Hydrostatic slipping in forward gears, L3750

heppeone

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L3750dt w/fel, woods box blade, woods rake, woods yard roller
Oct 24, 2014
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murrells inlet, sc
Only does this in forward gears, reverse works fine. Took FEL off, plus added shins to shuttle valve assembly as recommended. Tested with FEL still off and worked well, FEL back on and problem returned right away. I'm fairly confident that is not the clutch, the next thing I can think of requires splitting the tractor, looking to avoid that till I get a few farm projects taken care of. Any thoughts on the use of a heavier oil to increase pressure?

Btw, I have also tried changing the seasonal selection lever on end of shuttle valve, didn't fix the issue.

Not thrilled with my dealer, looking for dealer/mechanic that understands the hydrostatic system.
 

rbargeron

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If the model is really L3750 it's from the '80s and pre-dates Hydrostatic drive by several years. The L3750 is a gear tractor, but was available with hydraulic shuttle.

Can you say more about the why and how of the "shims" added to the shuttle valve? And a question I'm wondering about is how taking off the loader affects operation of the hydraulic shuttle.

While the loader was removed, was the control valve taken off and the hoses disconnected at the hydraulic block on the side of the tractor? Did you install the original cap or put plugs in the block's ports? When the loader was off did the 3-point go up and down ok?

Here's why I ask - With the loader disconnected and plugged, the shuttle would get full pressure from the pump and would work ok. But with the loader piped in at the block, oil from the FEL's PB hose is directed to the 3-point hitch function. A problem in the 3-point control under the seat could rob the hydraulic shuttle clutch packs of pressure, possibly allowing the forward pack to slip. The reverse pack might not be as worn and might have enough pressure to operate.

You could test this without taking the loader off. Disconnect the two hoses at the hydraulic block and put plugs in the ports. If Forward motion comes back, there's something wrong in the 3-point hydraulic control unit under the seat.

Sorry this is a long post - and likely not much help. I can't think of how else removing the loader would affect forward motion. As always, prompt cheerful refund if theory is bogus. Dick B.
 
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heppeone

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L3750dt w/fel, woods box blade, woods rake, woods yard roller
Oct 24, 2014
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murrells inlet, sc
Hello Dick. Thank you for the input, let me do some research to be able to answer your questions the best I can, though first, seems you are correct regarding hydraulic shuttle as opposed to hydrostatic. Not sure where I got that from.
 

heppeone

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L3750dt w/fel, woods box blade, woods rake, woods yard roller
Oct 24, 2014
22
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0
murrells inlet, sc
PHP:
Hello Dick. Here what I've got regarding hydraulic block and the hoses: I did not remove the block, I connected the feel line back into return, the third port remained shut via quick coupler and cap. I'll try to upload a picture, old hose has been replaced.

Regarding the shims: in my workshop manual, it shows to install shims in the selector valve assembly to increase pressure. I will also try to upload the pictures from manual.

(No luck uploading the pictures, maybe because I'm on a mobile devise. Feel free to contact me at my email, heppeone@gmail.com and I can share more. Interested in knowing how to test with FEL still attached but not hooked up, will bucket stay up when hoses disconnected? If you email me, plz put Tractor in the subject line so I know it's not more spam, thanks
 

rbargeron

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L5450, L48, L3250, L345 never enough attachments
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PHP:
.... I did not remove the block, I connected the feel line back into return, the third port remained shut via quick coupler and cap. I'll try to upload a picture, old hose has been replaced......
A picture would help - the tube going to the top of the transmission is an exhaust line - so if the two ports on the block were connected by hoses to the valve and back, it was acting as if the original cap was there. Unfortunately I think that trashes my theory above. I'll keep thinking about it but at the moment I got nuttin'.
 
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rbargeron

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L5450, L48, L3250, L345 never enough attachments
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L3750's with hydraulic shuttle also have a priority valve that insures the power steering gets priority flow, and anything else (3-point, shuttle, loader) share what's left. I'm not experienced with the internals of this valve (#170 on attached) but there's a related discussion here that might be useful. If the Forward shuttle clutch pack is worn, it might not be getting enough pressure to drive, especially if the priority valve is starving it.
 

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patchofpentaphyllum

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Aug 22, 2017
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GAINESVILLE
L3750's with hydraulic shuttle also have a priority valve that insures the power steering gets priority flow, and anything else (3-point, shuttle, loader) share what's left. I'm not experienced with the internals of this valve (#170 on attached) but there's a related discussion here that might be useful. If the Forward shuttle clutch pack is worn, it might not be getting enough pressure to drive, especially if the priority valve is starving it.
I am having a similar problem with my L3750. It is on at least its third priority valve now and symptoms of no loader/3 point power and slipping fwd reverse have returned worse than before, this priority valve is oem and less than 6 months old. ($523 each)

I checked out that discussion and it was useful, that person was able to file down his problematic plunger inside his priority valve. The L3750 has a different priority valve, and I am pretty sure the plunger is non serviceable (see photos). It is housed inside of a plug. (Photos are of a non OEM part that I pulled off my machine.)

Any ideas based on the diagrams and photos of how to service this plunger or bypass the priority valve. Could I rig up a priority valve from another machine?
 

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North Idaho Wolfman

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Have you measured pressures into and out of the priority valve?
 

heppeone

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L3750dt w/fel, woods box blade, woods rake, woods yard roller
Oct 24, 2014
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murrells inlet, sc
Sorry for long delay in responses, for some reason I don***8217;t get notifications regarding replies on my post. Only saw it because I***8217;m STILL researching and trying to diagnose issue. To answer your question, no, I have not checked pressure anywhere. Wish I had before splitting tractor in two for a clutch replacement, clutch seems fine. Though, found a couple hose issues while splitting it apart that I***8217;ve read could be issues, rubber connection hose on suction line in bad shape, my vent line under the steering column is exposed to the eliments, allowing rain water to enter system.