Rapid Pump Jack Rebuild Questions

[jacked_72]

Is there a thread poking around in which rebuilding this type of jack is discussed ala the overseas jack thread?

I've got one that I thought was OK until I tried to lift a car and sadly found that its no dice. I had it apart and the main cup seal -- the larger on on the ram-- looked good (I suppose it could be bad though). This seal looks similar to the ones in the standard overseas jacks. I don't quite understand how these jacks work, but in comparison to a normal jack, the ram is hollowed out and a hollow shaft goes up into it. I presume that this is part of the quick lift device. I'm presuming that there are seals/orings inside of the ram and that these could be bad. Unfortunately, I don't have a picture of this inner rod assembly to show you. Has anyone seen a schematic or a teardown of one of these?

This is a Shinn Fu jack that is branded as a MVP Superlift. From what I can tell, this brand was sold at places like WalMart.

 

[EDGAR]

The slim tube that goes in the ram from behind is indeed the quick lift. It has 2 O-rings sealing the tube. The o-ring that usually goes bad is the one at the bottom end of the ram itself. The typical quick lift has a round nut threaded on the ram end. Under that nut there is one back up washer, one o-ring and another back up. If this o-ring leaks, the quick lift stops working (assuming it is not simply out of adjustment).

At the base of the slim tube (inside the pump body) there is also another back up and o-ring set. Those last more because that is a static set. To remove this you have to remove the cylinder, remove a nylon back up and an o-ring that seals the cylinder (this of course depends on the specific model). Then remove the round plate and under that you will find the back up, o-ring, back up set. Be careful as there might be a loose ball, in a hole, under that plate. Be sure make a mark on the cylinder so you can tighten it close to the torque it was tightened at the factory, by returning the mark to its previous place. Sometimes the cylinders are a little loose so see if you can tighten it a little more past where the mark should be.

My recommendation is to only change the o-ring in the ram. The quick lift needs adjustment, and the easiest way to adjust it is to back up its overload bypass and then tighten it little by little until the quick lift works. Of course, this assumes that the O-rings are sealing. If there is another problem, the adjustment won't do anything.

The pump should have two overload bypasses. One is for the ram and the other for the quick lift. These valves have a heavy duty spring and usually a small ball (some have a needle or pointy part) closing against a seat. The quick lift needs to lift the arm quickly and then start bypassing the oil back to the oil tank the moment the arm or saddle makes contact with the chassis. The quick lift does not and can not lift any weight other than the weight of the lifting arm, so the adjustment is a light one. Adjusting it to tight will damage the small O-rings that seal the slim tube.

If anyone wants to find which bypass is for the ram and which is for the quick lift in their pump of any make or brand, after the pump is put back together, with new seals, back up both overload bypasses and then tighten one and see what happens. If the rams raises slowly, that's the ram bypass, if the quick lift works, that is the quick lift overload. These systems work independently, so one can work even if the other does not. The ram overload seat-of-the-pants adjustment is to tighten the overload all the way and then back it up a turn an a half to two turns. The ram overload usually has a threaded plug under the sealing cap and this plug is the one you adjust. The quick lift overload usually has only a sealing cap that serves as an adjustment plug.

The parts breakdown shown in the first picture is for a Shinn Fu Pro Lift jack model G737. This same pump is the one used in the blue Michelin 3.5 ton and the Craftsman 4 ton. The parts there may, or may not, be similar to yours. At least the way it works should be similar.

The second picture shows a Shinn Fu Omega 25030 pump. The blue arrow shows the quick lift overload bypass. The red arrow shows the ram overload. See that it also has the two sets of back ups and O-rings that seal the slim tube. The O-rings are marked with the letter B. The letters C and D are the back ups.

 

[jacked_72]

Thanks Edgar. The pictures look like my jack, but I could only get the ram cylinder to unscrew at the bottom. I'll try working on it this weekend and see what I come up with...or at least I'll have some pictures.