HST pressure tester?

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lightning337

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L48
May 14, 2025
25
5
3
Windsor, Ontario
Hi, I need to run some pressure tests on my HST. My unit is an L48 backhoe and the HST is extremely weak. I don't have high range. Low and medium ranges barely move the tractor.

Is there anything on Amazon I can purchase to test the pressures? I looked up the units listed in the WSM and I can't find them online.

I'm on the pressure testing stage of the diagnosis.

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MOOTS

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I’m reading those instructions as P1 is reverse, P2 is charge and P3 is forward. P1 and P3 will be up to 5100+ psi, P2 will be just under 400psi. Will probably need 2 gauges with those reading in or near center of their scale and any appropriate adapters to thread into the ports.
 
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PoTreeBoy

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lightning337 said:
It's pretty vague when the WSM says "Check Charge Pressure". Which port and where? I can only find "charge relief pressure".
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There was a recent report of a HST issue very similar to yours. Alas, the OP gave up and sold his tractor, so we don't know the outcome.

First, your L48 has a conventional, mechanical clutch. Let's check it first. Engage the PTO and watch it. Does it rotate when the tractor is moving? Does it still rotate when the tractor 'stalls'? If not, you have a clutch problem, not HST.
 
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lightning337

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L48
May 14, 2025
25
5
3
Windsor, Ontario
PoTreeBoy said:
There was a recent report of a HST issue very similar to yours. Alas, the OP gave up and sold his tractor, so we don't know the outcome.

First, your L48 has a conventional, mechanical clutch. Let's check it first. Engage the PTO and watch it. Does it rotate when the tractor is moving? Does it still rotate when the tractor 'stalls'? If not, you have a clutch problem, not HST.
Click to expand...
The pto engages and spins when still. With weak slow travel movement, I don't see a point to hook it up and put it under load when the tractor can barely move.

I'd much rather take a clutch issue over a worn hst issue! My fingers are crossed that the hst is fine. Praying my weak hst issues are valves...

I still got medium range and it moves forward and reverse with revs. So hoping it's a pressure issue. Could a slipping clutch cause the same weak travel movement?
 
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PoTreeBoy

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lightning337 said:
The pto engages and spins when still. With weak slow travel movement, I don't see a point to hook it up and put it under load when the tractor can barely move.

I'd much rather take a clutch issue over a worn hst issue! My fingers are crossed that the hst is fine. Praying my weak hst issues are valves...

I still got medium range and it moves forward and reverse with revs. So hoping it's a pressure issue. Could a slipping clutch cause the same weak travel movement?
Click to expand...
You don't have to hook anything to the PTO, as long as you can see the shaft turn or not turn. If the clutch is slipping, the PTO won't turn, even with no load on it.

The clutch test is quick, easy and requires no tools. That's why we do it first.

Then do the test in high range, or medium/low with brakes. When the tractor stalls, does the PTO stop turning? As @TheOldHokie said, yes.

The clutch connects the engine to both travel (HST) and PTO. If it's slipping, both stop.
 
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ruger1980

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As Stated check the clutch first. To test the hydrostatic pressures it looks like you will need at least 1 6000-10,000 psi gauge (I would lean away from a 6k psi gauge and go towards the 10k) I would use 2 in each P1 and P3 port and a 800-1000 psi gauge in the P2 port. From what I can see adapter 58 is PT 1/4 which is likely 1/4 JIS taper or BSPT. You will have to adapt your gauges to that.
Charge pressure is what I would look at first as it is the most important and telling measurement, especially measuring how much it drops when trying to travel. .
 
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ruger1980

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L4310 w/La682, L225
Oct 25, 2020
480
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CNY
Oh and the kits mentioned above will not work to check the high pressure but could be used to check charge pressure although less than optimally. Kinda like checking tire pressure on your ATV with a 150psi gauge designed for Class 8 truck tires.
 
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lightning337

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Equipment
L48
May 14, 2025
25
5
3
Windsor, Ontario
For now, I'm not even sure what to buy to test pressures. Can anybody point me in the right direction?

As for clutch, the other day I only engaged the pto while in neutral and it spun fine. Revved it up a bit and the pto rotated faster according to rpm. Seemed fine.

Tomorrow, 100%, I will try engaging the pto and throwing it in a few gear ranges. Totally forgot about trying to see if I can kill the engine to see if the clutch is slipping or not by trying to bog it down. I will get on that tomorrow when I get home from work.

Just want to thank everybody who has replied and offered help and advice. I will be sure to update the status of my progress in trying to sort out the weak travel speed.
 
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PoTreeBoy

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lightning337 said:
For now, I'm not even sure what to buy to test pressures. Can anybody point me in the right direction?
Click to expand...
There may be alternatives, let's see what the clutch does first.

Since you have a WSM, please post the hydraulic diagram. There may also be a separate HST hydraulic diagram.
 
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