doubleclutchinweasel

That's kinda why I asked that last one, O!

Based on what Onyx said, I would assume that one end of the valve ports pressure to "A" and dumps "B" to tank, and the other end ports pressure to "B" and dumps "A" to tank. The middle position would be "blocked", so it would stay in place wherever you left it. The only way it could leak down would be fluid leaking out of the side that is pressurized while lifting the bed...like past the piston. A leaky rod seal on the other end, as he said, would not allow fluid to escape. So, it would not cause leak-down.

Can you jack up a wheel on the front axle, leave the rear axle on the ground, put it in neutral, and see what happens as you turn the driveshaft by hand?

Sorry. Your last post came through while I was typing mine. Since it is a Mack setup, some of the guys on here will be able to talk in detail about the way it should work.

The valve probably has a "blocked" position when the lever is in the "hold" position. Generally, a hydraulic valve has 3 positions. Applying that common valve thinking to a dump truck, one position would port pressure to the cylinder, the middle position would hold what ya' got, and the third position would dump the fluid in the cylinder back to the tank. There are variations on this, of course. Some have an "open" center position instead of a blocked center. But, anyway, most valves/manifolds have an "A", "B", "Pressure", and "Tank" port. Shifting the valve connects these in various combinations to accomplish the desired effect. But, that's just generic hydraulic valve stuff. If the truck setup is different, I'm sure someone on here will chime in and correct it for me! If they do, use their info, not mine!

Are there any drive setups that use a "straight-thru" drive shaft (no inter-axle differential)? If so, then ANYTHING wrong in the front drive would cause it to do nothing, but still let the rear axle drive. Like, broken spider gears, side gears, ring/pinion. If there IS an "open" inter-axle differential in there, then a broken front drive should just allow the front driveshaft to spin and do nothing. In that case (with everything intact), if you jack up ANY wheel and put it in gear, that wheel would spin all day without the truck moving. That same setup, with an optional inter-axle differential lock, would give you the option of locking the IAD and forcing the rear axle to drive as well as the front. With some type of torque-biasing power divider (like what I suspect 67RModel is talking about), I suppose a broken front drive could still allow the rear drive to move somewhat, because of the effects of the "automatic" power divider. Still, more information as to exactly what setup is in there would help the guys on here narrow it down for you. What kind of truck is this even in? Pictures always help, too!

Definitely! And, there are many others.

Got any more information? Type of truck? Type of axles? Power divider or not? There are some great technicians on here, so the more info you give them, the better.

Heartfelt condolences and prayers to the friends and family.

Vmac! Definitely did not mean to slight him! You guys are being way too kind to include me in that group! I'm old and my knowledge is pretty limited, compared to "The Brain Trust". Now, if you want to talk about manufacturing roller bearings, we can talk! LOL!

I said it before and I'll say it again... The amount of knowledge a handful of guys on here have among them is freakin' amazing. Mechohaulic, Macktech, Jo-Jo, Glenn, and Onyx just to name a few. There are several others, too. Didn't leave anybody out on purpose. There's not much that gets by those guys.

That's what I'm thinking. The broken rings may have been a secondary symptom. Melting pistons points to a combination of too much timing and too lean a mixture. There's nothing like having Wiseco dripping out of the exhaust pipe! Sounds like he has a plan for the next go-round though!

"Perfection". Yeah, I think that's the word!

From his original description, that's what it sounds like to me. Cookin' the Puppy!

Wrong ring groove in the piston. Wrong ring end gap. Cylinders not round. Cylinder ridge. Cylinders warping at temperature (improper cooling). Detonation. This is a biggie. Can damage LOTS of stuff. (refer back to original melted pistons) (too lean, too much timing, too much compression, too low octane fuel, etc.) Improper piston/cylinder fit. Rings installed upside down. Woods sprites. Gremlins.

Great job, Mate!

Common sense? What's that?! LOL! Common sense is so rare these days it should be considered a super power. "Hello! I'm Sensible Man!" What you did with the trailer is very similar to one of our methods for raising and lowering machine tools..."rocking" or "levering" them up. I used to do stupid things under vehicles. Not any more. Now I want jack stands, cross-ties, timbers, or whatever I can find. That "what if" factor is super important to consider. You never work more safely than when you know that what you are doing can kill you. Kudos on your ingenuity and caution on that job.

I would recommend good jack stands even with high-dollar jacks! But, that's just me!

Little bottle jacks from Tractor Supply or Northern Tool don't cost much (Torin "Big Red"). 6 ton is about $35. 10 ton about $50. I have several of them in various sizes. Work fine. Cheap enough to throw away when they quit.

This one sure gets the Weasel's Seal of Approval!

Nice!

I doubt the ones they are talking about get programmed! LOL!

Lovin’ it! Great work.

I guess one important thing to determine on this one is IF it has the 24V system. If it does, the S/P switch would be suspect. If it doesn't I would look at the cables.

The old R600 I drove back then had the 24V start. Pushbutton to engage the S/P switch was on the dash. Seems like the key was on the left side and the pushbutton was on the right side of the steering column. The one I had more recently was all 12V. So, it did not have the S/P switch or the pushbutton.