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SCV on JD4600 - issues and resolution

9309 Views 8 Replies 4 Participants Last post by  Kennyd
This will be a long post if I tell my whole story. I'll try to keep it to the point. Please bear with me. I have a question or two to ask at the end.

When I first started using the 2001 JD 4600 (which I bought in August, 2011, with 435 hrs on it), the float position on the joystick did not seem to be working. Based on advice I got from reading threads in TBN, I tried "snapping" the stick ahead to get the float detent to lock in. When I did this with the tractor off, the detent seemed to work the way I expected it to. However, when I went to use the loader for backdragging, the action of the up/down valve got "sticky." It definitely had more drag than before, and didn't seem right. As I used the tractor in several sessions, the valve seemed to be freeing up somewhat. I thought that the detent had just been gummed up somehow, and it would probably work out of it.

With shorter days this September, I didn't use the tractor as often (very few after work sessions). When I had a good weekend session a couple of weeks ago, I backfilled a hole that I had excavated to repair a crack in my house foundation. That time, the up/down valve was even stickier than before. Also, I couldn't even make the valve stay in float mode by holding it forward.

Snow removal is part of my plan. I definitely needed to get the valve fixed or replaced in order for the Float to work. Last week, my CD copy of the Technical Manual, TM1679, arrived. The TM described the procedure for servicing the SCV valve, and implied that there might be an overhaul kit for it. I looked at JDParts online and printed out the applicable diagram and parts list. There didn't seem to be an overhaul kit listed.

Last Saturday morning, I went to the JD dealer. The parts man confirmed that there was no overhaul kit available for my SCV, and no parts breakdown for parts internal to the SCV. The SCV itself is available to order. With tax, that would cost me a little south of $700. He also gave me the business card of a hydraulics repair shop in the area.

I figured that I had nothing to lose if I took out the SCV and checked it out myself. If I found that I was over my head, I might take it to the hydraulics shop. In the worst case, I would pony up and buy the new one. Saturday afternoon, I had the SCV out on my bench.

This "Dual" SCV is actually a 3 spool valve, with the two outside ones having detents, and the middle one (bucket roll) having no detent. (As with several JD models, the 3rd spool is used with a kit of plumbing and linkages to provide the 3rd SCV function). My right-hand spool (up/down) was so stuck that I had to jig up a method to tap it out (without damage). The detent balls seemed to be free, and were covered with white grease. My original theory about the cause of the problem had to be wrong. I rubbed the spool wit a clean shop towel, then pushed a rag through the housing 3 or 4 times. I saw nothing come out on the rag. I tried again inserting the spool in the housing. It was sticky, but not as bad as before.

Since the 3rd spool had a detent, and was identical to the problem spool, I decided to swap them. At this point, I don't have the 3rd SCV rigged up anyway. This resulted in all 3 spools being movable by hand, though the up/down was a little sticky and the 3rd had somewhat more drag. I put the SCV back together.

The first time I remounted the SCV back on the tractor, I inadvertenly knocked one of the O rings out of place. After losing a quart of hydraulic oil in a hurry, I gave up for the night. On Sunday, I got a new pair of O rings, and got the SCV installed with no leaks.

Tonight after work, I remounted the loader and tried out SCV and its float function. What a difference! Compared to before, the up/down valve is very smooth. The float seems to work a bit different than I expected, though. I feel the detent when I push the stick ahead, but the stick doesn't stay by itself in the forward position. However, even if I release the stick, the loader seems to float until I move the stick again.

I only tested briefly tonight with a little backdragging. If it consistently works like it did tonight, I think I have won.:dance:

Now my questions:
1 - Is the stick supposed to stay forward when in float, or is the operation I experienced tonight normal for the 4600? (Valve stays in float mode, but stick returns to center.)
2 - Do you have any idea what could have caused the valve to stick? The previous owner said that the fluids had been changed by a JD dealer at 400 hrs. I'm at 512 now. I hope I don't have an issue with contamination in the fluid.
3 - Any other comments?
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If I'm not mistaken, hydraulic oil gets milky/cloudy in color with moisture in it. How much I don't know as I don't have that issue in our dry climate. Anyway is your hydraulic fluid a clear pale yellow color?
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