1978 John Deere 850 Project

   / 1978 John Deere 850 Project #31  
I've been following along on this one because I like these kind of projects.

I noticed there is a gear shift between your legs when you are sitting on the tractor. You need to check the rubber boot on those and make sure there are no cracks in it. What happens is the water runs down the lever and into the transmission if the boot is no good.
 
   / 1978 John Deere 850 Project
  • Thread Starter
#32  
So I ended up replacing the fuel pump, which resolved the starting issues. Unfortunately that made me aware of another issue. Once started, the tractor wouldn't move. After some time diagnosing the issue, I determined that something must have been wrong with my re-assembly and figured it was related to the pressure plate or release bearing. Turns out that the clutch shaft & coupling had shifted forward during the seating of the engine and ended up not actually attached to the transmission input shaft. The result was that it was rubbing the input shaft and turning the transmission, but not enough to actually move the tractor....also it was turning the transmission in reverse.

I split it again today which is how I figured that out. We have it back together, but not fully bolted up because I need to replace the clutch linkage (broke during initial troubleshooting/adjustment). Without the clutch linkage in place, I can't get the release bearing to seat properly. Maybe next weekend.....

You can see where the coupler was spinning against the front of the transmission here:
trans-input.jpg


I've been following along on this one because I like these kind of projects.

I noticed there is a gear shift between your legs when you are sitting on the tractor. You need to check the rubber boot on those and make sure there are no cracks in it. What happens is the water runs down the lever and into the transmission if the boot is no good.

I'll take a look next time I'm out. It's currently under cover, so less of an issue, but still should be addressed.
 
   / 1978 John Deere 850 Project
  • Thread Starter
#33  
Tractor is running, moving, and the front end loader articulates. Still have a good bit of work to do before I'd say that it's in usable condition, but we're pretty close. I was very pleased to drive it around yesterday under its own power. Getting the FEL back on with two people was a quite the ordeal, especially since I didn't mark the hydraulic lines and really have no experience with hydraulics other than a basic understanding of how it works.

Unfortunately, I don't have any pics or videos to show because I didn't have time to really get any. Maybe next weekend when I get my steering rod end replaced and can actually work it a little.

I do have a handful of questions that I haven't been able to figure out on my own, mainly surrounding the hydraulics. My tractor has three levers on the right side of the seat. One clearly controls the 3-point, and I think is described in the manual as a "rockshaft control valve". The other two are for the front end loader and are described in the manual as a "selective control valve" or SCV. There is also a screw in/out valve between your legs if you're sitting in the seat. Not knowing how the hydraulics work or remembering how the lines were hooked up, I flailed around for a bit and managed to get the 3-point to lift using a combination of the lever and the screw in valve under the seat between my legs. Likewise, we managed to get the lift circuit to work with the right hand SCV and the bucket circuit to work with the left hand SCV. We did have to open and close the screw in valve a couple times to make things function. Now, with that explained, I'm not 100% sure which SCV lever is supposed to go with which circuit or if that even matters. Likewise, I'm not sure that I have them correctly aligned or if they're backwards. I think I have at least the lift circuit reversed.

This picture shows the original seat pan. On the right are the two SCVs and the 3-point lever:
original-seat.jpg



I haven't actually tried lifting any weight in the bucket or on the 3-point yet. The bucket action seemed weak and I figured I have some adjustment or tweaking to do.

Can someone explain to me how the hydraulics on this tractor are supposed to work, what the function of the screw in (open/close) valve is and which lever should be connected to which circuit?

Also, I'm slightly confused by my fuel filter assembly. I purchased a new assembly that looks identical to this:
121254-55600.jpg


My assumption is that the C<-->O designation depicts the lever being in the (O) open position in this picture and that to close the valve, you'd flip the lever 180 degrees to the (C) closed position. What I've found is that with the lever in the 12 o'clock position, that fuel flows freely while in the 3 o'clock or 6 o'clock (pictured) position fuel doesn't flow or only dribbles out. Am I missing something here? I'm hoping that the 12 o'clock position isn't a bypass or something that flows unfiltered fuel.

My second question regarding the fuel filter has to do with bleeding. After we had the tractor running, having bled the lines again, I came close to running it out of fuel. The filter bowl was previously full and drained down to about 1/3 full before I noticed, shut off the tractor, and added fuel to the tank. Upon restarting and running a bit, the filter bowl never refilled. I'm assuming I should have bled that using the screws at the top of the filter housing. Is that correct?
 
   / 1978 John Deere 850 Project #34  
Tractor is running, moving, and the front end loader articulates. Still have a good bit of work to do before I'd say that it's in usable condition, but we're pretty close. I was very pleased to drive it around yesterday under its own power. Getting the FEL back on with two people was a quite the ordeal, especially since I didn't mark the hydraulic lines and really have no experience with hydraulics other than a basic understanding of how it works.

Unfortunately, I don't have any pics or videos to show because I didn't have time to really get any. Maybe next weekend when I get my steering rod end replaced and can actually work it a little.

I do have a handful of questions that I haven't been able to figure out on my own, mainly surrounding the hydraulics. My tractor has three levers on the right side of the seat. One clearly controls the 3-point, and I think is described in the manual as a "rockshaft control valve". The other two are for the front end loader and are described in the manual as a "selective control valve" or SCV. There is also a screw in/out valve between your legs if you're sitting in the seat. Not knowing how the hydraulics work or remembering how the lines were hooked up, I flailed around for a bit and managed to get the 3-point to lift using a combination of the lever and the screw in valve under the seat between my legs. Likewise, we managed to get the lift circuit to work with the right hand SCV and the bucket circuit to work with the left hand SCV. We did have to open and close the screw in valve a couple times to make things function. Now, with that explained, I'm not 100% sure which SCV lever is supposed to go with which circuit or if that even matters. Likewise, I'm not sure that I have them correctly aligned or if they're backwards. I think I have at least the lift circuit reversed.

This picture shows the original seat pan. On the right are the two SCVs and the 3-point lever:
original-seat.jpg



I haven't actually tried lifting any weight in the bucket or on the 3-point yet. The bucket action seemed weak and I figured I have some adjustment or tweaking to do.

Can someone explain to me how the hydraulics on this tractor are supposed to work, what the function of the screw in (open/close) valve is and which lever should be connected to which circuit?

Also, I'm slightly confused by my fuel filter assembly. I purchased a new assembly that looks identical to this:
121254-55600.jpg


My assumption is that the C<-->O designation depicts the lever being in the (O) open position in this picture and that to close the valve, you'd flip the lever 180 degrees to the (C) closed position. What I've found is that with the lever in the 12 o'clock position, that fuel flows freely while in the 3 o'clock or 6 o'clock (pictured) position fuel doesn't flow or only dribbles out. Am I missing something here? I'm hoping that the 12 o'clock position isn't a bypass or something that flows unfiltered fuel.

My second question regarding the fuel filter has to do with bleeding. After we had the tractor running, having bled the lines again, I came close to running it out of fuel. The filter bowl was previously full and drained down to about 1/3 full before I noticed, shut off the tractor, and added fuel to the tank. Upon restarting and running a bit, the filter bowl never refilled. I'm assuming I should have bled that using the screws at the top of the filter housing. Is that correct?

1) You normally bleed the filter by one of the two screws on the upper housing. If you had air in the chamber after some use, then there is a leak, probably at the bowl ferrule, bleeder screws or inlet hose. It may not be enough to leak when the tractor is static and parked, but when a slight fuel vacuum occurs during operation then air could be sucked into the bowl.

2) Not sure exactly what your question is about the hydraulics, I'll read the book later and see if I can come up with a cogent answer.
 
   / 1978 John Deere 850 Project
  • Thread Starter
#35  
1) You normally bleed the filter by one of the two screws on the upper housing. If you had air in the chamber after some use, then there is a leak, probably at the bowl ferrule, bleeder screws or inlet hose. It may not be enough to leak when the tractor is static and parked, but when a slight fuel vacuum occurs during operation then air could be sucked into the bowl.

I don't think it had air in the chamber until the fuel in the tank was exhausted. After refilling the tank, the air remained. I assume that is due to me not bleeding it after air (or vacuum) was introduced by the low fuel situation.

2) Not sure exactly what your question is about the hydraulics, I'll read the book later and see if I can come up with a cogent answer.

I'll see if I can narrow it down:

1. What is the function of the open/close hand screw between my legs when sitting in the seat?
2. Are the two selective control valves identical or is one dedicated to lifting the FEL and the other dedicated to the bucket?
3. Which direction should I pull/push the lever to lift the arms?
4. Which direction should I pull/push the lever to dump the bucket?

Thanks!
 
   / 1978 John Deere 850 Project #36  
I don't think it had air in the chamber until the fuel in the tank was exhausted. After refilling the tank, the air remained. I assume that is due to me not bleeding it after air (or vacuum) was introduced by the low fuel situation.

OK, I got lost in the chain of events



I'll see if I can narrow it down:

1. What is the function of the open/close hand screw between my legs when sitting in the seat?
Never ever used ours, it should be the control for the percentage of flow the rockshaft receives in relation to the SCV
2. Are the two selective control valves identical or is one dedicated to lifting the FEL and the other dedicated to the bucket?
One does have a float position for the loader boom. I did remove ours and replace with a aftermarket Prince valve on the loader itself in 1991
3. Which direction should I pull/push the lever to lift the arms?
Forward for both boom down and curl down (dump)
4. Which direction should I pull/push the lever to dump the bucket?
Forward

Thanks!

......
 
   / 1978 John Deere 850 Project #37  
1. What is the function of the open/close hand screw between my legs when sitting in the seat?
Seemed like an easy question, but I had to go thru my I&T and JD Technical manuals, as well as our owners manual to find the answer.

That valve is the rockshaft stop valve. It seems to be used to hold the rockshaft in a single position. It is also used in various positions during hydraulic diagnosis. Like I said, ours has never been used, and seems impossible to turn. Not wanting to create a proble where there is none, I haven't tried very hard.
 
   / 1978 John Deere 850 Project #38  
Seemed like an easy question, but I had to go thru my I&T and JD Technical manuals, as well as our owners manual to find the answer.

That valve is the rockshaft stop valve. It seems to be used to hold the rockshaft in a single position. It is also used in various positions during hydraulic diagnosis. Like I said, ours has never been used, and seems impossible to turn. Not wanting to create a proble where there is none, I haven't tried very hard.

On my tractor that valve controls the rate of drop on the 3 point.
 
   / 1978 John Deere 850 Project #39  
John Deere 650-1050+ have a seperate valve to control the drop of the three point rock shaft
 
   / 1978 John Deere 850 Project #40  
For normal operation, the knob between your legs should be fully counter clockwise. It regulates flow of oil into the rockshaft. The left scv lever should raise loader when pulled back and lower when pushed forward. There should be a detented position when pushed full forward to allow the loader to "float". the right scv lever should curl bucket back when pulling lever back and dump bucket when pushed forward.
 

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