So, dropped off the hydraulic pump for the brakes and pilot at the shop a few days back, the report is that its not economical to fix so they suggest getting a rebuilt one, seems their price is about $400 over the prices on the interwebs, the advantage would be a brick and morter type place being the front end. They report the rear cover is scored, my suggestion to myself is to dust off the lapping plate, so that's easy, the other thing is that depending on pump, Deere offers some reasonable priced rebuild kits. I think I have a plan, the pump made 500 psi so its a fair bit lower than the original pressure spec, but if I can get it up to 1000 even, the brakes should work dandy as they're not bad with 500, So my goal is to improve the situation. The 644E calls for a pump that has very few parts, this pump, the AT139444, is a newer 644G and Hitachi pump, and has a lot of parts listed. My goal is to get it to stretch out for a year and see about a replacement later if we can't get a good response out of the pump. I've never worked on a closed center pump so it should be a learning experience.
It ain't, as a friend used to put it "Making hamburgers" (as opposed to rocket science which only requires lighting a fuse and plugging one's ears) so what have you got to lose?
Lapping is only .0001ths. Fly cutting on a mill might take out grooves that you can see and feel. What you say seems like a hard way to save money, to me... PS: As much as the end cover is scored, the rotating group is worn shorter, too.
Yeah, so the shop says the cover is scored, yep they do, but we popped it open before sending it out, it wasn't what I call scored. I can't quite figure out how it makes that much pressure with a floating, rotating barrel. Anyway, before sending it out it made 500, maybe the spring down the middle is weak, the one that holds it against the valve plate. The main issue I saw is that there was one part, some part of a bearing that came apart. it looked like tin with some sort of red elastomer on it, my guess is that it sat between the swash plate chamber and the barrel to center/ stabilize it, with that missing, the barrel could torque a bit and might just be leaking internally. I understand shops have to make money and I'm not a big dollar customer that they can do a favor for, and they did look really busy, I'm guessing that tossing the pump out the door with a repair isn't in their best interests. I had thought about the shorter barrel, I could eliminate the end gasket and use anerobic sealer and pick up 10 thou if I need.
Give it a go, if you have the time to waste... Myself, I'd fix it once, and only 'cry once' about the price. PS: If it is leaking internally, one sign is that it will be *hot* when it is running.
I was thinking the same, but there's a 1/2 inch case drain line that ditches all the bypass fluid into the tank return. Its not hard to get to with the only pita being the draining of the hydraulic tank, maybe a good idea would be a cork on a stick to plug the suction line if service is needed. It'd be nice if the tank itself had a drain, I'd even consider putting a 1/4 pipe fitting on the main suction line.
FWIW, the pump makes heat when internal motion doesn't make pressure or when pressure is lost without doing work. The pump probably has a spec for case-drain flow, some maximum amount at working pressure; A flow meter on the drain is a routine diagnostic.
That's a good idea, i was also wondering about making a flow test setup, perhaps drive the pump with a 1 hp motor, 1725 rpm and see what it builds for pressure, Let it do a small amount of pressure flow using some 3/16 line. I have some high pressure hydraulic needle valves.
So I guess I'm getting the pump back in a basket, sounds like inspection and estimates might be free but reassembly isn't, no bother, I'm good with puzzles. I think I found out why the pump shop was pushing for a rebuilt unit, the back cover has some wear and isn't available from Deere. I was planning on lapping it on a plate anyway as its just iron and flat, pull the index pins and lap away!
Welcome to Hydraulic repair shop 101: disassemble to the last tiny component before giving estimate. Hydraulic repair shop 102: Bill for disassembly and estimate if the customer refuses the repair.
Hmmmm, well it said free estimates so I'll hold them to that, there wasn't an * and they're doing a rod replacement on a badly pitted ram and making a couple big hydraulic hoses.
I think we've come up with a plan for testing, make a simple test jig over on the lathe, supply pump with inlet feed, case drain and pressure line, attach a hydraulic needle valve and give it a whirl, I think it'll work reasonably well, might end up making a mess but that's part of the fun. I think the lathe is a 2hp that should be enough to get to 2000 psi with 0 flow, or whatever we can make for pressure. Will engineer up a bracket that combines with the tailstock to give good torque handling.
Just be careful. High pressure oil can hurt you, and things that stop spinning suddenly can hurt you, too.
learned the second half young, full fielded an alternator driven by a drill press yeah, will start with the pressure control backed all the way off and flow path open, then slowly restrict the flow path down to some minimum amount and then see about adjusting the pressure.
So, I think I have all the parts, sure enough, the one bearing that was damaged will keep the barrel centered in the bore, now there's two more bearings that the trunion / swash plate rides one, one is purely plastic of some sort, the other is like a con rod bearing, its a metal insert with a plastic overlay. I'm betting the metal one goes on the higher pressure side. Part of the plastic overlay has peeled away, so that's a little troubling, This all runs in an oil bath so I was thinking I could replace the damaged overlay area with jb weld, it claims to have a tensile stregnth of 3900 psi so it might work well enough after roughing up the insert surface and letting it rest against the trunion as a mold. I've looked at the fiche and can't see this bearing in the diagram, it'd be worth getting a new one from JD and I've also contacted oilgear to see what they have to say. Other than that, the pump looks okay.
I looked again at the overlay and it feels like delrin or UHMW impregnated into a fiberglass mesh backer, its .025 thick, same thickness as the other bearing that delaminated from the pump bearing, cleaned and sanded a chunk of the old bearing and attached it to the shell with superglue, will buff down the edges and call it good.