Difficult steering at idle

[Ted Couch]

  I have been having an issue with steering my 1989 Marquis while on idle. I have a 3208 CAT on a Gillig chassis. It does not seem to steer smoothly or easily when I try to turn the wheels while the rig is not moving. My understanding is that the steering and cooling fan both work from the same hydraulic pump. I am wondering if my steering issue is due to low hydraulic pressure, and if there is a way to measure the pressure currently being produced. The steering seems fine while driving down the highway; it is just when I am at idle or moving slowly that I have the problem.

Thanks in advance for any help or advice you may have.

Ted Couch

[Joel Ashley]

Ted, this is probably not relevant to a Marquis, but do you have an engine brake or an exhaust brake?  I assume it's an engine brake and my following comment not pertinent.  But just in case...

those of us with Exhaust Brakes can experience steering gremlins at low speeds.  The backpressure when the exhaust brake is on causes inadequate power to the hydraulic pump when the engine rpm's are low, such that we can get a weird feedback at the wheel.

Others more familiar with your particular model of coach will likely be more helpful, and it does sound more like a less-than-optimum pump or low fluid.  But until they chime in you might see if the steering issue exists with the engine or exhaust brake off.

Joel

[Gerald Farris]

Ted,
You are correct in that the same hydraulic pump powers the cooling fan and the power steering, and yes the pump pressure can be checked with the right equipment. You have to have a way to tee into the pressure hose to your steering gear for a pressure gauge that reads at least 2,000 PSI and have a snubber valve inline that can be closed to read maximum pressure. This arrangement will allow you to read the line pressure under all conditions and determine if low volume or low pressure is your issue.
 

There are several conditions that can be causing the condition that you are concerned about. I am not sure if the hydraulic pump on your coach is belt driven or if it is direct drive from the engine timing case. If it is belt driven, a slipping, worn, or improperly adjusted belt could be the cause. Other causes could be a defective pump, steering gear, or fan control (wax valve) that is that is diverting too much flow to the fan motor.

However, before you start chasing illusive issues, ask yourself how much the steering has changed. A stiffer steering feel while stopped is normal because it takes considerably more force to turn the front tires while stopped than it does when they are rolling and the hydraulic pump is operating at lower RPMs so the hydraulic force available is naturally reduced.

Gerald