78 Chevy 4x4 still vibrating, please help

Hey everyone, I have a 78 chevy 1/2 ton 4x4 with the 350/350.. anyway, for over a year now it has been 'galloping' really bad at 30-33 mph. If I brake
through that speed, it does it, if I accelerate and/or coast through that speed, it does it. It feels exactly like a tire being out of round, but i've swapped tires with my son's truck just to see and it still does it?? i swapped front and rear axles, and it still does it. thanks in advance for the help
TB
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Front shocks, steering stablizer. unbalanced driveshaft?
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What Digit said and bent crankshaft, wrong transmission flexplate, cracked flexplate, wrong harmonic balancer. There has to be a time that you noticed the vibration. Such as after some work was done.
Brian
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Have you checked the motor mounts:
The rear motor mounts and transmission/transfer case mount?
If you have a bad motor mount and bad rear motor/trans-transfer case mount, the motor will twist. Setting the front and rear drive shafts out of phase/alignment. Then when you brake, the vibration would be felt as feed back. Because the wheels become more of a unitized assembly when the brakes are applied.
Hence, when there is a bent wheel, you feel it slightly in normal driving, apply the brakes and the vehicle shudders.
I hope this helps?
Refinish King

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Check your u-joints, had a bad vibration in my blazer. Rear u-joint was shot, its fixed now no more vibration.
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Bent rear axle...???
| Hey everyone, I have a 78 chevy 1/2 ton 4x4 with the 350/350.. anyway, for | over a year now it has been 'galloping' really bad at 30-33 mph. If I brake | through that speed, it does it, if I accelerate and/or coast through that | speed, it does it. It feels exactly like a tire being out of round, but | i've swapped tires with my son's truck just to see and it still does it?? i | swapped front and rear axles, and it still does it. thanks in advance for | the help | | TB | | |
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====== snipped-for-privacy@bellsouth.net (Trailblazer) Wrote: (snipped, cut, diced, rearanged,titles added)
78 chevy 1/2 ton 4x4 with the 350/350
SYMPTOMS:
'galloping' really bad at 30-33 mph. It feels exactly like a tire being out of round,
CONDITIONS:
If I brake through that speed, it does it,
if I accelerate and/or coast through that speed, it does it.
ACTIONS TAKEN:
i've swapped tires with my son's truck just to see and it still does it??
i swapped front and rear axles, and it still does it.
thanks in advance for the help TB ======================
Take the rear driveshaft out and check the u-joints for signs of binding........and check for looseness in the pinion gear using the yoke on the differential, see if the yoke will flop around any.
Raise the vehical and check for roughness in the wheel bearings.....FRONT AND REAR! (sometimes you need to pull the tires to get a good enough feel on "slightly" rough bearings)
Come up with some more symptoms and we'll be glad to give you some more guess's.
~:~ MarshMonster ~has never heard the term "gallop" used to describe a symptom~ ================
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Just maybe:
He has too many horsepower under the hood?
Hence: It's galloping?
Refinish King
(Trailblazer)

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I'm flattered, really; but the poor ol' 350 in it was built about 8 years ago and bored, but it's well over 150K miles since the rebuild. I'm going to check the wheel bearings, motor mounts and u-joints this weekend.
Thanks again for everyone's input! TB
(Trailblazer)

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If it is an automatic, It may be a broken flexplate. I once had a bad vibration from a bad fan clutch bearing, but I could not tie it to a specific speed. Dan
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i recently had it rebuilt, it was vibrating before the rebuild,
thanks!
TB
"Dan Dunphy" <dandunphy at pcisys dot net> wrote in message

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. . ================(concerning the vibration outlined in the OP) "Dan Dunphy" <dandunphy at pcisys dot net> wrote in message
If it is an automatic, It may be a broken flexplate. I once had a bad vibration from a bad fan clutch bearing, but I could not tie it to a specific speed.
Dan ================== snipped-for-privacy@yourbusiness.net (Trailblazer)
i recently had it rebuilt, it was vibrating before the rebuild, thanks!
TB ====================Trailblazer, Did you ever pull the driveshafts and move the joints around to check for tight spots, binding??
jest fer giggles.....
try this... crawl under the truck and unhook the electrical connector on the drivers side of the tranny.
carry it for a ride and post the results.
We're trying to see if the symptom deminishes, or even perhaps disapears, when lockup isn't working.
Marsh ~:~
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