hello i have recently rebuilt the tandem pump on my case 1840 after it was loosing power when the fluid was getting hot. after putting it back in, the right side is good but the left side has no reverse. at first the stick positions behaved stop in middle and forward with no reverse. i then looked in manual and followed troubleshooting checklist it said to check the reverse bypass valve and after i did that it was even worse with it moving forward in middle position and having to pull it back into reverse to stop and spinning what seemed to fast in forward. stranger then that it was working before pulling the pump. that would lead me to thinking i assembled it wrong but if the left side is spinning it is getting constant pressure but and will be a servo valve???? i put new seals in those as well and set the bolt stick out through side cover the same as i pulled it apart. i will pick up some hose, gauges and bits to do a proper neutral stop set procedure as out lined in the manual. i doubt it will sort out my problem but need to do it to eliminate that i have the servo out of adjustment. any ideas on what or where to look. writing this i should have swapped the pressure reliefs around to see it problem moved but they all looked good no broken springs or the like from what i could see, and couldn't feel anything in the valve seat, ill try swapping them around tomorrow. any one have experience with this kid of thing before??? i will probably pull the pump apart again to see if it was assembly error but i don't believe so i was very careful to follow my pictures and manual. luckily its the front pump and can pull the shaft with the rotating group with the pump in place. if i had trouble with anything it was the yellow shell bearing not staying in place when i was lowering the shaft and endplate back into the pump on the bench. it seemed easier to do vertically then horizontally. the shell kept falling out with hydraulic oil on the back of them to hold them in place so i used a thin smear of grease to keep them there while i lowered it in place.
bump. still no luck with this i have bought some gauges and tried some diagnosis from the manual to no avail all pressures seem good except for left reverse which is still nothing because its not going into reverse. i can get it to stop spinning in neutral with a hose between the servo houseing while performing a "servo neutral posisition adjustment" but i cant wind the adjustment thraed far enough to get it to go backwards. only wind it out to get it to go forwards and then when you wind it back it still stays in forward but if you shut down the engine and restart it, then pump swash will stay in neutral posisition. for what ever reason i cant get the swash to go to reverse side and pump. putting the gauges on the servo test ports it shows pressure raising and lowering as if its trying to move the servo piston but weather its moveing or not hmm i guess not because its not going into reverse. i have included a pump manual i have found it has been helpfull with some more specific trouble shooting to my specific problem ie "cant find neutral" and "motors only travel in pone direction" and trying the guide i am still stuck. ports are clear, pilots are clear, check valves seem good i have swapped them from side to side to have the problem stay the same. i cant seem to see why the swash isnt swinging to get reverse is there something phisicaly inside preventing it? i have already pulled the front pump inplace to confirm it wasnt a assembally mistake like a big yellow bearing comeing out and jamming everything up. it all seems right and still doing the same thing. i pulled the servo as well again. unless i assembled the rotating group wrong twice in a row which i doubt theres not that much to these things i can see, it cant be anything to major i hope, theres not much more i could replace or make new in this thing other then get a new cigarette lighter for it. if any one is well versed in these pumps and has any ideas it would be much apreciated for your advice. if im here writeing and asking for help its because im stuck and its more then a basic repair which i can work out myself 99% of the time what has me most stumped is that it was working befor the rebuild and now all of a sudden its developed this problem. ill be pulling the front plate of next while leaving the rotating group in place on the shaft to see if there is something phisicaly preventing the swash from travelling in that direction.
forgot to mention while looking down the spool valve hole with spool removed, every thing looks good you can see the pistons touching the swash and the 3 pins(not all at once but there there) and moving the lever arm you can feel the swash moveing as the roll pin engages with the outer spool ring thingy. im going to become an expert in these pumps by the end of this if i want to or not lol
Paul, I'm no Sunstrand expert, but have been involved in repairng these systems since they first appeared in Case machines in the 90's. Personally, I won't overhaul these pumps for reason of their complexity & that a certified repair agent can carry out the repair/overhaul, & bench test the pumps. This gives me confidence, that I can fit them to a customers machine & I know that if I've done my part well - the machine will operate perfectly at the end of the job. I realise you maybe on a tight budget, sometimes you have to admit defeat & bite the bullet & send the pumps & both motors to a sunstrand agent. Note I said the motors as well. If the pump gerotor plates were damaged, the connected motor will have the same wear & will need either surface lapping or new parts. My guess is that the pump hasn't gone together correctly. You can't rebuild these things blindly - using the wrong service manual won't help. You are using a M46 manual when you have a M91 set of pumps..... It certainly seems like the servo piston is not moving as it should.
i know whats wrong with it...its got no gas in it. lol always wanted to say that now excuse me while i go stand in front of a mirror and give my self an upercut for putting it together wrong twice. third times the charm. so yes an assembly problem, i had the pump pointing up and put all the internalls in and then the end plate. because it needs the end plate to keep it located in place and must of been given an opertunity by myself to pop out of place as the end plate went on. the last bit of this procedure as you drop it in the last inch is done blind and i obviously got it wrong. im glad i found the problem, yes there difficult to build and work on but i do diesel rebuilds and injector pumps no worries just never put my hand to one of these befor. thanks for replying alrman im not adverse to spending money as long as i get the right person for the job. most people told me flat out no or gave me a cost prohibitive quote. with out chaseing my tail for a few days trying to find this fault theres only a couple of hours to tear one down and put it back together. i deffinbtly feel i learnt alot and would do another no problem. it deffintly a advanced skill level job but doable at home.
Glad you got it sorted out. I'd say if you've done injection pumps you'd have a much better chance than most at rebuilding a hydrostatic pump.
ended up spliting the pump to do it on the bench. glad i did i found a oring that got squished on the back of the feed pump thats why it was bypassing and driveing the wheels in neutral position. ended up being 2 assembly issues. just have to wait till monday to get the oring and finish it off. held it in palce with some grease as well hmmm.