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PTO hydraulics on a GMC Top Kick

Discussion in 'Construction Equipment Attachments' started by Willie B, Apr 21, 2018.

  1. Jonas302

    Jonas302 Senior Member

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    So did he have to fix much or were they just raking you over the coals on little stuff where you live are they state run inspections or private? Its all done in private shops here and can vary by who is working that day
     
  2. Willie B

    Willie B Senior Member

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    Privately owned stations.
    Vermont AOT & State police look the other way when a beater mini van, smoke billowing out of both front windows, six kids under age 8 crawling around inside like a litter of puppies, three donut spares, no working tail lights etc. etc.
    A truck on the other hand gets flagged out of service for very minor infractions. I heard yesterday of a driver hauling blacktop being pulled out of rotation for a roadside inspection. They fined him because driver's side washer jet hit too low on the windshield.
    Recent laws: they have to photograph the truck inside the garage for inspection & they have to document any issues if it fails, send that to the State AOT. Next inspector has to sign off on each fault.
     
  3. Willie B

    Willie B Senior Member

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    I don't object to being forced to attend to issues. My brake cans were functional. The front ones looked rusty from outside, Rear ones, I can't say why they weren't OK.
    When you set the parking brake on an air brake system all air is relieved from spring brakes. For a time there will be air bleeding off sound. I had been wondering how pressure was bleeding off, but couldn't find a leak. All air lines, tanks, and fittings are new. I guess the spring brake relay valve needed replacement, now it holds pressure much longer.
     
  4. Willie B

    Willie B Senior Member

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    Latest issue:
    A substantial shake. It seems to begin at low speed acceleration, or gentle uphill, or cresting the top of a steeper hill heading down. Rarely do I feel it in the steering wheel. It isn't a shimmy one would feel mostly in the steering wheel, this is the whole truck.
    Driveshaft has been partially replaced due to elimination of the fire pump. All six tires & wheels have been replaced & balanced. All brake cans are new. King pins, steering linkage, and all the usual wear parts have been checked.
    Odometer reads 32000, but 609 hours of pumping ran those miles up. The odometer runs when the transmission drives the pump. Likely rolling miles under 10,000.

    I've got a nagging suspicion the driveshaft is involved. 33 years ago I bought my 1956 Power Wagon. It behaved this way, but worse. It had driveshaft clocked 90 degrees out.
     
  5. 56wrench

    56wrench Senior Member

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    i would suggest to check u-joint phasing first and then driveline angles
     
  6. Willie B

    Willie B Senior Member

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    Exhaustive research, and talking with several people I hoped would know, I get opposite facts.
    I've tried it both ways. I can't say I can tell the difference.
     
  7. 56wrench

    56wrench Senior Member

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    Can you post some pictures from under and from the side as much as possible? Also check to see if there are wedge shaped shims between the rear axle and the springs. Fire trucks are loaded all the time and sometimes they get creative to compensate for sagging springs that change the ride height. From the look of the very first picture it appears that the back of the truck was low before you removed the fire apparatus so maybe they had done something to change the rear u-joint angle. Just a WAG
     
    DB2 likes this.
  8. Willie B

    Willie B Senior Member

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    The springs were beat, so in the process of shortening the frame it got new springs. I had choices of spring capacity. I chose 22000 rears. There are now, or before no wedges, no intentional changes in pinion angle. I can't get a straight section to gauge. I feel pinion & transmission angle are close, if not matched. They are nearly on plane, the U joints have very slight angularity.

    I'll get pictures tomorrow. I've been thinking how I can show all drive shaft components & their relation.
     
  9. 4x4ford

    4x4ford Well-Known Member

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    There isn’t a bottomed out slip yoke in there any where is there or one pulled almost to the end of the splines
     
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  10. 56wrench

    56wrench Senior Member

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    When you removed the fire pump did you add a steady bearing or put in a longer driveshaft? When you took out the fire pump, its like taking out a short driveshaft, so most often, on a longer wheelbase, you would add a steady bearing. On a real short wheelbase you may get by with a single, longer driveshaft
     
  11. repowerguy

    repowerguy Senior Member

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    You may well need to go down and dirty on this one, jack up the rear end and sit the axle on some good blocking with the tires up barely off the ground. Run through the gears and see if you can duplicate the shake with a helper. I've found some vibrations from imbalanced driveshafts this way.
     
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  12. Willie B

    Willie B Senior Member

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    View attachment 224828 carrier.jpg mid u.jpg differential.jpg View attachment 224828


    I'm afraid I made quite a mess of posting pictures. All want to post sideways. Repeated attempts at editing I can't delete the sideways ones. Yolk at trans, rear half of middle U joint & differential are all oriented the same. Until yesterday the rear was 90 degrees different. No change in oscillation by changing orientation.
    As I understand, angularity increases oscillation. There is no angle at center, little at either end.
     

    Attached Files:

    Last edited: Sep 24, 2020
  13. Willie B

    Willie B Senior Member

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    U joint trans.jpg carrier.jpg differential.jpg
     

    Attached Files:

  14. Willie B

    Willie B Senior Member

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    Now I have something new to be frustrated with. I can't post pictures.
     
  15. Willie B

    Willie B Senior Member

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    The carrier bearing was already there, a foot behind the pump. There was a short shaft with two U joints & telescopic spline between Trans. and pump. Behind the pump, another short two U joint shaft with carrier, then a longer shaft to rear.
    Axle has been moved about a foot forward, and a new shaft replaced the two short ones & the pump.
     
  16. Old Doug

    Old Doug Senior Member

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    Could there be a problem inside the axle ? Could you remove the driveshaft and tow it? Have you jacked it up and run it?
     
  17. crane operator

    crane operator Senior Member

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    So how long is your driveline, is it one piece from the trans, all the way to the rear axle? It should be two, one from the trans to the carrier, and then another one from the carrier to the rear. It shouldn't be just one.
     
  18. mitch504

    mitch504 Senior Member

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    Did you mean yolk, or yoke? Never mind, I'm just egging you on.
     
    petepilot likes this.
  19. Willie B

    Willie B Senior Member

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    I'll fix that in future.
     
  20. Willie B

    Willie B Senior Member

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    It is three universals. A yoke at transmission, and another at differential. Two sections of shaft. Front is tube, I'd guess 4" diameter, approximately 4' long. the carrier bearing is at rear end of this. Rear section is splined, about 3' long. That is next step, to jack it up & run at highway speed. At low speed there is almost no run out. Shaft is not balanced, but at 2000 RPM I feel it'd take a lot of out of balance to cause this much shake.

    I went to the fire house yesterday. The truck most similar in size is the rescue truck. It has the same configuration but smaller diameter & U joints. Each segment of the shaft is phased the same each end, like mine was before I turned it at the spline 90 degrees.

    Everything I find on the internet shows a two universal driveshaft. Middle section is always phased the same. Yokes at each end are the same angle. Nobody addresses what it should be for a three universal shaft.

    Oscillation is greater in sharply angled joints. None of the three in my shaft have more than a few degrees of angle. The middle has none. My logic has been that the middle joint is not contributing oscillation. Like a straight two U joint shaft, as in a pickup, both ends of the shaft should be phased the same.

    I rode as a passenger in my son's GMC 2500 towing a 25' long deck over trailer empty yesterday. I was thinking this rides similar to my bigger truck empty. I'm going to try letting some pressure out of the tires.