Hi all, Newbie searching for a CAT. I operated two CAT 426's of the first series today (7BC0). While I was evaluating, both seem to behave the same way for these two items, and I'm thinking there is a problem in both cases. Been looking through the archives, but still not completely clear. 4wd wheel spin: With all 4 wheels off the ground, with 4wd switch on - should the front wheels have power/spin at the same RPM as the rear wheels? I believe yes, but for both machines front wheels barely moved when all off the ground, but they each seem to have 4wd power when the back was on the ground and climbing. The fronts were in sync with the rear, but only under load. Drive shaft turning. I think from this thread: HeavyEquipmentForums this is going to be clutches and/or solenoids, but I don't understand the rear wheel relationship. Could the load on the rear wheels be translating to load in the front, or was I seeing things? Neutralizer buttons : Buttons on the floor shift/bucket control - should the behavior of these be the same as switching the shuttle into Neutral? In both cases, the machines would still seem to move when in forward/reverse and the button was depressed and the trans could not be shifted without grinding. If it behaves like shuttle neutral, are these buttons activating the same mechanism as the shuttle neutral, and therefore not a big concern if the shuttle neutral works fine (i.e. it's a simple electrical problem, versus mechanical within the transmission)? Thanks for any input. Don
Since no one has picked this up here is my take... RPM, no. Circumferential speed, yes sort of... but this test doesn't prove much with all the wheels off the ground. Configure the machine so just the rear wheels are off the ground, jam the front bucket into the ground, take a tiny bit of weight off the front wheels, select AWD and hit the go pedal. Both front wheels in this case (being a limited slip diff) should break traction and start spinning. If not, you have a problem. FYI when the AWD is engaged you have no centre differential because front and rear axles are fixed (locked) by a clutch. If wheels no spin and front driveshaft no spin, check pressure to the AWD clutch first before assuming the AWD clutches a worn.
I get the point about RPM versus circumferential speed - same rpms would be a problem. Regarding the test procedure, is the reason for keeping the front wheels on the ground to make sure that the clutches are strong enough to overcome some resistance? Meaning, if all four were in the air you might get enough power to provide rotation (very weak clutch contact), but they are not able to provide significant power? In each case, with all wheels off the ground, the fronts were just barely moving, no where near what would be required to keep up with the rears. I could see the drive shaft spinning. Thanks for the information.
Absolutely. I get what you're saying, it doesn't sound right and there is probably a problem, what I'm saying is... The AWD system provides all wheel drive in slippery ground conditions. Let's confirm it's not doing that first. As an added benefit, because you're testing it under load you have a better chance of picking up any other complications, eg one wheel spinning much faster then the other (worn clutches in the front diff?), chattering coming from transmission (worn/damaged AWD clutches?), just gives us a better picture of the fault. In regards to the neutraliser question, both neutraliser switches (buttons you refer to on the floor shifter & bucket control) activate the neutraliser solenoid in the transmission hydraulic control valve bolted to the top of the transmission. Exactly how the directional control lever connects to this transmission control valve, well, I'm hoping some one with a bit more experience on older backhoes can answer...
Unfortunately the machine is 2 hours away, so I"m trying to draw conclusions from the limited testing I did the other day. Darn my lack of experience! That said, I'm pretty sure that I understand how the system works now: solenoid triggers clutch via pressure, clutch turns drive shaft to front diff, diff turns wheels. If the solenoid doesn't work, no drive shaft or wheels turning while in the air. If we do see turning, we need to ask "how strong?" - worn clutches (or low pressure?) might result in weak contact/no power. Might get rotation without power. Little rotation while up in the air implies little power to the front, there is no crazy magic to power getting to the wheels (other than typical diff-magic). Given this context, your test makes complete sense. If the above is true, there is a problem with the machines, just don't know exactly what without more testing. Again, something that didn't seem to work and I'd like to understand this to know if this is an easy-fix or not. My thinking is that if the neutralizer is triggering the same thing as the shuttle, it's "just" going to be electrical. Been looking for schematics on line, etc, but it's hard to get a clear picture from the information I've been finding. Will definitely need the manual, once I get a machine. Anyway, thanks very much for your explanations and clarifications. I'll be ready for the next test drive! Don
Check your messages. YHM.
A quick follow up on this, in case someone wanders onto this thread in the future - based on diagrams of the system - the neutrailizer buttons control a solenoid actuated valve which is separate from the direction control lever/system This for the early 426s, I think things changed later. Thanks to Nige for help on this. Don
Don, There is a JD 410 that just came up on CL that looks awesome for the money. AlanD
Thanks Alan..I saw that too, and it does get the adrenaline flowing a bit, but I can't get there until after Monday. I suspect that it won't be there that long....but if it is still up I'll contact the guy. That said, I am heartened to see that (seemingly) good deals do tend to pop up and pretty close to home. Even it if passes me by, I'm definitely learning about pricing and desirability from observing the market. Don