Another 2840 Hydraulic problem...

[tjhunter61]

I just bought a 2840 (1979) JD. Motor runs great, no unusual noises, shifts fine, HI/LO seems to work good, PTO engages as it should, steering seems ok. Now the problem...the three point hitch jumps and jerks like crazy unless the motor is at 3/4 throttle or higher...any lower than that and it jumps and jerks till it's raised all the way up. I've tried it with every different combination of HI/LO, PTO In/Out, in gear/out of gear, to try and isolate any problem component. No difference...it always jumps unless the motor is revved up. I changed the hydraulic/tranny fluid, screen and filter. It was horrible, the screen was plugged with milky looking crap and the filter had been 'sucked in' it looked like. I didn't see any metal shavings anywhere that I could tell...looked more like it had gotten water in it (bad shifter boots) to me. I am a fairly capable mechanic but not too familiar with the Hydraulic systems on these. I've read every post on this forum about 2840 issues but didn't pick up on anything that would help me find my problem. The front pump doesn't make any odd noises and I haven't found any components that seem to get particularly hot. Anyone have any ideas on how I can troubleshoot this thing (please don't tell me to just set it on fire...that's just not an option for me right now!). Thanks for any advice!

 

[tim s]

I won't tell you to set it on fire,,but you should just kidding with you,,they are not a good model that is a fact,, but you got so lets give it a try to repair. With milky oil the chance for the brakes to be chewed up are "Strong", you should pull the final drives and find out first, if they are bad, lift the rock shaft and flush the best that you can, I know this is a job, but if you don't get a clean system you will be fighting a loosing battle, then with fresh oil and filter see what you have, a flow test of the trans pump should also happen in this process , mail me and I'll talk to you about it tomorrow...I don't like them at all but I have been dealing with them since they were new..

 

[Cliff Nelson]

Test clutch system pressure and hyd pump inlet pressure with gauges. Try destroking the main pump and see what the gauges do. The jerky 3 pt is an indication of a starving main pump whether be low inlet pressure or a high pressure to sump leak. Look in the trans oil filler hole and see if oil is spraying from the rockshaft valve as that is a common high pressure leak. Could be any number of other things but pressure testing should point you in the right direction.

 

[Tx Jim]

In addition to what Tim & Cliff stated I'd suggest to check stand-by pressure(2250-2350 psi),check pressure control valve(parts key #10) as it could be stuck and hyd filter relief valve(parts key #17 2nd photo).