partial power steering loss

[lakewoodpaul]

Has any one experienced a lack of power steering when applying the the brakes on a w22 wcc? This happens at any speed and I notice it while not moving,and apply brakes and turning the steering wheel.It is more prevalent when slowing down from high speed. 15K mi on an 2009 chassis.The power steering fluid level is OK. I believe the power assist to the steering is the same as to the brakes. Any ideas out there? I know its under warranty but were on the road and I would rather wait till I'm home to have it fixed.

[DriVer]

Originally Posted by lakewoodpaul

Any ideas out there? I know its under warranty but were on the road and I would rather wait till I'm home to have it fixed.

LWP, Take the vehicle to the service center for evaluation. Some owners have reported a few steering quirks on certain model year chassis. Let us know how you make out. I would expect that you can wait until you get home.

[gg]

The Power steering pump supplies pressurized fluid to the steering gear and the brake booster. If you have a pressure drop due to engine stoppage the electric motor should provide you a back-up. You should hear a noise if it comes on. (Check pwr steering tank and fill when cold)


Check the following: With engine a normal temp check you idle rpm.
rapidly turn the steer wheel to hard right then
hard left- did it turn smoothly? or lumpy?
If lumpy or the effort was high then the pump flow
is low.
Repeat the steering wheel movement and also
apply the brakes - if the effort is lumpy or high, again
low pump flow. repeat with rpm raised 300. did it go away?

Pump flow-- Positive displacement Vane pump
1. slow engine idle -adjust idle up via computer. -more RPM more flow -dealer

2. the pump flow control valve is out of spec, they used to be adjustable with a spring setting in the old US made systems.- dealer

3. bad pump performance due to internal leakage - dealer flow performace

4. leak down in the brake booster thus a pressure drop when recovering

5. The puzzle is - If the Hydro Max is triggered by low pressure the Electric Pump should come on to give you the extra assist.

On my 09 the - strg gear/pump/brake booster/ brakes are Robert Bosch-ZF - Linksystem. I hope Bosch gets to the bottom of this. like the pump pulley is to large.

Good luck

[DriVer]

Originally Posted by gg

The Power steering pump supplies pressurized fluid to the steering gear and the brake booster. If you have a pressure drop due to engine stoppage the electric motor should provide you a back-up. You should hear a noise if it comes on. (Check pwr steering tank and fill when cold)

5. The puzzle is - If the Hydro Max is triggered by low pressure the Electric Pump should come on to give you the extra assist.

On my 09 the - strg gear/pump/brake booster/ brakes are Robert Bosch-ZF - Linksystem. I hope Bosch gets to the bottom of this. like the pump pulley is to large

I don't know exactly what the problem is but here's my perspective on Item #5.

At idle ~600 RPM you are going to be realizing much more pressure from the Hydro Max pump than can be delivered from the emergency pump so the ePump will never engage under those conditions even to augment pressure. Now why the flow is not getting through the pump to the steering gear is the point that needs to be resolved. This could be as you suggested an adjustment or other serviceable item. We have even had owners here who remarked that a fluid type change made an improvement in reducing their steering effort.

As a point of knowledge do not expect that the ePump will provide enough force to effectively steer the vehicle. That will be helped somewhat but not a whole bunch, it's going to be a manual steering task if anything to clear the roadway. The ePump is designed to primarily augment the Hydro-Max brake booster which is needed to apply the brakes. This is why this system is triggered when you step on the brake.

[lakewoodpaul]

Thanks for the replies guys. maybe I forgot to say that this has just started happening. There is 15K mi. on the rig. Like I say the power steering is fine untill the brakes are applied moving or sitting still. Again Im not too concerned because it is under warranty, but I wont be home untill March and would hate to lose power steering while on the road in east jabbaba land. The power steering fluid level is Ok. By the way "lumpy steering" is a good description

[mfire1339]

Would not hurt to check the engine belt for slippage.


Mike

[gg]

lakewoodpaul

Would you post the model of your coach and Date of manufacture of the WH chassis. Shoud be by the chassis vin tag by the driver seat.

Check the belt for slippage due to oil would be good. It has a auto tension system so it should be adjusted right.

While your down there check the front of the power steering pump for a small oil leak that may have wicked down the pulley on to the belt/ pulley grooves.

If the RPM at idle is correct and you can fix the problem by increasing the engine RPM then points 2thru4 are still valid.

The comment by Driver that the electric backup won't provide any power assistance for the steering at low or no engine rpm indicates the mechanical pump system has changed since new. I thought the electric motor -HydroMax would provide power assistance to the steering and/or brakes in case of engine failure/ belt seperation.

How far is home for you? Do you feel you can control your coach with manual steering to get you off the road?

[DriVer]

Originally Posted by gg

The comment by Driver that the electric backup won't provide any power assistance for the steering at low or no engine rpm indicates the mechanical pump system has changed since new. I thought the electric motor -HydroMax would provide power assistance to the steering and/or brakes in case of engine failure/ belt separation.

gg, The primary function of the electric pump is to provide power to the most critical system, the brakes. The vehicle's direction will still be able to be controlled with increased effort. Applying the brakes to the Bosch Hydro-Max without a power assist will not yield a sufficient amount of pressure to stop the vehicle. The system was a requirement in order to get the DOT certification. You will see the exact same system on the F53 Super Duty chassis.

[Topflite51]

I personally would make an appointment with a WCC dealer and have it checked out. Better safe than sorry I always say.