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Old 09-12-2019, 01:09 PM
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Major shake at low speed?

I have a 23 t bucket, 350, powerglide, 57 rear end. Car runs fine. Problem is when I put a passenger in it with me it shakes so bad at low speed you would think i was driving over a speed bump. Person gets out and its fine. There are no leaks or squeaks or sounds when I drive it. I put it up on Jack stands and there is nothing that seems loose. Any ideas? I'm at my wits end.

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Old 09-12-2019, 01:48 PM
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My thinking goes like: What changes when a second person gets in? Maybe the body squats a bit and the drive train gets out of align. Most likely your driveshaft is VERY short so any change could cause this. First I would remove the driveshaft and check the U joints to ensure they are working properly, then check the trans/rear end for proper alignment. Sand bag to add about 300+ lbs and check it again.
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Old 09-12-2019, 01:50 PM
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could a shock be bottoming out?
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Old 09-12-2019, 05:08 PM
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Thanks, it makes sense, it is very short, I will load it up.
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Old 09-12-2019, 05:47 PM
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A flat spot on a tire or a separated belt can cause similar issues with weight or speed changes.
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Old 09-12-2019, 07:27 PM
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Quote:
Originally Posted by 39 master View Post
My thinking goes like: What changes when a second person gets in? Maybe the body squats a bit and the drive train gets out of align. Most likely your driveshaft is VERY short so any change could cause this. First I would remove the driveshaft and check the U joints to ensure they are working properly, then check the trans/rear end for proper alignment. Sand bag to add about 300+ lbs and check it again.
Makes perfect sense to me.........
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Old 09-13-2019, 12:19 AM
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Quote:
Originally Posted by 39 master View Post
My thinking goes like: What changes when a second person gets in? Maybe the body squats a bit and the drive train gets out of align. Most likely your driveshaft is VERY short so any change could cause this. First I would remove the driveshaft and check the U joints to ensure they are working properly, then check the trans/rear end for proper alignment. Sand bag to add about 300+ lbs and check it again.

X3, this sounds like a drive shaft angle problem at the U-joints.


Bogie
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Old 09-13-2019, 05:03 AM
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Quote:
Originally Posted by Gbstrike View Post
I have a 23 t bucket, 350, powerglide, 57 rear end. Car runs fine. Problem is when I put a passenger in it with me it shakes so bad at low speed you would think i was driving over a speed bump. Person gets out and its fine. There are no leaks or squeaks or sounds when I drive it. I put it up on Jack stands and there is nothing that seems loose. Any ideas? I'm at my wits end.

Two different thoughts on this depending on your actual symptoms.
Does it shake along with the speed, or does it shake with road surface.
Speed - driveshaft
Road surface - shock or something suspension bottoming out
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Old 09-13-2019, 07:28 AM
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Like mentioned above, I believe it is a pinion angle issue or a driveshaft phasing one. I would check the angle unloaded, then put weight in the driver's seat and check it again, then add the passenger weight for a third check. My guess is that the deflection of the rear springs is changing the angle.


Here's a good site with information that might help you:


https://www.drivetrain.com/parts-cat...asing-problems
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Old 09-13-2019, 08:26 AM
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Little short driveshafts don't usually vibrate the car at low speed unless out by a lot, just adding a little weight seems unlikely to cause such a dramatic change.
Driveline vibrations typically have a harmonic frequency to them, at some MPH they create a cyclical vibration that typically goes away as speed increases, and then comes back at 2X the original MPH with a frequency that is double but a small amplitude.
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Old 09-13-2019, 03:53 PM
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By the way, can you tell us what rear suspension you have? Coil spring, coilovers or transverse spring.
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