We are having trouble on our IT28G with the impliment hydraulics. When you let the boom down to the ground it will fall way faster than it should (cycle time of 2 sec when it should be 4 sec) and when it gets to the ground there is a "void/cavitation" in the cylinders. You have to keep the joystick in the down position for quite a bit before the hydraulics will catch back up and lift the front wheels off the ground or go against pressure. Also if you try and roll the bucket forward after it has reached the ground the lift cylinders will drift up until they reach the level of the oil. The tilt functions will do the same thing as well. We have tried a new makeup valve in the down circuit and nothing changed and we have adjusted the line relief valves for the tilt functions. If you run the loader at full throttle the tilt functions will work alright and never create a void/cavitation in the cylinder. The lower function will not do it as bad with the loader running full throttle (one time it might fall really fast (2sec) and the next time it will go down like its supposed to (4sec) that is only at full throttle though) The boom lower and the bucket dump will act the very same way with the engine off. Any help is greatly appreciated! We are stumped on this dude!
Did the problem start suddenly, or have you always had it? Also, ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
We actually bought the loader this year and it has had it's fair share of problems. The original owner had tranny problems and their mechanic went into the tranny twice and pretty much screwed it up worse everytime he was there. So as far as how long the problem has been there I can't tell you for sure. The serial # is DBT00510 it has 7600 hrs as well
Does your machine have ride control? Pilot pressure might be an issue, do you have gauges to measure the pressure?
The first thing that comes to mind is to check the hydraulic tank breather and lines for restriction. I believe this machine doesn't have a pressurised tank. The breather is an inline filter connected to a hose to the tank lid. Did the main control valve look like it'd been tampered with when you got it? I've not had one of these apart personally, but looking at the parts breakdown it looks as though it's possible to get the spool in backwards which would effectively disable the makeup valve's function. Another thought; Cycle times usually assume a GP bucket. If you've got a heavy attachment hanging off the front, cycle times will be faster.
It does not have ride control... I have checked the pilot pressure and it was correct, however I will do another check on it to get the actual numbers. We have tried running the hydraulic tank without the cap on to rule out the tank breather...The control valve looks to never have been apart. The only thing that has been messed with on it is the return line from the control valve to the manifold on the front of the tranny has been replaced and it is not a cat hose... Also all cycle times are with a 2.5 yd bucket
You could possibly have a problem with the pilot control valve in the cab not modulating correctly. Does the lower feel progressive, or does it just drop like a stone when you move the control. Maybe try temporarily exchanging the pilot hoses so up is down, and down is up. Or try making the tilt lever work the hoist and vice-versa.
All the functions are progressive and the pilot pressures are all correct. I have not changed the pilot hoses around because it effects all the circuits (lower, bucket dump and roll back) I have a video of the loader in action it will maybe help expalin what is going on. I just have to figure out how to post it
[video]https://www.facebook.com/video.php?v=10204693675560340&set=vb.1189740151&type=2&theater[/video]
That video is of the boom lower first (at low idle) and then bucket dump (at low idle). On the boom lower I returned the pilot control to hold position once it hits the ground and rolled the bucket forward and the boom cylinders drift up. On the bucket dump I rolled the bucket forward and returned the pilot control to hold position and lowered the boom to the ground and the dump cylinders drift then.
Are your cycle times on hoist and curl OK? Does the problem change as the machine warms up? Do you know what oil is in the tank? Maybe wrong viscosity? Edit; I didn't quite get the fact that both circuits were affected before. Thats puts the focus back on the main hydraulic circuit instead of the pilot circuit, as you rightly say in post #8. I would double check that tank breather filter. It may contain a check valve to make the tank build pressure.
The cycle times for hoist and curl are okay besides the lower cycle time is way too fast. It should be four seconds according to the shop manual and we are two seconds. You can get the lower cycle time to be correct every once in a while if you are running at full throttle. It is not only power down either it also is too fast when you going to float mode. Float mode and power down both at low idol are two seconds. It does not seem to change when it gets warmed up. And the hydraulic oil is brand-new oil Cat 10w. I will do some looking at the tank breather
Little update on where we are on the loader. •I called the local tech and he gave us a few ideas to look at. The first time was he thought maybe the vane pump might be weak and not pumping enough oil. We have tested the pump flow and it tested 40 gpm at 1000psi @ Full throttle which is right what its supposed to be. •The next place he said to look was the main control valve so We have the main control valve out and tore apart right now. Everything looks and seems to act like it should. We couldnt find anything wore or looked wrong in there. •It seem like to me (which I am new with these systems) is the make up valves in this system are supposed to take care of this problem on the boom lower, bucket roll back and the dump circuits. How much do these systems rely on the make up valves? • It bothers when you are activating the valves slow or if you push the lever right to the max it will just not get as much of a void at slower speeds compaired to fast. •At low idle and dead engine it creates the biggest void •Half throttle the void is still there in the lower circuit but is almost gone to very little void in the dump cylinders •Full throttle the loader acts like it should. •The lower cycle times slow down to their correct speed (2 seconds at low idle 4 seconds at full throttle) •The void in the system will be gone in both circuits Why is the power down cycle time to fast at low idle and is correct at high idle??