I have a Case 465 skid steer with M46 Danfoss Hydrostatic Drive pumps in the tandem configuration off the engine. My hydraulic gear pump needed to be rebuilt, so I removed it, had it rebuilt and reinstalled the gear pump which sits at the front of the tandem hydrostatic drive pumps. Filled everything with oil as best I could, cranked the machine with fuel relay removed to move some fluid through the pumps before starting. Now I have a warning light for charge pressure and no drive functions at all. Pressure gauge reads zero off the charge pressure test port but it does pump fluid out at a pretty good volume. Gear pump for the hydraulics works fine - hydraulic functions all work on the boom, just no drive. Charge pump sits between the tandem pumps - I split the tandem pumps to check out the charge pump which looks completely fine. The only thing I can think of is that I'm not bleeding something properly but everything appears to be full of fluid. I've purchased the repair manual but I feel like I'm doing everything right according to the manual. Any thoughts? I've been working on this for a month or so and just can't seem to figure it out! Thanks!
1. Why did the gear pump need rebuilt? 2. Who rebuilt it? 3. Were genuine parts used for the rebuild? In a lot of hydrostat pumps, the charge pump gear is keyed to the shaft. Are you sure the key didn't fall out when you inspected the charge pump? You will get nothing with no charge pressure.
I've done this twice, just too long between to remember. . . Both times the charge pump outer ring was installed upside down, or 180 degrees off if you will. There is a dowel pin for a key, and a matching hole BOTH top and bottom. The top hole is tucked up and sorta out of sight, and just seems right to align the key with the bottom hole.
Thank you both for the ideas and information. I suppose I'll be going through the fun of taking it apart and looking at it again. The gear pump was leaking - its an aftermarket high flow system from BIC (I guess back in the day this was a quasi - factory option from Case). Parker pump, resealed by a Parker hydraulic shop. And the gear pump seems to work fine, I'm just at a loss as to what I could have done to cause the lack of charge pressure in the hydrostatic unit. When I first replaced the gear pump I hadn't touched the hydrostatic pump and had no charge pressure. I'll split the pumps and take a closer look at the dowel pin key and orientation of everything - definitely does have the down pin key you mentioned. Thanks again!