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treadle valve fittings


BACKinMACK

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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.

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Edited by BACKinMACK
left out piping material ,add pics
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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

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

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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.

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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.

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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.

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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.

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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 by BACKinMACK
missed a word
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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).

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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.

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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.

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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 by Onyx610
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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.

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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. 

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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 

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