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Author Topic: Clark 4 speed  (Read 515 times)

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Offline Ky Logger

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Clark 4 speed
« on: September 11, 2017, 12:05:51 AM »
Clark 4 speed -Loosing pressure when I shift to reverse,sometimes it takes reverse good sometimes I have to rev the engine to get it to take reverse. It goes into forward gear good, I also have to rev engine to get the winch to release (John Deere 4000 winch) could someone give me some ideas on what is going on with transmission. Could reverse and the winch be same problem?

Offline longtime lurker

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Re: Clark 4 speed
« Reply #1 on: September 11, 2017, 07:31:59 AM »
Which Clark 4 speed, what's it in?
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Offline kiko

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Re: Clark 4 speed
« Reply #2 on: September 11, 2017, 07:37:45 AM »
Low transmission pressure.

Offline mike_belben

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Re: Clark 4 speed
« Reply #3 on: September 11, 2017, 07:24:47 PM »
Low transmission pressure.

To expand on that.. As the hours pile on, the clearances in pump gears and housings add up, the wear rings in every poppet valve get a little deeper and every component leaks a little more until the various valve bodies and clutch packs and so forth just dont operate with the pressures they were designed around.   If you are inclined to tinker, alot of hydraulic and hydrostatic equipment can brought back to a state of life via lapping compound, springs shimmed via washers or doubled up springs from the hardware bin, by relapping and surfacing end plates and pump cam sections and so forth.   Ive rescued a lot of junk with basic tools, a pressure gauge and a theory of operations writeup. 

What a shame it is to scrap a good machine over a rusty relief valve and flat tire or two.  It happens every day.
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Offline Ky Logger

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Re: Clark 4 speed
« Reply #4 on: September 11, 2017, 09:56:08 PM »
It's in a 450 timberjack not even sure the year it does have the Deere winch if anyone knows what year the donkey got put on the Deere winch, the transmission was redone just a couple of years ago or maybe 3-4 years I'm not real sure but sure it was done  but I don't know if the pump was replaced or even if the control value was worked on .

Offline Ky Logger

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Re: Clark 4 speed
« Reply #5 on: September 11, 2017, 10:02:41 PM »
It's not my skidder it's my brothers, I've been running it and I've always asked them about the transmission pressure gauge, it's not in the mark it's supposed to be in , they say its never been in the mark , I guess they assume if it's moving its working. Will low pressure cause internal damage or just keep getting Lower and quit pulling , I could put a pump on with a new gauge or just check the pressure with a external gauge I guess that would be the best place to start.

Offline kiko

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Re: Clark 4 speed
« Reply #6 on: September 11, 2017, 10:32:17 PM »
Pull the kick panel and the trans pump will be the one in the middle with aluminum housing , the regulator is sandwiched between the pump and the trans.   These pumps are usually not serviceable because of the aluminum housing.  However the regulator can be monkeyed with as Mike says.  The pressure tap for the gauge is located on the fitting on the pump.  That little fitting where the line to gauge hooks up is an orifice and needs to be in there for the dash gauge.  You can tap a hydraulic test gauge in right there.  Trans pressure should be about 280 psi .
Also the trans pump oil hoes through the trans filter then to the control valve. Has it been changed lately. There is no bypass valve in the filter head so if it is stopped up low pressure can result.  And yes low pressure will certainly lead to trans failure.

Offline mike_belben

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Re: Clark 4 speed
« Reply #7 on: September 15, 2017, 10:41:05 PM »
Pumps make flow.  Restrictions to that flow make pressure.   Poppet valves and springs decide when to leak in order to limit max pressure and prevent destruction.

Pump clearances may be causing leakage and low pressure, but id suggest atleast seeing if you can shim the relief valve (regulator) spring first.  And verify that the seating faces are in good shape, not rusty, pitted, cracked or pounded in. 

If the pressure wont climb with some shimming of relief spring (i fixed my bobcat project with a lockwasher under a cold bypass relief spring.. Its not rocket surgery) then id start saying okay the pump is leaking too much into the case clearances... And tear it down.  Sandpaper on a mirror has rescued a lot of marginal pumps.
Revelation 3:20


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