Vibration when "floating" throttle

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Oct 8, 2006 | 10:19 AM

vls

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Vibration when "floating" throttle

I took my 79 F250 4WD 400 C6 down from the mountain to fill it with gas. Much cheaper down there. When on the freeway, I get a very fast (much faster than wheel problem) vibration I can feel through the floorboard, but only when I let off the gas and "float", but don't actually decelerate. Does that sound like U-joints, tranny, or what? Makes no noise, no ringing from the driveshaft, etc. Can't feel any slop in the drive train when I have it up on jackstands. I'm kinda at a loss.

Oct 8, 2006 | 11:43 AM

timothy47129

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From: southern Indiana

So while at highway speed if you give it gas and let off quickly you dont feel a thud or any slack in the drive train?How about the fluid level in your transfer case and differential?Have you checked or changed them lately?

Tim

Oct 9, 2006 | 01:49 AM

Alvin in AZ

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From: Gadsden Purchase

Mine did that for the first time on a trip and when I got there I asked my friend about it and he said without missing a beat that it was my carrier bearing. Sure-enough was too! :)

What I did when i got home was set it up on blocks and started it up and saw for myself something was sure-as-heck wrong with the driveline... before taking it to a driveline shop.

Dangged drivelines are one of those things you can't really fix "right" yourself, you're gonna need help with it. :/ They will straighten and balance it and it ain't so awful much.

Carry-in is cheaper than driving-it-in too.

Let us know what you find ok? :)

Alvin in AZ

Oct 16, 2006 | 02:47 AM

Purdue Offroader

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From: Purdue

My 79 f150 does this all the time too. usually I lose a U-joint shortly after I notice it. I'd check the u-joints for slop. Could be a bearing though too.

Oct 16, 2006 | 02:40 PM

Alvin in AZ

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From: Gadsden Purchase

Quote:

Originally Posted by Purdue Offroader

My 79 f150 does this all the time too. usually I lose a U-joint shortly after I notice it. I'd check the u-joints for slop. Could be a bearing though too.

While at the drive line shop they let me watch every aspect of the straightening and balancing work. :) The carrier bearing was for-sure bad. Couldn't tell that for sure until I got the driveline off the pickup and spun it.

In my case... the U joints had very-little "wear" and I commented on that since they were stock and it had like 125,000 miles on it and they didn't have zerks on them neither. :) Looked pretty dangged good I thought. :)

He said "yeah and that little bit of damage was probably caused by the bad carrier bearing in the last week too".

All the systems work together see?

My latest improvement in my steering was new rear wheel bearings. ;)

Alvin in AZ

Oct 16, 2006 | 02:47 PM

Purdue Offroader

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From: Purdue

Yea I'm pretty sure I need to have my rearend redone too. I know i've got either a bad wheel bearing or a bent axleshaft. And I've had two rearends in it already (same guy did it both times and I'm not realy confident in his work since the first time he did it the bearings fell out or something within 2000 miles.

Oct 17, 2006 | 07:41 AM

MacFastStang

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It sounds like u-joints. Most other driveline problems will either vibrate all the time and worse at higher speed or vibrate more under a load. If you are going to check under there its always best to check everything. Bad u-joints will cause other problems like the tailshaft bushing to wallow out or rear pinion bearing and seal problems.