420 Hydraulic Pump

[Mark L in Tucson]

Late last year I refurbished the seals and gaskets on my 1958 420 3 Point Hydraulic System. It seems to have worked fine, the 3 point raises and lowers and the rear end leaks are gone. However, the hydraulic pump has developed a leak at one of the seams (it is a 3 piece assembly), the leak is at the aft seam of that assembly. Before I tear the front end of the tractor apart and buy a remanufactured pump, I have begun to wonder there is anything that I could have done at the back end to cause issues. Is it possible that I did something such that the bypass valve and pressure relief valve are both not functioning properly? That would create a condition where the pump is building up pressure but not dumping oil back into the reservoir and thus forcing oil through the internal gaskets in the pump. I don't think this is the case, but wanted to find out if anyone with more experience with these systems has some ideas.

 

[backyard mechanic]

All of the hex head bolts are tight ?

 

[Rusty wheel]

If your pump was dead heading and building up that kind of pressure it would be getting very hot and it would only be a few seconds until the three bolts in the coupling would break. Is the oil just running out or dripping or does it come out in a spray like it's under pressure? You could put a gauge in the pressure port and check the pressure. Does the engine seem like it's running under a load? Is the pump extremely noisy? Is there excessive heat build up in any part of the system? Just some things to check before you tear it down. Those pumps are costly.

 

[Jim.ME]

From your description here; not knowing just exactly what you had apart and may have turned for adjusting screws; it is possible it has been running over pressure.

Some questions for you to answer.

Do you have a manual? And if you do, which one is it?

After you worked on the system, did you check the hydraulic pressure?

Do you have a gauge you can check the pressure with?

The pump may be ok other than needing to be resealed. There isn't much to those pumps you may want to reseal it yourself and continue to use it, if it has been working ok other than the leak. As far as I known new ones are NLA from John Deere. Some people have not had good luck with those purchased as rebuilt.

 

[Mark L in Tucson]

Thanks for the response. Yes, I have the shop manual and followed it for the repairs I made. I did not do anything that would require re-setting the check valve per the
shop manual. I did not take out the check valve, only the other components that the manual provided instructions that didn't require a significant calibration process like
the check valve. I had the entire hydraulic unit apart per the manual and thoroughly flushed everything before putting it back together. I needed to replace all of the
gaskets and seals including the rocker arm seals, so needed to disassemble the entire unit.

I did not check the pressure after re-assembling other than functional testing, including with a fairly heavy 3 point blade. The system functions both raising and
lowering implements. I do have a gauge that I should be able to check pressure with. I just found in the manual how to hook up to test pressure so I can do that.

Finding pumps looks to be a project in itself. If I can find the parts to re-seal, I'd rather do that.

 

[Mark L in Tucson]

Oil is just running out, more of a spirited oozing out, not a spray. Engine doesn't seem to be struggling. Not noticing a lot of noise from the pump. I'll check for excessive heat.

Thanks.

 

[Mark L in Tucson]

They seem to be tight. Pretty much have to tear the front end off to even confirm that.

 

[Jim.ME]

Mark,

Unless someone here rebuilds these pumps, try contacting Lavoy Wilcox by email ([email protected]). He works on the JD crawlers of this vintage and may be able to rebuild your pump or have some ideas for you. I believe the 40 series pump used different size inlet and/or outlet ports from the 420 pump, in case you consider buying one you might find.

 

[M-MAN]

You need to wash it good with brake cleaner so you can be positive about where the oil is coming from. Most likely it is the line or the fitting for it in the pump and it is seeping down. If it is actually seeping through the O ring about $50 will get you all the soft parts for the pump from Deere. You won't know for sure about the needle bearings until you tear it apart.

 

[Mark L in Tucson]

Thanks, I'll definitely keep that in mind if it comes to that. I'll be pressure testing the system, hopefully tomorrow afternoon. If not then, it will be next weekend.

 

[Mark L in Tucson]

I pressure washed the tractor and engine compartment before bringing it in to start working this problem. When I had the tractor apart last year, my next project for it was to start working front end leaks -- there was a significant amount of old oil/grease from various sources caked on so I wanted to clean it up before starting to work on it. The seeping from the component joint is pretty clear. One of those few times when the problem was actually on a side of a component you can actually see.