Bottom Line
MaintenanceQ&A
Bumpy rides and bad gauges

By Paul Abelson
Senior technical editor

 

Q: I have a 2003 Freightliner Classic, and I have replaced every item to fix a bottoming/topping out problem with the sleeper. I have taken it to a Freightliner dealer and was told it has 135 pounds of pressure in the system. They have tried to readjust it four different times. I have replaced everything – the idle arm adjuster, the bags, shocks, even the valve at the tank and the sway bar. It still bottoms and tops out. Do you have any suggestions?

A:  The 135 pounds of pressure in the system is above what the pressure should be. That should have been obvious from the primary air gauge in the dashboard. Air in the cab suspension system cannot be any higher than in the main tank. It should have been regulated to 120 psi, plus or minus 5 psi. If the dealer could not adjust the compressor, it probably had a bad D2 governor. That should have been replaced first.

It seems as if your dealer was playing guessing games at your expense, replacing parts until he found something that worked. When you say he replaced the “idle arm adjuster,” I assume you are referring to the leveling valve for the sleeper. It should have been ordered according to your truck’s VIN. Any authorized dealer should have looked it up. You cannot use just any leveling valve. It must be specific and adjusted properly. Adjustment is critical.

Some of the replaced parts have nothing to do with sleeper cab ride. The air valve at the tank is just there to shut off air to the suspension if pressure drops below 70 psi, only to maintain air to the brakes. The sway bar is for just that – side-to-side sway. It has nothing to do with bottoming or topping out. With so many parts having been replaced, I’d check to be sure that there are no mismatched parts or wrong part numbers.

These suggestions should fix your problems. Please let me know if they do the trick.

Q: I have a 1996 International 9600. It was an old fleet truck that had a Qualcomm in it. Somebody cut all the old Qualcomm wires out. Now the speedometer points down and doesn’t work anymore. The check engine light stays on all the time. When the key is first turned on, the gauges work. Then the speedometer clicks and the check engine light comes on. Any ideas?

A: While I know a bit about mechanicals, fuels and lubes and things you can touch and feel, I call in the cavalry for things electronic. I am blessed with friends who are willing to help when I am in need. To answer your question, I turned to Carl Tapp, VP of maintenance of a 2,000-power unit fleet that uses Qualcomm equipment. Carl wrote:

 “Looks like they have cut the J1708 wires. These wires provide ECM data to the Qualcomm. If they are cut, the speedometer will not work and the ECM will also send a code. That’s why the check engine light stays on. It should be a simple fix.”

Just have your dealer check continuity on the J1708 wires. J1708 is a Society of Automotive Engineers standard for electronic communications within a truck. An International dealer should be able to get a wiring diagram for your specific truck using the vehicle identification number (VIN). LL

 

Paul Abelson can be reached at
truckwriter@anet.com.

March/April
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