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Vibration during deceleration

Mark1972

Mark1972

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I wasn't sure where to put this, so I'll post in this area. Now that I've been out driving by my car at various speeds, both city and highway, I've noticed a vibration once I take my foot off the gas, most notably while slowing down from highway speeds. To be clear, I'm not braking, just removing my foot from the gas pedal. I'm not sure how to start diagnosing this problem. It feels like the front of the car. The suspension is all new PST, and the vibration didn't occur on the chassis dyno last week. The wheel alignment was done 3 weeks ago, because of the swapping in of the 440/727. The alignment was fine. Everything is tight. Any thoughts on where to look or what to check first? As always, thanks all.
 
U joint? Bearings are probably on there way out .
 
Brand new driveshaft and u-joints. Balanced and certified. Honestly, if the shop that did it wasn't very reputable, I'd think the same thing, but I figure it would then vibrate on acceleration as well.
 
were is the vibration,steering or shifter? Could you have lost a weight off of a tire when you did the dyno test?
 
Well it feels like front area of car. Doesn't come through the steering wheel though. It feels like it's coming through the floor.
 
I think I would have then check your front end again, how old are the tires?
 
I know you said feels like front of car, but any chance you have just had rear end or transmission work done?
My thoughts are if it only happens when you are coasting, not under acceleration, then it may be drive train related. Again just tossing out ideas, from info you have given, but under acceleration,(trans/driveshaft/rear) are under torque, to move the car, when not under power is when you say the issue starts. And those same parts are now not under load.
(thinking u-joints, or bearing pre load not correct, or worn output shaft bearing??)
I had a rear end do this once after I had the gear ratio changed, it only would vibrate on coast, had to have the center section, rebuilt by different shop.

Best of luck!!!!!
 
Check the pinion nut. If this gets loose it's great under load and pulls in to the ring gear when off the gas and vibrates. Turns really bad if left alone.
 
Nate S,
I have never had an issue with this, but the 489 rear uses that "crush sleeve" to set preload, so when changing the pinion seal, what is best way to retorque this with out crushing the sleeve any more, but also not leaving it loose?
Again I have done this a few times, with no issues, but it always screwed with my head, like as soon as I did it I expected issues down the road LOL!!!
 
U-joints would have been the first place I looked, too. Wheel balance problem *should*(there's that word again!) happen at the same speed regardless if you're on or off the throttle. You might check your slip yoke for excessive play in the tailshaft, and the transmission mount while you're under there too.
 
The engine, transission, and rear end were all rebuilt. The diff was just done two weeks ago. I'll have to call them and see if they can get it in. The tires have maybe 800 miles on them. No issues there.
 
Think beanhead's right on point with the slip yoke, tail shaft bushing, trans. mount would be the items to check out.
 
Last edited:
Tension is completely different on accel, as opposed to decel. Look to Beanhead's advice first.... if you come up empty handed, then you could be right, it's up front.....
This isn't a ball-n-trunion driveshaft right?? And you didn't overgrease anything in the driveshaft right? How 'bout the output shaft on the trans, could it have wear? And the slip yoke is new with the driveshaft?? Best of luck, Lefty71
 
Pinion angle
Motor mounts
Trans mount
Water pump/ fan blade/clutch (remover belt and try it)

If the pinion nut was loose it makes a hell of a loud whining noise when coasting.
 
Excessive pinion angle will vibrate on decell only.
Doug
 
I had a similar vibration not long ago that I accidentally fixed. I decided to make some changes to the exhaust system (side exit to rear exit), upon finishing it the first test drive revealed no more vibrations. I investigated the removed pieces and found where it had been touching in one spot as a result from dragging it to many times. The vibration was always slowing down much like drone. Vibrations can be a real pain, I've had busted cords, pinion angles, etc... Problem is there's to many places to look.
 
I'm going to have a really good look at pinion angle this weekend, but it was never an issue before, and the angle of the differential should not of changed at all. The new Yukon DuraGrip was installed, but the angle shouldn't have changed. I grabbed the drive shaft and put a bunch of force on it in every direction, and couldn't budge it. I'll look closer this weekend. There is good or clearance in my exhaust as I'd had some rubbing before and fixed it. When, I mean if, I ever figure it out I'll post the problem. Thanks again for the help all.
 
Mark1972 said:
Brand new driveshaft and u-joints. Balanced and certified. Honestly, if the shop that did it wasn't very reputable, I'd think the same thing, but I figure it would then vibrate on acceleration as well.
Click to expand...

Not necessarily. I'd pop the rear U joint out make sure all is clean, make sure front yoke clips are properly in place. Just a thought.
 
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