8N Hydraulic Leakdown

JKW1959

New User
This site has been a great help to my 8N rebuild and it's almost done. Thanks for all the insight and info! Now I need advice on my last issue (for now).

My hydraulic lift leaks down overnight with a light load. It originally had a lot of condensation and the fluid was milky. When I tore it down to clean everything up, I found the lift cylinder scored and the pump pistons also had some scoring. There were a couple chipped pinion teeth, which probably contributed to scoring. I replaced the ring gear, pinion and bearings. I also replaced lift cylinder and piston (NAA o-ring style), pump pistons, bushings, valves and springs, as well as the safety valve. The oil is Travelers 90 weight mineral oil equivalent sold at tractor supply. The lift works perfectly otherwise and I'm sure both pressure tube gaskets are well sealed along with the lift cylinder port gasket. I have a wooden bed with stake sides that mounts on the 3 point hitch (less than 150 lbs. and only 4' long) that I want to stay fairly level for at least a few days. I have heard that when everything is right an 8N should hold a heavy implement up for a couple of days.

Any suggestions?
 
(quoted from post at 23:02:50 10/26/14) This site has been a great help to my 8N rebuild and it's almost done. Thanks for all the insight and info! Now I need advice on my last issue (for now).

My hydraulic lift leaks down overnight with a light load. It originally had a lot of condensation and the fluid was milky. When I tore it down to clean everything up, I found the lift cylinder scored and the pump pistons also had some scoring. There were a couple chipped pinion teeth, which probably contributed to scoring. I replaced the ring gear, pinion and bearings. I also replaced lift cylinder and piston (NAA o-ring style), pump pistons, bushings, valves and springs, as well as the safety valve. The oil is Travelers 90 weight mineral oil equivalent sold at tractor supply. The lift works perfectly otherwise and I'm sure both pressure tube gaskets are well sealed along with the lift cylinder port gasket. I have a wooden bed with stake sides that mounts on the 3 point hitch (less than 150 lbs. and only 4' long) that I want to stay fairly level for at least a few days. I have heard that when everything is right an 8N should hold a heavy implement up for a couple of days.

Any suggestions?
o you realize that the control valves are simply metal spool in a metal sleeve? No sealing rings of any type. Not to mention that they probably have 50 years of wear. If you need it to stay in position for days, then might I suggest a jack, jack stands, chains?
 
Thanks for your thoughts JMOR. I'm with you on the wear factor - not sure what that would be in terms of drift down. On the other hand, I've been in the forklift business for 30 years and the spool valves don't have seals between the ports, but will hold a load up with minimal drift overnight. Forklifts have very thin 10 to 15 weight fluid as compared to 90 in the 8N. The spool seemed to fit pretty well in the pump housing, but I didn't mic it either...

Maybe my time would be better spent on a mechanical latch on the bed attachment to hold it level. That sounds like a nicer day than pulling the pump again!
 
(quoted from post at 13:55:53 10/27/14) Thanks for your thoughts JMOR. I'm with you on the wear factor - not sure what that would be in terms of drift down. On the other hand, I've been in the forklift business for 30 years and the spool valves don't have seals between the ports, but will hold a load up with minimal drift overnight. Forklifts have very thin 10 to 15 weight fluid as compared to 90 in the 8N. The spool seemed to fit pretty well in the pump housing, but I didn't mic it either...

Maybe my time would be better spent on a mechanical latch on the bed attachment to hold it level. That sounds like a nicer day than pulling the pump again!
robably. Interesting analysis in that the ram cyl only holds about a cup & if only raised half travel of ram, then it only needs to leak a bit over two shot glasses to be on the ground. Too many differences to compare to the fork lift. Likely large volume differences, nice, clean, filtered hyd system without the sharing of fluids with transmission, differential, and 50+ years of dirt & water, and .................
In a nice nearly sealed hydraulic jack, in perfect condition, I have seen one hold up much more that its rated capacity for days without dropping even a quarter of an inch, but not really apple & apples, either. Most, including myself, a 'great' 8N lift will hold up less than an hour. Happy days! :)
 
My 9n lifts great,but will leak down in a little while. I have all the gaskets,parts to do a repair,just not time. I've gotten into old Yamaha Enduro racing bikes[70s] and have been sick,but maybe this winter,I'll tackle it. lha
 
I guess I should count my blessings and move on. Mine actually takes a couple of days to leak all the way down from fully raised with the bed attached. Thanks again.
 
Way back when, the Massy factory rep said the MF were designed to leak down. Same design, just older.
 
I rebuilt my 8N hydraulic system a few years back. It had a scored cylinder that I honed and used the NAA o-ring piston. I remember testing it back then and it would hold up my bush hog overnight.

If you want to hold a load on the 3 point, you should rig up a set of stop chains from the lower pins at your wooden bed to the top link at the tractor. Flame cut the ends out of steel plate and weld or link them to the chain at the appropriate lengths. This assumes that you have a Torch set or Plasma cutter, and a Welder.

The chains allow the 3 point to still be lifted with out damaging anything, but will only lower as far as the set allows.
 
Thanks Brad. That's a great idea. I have all the necessary tools so it should be easy to fabricate. Due to the design of the bed I will need to rig it from the center of the lower lift arms using the same design you describe. I should be able to put an eye there and use a link with a pin on the end of the chains to attach them. Thanks again.
 

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