Frequently Asked Questions

Possible Cause: Air in-cylinder – bleed cylinder using the following procedure.

• Raise the dump body and cylinder to full extension.
• Lower the dump body and cylinder till the front of the dump body is approximately 2 feet off of the chassis frame.
• Put the body up lever in the hold position (center).
• If you have an outside bleeder valve, crack the valve open at this time.
• Wait until all trapped air has escaped from the valve and a full stream of hydraulic oil is escaping from the valve.
• At this point the cylinder is bled, close the bleeder valve.

If your bleeder valve is located on top of the cylinder you will need a 9/16″ wrench to remove the dog box cover and you will need to move to the inside of the dump body.

• Remove the dog box cover and crack the bleeder valve open at this time.
• Wait until all trapped air has escaped from the valve and a full stream of hydraulic oil is escaping from the valve.
• At this point the cylinder is bled, close the bleeder valve.
• Trucks built after the beginning of 2012 have bleederless cylinders in them. The new cylinders bleed themselves back through the oil tank. If you believe that you have air in the cylinder, raise the body to its fully extended position. Then lower the body back down to the frame. Continue to hold the body lever in the lower position for about five to ten seconds. That should purge any air out of the system and escape through the hydraulic tank. If air continues to escape into the hydraulic tank while holding the body control lever in the lower position you may have a faulty air shift actuator on your pump.

Possible Cause: Air in the hydraulic cylinder.

• See procedures to bleed air out of the cylinder in “Cylinder operation is jerky or cylinder slow coming down” above.

Possible Cause: Head nut too tight on one of the cylinder stages.

• Identify the stage that is hanging up.
• Backhead nut off 1 full turn, then re-tighten 3/4 turn.

Possible Cause: Dump truck is being operated with the body up lever unlocked in the down position.

• The body up levers (cable actuated) must be manually locked into the center position with every use, they are not self-locking.
• The body up lever not being centered is the most common problem with excessive air in the hydraulic system.

Possible Cause: The oil level in the hydraulic tank is low and the suction hose is sucking the air out of the tank.

• Top off the hydraulic tank with hydraulic oil.

Possible Cause: Cylinder head nut needs tightening (normal maintenance item)

• Refer to dump body owner’s manual, cylinder section.

Possible Cause: Bleeder valve left open at the top of the cylinder.

• Remove the dog box cover inside the dump body with a 9/16″ wrench and tighten the bleeder valve.

Possible Cause: Cylinder wiper or packing protruding above head-nut.

• Call J&J Warranty Dept. (800.777.2671) with the dump body serial number and discontinue the use of the cylinder.

Possible Cause: We receive many calls on what appears to be loose cylinders.

• A telescopic cylinder mounted to a dump body and chassis frame needs a certain amount of play so the cylinder does not destroy itself when operated in motion or slightly off level. This play in the cylinder is normal.
• If after further analysis, the operator detects a problem outside of the above explanation, please call the Warranty Dept. at J&J Truck Bodies (800.777.2671)

Possible Cause: (See Cab Controls)

Possible Cause: (See PTOs and Pumps)

Possible Cause: Body up cable may have been impacted from underneath damaging either cable or cable connection to the pump. This may result in the pump spool being unable to return to the center.

• Inspect cable and connection kit.
• If damaged, replace damaged components.
• Call 800-777-2671 and ask for the Parts Department. (Body serial number needed)

Possible Cause: (Cable actuated pump) Cable is binding.

• Within the 12 warranty period call, 800.777.2671 ask for the Warranty Department, after the 12-month Warranty period ask for the Parts Department. (Body serial number needed)
• If you replace the cable please examine the connection kits between the cable and pump. Replace the connection kit if excessive rust is apparent.

Possible Cause: (Air actuated) Body up lever a.k.a. feather valve is defective.

• Release airlines at the pump for the feather valve.
• Operate feather valve and check airline pressure with airlines unattached; 90 PSI required.
• If one of the airlines is not producing enough pressure to operate the shifter spool on the pump, the feather valve may be defective.
• Replace the feather valve.
• Within the 12-month warranty period call, 800.777.2671 ask for the Warranty Department, after 12 months ask for the Parts Department. (Body serial number needed)
• Another possible cause could be the air actuator on the pump.

Possible Cause: (Cable-operated) Cast aluminum ear at the bottom of the body up lever, where the cable attaches, has broken off. (This would normally be a symptom of a bound cable, and the lever has been forced.)

• Within the 12-month warranty period call, 800.777.2671 ask for the Warranty Department, after 12 months ask for the Parts Department. (Body serial number needed)

Possible Cause: Air tailgate cylinder bound and bypassing air through cylinder seal and exhausting in the cab.

• Check all pivot points on the air tailgate cylinder and make sure they are lubricated and moving freely. (Air tailgate cylinder mounting bolt is to be LOOSE to allow the cylinder to pivot.)
• Remove the pin from the yoke that attaches the air tailgate cylinder to the tailgate linkage.
• Operate the air tailgate switch with the air tailgate cylinder unattached.
• If it is still exhausting in the cab, replace the air tailgate cylinder.
• If it stops exhausting in the cab, see (Tailgates: Air tailgate cylinder).
• To replace the air tailgate switch, within a 12-month warranty period call 800.777.2671, ask for the Warranty Department after 12 months ask for the Parts Department. (Body serial number needed)

Possible Cause: Shifter head is malfunctioning.

• Replace shifter headcover.
• Within the 12-month warranty period call, 800.777.2671 ask for the Warranty Department, after 12 months ask for the Parts Department. (Body serial number needed)

Possible Cause: Electric over air switch blown fuse – factory switch.

Possible Cause: Flexible switch extension needs to be adjusted to come into contact with the body on the way down.

• Adjust the switch to the appropriate angle to catch the dump body, long members, as the body is lowered.

Possible Cause: Body up switch may have been damaged by falling material or another unnatural cause.

• Replace body up switch.

Possible Cause: Faulty switch

• Remove screws to body up switch cover, unhook both wires and cross them. The body light should come on while the ignition switch is on.
• If the body up light comes on when crossed the problem is internal to the body up switch.
• Replace the switch.
• If the body up light still does not come on check for broken wires or a blown fuse! Within the 12-month warranty period call, 800.777.2671 ask for the Warranty Department, after 12 months ask for the Parts Department. (Body serial number needed)

Possible Cause: Tailgate top hardware pins need to be greased. (This is a weekly maintenance item.)

• Tailgates top pins left for prolonged periods of time without grease will guald in the top hardware bushings.

Possible Cause: Tailgate linkage needs to be tightened.

• Loosen the jam nut on the tailgate linkage turnbuckle and tighten the turnbuckle as needed.
• Re-tighten the jam nut back against the turnbuckle. Be sure that the tailgate cross rod snaps over-center up against the body floor. If the turnbuckles are adjusted too tight the cross rod will not snap over the center.

Possible Cause: Tailgate linkage is broken or out of adjustment.

• Within the 12-month warranty period call, 800.777.2671 ask for the Warranty Department, after 12 months ask for the Parts Department. (Body serial number needed)

Possible Cause: Tailgate linkage is too tight.

• Loosen the jam nut against the turnbuckle, back the turnbuckle off until the tailgate linkage locks over the center, and re-tighten the jam nut against the turnbuckle.

Possible Cause: Material may be wedged in bottom hardware or trapped around tailgate linkage.

• Remove trapped material. (Trapped material in bottom tailgate hardware will often stretch tailgate linkage. The linkage may need to be adjusted after the material is freed from the bottom hardware.)

Possible Cause: Air Tailgate cylinder is bound.

• Remove the pin from the yoke that attaches the air tailgate cylinder to the tailgate linkage.
• Make sure the air tailgate cylinder mounting bolt is LOOSE, and the cylinder can pivot easily on the mounting bolt.
• Pivot the air tailgate cylinder on the bolt and make sure the air tailgate cylinder yoke, that attaches to the tailgate linkage, swings easily into its attachment point without unnaturally cocking the cylinder.
• If the air tailgate cylinder continues to exhaust in the cab, the cylinder may be defective.
• (See Also: Cab Controls – Air Tailgate Switch)
• Within the 12-month warranty period call, 800.777.2671 ask for the Warranty Department, after 12 months ask for the Parts Department. (Body serial number needed)

Possible Cause: There may be a number of reasons for a PTO or pump to be leaking.

• Wipe down the leaking assembly to determine where the unit is leaking.
• Note the color of the fluid leaking. (Clear: Hydraulic oil – Red or Green: Transmission Fluid)
• Call the Warranty Department immediately with the details.
• Call 800-777-2671 and we will have a technician troubleshoot with you over the phone. (Body serial number needed)

Possible Cause: There are numerous reasons a PTO or pump may be making excessive noise.

• DISENGAGE PTO IMMEDIATELY and call the Warranty Department at 800-777-2671 with details.
• We will have a technician troubleshoot over the phone. (Body serial number needed)

Possible Cause: The relief cartridge in the pump may be contaminated.

• Dirt in the relief valve may hold the relief valve open slightly allowing hydraulic oil to bypass the valve, causing the dump bed to drift down.
• Replace the relief cartridge.
• Within 12- a month warranty period call 800-777-2671, and ask for the Warranty Department, after 12 months ask for the Parts Department. (Body serial number needed)

Possible cause: If the relief cartridge has been replaced and the body is still not holding, call 800-777-2671, ask for Warranty Dept. and we will have a technician troubleshoot with you over the phone. (Body serial number needed)