[AT] OT truck tires/driveshaft?

[Cecil R Bearden]

At 40mph the rear wheels are turning about 344 rpm and 515 rpm at 60mph. 
    The vibration from an out of round tire would be 5-6/second (hz) at 
40mph and 8.5hz at 60. If the out-of-roundness was on opposite sides in 
a dual wheel pair, then this would double.  If the vibration changes 
after turning a corner, then it would indicate out of roundness in the 
tires and within the dual wheel pairs.
Most truck rear end ratios are in the range of 6:1, so this would equal 
an engine rpm of 2064 (34.4hz) at 40mph to 3090 (51.5hz) at 60mph.   I 
would check the driveshaft to be sure the yokes are aligned on each 
section of the shaft and that all the yokes are in alignment on the 
entire shaft.  if there was no master spline on the splined slip joint, 
then one spline out of alignment would cause a vibration.
Also, there can be some vibration from the engine harmonic balancer.   
Try running the engine from 2000 up to 3000rpm while in neutral and see 
if the vibration occurs.

This is just some of the things I look at when diagnosing truck 
problems.  With most of my trucks, I don't have time to find out the 
cause and just have to live with it.  However if it can be fixed quickly 
I can do it.

Cecil in OKla

On 5/12/2014 5:33 AM, charlie hill wrote:
> Yeah you are right Ron.
> Wasn't thinking right for a second when
> I wrote that.
>
> Charlie
>
> -----Original Message-----
> From: Ron Cook
> Sent: Monday, May 12, 2014 1:36 AM
> To: Antique tractor email discussion group
> Subject: Re: [AT] OT truck tires/driveshaft?
>
> Charlie,
>       If there is only one gear in the rear, I think the driveshaft is
> going to rotate at the same rpm at a given mph regardless of which gear
> the transmission is in.  It is the engine crankshaft speed that will change.
>
> Ron Cook
> Salix, IA
> On 5/11/2014 8:02 PM, charlie hill wrote:
>> John you probably don't wind that truck up through the gears any more than
>> necessary and shift to high gear at a relatively low speed right?
>> If that's the case try running it in 3rd gear up to maybe 30 mph and see
>> if
>> you get the vibration at a lower speed than you do in high.  That will
>> accomplish the same thing as running the rear in low range (if you had
>> one).
>>
>> Charlie
>>
>> -----Original Message-----
>> From: jtchall at nc.rr.com
>> Sent: Sunday, May 11, 2014 8:25 PM
>> To: Antique tractor email discussion group
>> Subject: Re: [AT] OT truck tires/driveshaft?
>>
>> Was so sure it was/is a tire issue we only did a slight check on the
>> driveshaft yesterday. The truck does not have a 2 speed rear. Haven't
>> tried
>> greasing it to see if it helps, it shouldn't be dry no more than the truck
>> is driven considering how often I grease it. Still doesn't mean something
>> isn't trying to lock up, worth greasing to see if it helps.
>> The center driveshaft hangar was replaced a 4 or 5 years ago, not many
>> miles
>> on it and it still looked good yesterday. I did notice a little slop on
>> the
>> driveshaft spline, I would think a little is acceptable on a machine of
>> this
>> age?
>> Haven't tried pushing the clutch in once the vibration starts.
>> I tried a pry bar under the tires on one side while it was jacked up,
>> didn't
>> notice any slop. I will say things are a tad noisy when you jack one side
>> of
>> the truck up and put it in gear. Sounds loudest around back, normal?
>> Didn't
>> really give it any gas when we were checking. You don't hear any strange
>> noise in the cab while on the road, then again it's not very quiet in
>> there
>> to start with.
>>
>> John
>>
>>
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