fit. Can I replace the 1/2" compression with 1/2" push to fit? Or is there a reason those are compression? All piping to and from valve are plastic. I just added pictures. Can anyone tell me what the piece is to the left plumbed into the top section. I am guessing a check valve? Maybe a pressure regulator? Thanks in advance for any help. Edited January 12, 2022 by BACKinMACK left out piping material ,add pics Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/ Share on other sites More sharing options...
doubleclutchinweasel Posted January 12, 2022 Share Posted January 12, 2022 There is usually a check valve or a double check valve right there. Attached is some double check info. I don't care much for the push-lock fittings, personally. YRMV. The "plastic" compression stuff is probably DOT air line tubing and fittings. Really good stuff. DC Valves.pdf Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-486939 Share on other sites More sharing options...
doubleclutchinweasel Posted January 12, 2022 Share Posted January 12, 2022 This was a R-model schematic. Note the Stop Light Switch and Double Check Valve near the treadle valve. Not sure if this is the same on your newer unti, but it might give you some ideas Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-486940 Share on other sites More sharing options...
BACKinMACK Posted January 13, 2022 Author Share Posted January 13, 2022 Thank you double clutch. Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-486994 Share on other sites More sharing options...
BACKinMACK Posted January 13, 2022 Author Share Posted January 13, 2022 21 hours ago, doubleclutchinweasel said: There is usually a check valve or a double check valve right there. Attached is some double check info. I don't care much for the push-lock fittings, personally. YRMV. The "plastic" compression stuff is probably DOT air line tubing and fittings. Really good stuff. DC Valves.pdf 852.72 kB · 0 downloads You nailed it Double Clutch. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-486996 Share on other sites More sharing options...
mechohaulic Posted January 17, 2022 Share Posted January 17, 2022 the valve in question should be the double check valve for the trolley valve on the steering column . pedal application has air through the valve to back brake valve same time the shuttle in the check valve closes air to the trolley valve. pulling down trolley sends air through check valve switches shuttle to close off pedal and send air brake valve .keep in mind, i discussing older vehicles. not many have trolley valves from what i hear.without the check valve there would be and exhaust of air from application not being used. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487218 Share on other sites More sharing options...
h67st Posted January 17, 2022 Share Posted January 17, 2022 2 hours ago, mechohaulic said: the valve in question should be the double check valve for the trolley valve on the steering column . pedal application has air through the valve to back brake valve same time the shuttle in the check valve closes air to the trolley valve. pulling down trolley sends air through check valve switches shuttle to close off pedal and send air brake valve .keep in mind, i discussing older vehicles. not many have trolley valves from what i hear.without the check valve there would be and exhaust of air from application not being used. Mechohaulic is dead on...the double check valve keeps the trolley valve from sending air to the tractor brakes. Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487225 Share on other sites More sharing options...
BACKinMACK Posted January 17, 2022 Author Share Posted January 17, 2022 2 hours ago, mechohaulic said: the valve in question should be the double check valve for the trolley valve on the steering column . pedal application has air through the valve to back brake valve same time the shuttle in the check valve closes air to the trolley valve. pulling down trolley sends air through check valve switches shuttle to close off pedal and send air brake valve .keep in mind, i discussing older vehicles. not many have trolley valves from what i hear.without the check valve there would be and exhaust of air from application not being used. Thanks for the information. I do have the trolley lever in my 1999. I did see a line in the schematic that Double clutch posted that went to the trolley also. Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487227 Share on other sites More sharing options...
BACKinMACK Posted January 17, 2022 Author Share Posted January 17, 2022 (edited) 10 minutes ago, h67st said: Mechohaulic is dead on...the double check valve keeps the trolley valve from sending air to the tractor brakes. I did not know that. I thought the trolley activated the tractor rear brakes as well as the trailer brakes. But your saying the trolley only activates the trailer brakes. Edited January 17, 2022 by BACKinMACK missed a word Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487229 Share on other sites More sharing options...
h67st Posted January 17, 2022 Share Posted January 17, 2022 Just now, BACKinMACK said: I did not know that. I thought the trolley activated the tractor rear brakes. But your saying the trolley only activates the trailer brakes. Right. Treadle valve operates both, trolley valve only operates the trailer (if the check valve is working correctly and installed right). 1 Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487230 Share on other sites More sharing options...
Onyx610 Posted January 17, 2022 Share Posted January 17, 2022 One of our trucks has that double check valve but no trolly valve. Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487232 Share on other sites More sharing options...
mechohaulic Posted January 17, 2022 Share Posted January 17, 2022 it also depends on the unit. a dump truck might have a trolley on the column which would also apply the truck service brake providing the dump was NOT set up to pull a tag trailer with air brakes. some double check valves have the brake light switch allowing the brake light to work with pedal or trolley application. Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487233 Share on other sites More sharing options...
BACKinMACK Posted January 17, 2022 Author Share Posted January 17, 2022 3 minutes ago, Onyx610 said: One of our trucks has that double check valve but no trolly valve. Is yours set up for a trailer? Mine is a tri-axle dump truck and it is plumbed for a tag along trailer. It also has the thee valves in the dash. Yellow red and blue. Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487234 Share on other sites More sharing options...
Onyx610 Posted January 17, 2022 Share Posted January 17, 2022 (edited) No it is not, other trucks have a trolly valve but they are newer so different style/location of the treadle valve. The truck I’m talking about is a 2002 rd688s 10 wheeler dump. Edited January 17, 2022 by Onyx610 Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487235 Share on other sites More sharing options...
BACKinMACK Posted January 17, 2022 Author Share Posted January 17, 2022 2 minutes ago, mechohaulic said: it also depends on the unit. a dump truck might have a trolley on the column which would also apply the truck service brake providing the dump was NOT set up to pull a tag trailer with air brakes. some double check valves have the brake light switch allowing the brake light to work with pedal or trolley application. My truck brake lights come on with the trolley activated. If I remember correctly when I brought the truck home this fall the trolley lever when pulled down slowed the truck(no trailer). Not sure though, I have not driven it since. Doing some repairs for this spring. Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487237 Share on other sites More sharing options...
mechohaulic Posted January 17, 2022 Share Posted January 17, 2022 double check without trolley might be the dual air system , dump plumbed for tag basically is same system as tractor set up for hooking a trailer. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487238 Share on other sites More sharing options...
Onyx610 Posted January 17, 2022 Share Posted January 17, 2022 Ahhh ok that is probably what it’s for then. Yes the brake lights come on when the trolly valve is used. I use that to check brake lights when doing state inspection. Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487239 Share on other sites More sharing options...
Onyx610 Posted January 17, 2022 Share Posted January 17, 2022 I believe another use for that valve is when your owner operator and hauling someone else’s trailer you use it to slow the truck down using the trailer brakes 😏 1 Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487240 Share on other sites More sharing options...
BACKinMACK Posted January 17, 2022 Author Share Posted January 17, 2022 10-4 Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487242 Share on other sites More sharing options...
mechohaulic Posted January 17, 2022 Share Posted January 17, 2022 triaxle dump without tag set up will have the trolley hooked to rear brakes. your truck should slow down with the trolley. even with a tag set up,if you have the 2-3 button set up on dash for trailer brakes the brake lights might still work with the trolley without a trailer connected. Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487243 Share on other sites More sharing options...
mechohaulic Posted January 17, 2022 Share Posted January 17, 2022 i learned the wrong way many yrs ago about the trolley being hooked to rear brakes short version;;i picked up a brand new DM600 triaxle chassis from boston mack was heading back to waterbury ct mack. passing a truck ,he gave me "the lights" for ok pull back in right lane. as a thank you instead of putting 4-ways on i pulled the trolley !!! not good when you are in left lane with your foot to the boards. instead of just the flash of brake lights for thanks;; that chassis jumped and hopped almost went in ditch. as a youngin i didn't piss my pants but it was close 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487244 Share on other sites More sharing options...
mowerman Posted January 17, 2022 Share Posted January 17, 2022 We have all done dumb shit…. Bob Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487294 Share on other sites More sharing options...
Steel Nose Posted January 17, 2022 Share Posted January 17, 2022 That double check valve is Mack part# 20QE2199R and Bendix part# 289296N both numbers are readily available 1 Quote Link to comment https://www.bigmacktrucks.com/topic/69052-treadle-valve-fittings/#findComment-487304 Share on other sites More sharing options...
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