BAC Forum
General Boards => Technical Support => Topic started by: rollin sorge on October 16, 2009, 03:37:25 PM
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We have an 2007 Cdontessa, At random times, no pattern, when I start a turn the steering locks up ,but only for a second and then resumes normal assist. You never know when it will happen . Anyone expierience anything like it?
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I have never heard of this problem on a coach, but it was fairly common on cars before serpentine belts became standard equipment. The problem is usually caused by a momentary drop in hydraulic pressure. About the only thing that you can check is the level of the hydraulic fluid.
The hydraulic system on your coach operates the engine cooling fan and the power steering systems. If you have not serviced the hydraulic system, it is possable that you have a restricted hydralic filter, but that is just a quess.
Gerald
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Yup, our 2006 Monterey has done that or something like it every so often since it was new. You'll be usually in a slow speed turn, often just pulling away from being stopped, and, BAM! It feels like you hit something except it's almost like someone grabbed your steering wheel and jerked it in the opposite direction. It's disconcerting because you nearly lose your grip. Thankfully it is quite brief and momentary and you don't lose control. It is so rare that I keep forgetting to ask about it when in Bend for annual service. So I am as mystified as you, I'm afraid, unless Gerald is on to something re the h fluid filter. But I wouldn't expect that on new rigs.
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I have a 06 Montery and it will do the same thing.
With my unit this happens when the tranmison shifts and i am in a turm.
I have changed the filter and checked the fluid.
This happens only in a slow turn and at shift points
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If the problem occurs in a turn only at shift points, it is probably because the engine RPMs drop when the transmisson shifts and therefore the hydraulic pressure drops. This may only happen when the engine cooling fan is also running therefore increasing the hydraulic demand. If this is the problem (original engineering), I do not see an easy correction other than increasing the pump size which can create it's own problem.
The best thing to do is talk to the people at Beaver Coach Sales in Bend to see if they have run accross the problem before and found an acceptable correction.
Gerald
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We had this problem with our '98 Marquis. Adding hydraulic fluid to the reservoir seems to have cured it.
Mike
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This is an interesting problem. And I am sure to those it is happening to, quite disconcerting. I taught Industrial hydraulics for many years so I will add my two bits worth. I believe that the problem is a sudden loss of pressure for a moment like Gerald says. This could be caused by the turning on of the hydraulic motor that runs the fan. Most said that the problem occured when at low speed and when pulling away from a stop. It seems that would be the time when the fan would kick on to full speed to pull away the perculating heat from the engine. If this be the case the momentary demand for extra volumn of fluid would cause a momentary drop in pressure making the loss of assist in steering seem like a lockup or a reversal. Kind of a long winded answer to what might be the cause.
But a good solution to the momentary demand for extra fluid to prevent that momentary pressure loss would be a hydraulic accumulator which is a pressure vessel much like the accumulator used in the water systems to smooth out the pressure surges from the pump cycling. Hydraulic accumulators are hi pressure vessels or small tanks that have a rubber bladder on the inside that is usually set to about 2/3 system pressure. When the hydraulic system operates the fluid compresses the pressured bladder to a smaller size and when there is a momentary loss of system pressure or demand for extra fluid in the system the bladder pushes fluid under pressure back into the system to support until the system can recover.
Just some ideas.
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I forgot to add that the accumulator is not that large and should be added after the pump and before the valving that split the fluid to the steering and the fan or could be put directly in the line to the steering. I believe that a one quart or maybe a 2 quart size would be very adequate.
Arden Smith
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Was a solution ever found for this problem? I have the steering problem in my 2006 Monterey and had found this link previously but no solution for the steering problem.
Yesterday I met Russ Mann who owns of a 2006 Monterey 400HP cat. He had the same problem with his Monterey he purchased in 2006 from Beaver Coach Sales.
While still under warrantee Beaver Coach spent a lot of time eliminating a number of things they thought might be causing the problem.
The final diagnosis was that when the exhaust brake was activated the hydraulic cooling fan was also activated, if he was making a turn at the same time the steering wheel would jerk because of loss of steering assist. It was caused by the dual demand of the cooling fan and steering assist on the hydraulic system under no throttle.
Beaver Coach took the coach to Cat for reprograming. According to Russ the problem has never occurred since the programing change that eliminated the cooling fan activating when the exhaust brake activated.
Has anyone heard of this solution or have you found another solution?
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I think your reported cause reflects pretty much Arden's theory. Except I don't believe my exhaust brake was involved, given I don't use it except on long downgrades. My incidents like others' were at minimal speeds turning from a stopped condition.
I think Arden's canister to mitigate sudden pressure loss is still a good idea, like an accumulator tank to smooth out a pump water system. That said, if reprogramming's no big deal, I may be stopping in at Petersen CAT in Redmond too the next trip to BCS, and at least consult with them. The problem was infrequent enough that I failed to broach the issue when in Bend last, 2 years ago. But when it happens it is rather startling; if my wife was driving the wheel could conceivably hurt her - it did a number on my wrists once or twice.
Thanks for the new information.
Joel
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I had forgotten about Arden's thought on using a canister.
Last spring I replaced the filter and fluid. I still experienced the steering problem on our travels during the summer, in addition the pressure gage failed. As Joel mentioned when it occurs it can a real abrupt jerk, but for sure it freaks me out.
Not knowing about the possibility of the programing change, just last week we had the filter bracket changed from the small 3.67" filter to a larger bracket for a 5" filter. ( Worked through this change with Jeff at Bend RV Repair)
The flow on the smaller filter was a rated 24 GPM. The 5" filter is rated at 50 GPM. We have only driven a few miles with this set up. Because of the infrequent occurrence of the steering problem it will be a while before I can report if this is another solution to the problem.
Gary
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Don't hesitate to alert us if it occurs again, Gary.
Joel
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Gary,
Since the filter is in the low pressure side (return) of the fluid circuit, I can not see how changing the filter could correct your issue. That being said, I think that the filter change was a good idea on you coach because I have seen two hydraulic cooler failures on the late Monaco era coaches from low side restriction when using AW 46 oil in cold weather.
Gerald
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Is a hydraulic filter replacement easy to do? Is it just a matter of spinning the filter off and spinning the new one on?
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Adam,
Yes, it is that easy to change the hydraulic filter if you have a canister (spin-on) filter. However, there is one thing that makes for an issue when changing the hydraulic filter on some coaches, and that is fluid loss. If your filter is located on the bottom of your hydraulic tank, the hydraulic tank will probably drain about 3 to 4 gallons of oil when the filter is removed, so be prepared for a large fluid loss when removing this filter. Other hydraulic filters will loose varying amounts of oil, so be prepared to catch it and have new oil as a replacement. The latter Monaco design inline filters loose much less fluid.
Some coaches have a cartridge filter that is located inside of the hydraulic reservoir, so those are a little more work, but there is very little fluid loss when changing them.
Keep in mind that the hydraulic fluid has a change interval just like engine oil, although not as often. I changed my hydraulic system from Dexron III to TranSynd to extend this interval.
Gerald
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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.
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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.
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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
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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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Gentleman, if check valve on oil cooler is stuck to open would affect pressure greatly.
Dave Atherton Retired Cat Mechanic
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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
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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