Ok, machine has been fixed. It ended up being a very simple repair. I will start from the begining. In August of 2013 the lift cylinders began drifting. A few weeks later the left hoist cylinder began leaking from under the head (where it bolts to the barrel). We decided to run machine until we could shut it down during the winter repair season as this is our main yard loader. As luck would have it, one week before it was scheduled to come to the shop (January 2014) the seal (o-ring) under the head failed. Removed rod from machine and replaced all the seals in the head and on the piston. Bore looked good. Lift cylinders still drifted. In March of 2014 the right side lift cylinder head o-ring failed. Removed rod and head assembly. Replaced all the seals on the piston and in the head. Bore looked good. Lift cylinders still drifted. Hauled machine to the shop a couple weeks later. Removed shuttle valve from ride control valve as per CAT trubleshooting manual. Found o-rings blown). Lift cylinders still drifted. Removed load check valve from main control valve. Found visible wear on needle valve. replaced valve. Lift cylinders still drift. Disconnected lines from ride control valve mounted at right side of front loader frame. Drift slowed down, but not eliminated. Removed ride control valve. Disassembled valve. Inspected all parts. Found a blown back-up ring on solenoid valve. Replaced all o-rings. Reinstalled valve. Still drifts. Read system operation in CAT manual. Found out there is a 1/4-turn ball valve mounted at right side of front loader frame above the ride control accumulator for lowering the bucket if the engine won't run. Turned ball valve one direction. Still drifts. Turned valve the other direction. Still drifts. Disconnected and blocked lines at valve. Still drifts. Reconnected lines. Disconnected and blocked all the hoses that go to the diverter valve for the ride control. Still drifts. Removed main control valve and disassembled. Measured spool and bore diameters. Both were within new specs. Hard to believe since machine has 12,000 + hours on it and CAT has a service magazine dated april 4, 2007 for an updated valve that is made of better iron to reduce wear and we have the old style valve that was a problem. Rebuilt valve and replaced both tilt releif valves and main relief valve as they showed wear on the needles and seats. Reinstalled valve and set pressures. Still drifts. What the hell is going on here? Contacted CAT to see if any other customers were expiercing this. Nothing, we are the only ones. OK, let's retrace our steps. Let's start from square one. Decided to isolate each lift cylinder one at a time. Couldn't be those though, we just reseale them right? Isolated right side cylinder. No drift. Isolated left side lift cylinder. It drifts! Removed rod and head again. Found the piston seal had rolled out of the piston groove and was cut. Bore looked good. Replaced cut piston seal. Reinstalled rod. Still drifts! WTF?! Everybody is getting tired of this loader. If we had gasoline and a match this thing would be scrap! Not to mention the labor we have into it. OK, what to do now? Isolated diverter valve again. No drift. Must be in the diverter valve, right? It's the only valve left in the lift circuit we haven't touched. Removed diverter valve and disassembled. Measured spool and bore diameters. Like new. Found some o-rings and backup rings that appeared theycould have been leaking. Replaced all seals and o-rings, tested solenoid valve (OK). Found a blown/cut o-ring on the shuttle valve. Surely this has to be it. Reinstalled valve and tested machine for drift. Still 'effin drifts! We are officially out od ideas. Could our visual inspection of any of the many valves we rebuilt missed something? Maybe a crack in a housing? A valve seat? Maybe we cut a valve seal? Our minds are second guessing everything at this point. Back to square one. Didn't we try this before? Here we go again. Isolated the lift cylinders one at a time. No drift. Isolated main control valve, still drifts. Disconnected dead engine 1/4-turn ball valve, no drift. What?, no drift? Reconnect valve, drifts. Turn ball valve the other direction, no drift! Machine is fixed.
To summarize: We should have isolated the lift cylinders to test for drift right from the begining. We didn't because we had just resealed them. The dead engine valve was accidently left open during our testing even after finding the cut pistion seal in the left lift cylinder. I know some would say this is humiliating, which it is. I'm posting this for two reasons. 1. It's really disappointing for people to start threads and NOT post back to what the final solution was and 2. Remind anyone who reads this, that even the most experienced mechanics sometimes forget the basic steps required to diagnose problems quicky and effeciently, especially when they are frustrated. :Banghead
