• Thank you for visiting HeavyEquipmentForums.com! Our objective is to provide industry professionals a place to gather to exchange questions, answers and ideas. We welcome you to register using the "Register" icon at the top of the page. We'd appreciate any help you can offer in spreading the word of our new site. The more members that join, the bigger resource for all to enjoy. Thank you!

The JLG 40F Boom Lift Dilemma

OFF

Senior Member
Joined
Sep 30, 2009
Messages
1,047
Location
Alberta, Canada
Occupation
HD Mechanic
Welcome Kbitt.
The holding valve for the boom lift cylinder is a rectangular aluminium block bolted to the hydraulic piping on front of the boom lift cylinder. They do go bad sometimes. JLG part number 4640265

The other possibility is a leaking manual decent valve. Make sure all 3 valves are tightly shut.
 

Kbitt105

New Member
Joined
Aug 6, 2019
Messages
2
Location
SW, Pennsylvania
Welcome Kbitt.
The holding valve for the boom lift cylinder is a rectangular aluminium block bolted to the hydraulic piping on front of the boom lift cylinder. They do go bad sometimes. JLG part number 4640265

The other possibility is a leaking manual decent valve. Make sure all 3 valves are tightly shut.



So is a holding valve the same as a counterbalance valve then? If so could I pull the return line back to the valve off and see if I get fluid from there? would that be an accurate way to diagnose if it is the counter balance valve? I am speculative of the manual descent falls. It is an older machine that set for quite a while. I used it quite a bit over the summer. Had the lift cylinder rebuild at the end of summer. Had no problems for a while after and then it slowly started leaking off.
 

OFF

Senior Member
Joined
Sep 30, 2009
Messages
1,047
Location
Alberta, Canada
Occupation
HD Mechanic
yes, same as counter balance. How fast is the boom dropping? Were the manual decent valves used/disturbed at all over the summer?
 

maple2

Member
Joined
Sep 10, 2014
Messages
15
Location
vermont
When I retire, I think I'm going to travel north america repairing old JLG "F" series
Good way to see the country, right?? :drinkup

I will hire you today! My 40f worked fine last fall when parked. Tried to get it going today. The drive, lift, swing will not work from the ground control or basket control. Is this more apt to be an electrical problem or hydraulic? If its electric would it be the wiring in the basket?
Thanks for any help!!!
 

OFF

Senior Member
Joined
Sep 30, 2009
Messages
1,047
Location
Alberta, Canada
Occupation
HD Mechanic
I will hire you today! My 40f worked fine last fall when parked. Tried to get it going today. The drive, lift, swing will not work from the ground control or basket control. Is this more apt to be an electrical problem or hydraulic? If its electric would it be the wiring in the basket?
Thanks for any help!!!

More than likely, it's the solenoid for the dump valve on the proportional valve body. There's a cross member behind the engine, on the underside of that cross member are about three silver 12 volt solenoids. One for the dump valve, one for the horn, and the other for aux power. Might be four of them down there. Horrible spot. Take a good jumper wire/test lead and test each solenoid by connecting the large terminals of each solenoid together. One will blow the horn, etc. One should make your drive/lift/swing function.
solenoid.jpg
Common stuff, available at pretty much any auto parts store
 

maple2

Member
Joined
Sep 10, 2014
Messages
15
Location
vermont
More than likely, it's the solenoid for the dump valve on the proportional valve body. There's a cross member behind the engine, on the underside of that cross member are about three silver 12 volt solenoids. One for the dump valve, one for the horn, and the other for aux power. Might be four of them down there. Horrible spot. Take a good jumper wire/test lead and test each solenoid by connecting the large terminals of each solenoid together. One will blow the horn, etc. One should make your drive/lift/swing function.
View attachment 214820
Common stuff, available at pretty much any auto parts store

OFF Once again you saved the day!! Put a jumper on the solenoid, and that was the problem! I will pick up another solenoid at the parts store. Looks like the standard 12 volt solenoid.
I want to thank you again!
 

NdnKirk

Member
Joined
Jun 4, 2020
Messages
9
Location
Yerington
Occupation
Retired Power Lineman
Welcome to the site Jonesy!
Picture are always very welcome and they help us help you better when we can see what you have there. Get 3 posts in and then private message me your email address so I can send you the operators/service/parts manual set in PDF.
Just acquired a '79 JLG 40F, s/n 751138 everything seems to work. The kingpins or bushings are toast, I wonder if replacements are available? Steer tires are junk, new ones are on the way. There are over 90 trees on the ranch, a couple dead ones. I quit climbing 15 years ago.
 

OFF

Senior Member
Joined
Sep 30, 2009
Messages
1,047
Location
Alberta, Canada
Occupation
HD Mechanic
Welcome!

the mercury switch seems to be hanging there. It should mount on the side of the rear boom cover. They break real easy. Nice looking machine for it's age. Hopefully all Racine valves. :D

I'd be surprised if those king pins and bushings are still available. Know any machinists?
 
Last edited:

OFF

Senior Member
Joined
Sep 30, 2009
Messages
1,047
Location
Alberta, Canada
Occupation
HD Mechanic
I was wrong. Do a Google search for JLG #3420308 King Pin and #0960301 bushing, I see several places offering them for sale.

The pin is a little rich at $240, but the bushings are only $12 something each.

If you need a set of 40F manuals, message me with an email address I can send them to.
 

NdnKirk

Member
Joined
Jun 4, 2020
Messages
9
Location
Yerington
Occupation
Retired Power Lineman
Thanks for the reply. That's the butt connector where a switch used to be. What's the mercury switch for, too much boom angle or lean? Probably takes four bushings? I really need manuals, not sure where to click to message?
 

OFF

Senior Member
Joined
Sep 30, 2009
Messages
1,047
Location
Alberta, Canada
Occupation
HD Mechanic
Thanks for the reply. That's the butt connector where a switch used to be. What's the mercury switch for, too much boom angle or lean? Probably takes four bushings? I really need manuals, not sure where to click to message?

The mercury switch senses the boom angle, or at least it did in 1979. These days it's all done with micro-switches. The purpose was to cut out high engine RPM and high drive when ever the boom was above horizontal. Safety device.

Yes, 4 bushings.
 

NdnKirk

Member
Joined
Jun 4, 2020
Messages
9
Location
Yerington
Occupation
Retired Power Lineman
The mercury switch senses the boom angle, or at least it did in 1979. These days it's all done with micro-switches. The purpose was to cut out high engine RPM and high drive when ever the boom was above horizontal. Safety device.

Yes, 4 bushings.
Should I replace the switch, are they available?
 

OFF

Senior Member
Joined
Sep 30, 2009
Messages
1,047
Location
Alberta, Canada
Occupation
HD Mechanic
Should I replace the switch, are they available?

I don't think they are available anymore. Society doesn't like liquid mercury used these days in anything. Pretty toxic stuff I guess.

Not that a 40F is a fast machine, but you wouldn't want to be traveling 40ft up in the air in high drive & high engine. That's playing with fire. Let your fear guide you, remember to shut down the faster functions when up in the air. Being a lineman though, you probably have no fear.
They were over-designed however. I remember them telling us you could blow a wheel off with dynamite, while fully extended, and they wouldn't tip.
 

NdnKirk

Member
Joined
Jun 4, 2020
Messages
9
Location
Yerington
Occupation
Retired Power Lineman
I have fear, that's how I stayed safe for over forty years. I was thinking if I have a senior moment and forget to throttle down I might have a wild ride. Over design is a good thing, we count on it.
Are Racine valves easily identified? New steer tires just arrived. Thanks for all the help.
 

OFF

Senior Member
Joined
Sep 30, 2009
Messages
1,047
Location
Alberta, Canada
Occupation
HD Mechanic
I have fear, that's how I stayed safe for over forty years. I was thinking if I have a senior moment and forget to throttle down I might have a wild ride. Over design is a good thing, we count on it.
Are Racine valves easily identified? New steer tires just arrived. Thanks for all the help.

Here's what a 40F with Racine proportional valves looks like, marked as circle #1 in the picture.
JLG 40F Racine pic.jpg

this is Bertea valves. Note the big knobs.
Bertea valves.jpg

I have very little experience on 40F's with Bertea valves. Because they crapped out in the cold, JLG didn't ship Bertea machines to Canada. I only saw one or two Bertea machines, (maybe the same machine twice) so I never learned how they operate well enough to diagnose & repair over the internet.
 

NdnKirk

Member
Joined
Jun 4, 2020
Messages
9
Location
Yerington
Occupation
Retired Power Lineman
Uh oh, I have Bertea. Probably can't get the joystick rubber bellows any more have you heard of any substitutes?
I lived in Anchorage for 25 years, drove through Canada a number of times, eh. My son is in Fairbanks, he's moving down here next year but is keeping a cabin up there.
 

NdnKirk

Member
Joined
Jun 4, 2020
Messages
9
Location
Yerington
Occupation
Retired Power Lineman
MSC Industrial Supply in AZ (928) 775-4918 has the JLG (Bertea) joysticks and parts for the joysticks; p/n B1 knob covers and p/n B6 boots are in stock and plentiful; not cheap but not crazy! They have other control parts too. I may have found a non-mercury replacement for the mercury switch. I haven't decided whether to order and try it yet. I'll let you know.
 
  • Like
Reactions: OFF
Top