Many thanks for this forum. My 641 power assist steering suddenly quit so I had to muscle the steering wheel to guide the tractor about a hundred feet to my shop. I used this forum to guide me through the power steering control valve removal and dis-assembly, where I found one of the three plunger springs was broken. I cleaned all the components, lubricated them, replaced the three springs and the seals with new CNH parts, and reassembled everything being careful to allow for proper amount of torque on the thrust washer. Still no power steering. I noted that, while running, the PS fluid in the reservoir does not roil, even when I gently try to move the steering wheel. My thoughts are as follows. 1. I may have installed the spool wrong, with the ID machined groove up. 2. When the PS originally quit, maybe it was the pump that failed, then maybe I broke the plunger spring when I muscled the steering to the shop. Any insight is greatly appreciated.
Ultradog MN
Well-known Member
- Location
- Twin Cities
I doubt the spool in the power block is the problem. I am pretty sure mine is upside down too from when I put it in wrong 6 years ago.
My thoughts are it's your pump. Though a pump doesn't usually fail just all of a sudden.
But trying the simplest things first here:
Have you changed the filter in the reservoir lately?
I wonder if it could be the pressure relief valve in the pump. Possibly the little plunger got stuck or maybe the spring broke.
If you are sure your filter is ok then I would look at the prv.
Parts related to #12,13,14, etc in the photo below.
I don't know if you can remove it without taking the pump off the tractor. Am less familiar with those than the 3000 style pumps.
My thoughts are it's your pump. Though a pump doesn't usually fail just all of a sudden.
But trying the simplest things first here:
Have you changed the filter in the reservoir lately?
I wonder if it could be the pressure relief valve in the pump. Possibly the little plunger got stuck or maybe the spring broke.
If you are sure your filter is ok then I would look at the prv.
Parts related to #12,13,14, etc in the photo below.
I don't know if you can remove it without taking the pump off the tractor. Am less familiar with those than the 3000 style pumps.
Thanks for your advice. I drained the PS fluid and found no filter in the reservoir, only the "hollow stud". I had the front axle replaced in 2010. Maybe they forgot to replace the PS filter. If the pump became clogged at the inlet, I should probably remove and clean the PS pump and flush everything else and see if it still works? What do you think?
It was fun pulling the PS pump through the loader frame. However, I was pleased to hear the pump puffing when I hand-spun it. I am going to replace the rubber parts inside the pump.
As I mentioned above, there was no filter or filter retainer in the PS reservoir when I opened it. The new filter I just received leads me to believe that there has never been a filter in the PS reservoir for the last 27 years, since I've owned tractor. I have added 134 fluid to it once in a while but....should've looked closer.
Since I'm removing and re-cleaning the control valve, I have the chance to flip the spool, if necessary. I installed it with the inside groove up. So far, I gather that it may not make a difference which side is up. The manual says to put it in the same way it came out. Could this be just for re-seating? Also, I'm air-blowing out all the lines. How can I clean out the two hydraulic cylinders?
As I mentioned above, there was no filter or filter retainer in the PS reservoir when I opened it. The new filter I just received leads me to believe that there has never been a filter in the PS reservoir for the last 27 years, since I've owned tractor. I have added 134 fluid to it once in a while but....should've looked closer.
Since I'm removing and re-cleaning the control valve, I have the chance to flip the spool, if necessary. I installed it with the inside groove up. So far, I gather that it may not make a difference which side is up. The manual says to put it in the same way it came out. Could this be just for re-seating? Also, I'm air-blowing out all the lines. How can I clean out the two hydraulic cylinders?
Thanks for the pics. I will install the spool groove up. I just got the PS pump apart and need to ask advice on the following pics. There is some wear on the pump body, but don't know if there's evidence of sudden failure of the power steering. Is the scoring normal for the age of the 641? The scoring is not deep, just on the surface. I'm also not sure what looks like a crack on the wall of the groove is supposed to be there. Thanks.
I'm thinking the same thing. That "crack" sure looks like a casting defect. Not much you could do about that.
The surface is damaged. A good machine shop could probably true that up, but I'm not sure what that would do to clearances. I think I would try to use it as is and see what happens. Only other choice it to find a used valve body (or more likely a donor steering gear).
I hate these kind of choices!!!!
Thanks guys for the replies. Now I know what a "cold shut" is. Also, I will give the PS pump another chance.
Sorry for the delay in my response but life and wife have demanded attention away from my broken 641 in the shop. However, today I was able to continue my adventure into power steering repair.
Since the PS pump was apart, I replace the seeping shaft seal and the o-rings and installed the new filter with the new retainer spring assembly. I also disconnected and air-blew out all the lines and purged the cylinders by removing the front connection and pumping them by hand. When I did that, they would breath in one port and blow out the other. Then, I installed the PS pump, connected lines, filled with 134 fluid, pulled the coil wire, cranked it, added more 134 until the reservoir stayed full, started the engine and ....no power steering.
Back to testing. I disconnected the front of each cylinder and found that with force, I could pump each slowly in and out. Could hear a little air in the system too. I repositioned the rods close to their connections, tugged the steering wheel a little with the engine running, and watched the rods very slowly move properly. Later, at one point, while I was watching the right rod move slowly in and out, the left rod slowly moved all the way out.
Next, I disconnected the pressure line of PS pump, clamped on a short hose to guide the flow downward, disconnected the coil wire and cranked the engine. The fluid was pumped out quickly however, I don't know if it was pushed out with 700 lb. of pressure.
The only other thing I can think of is when I reassembled the PS valve block, I re-used the bearing lock nut because it was still "stakeable" but more importantly, it seemed to be staked in the correct spot for bearing load.
In the vast experience of this forum's members, can this roller vane pump move a good volume of fluid but not produce enough pressure? Also, am I working in the right direction? All advice is very much appreciated!
Sorry for the delay in my response but life and wife have demanded attention away from my broken 641 in the shop. However, today I was able to continue my adventure into power steering repair.
Since the PS pump was apart, I replace the seeping shaft seal and the o-rings and installed the new filter with the new retainer spring assembly. I also disconnected and air-blew out all the lines and purged the cylinders by removing the front connection and pumping them by hand. When I did that, they would breath in one port and blow out the other. Then, I installed the PS pump, connected lines, filled with 134 fluid, pulled the coil wire, cranked it, added more 134 until the reservoir stayed full, started the engine and ....no power steering.
Back to testing. I disconnected the front of each cylinder and found that with force, I could pump each slowly in and out. Could hear a little air in the system too. I repositioned the rods close to their connections, tugged the steering wheel a little with the engine running, and watched the rods very slowly move properly. Later, at one point, while I was watching the right rod move slowly in and out, the left rod slowly moved all the way out.
Next, I disconnected the pressure line of PS pump, clamped on a short hose to guide the flow downward, disconnected the coil wire and cranked the engine. The fluid was pumped out quickly however, I don't know if it was pushed out with 700 lb. of pressure.
The only other thing I can think of is when I reassembled the PS valve block, I re-used the bearing lock nut because it was still "stakeable" but more importantly, it seemed to be staked in the correct spot for bearing load.
In the vast experience of this forum's members, can this roller vane pump move a good volume of fluid but not produce enough pressure? Also, am I working in the right direction? All advice is very much appreciated!
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