Hydraulic Gurus: Lift power pack problem...

[Zaxxn]

So some time ago I bought a Mohawk System II lift from a dealership that replaced them. Did all the mechanical work, new bearings, etc. The lift was in use to pretty much the day I picked it up, but I didn't take it apart myself, just picked up the pieces. Finally got it all installed, all the hydraulics hooked up, system bled according to Mohawk's instructions, all went well, no leaks, both pistons in the upper locks after bleeding. Released the locks, pressed the lowering valve, heard a "PLUNK" and that was it. Nothing lowering. Not a bit. Not even with putting weight on the "sleds". Since I have another Mohawk lift, I know the power unit, albeit almost new (2018), isn't the original Mohawk unit.
However, both, the original Mohawk unit and this one have what I think could be a check valve on the output port (the two part, rust colored hex unit connected directly to the pump body), and I am not so sure it should be there at least for the new power unit, and I am wondering if the power unit they gave me wasn't with this lift originally or so. I attached a couple of pics of the unit.

So, two questions now: First, should the check valve even be there, if it is one. And second, how do I remove the pressure out of the system now that the cylinders are all the way up and the system most likely with a lot of pressure in it?

Sorry for all the questions and thanks for your help already in advance. Somewhat of a hydraulic noob...

--Zax

 

[matt_i]

If that's a classic one-way check valve then yes that would cause the problem you are seeing.

The steel tubing looks to me like it would be perpendicular to the earth with the elbow attached directly to the pump-body, as another hint its not original.

As far as how to remove it, block up the lift arms, I'd use 2x framing timber in normal times as a post, c-clamp, etc so it can't slip out. You'll lose some fluid. Its always more than you want but it won't be driven by the weight pushing the pistons down.

If you knew exactly what type of tube fitting it was, you might be able to buy a deadhead plug that matches to screw into the tube-nut to minimize fluid loss while you rotate the elbow to attach it back to the pump body.

 

[Zaxxn]

If that's a classic one-way check valve then yes that would cause the problem you are seeing.

The steel tubing looks to me like it would be perpendicular to the earth with the elbow attached directly to the pump-body, as another hint its not original.

As far as how to remove it, block up the lift arms, I'd use 2x framing timber in normal times as a post, c-clamp, etc so it can't slip out. You'll lose some fluid. Its always more than you want but it won't be driven by the weight pushing the pistons down.

If you knew exactly what type of tube fitting it was, you might be able to buy a deadhead plug that matches to screw into the tube-nut to minimize fluid loss while you rotate the elbow to attach it back to the pump body.

Hi Matt! That's definitely helpful. I can absolutely place a couple of screw jacks under the sleds, but I think the rams itself will still slide down. Not too worried about loosing the fuel, more about the pressure that may be in the system and the mess it'll make. This lift runs on regular atf, so it's fairly inexpensive and I've got a 5gal pail.

Thanks so much!

--Zax

Sent from my ELE-L29 using The Garage Journal mobile app

 

[matt_i]

Are the rams (cylinder rods) pinned or otherwise attached to the lift arms?

(If they weren't and you set the load on the safety locks, couldn't the cylinder rods drift down?)

I don't know for sure but that's an important detail to figure out first. Maybe the exploded view of the assembly could help (?). If not you could probably C-clamp the rod with V-notched pieces of wood to cushion the clamp's steel parts.

Mohawk might have a velocity fuse in case something ruptured (essentially it instantly "checks" if the flow thru the fuse gets too high vs the normal straight-thru condition.) But you don't want to depend on that!

 

[Zaxxn]

Matt, you are absolutely right. It's not a check valve, it is such a fuse I am pretty certain that's on the power unit.

Got everything working just fine now. All it was, which I would have never thought, a kind of an air lock or so. I carefully opened the plug on the off side cylinder (and got atf sprayed right in the face! Lol!), relieved some pressure that way, and suddenly everything started working. A couple up and down rides, and the sides equalized perfectly fine, both sleds in sync.

Thanks for all your help! Much appreciated!

--Zax



Sent from my ELE-L29 using The Garage Journal mobile app