John Deere H hydraulic pump repair

The hydraulic pump on our '45 H has been slowly getting worse over the past 30 years. It's still working, but will only lift the cultivator about half way. The fluid level is fine and the cylinder isn't leaking down, so we are pretty sure the problem is the pump.

Is a pump rebuild something best left to the professionals or something that most people can attempt in their own shop?

Thanks for the advice.

Not much to repair in there because likely no new gears or housings can be found. Seals can be found if it is leaking oil.
JD offers a seperate repair manual that covers that hyd. system. Check/adjust the pressure might be a good first step.

usually u can just have a machine shop clean up the housing surfaces & sides of the gears on a stone surfacer or mill. only 2 gears in there & bushings & shafts can be made. will be much improved. you can even have new gears made if u got benjamins. b&b gear 937-687-1771 will make them. even the housing can be milled out of a chunk of steel. if u want to pay anything can be fixed or reproduced.

Mathias:

If you are handy at all, you can do anything you need to get that pump back into shape. You sure can't hurt it if it is not now lifting full range.

Anyway, if the cylinder is not leaking down, then you know that the check valve (H 848 R) is probably all right. What I'm confused with is why would it lift some, and not all the way. If it were by-passing oil past the sides of worn gear to plate clearance, it should continue to lift, albeit slowly, until it makes it to the top.

So, do as Mike suggests and check the pressure so that you know if it can be adjusted back into spec. If not, you might have to go inside and check the by-pass valve spring, along with by-pass valve seat (H 833 R). Take a look at the parts catalog page 43. It's all there.

On those sorts of gear pumps, I've fixed many and never had to buy a gear. Typically, the wear occurs on the side plates so that oil pours aoround the gear. In the worst cases, I have had those plates and gears sides ground, and I mean on a nice, tight, Brown and Sharpe or equivalent surface grinder, that any good machine or tool and die shop will have. I have a little 9x18" that does fine for things like that. Anyway, look in the book and find out what the clearance on the gear to pump side plate needs to be. Then grind the sides of the gears as a pair laid flat on the mag base, until both sides have no wear lines. Then you lay the body on the grinder and inside where the gear bores are, put a piece of shim stock the thickness of the side clearance. Now you put the gears in the bores, turn on the magnetic base, and grind the whole shebang until it cleans up all the way across. When you remove the body and gears, the gears will be thinner by just the side clearance that you need.

Last and toughest, if there are excessive wear lines in the sides of the pump, they may have to be surfaced. On a "H" pump, which is an integral design, you'll have to remove quite a bit of hardware so that you can get the flat surfaces oriented on a grinder correctly.

The amount of work just depends on the performance that you want to have at the end, but check the easy things first like the by-pass valve seat and valve (maybe lap them together to freshen things up), and adjusting spring. It might just be set too tight, or the spring might be otherwise fouled.

Thanks for the replies. We have the service manual for the pump, so that should tell us the details. The tractor hasn't run in about a year, but my dad and I are headed to bring it home tomorow night (it's in my Grandmother's barn).

It sounds like the first thing we should try is plumbing a pressure gauge in-line with the lift cylinder. This should tell us what pressure we are reaching. If I recall correctly, it will lift completely when not loaded. But when it tries to lift the both side of the front cultivator it will barely pull them off the ground. With any luck we have a dirty pressure relief valve and won't have to get into milling the pump casings.

Thanks again.

On the gear type power steering pumps I have worked on the problem areas of wear were the gear O.D. and the housing I.D.
Only fix I can think of would be oversized gears or new gears and center housing section.

I almost always see side wear as the problem, along with bushings. Unless there was a ton of grit in the system, only oil should touch the body figure and gear tips, whereas the sides can rub from side pressure of the mechanism. You can build the tips up and od grind those back to size. Some adventurous types drizzle a bit of brass on the tips in a down position, but it can get all over the place. Then you almost always have to wring them back into form with lapping compound. We used to have the tips of gears chromed and then we would grind them back down, so as to regain the .005" or so lost over the years. This was in hydro-pumps on milling machines that carried around 1500 psi.

Yes, if it lifts no load, but the cylinder stalls under load, you probably have a relief valve problem.

Just put the gauge at the end of the hose. Then engage the lever and watch the dead-headed pressure top out. That pressure is where the relief valve is opening or the max that the pump can put out. If the pressure is too low, try tightening up the adjusting screw under the pump to put more pressure on the relief valve spring. The pressure should climb as you crank it in. If no adjustment occurs, you have to go deeper.

Lots of grit going through these old farm tractors that have no filter in the systems. I have seen some pretty badly worn power steering pump housings.
Seen many H pumps with frozen cracked housings so wasn't worried about wear so much as finding a good one.

Yeah, many "H" hydraulic units seem have a nickle weld bead on the "tank" area. I wonder if that might be a weak spot that cracks from over pressure events, but I have only had two "H"s with hydraulics, so I'm no expert. But both had/have a crack there. I'll need to re-repair the one I have with "Muggy Weld", because the nickle repair looks so ugly, but it doesn't leak.....I hate to try to make it look pretty and end up with a fix that was not as permanent as I already have, but it looks rough.

The only way to increase presure on the relief valve spring is to open the "soldereed shut" cap which gives you access to the relief valve. Then, you add flat washers on the relief valve cap screw in order to add spring tension. If a person goes to this extent (That is, if one opens the relief valve) installing a new spring is a very wise move.

Also -- on the "H", dead head pressure may not hold very long -- will not hold long for a working unit. The reason is that once cracking pressure is reached, (1) the relief valve opens, and shortly thereafter, (2) the by-pass valve opens -- with the result being a low pressure circulation of oil, reservoir-to-pump-to reservoir. And this valve action is fairly quick. (PatB)

I have just finished a re-write for the sections of the John Deere Model "H" Service Guide that deal with this tractor's hydraulic lift system. At this stage, it is available on CD only, but this will provide the detailed guidance you need.

Also, the pump can easily be damaged by water in the oil and then being in a freezing environment -- lots of broken pump bodies out there! I have both -- pump bodies and almost NOS gears if you find yours worn out. One thing many folks did over the years is ignore keeping oil in the reservoir during periods when the unit was not being used. This is a big mistake because whether used or not, the pump runs all the time, and dry-running gears take it in the shorts!

Finally, in trouble shooting the lift unit. the relief valve is the very LAST one I'd consider. It is basically a sealed-in valve -- it is the one under the copper (or brass) cap you see soldered in on the pump.

It was mentioned to install a pressure gauge "in the line". Unless you install the gauge in leiu of the cylinder (in dead-head mode), you may not learn much. I do suppose, however, you can monitor operating pressure which, for the "H" tractor, should be roughly 555 PSI. You know you aren't there, or the cultivator would rise! And in a serviceable unit, the lift should crack (or trip) at from 680- 720 PSI.

My email is [email protected] and I am here for your questions, or if you have a need. You may also call (830) 627-0430. (PatB)

But if you screw a gauge into the end of the hose, or at the pump aparatus, just like you would hook it to the cylinder, and move the control lever to the lift position, the pressure will build as if the cylinder is extending, and when the cylinder reaches its extent, or the gauge reaches equilibrium between its movement and the line pressure, and then if any reliefs open, the check valve at the bottom where the gauge/hose is attached, will trap the existing pressure in the hose up to the gauge and you will maintain the maximum reading on the gauge until the check leaks off, or you move the control lever. How else would the cylinder stay up? Just like it would do if you had a gauge attached to the side of the cylinder body. Pretty sure that it works that way on this single acting system.

That, my friend is true -- the check valve is a "built-in". I reckon I should regroup to say -- placing the gauge in as a sub for the cylinder (dead-head) will provide the most reliable result --and that I am not so sure that "teeing" a gauge into the line would reveal as much. Thanks Frank. (PatB)

It should if you let the cylinder extend all the way to max out. Thhe gauge will be part of the pressure vessel.

You can also do it the way you check Powr-Trols, but in the single acting way. Put a tee, then a gate valve, the a return hose back into the fill port of the hydraulic unit. Then acutate the lift lever and begin to close the gate valve. When the pump starts to stall, or the first relief valve lift off, you'll be able to read the prsure on the gauge. Continue to a completely closed valve, and you get the following reading for the final relief or by-pass or what ever thay call that valve.

Roger that - Thanks again - (PatB)

mike I know this is an old post but how to adjust pressure
on the pump ?

Mike I have 500 psi at high rpm but the lever does not kick out
can I ad washers to the relief valve to bring the pressure up on
the 1946 H