link arms stuck

[woo003]

hi, I have a David brown 780 with a 3 point that isnt working fully. when the arms are down the lift works exactly as it should they will raise and lower just fine. however when they are raised all the way to the top the link latch always locks them up and won't let them down. this means I have to stop the tractor and pull the lift lock out for them to go down again. is there a reason why the links always lock in the up position when raised? also, when the links get locked up the 3 point lever seems to become springy when put in the down position meaning it wants to spring to the link lift position when put in lower. ( this doesn't happen when the link lock is released and the arms are lowered again. does anyone have any ideas? thanks

 

[RGMartin]

Sounds like it is working fine except that your lift latch is possibly broken(is there a plastic handle on the latch?, does the pin/handle come rearward when you rotate the lever 90 degrees?) and the "Select" spring on your quadrant lever might need adjusted.

 

[woo003]

hi, I don't really know how to operate the lift latch properly, should it engage every time the link arms go to the top? or is that a fault? the link lock doesn't have a plastic handle on it it has a welded piece of box section instead. when the link arms are locked up, how should you go about unlocking it? it is very stiff but the lift latch will pull out but not turn? thanks.

 

[RGMartin]

The latch when rotated 90 degrees or so will cam outwards on steel pins on the back of the housing. The plastic latch handle has the cam molded into the back of it. I have seen many broken handles and steel pins through the years. The steel shaft shouldn't turn, the plastic handle turns on it and pulls it out as it turns. An easy temporary fix is to pull the latch out and clamp a set of vice grips on it so it can't lock.

Also there is supposed to be a spring in the guide for your lift lever. The spring prevents you from pulling the lever completely to the rear accidentally(about 1" of travel). When the lever is pulled completely to the rear(full up), you are in "select" mode, which allows you to change from height/depth/or TCU mode on the knob. and also allows full flow of the hydraulics for some special applications where remote hydraulics are run through the 3 point control valve, it also raised the arms a little further than they normally go, which allows the latch to snap in and lock the arms up.