Author Topic: Loss of steering assist  (Read 14959 times)

Gary and Judy Doran

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Re: Loss of steering assist
« Reply #15 on: October 26, 2015, 07:41:24 PM »
 In a  previously post I mention that I had changed the size of the hydraulic filter from 3.67" to 5" in an attempt to solve the problem of the steering wheel jerking from loss of steering assist.
   After traveling last spring and summer though a lot of hard turns at low speeds I can report that this change eliminated 80+% of the jerking that use to occur.  I never once had the hard jerking that would almost rip the wheel from your hands, only a slight jerking in the steering on a few occasions.
  Two months ago a Cat dealer changed the setting, which I believe reads, " exhaust brake activated the hydraulic cooling fan activates".  Since then I have not experienced any movement in the steering wheel signifying a loss of steering assist.
  As a note: Everyone has different driving patterns . I travel with the exhaust brake on most of the time and probably tend to enter into turns a little further and therefore turn somewhat sharper then some do. I can also notice a difference in how the motor home reacts since it no longer has use of the drag of power from the activation of cooling fan.
 If you experience a steering jerk in a turn with the exhaust brake having been activated I suggest that you have setting changed and see if that is enough to eliminate most of the problem. It takes just a minute or two to hook up a computer the option off.
   Happy to say this is one problem solved for me.   

Mike Nunn

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Re: Loss of steering assist
« Reply #16 on: October 26, 2015, 08:21:49 PM »
Our 2007 contessa has done this since day one, just a slight bump at low speed turns. I have had hydraulic system serviced more than once, cat has checked the power steering pump but no solution.
I have just more or less ignored it last couple of years. It does not seem to happen very often.

Joel Ashley

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Re: Loss of steering assist
« Reply #17 on: November 28, 2015, 04:02:40 AM »
After driving our coach some distance the last month, following a 3 year hiatus and being cognizant of this thread, I've paid more attention and can report that almost every time I engage the Exhaust Brake there is a reaction in the steering wheel.  At road speeds it may be little more than a slight movement, but it's there nonetheless.  Going down hills of course is where the EB is most often engaged, and where at the same time is a lowered RPM as the foot comes off the throttle at the top of the grade.  The lower RPM seems to result in a little stronger steering reaction, albeit nowhere near as strongly as when at minimal throttle in a parking lot or campground maneuver.

This all supports the theory that BCS put forth for Russ Mann's coach.  My question for the mechanics here, like Dave A. or Gerald: why does the hydraulic cooling fan kick in by apparent default when the exhaust brake is activated?  I'm not questioning that it should or shouldn't, but rather curious about the physical, mechanical necessity.  I'm presuming that exhaust backpressure increases engine temp., especially at lower RPM's, and the ECM automatically pre-anticipates the heat, or is it some other reason?

I've yet to drop in on a CAT facility for the recommended reprogramming.  I intended to, but elected to have Henderson's do the engine service while I was there for other work.  They were not aware of this issue, so I didn't have them address it.  I'm presuming that reprogramming so the cooling fan doesn't automatically initiate with the EB won't affect the normal cooling fan engagement at its normal high temp points.

Thanks,
Joel
« Last Edit: November 28, 2015, 04:12:51 AM by Joel Ashley »
Joel and Lee Rae Ashley
Clackamas, Oregon
36.9 ft. 2006 Monterey Ventura IV, aka"Monty Rae"
C9 400HP Cat

Gerald Farris

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Re: Loss of steering assist
« Reply #18 on: November 28, 2015, 02:35:19 PM »
Joel,
The only reason that I can think of to engage the cooling fan when the exhaust brake is engaged is put more drag on the engine by making the hydraulic pump work harder. Heat should not be the reason because the ECM (engine control module) cuts off fuel when the exhaust brake is engaged.

Gerald 
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Dave Atherton

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Re: Loss of steering assist
« Reply #19 on: November 28, 2015, 08:50:39 PM »
Gentleman, if check valve on oil cooler is stuck to open would affect pressure greatly.
Dave Atherton Retired Cat Mechanic

Dave Atherton

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Re: Loss of steering assist
« Reply #20 on: November 28, 2015, 10:10:56 PM »
Gentleman back again, the jerking will indicate low pressure or lack of fluid. I think from
way some hydraulic's are put in ( They have a a split valve off hydraulic pump that is
also power assist with steering ) and fan and shifts off pressure. Ran into sticking valve from
shifting. Number 2 replacement hydraulic hose with smaller size end that would still connect
but would not allow correct fluid to pass and give incorrect value to volume and pressure.
there has beem many problems with check valve sticking on oil cooler with heui pump operation
and loss of power, but thinking about it this will not pertain to above problem.
Dave Atherton Retired Cat Mechanic

Dave Atherton

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Re: Loss of steering assist
« Reply #21 on: November 29, 2015, 03:14:11 AM »
Gentleman, I would like to make a suggestion, ( in my 42 years of being a mechanic, our work was real heavy
in hydraulic fluid power as well as engines ). After looking at many post on this subject lets get into the hydraulic
system and connect a flow meter after hydraulic pump and before hydraulic valve and tee a pressure gauge into the hydraulic return line ( to check for fluid back pressure to tank ) Have mechanic record flow and pressure at different
rpm.  Step 2 connect flow meter after the hydraulic valve going to steering and again record flow and pressure, do
not remove gauge in the return line to tank. Step 3 after hydraulic valve to fan and again record hydraulic flow and pressure at different rpm still leave gauge in hydraulic return to tank. In this troubleshooting, hydraulic system back
pressure ( cannot be over 25 % of system hydraulic pressure.) Note use of flow meter before and after hydraulic valve
will bring out the problem. Feel you are going to find sticky shifting valve spool, very high hydraulic system back pressure,
kink in hydraulic hose or steel tubing, too small hydraulic return hose I.D. or incorrect hydraulic fittings replaced at
some point. Last the hydraulic pump itself worn and incorrect flow and pressure. Do not know where motorhome
is located but a Cat Dealer or hydraulic pump rebuild shop will know how to preform the above troubleshooting
of problem.  Dave Atherton Retired Cat Mechanic
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