JD450 boom decay

Post support questions about your JD350 and newer crawler here
Post Reply
User avatar
JimParent
MC crawler
MC crawler
Posts: 2
Joined: Tue Jul 16, 2019 11:25 am

JD450 boom decay

Post by JimParent » Sun Apr 04, 2021 8:56 am

Hi all,
My straight 450 crawler loader has boom decay, whereas if I lift the boom anywhere between full height or a few inches off the ground, it will steadily drop until it lands back down. There are no external leaks and fluid level is normal.
If I lift the boom and turn off the engine, I can hear fluid rushing somewhere in the boom valve - so I know there is an internal leak.
I'm pretty sure this is not being caused by the anti-cavitation check but rather, the lift check valve or the spool valve itself (which I highly doubt) - but the shop manual is ambiguous in terms of identifying where the lift check valve is located...
I'm attaching a photo with hopes someone can confirm I'm in the right spot in thinking the highlighted area is the lift check valve.
Thanks!

Image

User avatar
jsal
1010 crawler
1010 crawler
Posts: 363
Joined: Sun Oct 28, 2012 6:27 pm
Location: armada Michigan

Re: JD450 boom decay

Post by jsal » Mon Apr 05, 2021 3:34 am

sounds like your packing on your cylinbers are wasted need to take lift cylinders off and rebuild JIM

User avatar
LeonardL
350 crawler
350 crawler
Posts: 869
Joined: Thu Oct 06, 2011 7:11 pm
Location: Missouri

Re: JD450 boom decay

Post by LeonardL » Mon Apr 05, 2021 7:10 pm

I agree with Jim that usually the cylinders are the culprit when it comes to your boom drifting. However besides what Jim pointed out and if you can hear the fluid bypassing inside the valve then I would suspect it as well. The spools can and do get worn enough to bypass like you described. They can also not be centering correctly so I would check that first. make sure the spool is stopping in the hold position and not slightly off center. That can be caused by worn linkage, a bad detent or a weak or broken spring. The bypass is located in the valve body as well. It should be to the side where the outlet or return port is located on the valve. When they bypass they dump directly into the return side going back to the tank. It could be out of adjustment or a broken spring allowing fluid to be dump directly to the return. That issue is usually only when you are in a pressure position of the control valve. The bypass doesn't have anything to do with the valves ability to hold the boom in place. It controls how much pressure is delivered in a given direction. The spools in the valve and the pistons along with their packing is what holds your cylinders in place. I hope this makes sense...
40 plus years working on JD 350s, 400Gs, 450s and other equipment both Ag and Construction.

User avatar
JimParent
MC crawler
MC crawler
Posts: 2
Joined: Tue Jul 16, 2019 11:25 am

Re: JD450 boom decay

Post by JimParent » Tue Apr 06, 2021 11:32 am

Great comments and help.. thanks!
I re-sealed both cylinders last year so I do not suspect those seals leaking.
According to the shop manual, Deere uses "lift check valves" to seal the functions of boom, bucket and aux. This lift check is what I'm looking for.
Again Deere is ambiguous and change terminology from S/M to parts manual whereas a poppet becomes a collar or a collar becomes a poppet.
The 450 uses separate and independent boom, bucket and aux valves and all three have lift checks (or what I used to refer to as load valves) to hold the functions accordingly.
I removed a large slotted screw located underneath the boom valve and between the inlet and outlet boom ports - that valve uses a spring and poppet but was in good condition (although I can't vouch for the strength of the spring itself) and perhaps it isn't applying enough force to seal its passage and if it isn't the lift check, I do not know what its purpose would be. It is certainly not built like a typical relief valve designed to crack at excessive pressure.
I will continue to check - I removed the end of the spool (and of course you can't remove it mounted); spring and float mechanism were in good shape and for how much I could pull the spool out, it was tight in its bore - I was really hoping to feel a lot of play but virtually none.
Jim

Post Reply

Who is online

Users browsing this forum: No registered users and 44 guests