Bad Vibrations - Pontiac GTO Forum
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post #1 of 7 (permalink) Old 11-15-2018, 11:54 AM Thread Starter
 
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Bad Vibrations

Last year I posted a thread about motor mounts because I had a vibration after I pulled the engine to repair oil leaks and paint it.
I have been living with this vibration which occurs around 55 to 60 mph. I have done numerous things that I wont go into but have now isolated it to the rear of the car. Had the driveshaft balanced and I have replaced wheels and tires.
With the car on a lift, wheels and drums removed the car doesn't vibrate when brought up to speed.
If I put the drums on with a few lug nuts (no wheels), car still vibrates. Warped or bad drum right? Nope. Bought new drums. Still vibrates.
So, with nothing bolted onto the axles, the car doesn't vibrate. When the slightest amount of resistance is applied, it vibrates. When road testing, I would bring it up to 80 mph, drop it to neutral and the vibration would NOT go away till speed dropped to under 55.
It must be coming from an axle or the diff?
I did read an old post of a similar problem that seemed to be the back-lash. The poster had the differential rebuilt and problem was resolved.
What do you guys think?
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post #2 of 7 (permalink) Old 11-15-2018, 03:02 PM
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It could be a bad bearing, that may explain no vibrations when the wheels are removed.

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post #3 of 7 (permalink) Old 11-15-2018, 03:27 PM
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The very first thing I would do is verify that the driveshaft u joints were phased properly, and after that, verify the driveline angle. Very easy to mess this up when working on the car. You DID mark and phase your driveshaft when you removed and replaced it, didn't you?
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post #4 of 7 (permalink) Old 11-15-2018, 04:37 PM
 
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a bent axle .......?

did you try 1 drum at a time to isolate the side ??
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post #5 of 7 (permalink) Old 11-15-2018, 11:27 PM Thread Starter
 
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I am starting to believe the vibration is coincidental with the R and R of my engine. I took the driveshaft to a machine shop that specializes in DS. He welded on a new front yoke and hooked me up with u-joints. Never heard of 'phasing' so obviously I didn't do that but it vibrated before and after working on the shaft. Took the car to a transmission shop and he checked the angles, said it was good. I had already replaced the axle bearings so they are new.
Today I did try 1 drum at a time to isolate but it vibrates with one drum on either side,, it did seem less, but still got vibration. Also today I pulled the differential plate off so a mechanic friend could inspect the gears and he noticed a lot of pitting on almost half of the ring gear teeth. He also said it was very tight and recommended r an r of the ring and pinion. He couldn't see how this could cause the vibration though. Gonna wait till after the holidays and paying property taxes before I lay out almost 500 bucks for parts.
I put it back together cause I have a cruise on Saturday. I will keep updating if I find anything. Any other ideas are great too
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post #6 of 7 (permalink) Old 11-16-2018, 06:50 PM
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Garage
Check the driveline angles yourself. It's not very hard to do with the proper tools. You need one of these (or something similar)

https://www.summitracing.com/parts/upi-3007/overview/

See the attached image for how things should be. You'll get a vibration if things are off.

Bear
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post #7 of 7 (permalink) Old 11-16-2018, 07:24 PM
 
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If you have not already checked, how about the transmission mount?
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