Lull 844, 944 Why does rear end lock?

Why does the rear end lOck above 20*? When you boom down and release the brake the machine jerks violently as the rear end unlocks. IMO JLG makes a primo telehandler compared to their sister company lull. I cringe when RSC shows up with a lull just for that very reason. Does anybody else agree with me?

4 point stabilty

My 1044c does the same thing. I had the carriage rolled all the way forward and the boom extended all the way setting some material on a hospital last week. Was running the boom in and i about crapped my pants when the axle unlocked, i thought a car ran into the back of the machine it was so bad! They must build a ton of pressure or something??

"Why does the rear end lock above 20*?"
Speedpup is right, stability. A 4 legged chair is more stable than a 3 legged one.

"When you boom down and release the brake the machine jerks violently as the rear end unlocks."
The reason is that you have your foot on the brake. If you read the manual, which you agreed to do when you got your operator's license, you would see that the service brake actives the stability system on Lull C-series and newer (and Sky Trak legacy and newer). The exact functionality is somewhat different with the different models. It was found to decrease the chance of a tip-over because when a machine starts to tip most operators will stomp on the brake (unless they are too stupid to try jumping out).

On the E-series machines:
<40° - rear axle is in free pivo mode
Note: SN 0160003881 & before: depressing the service brake below 40° will engage the slow pivot mode. See below.

>40°, in gear, park brake off, service brake off - rear axle is in slow pivot mode.
This mode was created to satisfy operators moving hydro-scaffolding, which requires the boom to be >40°. Earlier models would be locked at this angle. Note that lifting a wheel while driving in this mode does NOT necessary mean that you are tipping over. If you put a chair on an uneven floor you will always lift the lightest leg. Lift two wheels = .


>40°, with park brake on and/or service brake depressed and/or shifter in neutral - rear axle is locked to the frame.

The trick to minimize or eliminate the jerking is to go from locked to slow pivot mode before going to free pivot mode.

On the C-series machines the rear axle locks whenever the service brake is depressed. And no, they don't "build pressure" but what normally happens is...
- operator drives up to the drop point while partially extending/hoisting the load
- at some point the service brake or park brake is engaged. If one of the rear wheels has lifted the stability cylinder will lock it in the raised position.
- the load is dropped off and the boom is retracted.
- at some point the stability cylinder is unlocked and the weight shifts to the rear axle
- if the weight shifts too far back before the cylinder unlocks the rear of the machine will drop suddenly.
To my knowledge this isn't much different than any of the other machines with a stability system. In fact many of them would probably be like the Lull system except they put a patent on the functionality. Sky Trak kind of worked around the patent, but when they merged both brands moved towards a common functionality.

ISZ

Thanks ISZ for your info, I haven't had much time behind the seat of a lull but have on many other telleys. I've noticed that some models would lock above 40*.
Before reaching my drop point I would have a tough time keeping boom under 20* because of line of sight being blocked due to a custom faricated scale pan made to fit a 60" carriage. I am on an uneven slope pitching towards building. On couple of occasions two wheels were lifted.
No owners manual found except for maintenance chart and customer responsiblity list. Our rental yard had to rent from another "micky mouse" company to fill our order. Hope its a sign of the industry heading in the right direction

The angle at which a specific telehandler model locks up is determined by the stability testing that is done by the OEM. They have to put the units through several tipping scenarios, one of which is tipping the machine on an imaginary line drawn thru a front tire and the rear axle pivot. The higher you lift the boom, and the higher the load, the harder this test is to pass. At some point it becomes a trade off of what number they want to put on the load chart vs. adding more counterweight to the front of the vehicle vs. forcing the operator to be in locked mode. And some companies are more conservative than others with their rating protocol because the testing standard has some gray areas.

Some of the original stability systems put the transmission in neutral above X°. This didn't work out too well because the users would disable the system, with the unfortunate outcome that someone would have an accident. Often times the system was re-enabled before the scene was fully documented.

At any rate, glad I could help and keep it on 4 wheels.:cool2

ISZ

Its interesting you say that some manufacturers are more conservative than others.
We are going to buy a newer 10,000lb machine this fall and this question has crossed my mind. Which manufacturer has the best "Realistic" load chart? I have been considering forward outreach length and weight capacity.
Thanks

Forward tip, especially with outriggers down, if fairly straight forward. At low boom angles the wind will not have an affect and all the tire variables (besides weight) will be fairly irrelevant. In Europe they go beyond the US/Canada requirements by doing a drop-and-catch, but they don't have to use that load chart here and probably don't because it would put their marketing department at a disadvantage.

Unfortunately I didn't test many 10k machines so I don't have any data to go off of. If you can narrow it down to a couple of machines see if you can try them out by lifting a load slightly higher than what it is rated for, ideally the same load for both machines. (i.e. if rated for 2000 try to lift 2500) See how light the rear wheels get and compare.

One clue is to look at what carriages the load chart covers. If you want a standard carriage, but the load chart also covers tilting carriages, you will in reality have more capacity that the chart states. The same idea goes for carriage width, large forks, and axillary hydraulics.

And you could always post your final choices here for real world user experience.

ISZ

Well i just sold a nice Gehl 1155, and i can tell you from experience that the Lull 10k will out lift that machine any day of the week. The Gehl is more comfortable and still a nice lift but with the odd things we do i can promise that something would get badly damaged, that is why i sold it.
We also have a Genie 1056 and it is pretty nice, i just dont like the sight lines to the forks and the machine is waaaaayyy to long and tall. Probably wouldnt buy another one, but i say again they arent bad and pretty heavy duty.
I have ran a Skytrack 10k and i didnt think it was all that bad, but the bad part is it isnt a dedicated 10k machine, its an 8000 with outriggers and another boom section and more weight (as i understand it to be)
I would really like to try a JLG or Cat machine, they look pretty rugged. Also a Carelift or Ingersol Rand, but the bad part with those is hardly anyone carries them let alone the parts.
Still leaning toward the Lull, i just know we cant kill them and they will do what i need it to.

I dont mean to highjack this thread, if it goes any farther i will start a new one!

tough to beat a Lull. i know one company that has to put a cooler on hydraulics to cool them they run'em so hard.

JLG 10K all the way. Operator line of sight, load, stability and strength is all packed in there with minimal operator fatigue. The knob that adjusts the speed of tilt up/down on the forks becomes very useful.

Never had the chance to run a JLG yet. Are they better than the old Gradalls? I never liked the fact you couldnt change the steering, just rear turn. They were pretty decent machines though, we had a 8000 rented for 6 months several years ago. I got to where i was better with that than the Skytrak 6000 we have (which is pretty easy to operate).

Dmconstruct said:

JLG 10K all the way. Operator line of sight, load, stability and strength is all packed in there with minimal operator fatigue. The knob that adjusts the speed of tilt up/down on the forks becomes very useful.

Click to expand...

How does the leveling landing system work on the JLG? Gradall tried it years back and scrubbed it. I do like the traverse option on a Lull.

Leveling landing system?? Are you talking about the tilt motion, side to side, of the carriage(III) ?

They had a system where you push a button and then it was supposed to land like a Lull traverse. I don't see it on the web site so it must have failed agoin. It was Accuplace I think.

Found it with google. http://equipment.forconstructionpros.com/product/10091425/JLG_Industries_Inc_AccuPlace_System

Was it called the place ace?

The AccuPlace system is a completely hydraulic and electronic based system. Sensors measure the boom angle and extension, then meter oil to both the extend and hoist cylinder to achieve vertical and horizontal movement. I think that eventually the whole industry will move to this type of a system but for now it costs too much, probably will have more down-time, and is difficult for a typical rental yard service tech to diagnose.

Now if you were thinking of the old SquareShooter system, it tried to do the same thing with mechanical valves and bicycle chain. I tried one out once, and when the SquareShooter system was activated the boom function speeds dropped by ~50%.

ISZ

I think when Gradall tried it years back they had problems when the hydraulic oil had different viscosity in different temperatures. I'll take a Lull transverse which also gives you more forward reach.