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PTO hydraulics on a GMC Top Kick

crane operator

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Mar 27, 2009
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Which shaft isn't balanced? You made the shaft yourself after removing the pump?

And yes, the truck will ride rough with no bed no weight:)

I used to work at a place that had a big chevy like yours, we pulled a heavy gooseneck. It would toss you all over without the trailer.
 

Willie B

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Which shaft isn't balanced? You made the shaft yourself after removing the pump?

And yes, the truck will ride rough with no bed no weight:)

I used to work at a place that had a big chevy like yours, we pulled a heavy gooseneck. It would toss you all over without the trailer.
No, I had an engine rebuilder build the front section of shaft. I asked about balance. He said he takes great care to keep everything balanced, and has never had a balance issue. This shop has rebuilt several engines for me, I have a lot of confidence in them.
 

Old Doug

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Mo
I cant remember how many drive shafts i built over the years and nun were balanced. I have seen some realy messed up home made drive shafts that ran smooth. We had a truck with a problem like yours it had a bad pinion bearing.
 

Willie B

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Put the shaft in late afternoon. Sitting not level I got a transmission shaft measurement of 4 degrees, a front shaft of 2 degrees. It is not conclusive the pinion angle, I think I'm off by a degree. I'll study more on it tomorrow.

It runs far more smoothly!
 

Willie B

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Scratch that. Downhill it is bad as ever. I say downhill, I don't mean steep. Today I went to Danby Four Corners 1000 feet higher in elevation than home. Coming down four miles the shake is worse than ever. It's driving me crazy! I've spent a fortune, now it seems nobody has a suggestion.
 

crane operator

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Tires? I thought you said you put on new rears, but not new steers. I'm just throwing out suggestions. Its frustrating when things don't go right.

Does it seem to come and go with throttle applied vs. coasting? Have you checked the nut on the yoke on the rear of the trans? My allison in one of the cranes had a vibration and the trans yoke nut had worked loose.

That's the problem with used trucks, you don't know if this is something you caused in shortening, or if its always been like this.

How's the steering joints/ kingpins etc? Everything good and tight up front?
 

Willie B

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Thus far: New wheels (6) new tires (6) brakes checked approximately 10,000 highway miles total. New brake cans. Steering checked, driveshaft worked over by Charlebois 100 miles away, said to be the best. New universals93) new carrier bearing. Charlebois technician showed me a video. Total run out at front yoke at transmission .058 (.029 off center) corrected & balanced. 6 tires balanced.

We jacked it up, blocked it up, ran it at 60 MPH & less, far less shake.

Braking doesn't seem to aggravate it. All new brake cans, new hoses, Steering doesn't seem to aggravate it. It is most pronounced on gentle grades up & especially down. Seat shakes constantly Much worse sometimes. I look at my foot on the accelerator It is shaking constantly. My pant led actually flaps. A bottle of water on the dash is crashing around. I feel it mostly in the seat. Coming down hill today, I kept noticing a strange flutter noise. It was the flapper on the stack exhaust fluttering with the shake of the whole truck.
 

colson04

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Apr 11, 2016
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Delton, Michigan
Is the engine out of balance (flywheel, crank?) or something in the transmission (torque convertor?) out of balance? I'm no truck mechanic, but I have dealt with finding various vibrations in equipment and large rotating shafts. It can be a pain tracking them down when all the obvious components have been inspected or replaced and very frustrating.

Did you get to drive the truck much before you did a bunch of work to convert it to your dump truck? I remember it was an old firetruck, did it have a vibration back then? Also, when discussing natural harmonics, increasing the weight (mass) of an object changes its natural resonance and can get rid of a vibration at the desired rpm range. So, if your driveshaft is too light for the specific design length, it might shift the vibration to a different frequency if the driveshaft is slightly heavier. Did anyone ever chuck the driveshaft up in a lathe and check runout along the shaft at various points to prove that it isn't slightly bent? That would certainly affect its natural harmonic as well. Just some thoughts.
 

Willie B

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Jan 2, 2016
Messages
4,039
Location
Mount Tabor VT
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Electrician
Is the engine out of balance (flywheel, crank?) or something in the transmission (torque convertor?) out of balance? I'm no truck mechanic, but I have dealt with finding various vibrations in equipment and large rotating shafts. It can be a pain tracking them down when all the obvious components have been inspected or replaced and very frustrating.

Did you get to drive the truck much before you did a bunch of work to convert it to your dump truck? I remember it was an old firetruck, did it have a vibration back then? Also, when discussing natural harmonics, increasing the weight (mass) of an object changes its natural resonance and can get rid of a vibration at the desired rpm range. So, if your driveshaft is too light for the specific design length, it might shift the vibration to a different frequency if the driveshaft is slightly heavier. Did anyone ever chuck the driveshaft up in a lathe and check runout along the shaft at various points to prove that it isn't slightly bent? That would certainly affect its natural harmonic as well. Just some thoughts.
I drove it as a fire truck maybe 70 miles total. Seth drove it another 50. We noticed none of the shake it now has. I believe the shake developed after alterations. We shortened the frame roughly a foot. The fire pump & the fire body were removed. Because the pump served as a sort of transfer case, it was inline of the driveshaft. A short shaft two universals & slip joint ran transmission to pump. A shaft ran through the pump, mated to another U joint, a short shaft reached the carrier bearing, then another u joint, then another slip spline. It ended at the pinion with the last U joint.
New drive shaft has U joint at rear of trans, a carrier bearing, another u joint, a spline, at pinion another U joint. Present shaft is three U joints a carrier bearing, and one slip joint. The foremost driveshaft shop replaced three U joints, a carrier bearing, cut the yoke off & corrected out of center. They then balanced the whole assembly.

Trying to correct the shake the whole truck got new wheels & tires. The 10,000 mile brake drums have been checked for run out. Tires have been back for rebalance. Rear spring equipment down to bolts is 100% new.

Spicer says U joint at transmission needs at least 1 degree, not more than 1-1/2 Degree angle. The angle of front section of shaft must match pinion. None of this seems to be more than a degree out of spec. New angle gauge is ordered.
 
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