Pallet Jack Diagnosis

[agftemp]

I wanted to see if anyone could offer some help trouble shooting the jack on my Clark pallet jack. I have removed it from the machine to enable easy access to it. Here are the symptoms.

1. It won't extend if there is force acting against the cylinder
2. It will extend if there is no force acting against the cylinder
3. If extended, it will slowly collapse with my body weight applied (takes about 10 seconds)
4. If I apply force to the cylinder by hand while pumping the jack, I can feel the pressure expand it but it then quickly goes back the same amount it expanded. Feels like the oil that gets pumped in goes back out.
5. There are no external leaks on the either of the two pistons or anywhere on the jack.

It had oil in it, and I added a little more but oil level doesn't seem to be the problem.

I was thinking there might be something with the valves that are preventing it from retaining the oil, since I don't see any oil leaking from the seals.

Any thoughts on what could be causing this? Any suggestions on what to try to diagnose or repair it?

Thanks,
Alan

 

[Hiball]

Main rod seal is compromised, if you have it out of the frame, it's a easy check.

 

[Wamsutta]

I agree with Hiball. Same thing happens to master brake cylinders.

 

[txvwnut]

As stated above the seal in the lift cylinder could be bypassing or the spool on the release valve is leaking by.

 

[agftemp]

Is there any way to check if it is the main seal or control valve without taking it apart?

Thanks,
Alan

 

[Hiball]

Is there any way to check if it is the main seal or control valve without taking it apart?

Thanks,
Alan

No Magic Pill... since it’s out of the frame, the most straightforward thing would be to simply remove the tank nut/pull the ram and put eyes on the rod/piston seal.

I’m not sure what model you have, but obviously external signs to look for would be a bound release linkage (if equipped), my gut based off your description/plus my experience tells me it’s the main ram seal. It’s possible that it’s a internal valve issue, but since the cylinder loads up when light, I’m fairly confident it’s a seal issue.

 

[agftemp]

Hiball, you were correct on the diagnosis! After I borrowed a 2.5in socket and purchased a 1in impact hammer I was able to get the tank nut off. The seal on the piston was split. I have attached a picture of it as I have never seen a seal like this before. It looks to be made out of a hard plastic. Would Hydraulic Parts Supply carry some thing like it?

Thanks,
Alan

 

[Hiball]

Hiball, you were correct on the diagnosis! After I borrowed a 2.5in socket and purchased a 1in impact hammer I was able to get the tank nut off. The seal on the piston was split. I have attached a picture of it as I have never seen a seal like this before. It looks to be made out of a hard plastic. Would Hydraulic Parts Supply carry some thing like it?

Thanks,
Alan

It's just a Piston style Poly Ucup, when seals get some age on them, they harden and split/deteriorate. I'm sure HPS would have it in stock, but I buy all my pallet Jack parts from Generic Parts supply, they specialize in pallet Jack parts and I've found there prices hard to beat, it wouldn't hurt to do some price checking.



If you measure the Bore = OD, Measure the Ram where the seal sits = ID and overall thickness = Height you can probably save some money shopping via a seal supplier or at Min know what size to ask for. I suspect it's Metric btw.

I did a quick search thru Generic parts supply here and it only has one Clark model showing, but the entire seal kit is only $30 and some change. It's probably good insurance to go ahead and service the hydraulic unit while it's out. If you have any questions, don't hesitate to call them, they are very knowledge all people.

 

[agftemp]

OK another jack rescued! I was able to get a new seal at MFP Seals. I live in the Detroit Metro area and their headquarters are in Troy MI so I got the part and fixed it the same day.

After installing the seal, the pallet jack works like a champ. I wouldn't have gone through the effort of rebuilding it if the original pallet jack wasn't so well built. I looked at the new units and they just don't have the same level of material and robustness.

Thanks for all the help diagnosing the problem!

Alan

 

[Hiball]

OK another jack rescued! I was able to get a new seal at MFP Seals. I live in the Detroit Metro area and their headquarters are in Troy MI so I got the part and fixed it the same day.

After installing the seal, the pallet jack works like a champ. I wouldn't have gone through the effort of rebuilding it if the original pallet jack wasn't so well built. I looked at the new units and they just don't have the same level of material and robustness.

Thanks for all the help diagnosing the problem!

Alan

Good company to deal with... I buy all my seals in bulk from them, for the average joe buying 1 or 2 seals they really don't accomidate due to shipping costs etc... But local pickup is a Win/Win as you are buying at 10-20% of what most hydraulic shops charge.