Several years ago I bought a late model 955H pedal steer that needed a little TLC, but was in my price range. I have gradually fixed its problems and now with the exception of needing pins and bushings/chains, it is a very nice operating loader, with one small problem. When the loader frame is raised, and the bucket is tilted in either direction, the loader frame lowers. This makes loading trucks when the loader needs to be a maximum lift a little tricky, since when you dump the bucket, the frame lets down on the truck bed. As long as the tilt lever is not touched, the loader frame will stay up for at least a week (as long as I let it sit still). It doesn't matter whether the engine is running or not, when the tilt lever is moved to roll the bucket, the loader frame lowers slowly. From this I assumed my cylinders should be OK, and the problem must lie with the control spool. This week I aquired a spare hydraulic tank and spool assembly and tore mine apart. From the service manual, I figured to find a problem in the check valve for the lift, since it is supposed to hold the oil in the cylinders until the spool gives it presure to raise or lower. It indeed was not seating, so I cleaned its bore thoraughly and lapped the valve with valve grinding compound. I checked everything else that looked questionable, and found no other problems, so I bolted it back together and poured the oil back in. It still lowers when the tilt lever is operated the same as it did before. Does anyone have any ideas where to go next? I had read the manual, even though it leaves a lot to be desired, and thought the check valve would be the only possible cause, but I guess there is something else, now finding it is the problem. Is there any way oil from the tilt circuit can enter the lift lower circuit to unseat the check valve? I am now in desperate need of a good opinion, and any advice is greatly appreciated.

That's a good one:D
It is a series circuit where oil exhausted from the tilt cylinders is used to actuate the lift cylinders (if the lift spool is moved) but the check valve is on the supply side and flow is blocked at the spool until moved. There are make up check valves on the lift cylinder lines that could leak down but that possibility is canceled by the fact that the lift cylinders hold.
Any reason to suspect the lift spool is not in true detent center position?
Do you detect any movement of the lift spool when actuating tilt?
Any restriction in the return line to the sump?
That's about all I can think of right now:rolleyes: It's way past my bed time:D

The lift spool has a very distinct "snap" to the detent, for centered, detent raise and float. I have not noticed any drifting of the lever, but I will certainly check closely for it. I had the sump suction apart and everything looked very good. The make up valves seemed to work freely and when pushed in, fluid folws out. The thought also occured to me to check for the tilt drifting when the lift is actuated. It wouldn't be as noticable as the lift going down, and may actually happening as well. It is very depressing to tear into something and not see something really messed up so you know its the problem. If only they hadn't put the valve inside the tank! Thanks for any help.

Have you checked the adjustments for the bucket kick-out? This linkage automatically moves the bucket lift control lever from the raise position to the hold position before the lift cylinders reach the end of their stroke. If out of adjustment it would effect the positioning of the spool.

This message is from Bob/Ont..........who is having computer problems and asked me to relay this info: Good luck, hope that's it. It's the simple things that drive ya nuts:)

Pete, have puter isues and can't get on the board so send a message for me
> please. The guy with the 955H that drops the lift arms when he dumps the bucket
> needs to reseal the Dual Sensing line relief valve. I forget what actually is
> happening but it's a line relief that protects the lift circuit and also
> senses the tilt rod end pressure. Whe you release the tilt pressure to dump the
> valve opens and dumps the lift cyl oil and the arms fall. Just a small O ring in
> there leaking.
> Later Bob </HTML>
>

Here is the hydraulics schematic:
Can't see how the tilt operation would effect the lift circuit when lift is in hold position but then I guess that's been the question all along:)

Thanks for posting that for me OM. It has to be a Dual Sensing valve to give that problem. It's a tilt line relief valve that senses the rod end of the tilt and the head end of the lift cyls on seperate slugs in the end of the valve. The seal in question keeps the two pressures seperate. If they mix when you dump the bucket lift pressure will escape. The dual sensing valve will have a 1/4" tube bringing lift pressure to it. THis was a much talked about problem 30+ yrs ago.
Later Bob

Hi Bob/CatDog,
Need the serial number of your unit.
My 60A1-Service manual shows the lift cylinder limit control to be a mechanical linkage function. Also there are a couple versions of the relief valves and differential tilt relief valves plus the differential tilt relief conversion group that Bob refers to.
Also if you can any arrangement number off the hydraulic tank.

Pete, could you post a pic of the hyd valve that shows a line relief valve with a small tube going to one end, if you have one please. Cat Dog, when you have the tank apart I would take the complete valve out and replace every seal in it and under it at the tank wall. They will all be hardened and leaking Make sure the bucket is on the ground and work all levers with engine off before starting to work on it.
Later Bob

Hi Bob,
Is this the stuff your looking for. Man is the 955 messy, never seen so many revisions and options.....must have been Cats hydraulic training ground:D ......I wonder if they ever got it right:rolleyes:

Really need that serial number to pin it down.