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1520 rockshaft disassembly

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OregonAaron

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Today I plan on removing the rockshaft assembly for repair assuming nothing else robs me of the time to do it. From my shop manual it looks fairly straightforward however I have one question. There is a long lever that goes into the transmission housing for load/depth control. Will this come out with the rockshaft housing or is there a pin that I need to disconnect or does it require additional disassembly prior to me removing the rockshaft housing? The manual is not very clear on this and I don't want to break it!
 

L/D cam follower(shaded outlined part) slides out of rockshaft control linkage when raising housing & must be lined back up when reinstalling rockshaft housing
mvphoto90126.png
 
Okay, I'm sure it will make sense when I see it. Thanks. I will post pictures of this process for future folks working on this area of their tractor, and I'm sure I will have a question or two.
 
Rockshaft controls will lift off arm lever / finger. When lowering assembly back on there is a certain place
lever has to be placed as you lower rockshaft back onto case. There is a slot / guide in control linkage that
lever will fit into to guide / maintain position of lever to place lever finger against the rockshaft cam. If
you study it when off you will see the place for it to be when it goes back on. Better yet look under
rockshaft housing as you are lifting it off to see where the lever is placed at. Not hard to do just be aware
it has to be aligned when it is put down on case. DW
 
Well, I didn't get it apart today but almost. I need to bring out my air compressor to clean off dirt and debris so that it doesn't fall inside the transmission. I have a chain hoist rigged up so I can raise it slowly and see how everything is positioned. Does the control lever (raise/lower lever) just slide out of the housing once the mounting screws are removed?
 
I got the rockshaft assembly off today. Not too hard but it sure is heavy. I have not disassembled it yet, however my parts have not arrived yet either. Doing an inspection of this on thing I noticed is a fitting that is threaded that has nothing in it and it sure looks like it should. In one picture I outlined the area. Here are some pictures, I also included a couple pictures of the transmission. It looks pretty clean and nice inside, y'all be the judge
mvphoto90234.jpg
 
I will tear into this soon. If there are any trouble area I should pay special attention to please let me know. The rebuild kit should arrive next week.
 
So I removed the cylinder/valve assembly from the rockshaft housing today. Everything looks to be in good shape inside. I didn't realize it but I did not need to remove the roll pin that attaches the piston rod to the crank arm. I am very glad that I did because I found out that this roll pin was actually broken. Does it matter if I replace it with a john Deere roll pin or can I just use one from the auto parts store? I don't know if it's a special hardened type or what, what I do know is I don't want to do this again because I bought the improper roll pin! Since my seal kit did not come with a new thermal relief valve should I replace that with a new one too? I'd rather replace it now if I should. Should I replace any seals on the actual piston itself? I plan on just leaving it in it's bore if not, why tempt fate I suppose. I will post some pictures later. So far this has been pretty straightforward.
 

If it was my repair I'd replace piston seals, control valve seals, roll pin from anyplace & leave thermal valve alone. Roll pin from JD is a 34H320(1/4X2-1/4) @ $1.69 & thermal relief valve is AT21781 @ $98.66
 
Okay, sounds like a darn good idea. On the JD parts site I didn't see much on the actual piston seals. I assume they are some sort of o-ring. Is it much trouble to replace them? The thermal valve seems to be not of any concern so I will leave it be. Are the control valve seals much more than what came in that seal kit I purchased?
 

3pt control valve seals consists of o-rings & backup washers. Shown in photo is part #s for rockshaft piston seals. Piston seal is easier to install on piston if warmed in warm water or oil

mvphoto90463.png
 
I'm about to dive into the cylinder/valve final disassembly. Since the piston will not slide out of it's bore my manual says to remove the pipe plug at the other end of the cylinder to push out the piston. When I am assembling this is there any sort of thread sealant that I should use on this plug? Also, one more question about this thermal relief valve- my manual says to test it, how would I go about testing it's opening pressure? You (TXjim) don't seem concerned with this valve, so I'm assuming it does not fail often?
 
(reply to post at 18:28:25 04/08/22)
Click to expand...
I've stated previously on several occasions that I've only witnessed thermal relief valve fail a very minimal # of times.

Yes I'd advise utilizing thread sealer on a plug utilized on a hyd system.

I've never tested a hyd thermal relief valve but I think a hand operated fuel inj tester with correct fitting would surfice for that task.
 
I finally got a little time to mess with this rockshaft assembly today. I did not remove that pipe plug to get the piston out, a little compressed air and it slid out nicely. The seal on the piston is different from the one on the John Deere parts page. My seal does not have the "washer" (as Deere calls it) it is a solid black rubber seal. From the diagram on the Deere site it shows a rubber seal with an additional retaining ring- maybe a design change? Anyways, I'm still waiting on parts so this project is stalled for now
 
So finally I got a chance to get this all back together. It was all fairly easy and straightforward. I replaced all seals that came in the rockshaft seal kit along with the roll pins and did the piston seals. Piston seals were easy enough, although I was afraid of tearing the outer one. Seems like once you get it positioned just right and apply pressure in the right spot it goes right on. I also replaced that thermal relief valve, figured I should just in case. I had planned on doing a write up on this, but I have had very little free time in the last couple months. Anyhow, fired her up yesterday and the hydraulics worked great, no leaks, no strange noises. Thank you TXjim for all help you have provided. Since my tractor has rops with a canopy I was able to use the canopy to attach my chain hoist. Not ideal, but it worked just fine.
mvphoto92338.jpg
 
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