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Transmission pressure light flashing between forward and reverse

aidank

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Jul 5, 2008
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30
Location
ireland
Quick question for the more knowledgeable than me.

Our Volvo l30 bm with Clark 18000 transmission is flashing the transmission pressure light when changing between forward and reverse. It just flashes for .25 seconds when you pull the lever to change between the two.

No problems when working, all pressure seems to be delivered as required. It will spin wheels when asked and climb on demand.

All filters are clean and oil is correct.

It takes 2 3 seconds for the pressure to build at startup and the transmission monitor lamp to go out.

Any ideas?
 

aidank

Active Member
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Jul 5, 2008
Messages
30
Location
ireland
I'm not familiar with the machine but with those symptoms when cold is it possible you could have an air leak on the pump suction side..?

I don't think I do tbh, should the light go out instantly on startup
 

Nige

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I don't think I do tbh, should the light go out instantly on startup
With cold oil, pretty much instantly IMHO, certainly not 2-3 seconds.
Again I have to stress I'm not familiar with your particular machine and a lot depends on which transmission clutch(es) are engaged in neutral.

All filters are clean and oil is correct.
For the HEF experts on Clark transmissions it might help to indicate what filters and oil you are using.
 

aidank

Active Member
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Jul 5, 2008
Messages
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Location
ireland
With cold oil, pretty much instantly IMHO, certainly not 2-3 seconds.
Again I have to stress I'm not familiar with your particular machine and a lot depends on which transmission clutch(es) are engaged in neutral.

For the HEF experts on Clark transmissions it might help to indicate what filters and oil you are using.

its a Volvo filter

oil thats in it is 10w 30 transmission oil,

https://www.google.ie/url?sa=t&rct=...fwEt6yn11eL1YwaxMkASSg&bvm=bv.117868183,d.d24

hope that link works brings you to the manual, its 15mB
 

Nige

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I've read through that link and I see no reason why it couldn't be a leak on the suction side of the pump, or even a worn pump that is battling to build up pressure when cold through internal leakage and when hot can't supply enough flow during a directional shift to maintain pressure above the required minimum.

Has the problem got gradually worse over time or has it appeared literally overnight..?

Have you checked the pressure sensor or switch that supplies the signal to the warning light to rule it out as a potential cause of the problem..?

The oil you are using intrigues me, because for your climate the recommendation from the Clark manual is a straight 30 oil, not a 10W30. TBH I wasn't even aware that multigrade transmission oils existed, I thought they were all monograde.

In your OP you noted "all pressure seems to be delivered as required". What exactly were the pressures you measured and how do they compare to the manual specifications..?
 
Last edited:

aidank

Active Member
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Jul 5, 2008
Messages
30
Location
ireland
I've read through that link and I see no reason why it couldn't be a leak on the suction side of the pump, or even a worn pump that is battling to build up pressure when cold through internal leakage and when hot can't supply enough flow during a directional shift to maintain pressure above the required minimum.

Has the problem got gradually worse over time or has it appeared literally overnight..?

Have you checked the pressure sensor or switch that supplies the signal to the warning light to rule it out as a potential cause of the problem..?

The oil you are using intrigues me, because for your climate the recommendation from the Clark manual is a straight 30 oil, not a 10W30. TBH I wasn't even aware that multigrade transmission oils existed, I thought they were all monograde.

In your OP you noted "all pressure seems to be delivered as required". What exactly were the pressures you measured and how do they compare to the manual specifications..?

thanks for the suggestions, Apologies in advance Im not v familiar with these transmissions,

how do I check the pressure switch, measure the resistance across the terminals is it

Ill have to get out the pressure gauge to measure the actual pressure which the transmission is giving out, there is a spec in the book 180 to 220 I think it is

by pressure being delivered as required I meant, the loader never fails to spin wheels when digging or climb any hill it is asked, the problem appears to have got worse over time only recently the flashing started during directional changes, it might give a flash 50% of the time

where do I begin to look as to where it could it be sucking air, not a drop of oil leaking, nor any bubbles and plenty oil in the transmission

that oil I mentioned is the same oil as one would put in the back axle of a tractor
 

Nige

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I'm not familiar with them at all....!! Everything I'm getting is from that manual to which you sent me the link.

I would pressure test the switch/sender by removing it from the machine and hooking it up something like a portapower pump to it and gently pumping up the pressure until the switch changes from closed to open or vice versa. I think it should be normally closed (to light the warning lamp) then open at around a certain pressure. Note the pressure at which this happens, that will tell you if the switch is working right.

Regarding individual clutch pressures from the tone of your post I thought you'd measured them all already. According to the manual they should be in the range of 180-220psi with no more than 5psi difference between all the clutches. I would suggest that measuring the pressures should be your next step.

If there is no frothing of the oil inside the transmission then the likelihood of a suction leak is reduced but not necessarily totally eliminated.

By the sound of what you're now saying about how the problem has gradually got worse over time I would say it's displaying the classic signs of a transmission that is coming to the end of its life. Whether the wear is in the clutch packs, clutch piston seals, pump, control valve, or a combination of all of them, is still undetermined IMHO.

Regarding the oil you are using, the manual calls for a straight SAE30 engine oil. I'm not sure that a multigrade oil is 100% correct for that usage. Do you have a brand name and any other details..? I'd comment that if you have been using the same oil for a while with no issues it's very likely that the oil is not the problem now, although it remains to be seen if the oil is contributing to the problem by being the wrong oil for the job.
 
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aidank

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Location
ireland
You say filters are clean, does that include the suction strainer in the bottom of the gear case?

yes perfectly clean

question the oil is sucked up by the charge pump from the sump of the transmission, therefore am I correct when I say there must be a pipe from the suction screen to the charge pump
 

Nige

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question the oil is sucked up by the charge pump from the sump of the transmission, therefore am I correct when I say there must be a pipe from the suction screen to the charge pump
There must be, maybe even more than one of them, and I can't recall if the flanges on the suction pipe(s) are sealed with gaskets or o-ring seals.

Looking at the manual in your link I can see the following that might cause suction leaks. They might not be the only things but they're what jump out and hit me immediately.......

Page 10/11 - Item 1 & 2 - Pump to housing gasket & O-Ring
Page 15/16 - Item 44 & 45 - Suction Line and O-Ring
 

Nige

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Another thought. Why not try rigging up a gauge to the transmission pressure test port and run it into the cab where it can be monitored while the loader is operating...? That way you could see what the pressure is doing when the oil is cold or warm and for whatever gearshifts are made.
 

aidank

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Location
ireland
Another thought. Why not try rigging up a gauge to the transmission pressure test port and run it into the cab where it can be monitored while the loader is operating...? That way you could see what the pressure is doing when the oil is cold or warm and for whatever gearshifts are made.

my thoughts exactly
 

jcb jeff

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Nov 23, 2014
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Possible pressure switch fault first look see but should get a little dip in pressure i would expect between f / r if clutch packs are wearing it takes longer to engage fully thus the dip in pressure but i would for the cost of it put a new pressure switch on or like Nige said hook up a gauge is a good idea when running but i think your oil is incorrect which wont help on start up for sure.I should have a paper manual for the JCB version that its in back at home .
 
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Jan 31, 2023
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New Abirem, Ghana
Hi,
New here. In my experience it sounds like the pump can be worn and most probably because of the incorrect 10w30 oil which viscosity is too low when cold.
Curious as to what the outcome was?
Regards
 
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