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Old 02-21-2019, 07:30 PM
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Rear vibration at 55 mph

I have a recently acquired 1948 Plymouth hot rod with SBC, THD350, and 10 bolt rear end. There is a vibration at around 55 mph. Besides pinion angle, which I have not checked yet, what else would cause this?

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Old 02-21-2019, 08:38 PM
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Possible bad universal joint at the rear of the shaft. I would also check and make sure that the pinion gear doesn't have any excessive clearance in it. I have had that one happen before and it really screws up your day. Not likely but a rear cap on the diff can be an issue as well as axle bearings. Kind of depends on how bad the vibe is. I also wouldn't overlook a tire/wheel throwing a weight but I am never that lucky.
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Old 02-23-2019, 10:13 AM
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Yes, I thought about the universals. Next step- pull driveshaft. Thanks!
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Old 02-23-2019, 01:51 PM
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Quote:
Originally Posted by Jester66 View Post
Yes, I thought about the universals. Next step- pull driveshaft. Thanks!
Don't jump the gun.
Could be as simple as balancing the tires. I'd think I'd start with the simple things first. Check the tires air pressure and for balance, run out and abnormal tire wear ( cupping , out of round ). Maybe switch tires from front o back see if the vibration changes.
Check your suspension ( shocks).
If the above checks out ok then u joints hanger bearings pinion angle.
id also check the driveshaft for bends, balancing and Ujoint orientation. Bothe the front and rear joints need angle. I've seen shafts put in with not enough angle and the shaft acts like a wip when spinning.
A lot can go wrong when altering the original...
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Old 02-23-2019, 02:35 PM
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Thanks for the ideas! I have already pulled the tires and had them balanced. The u-joints look like a ball of rust. Did I mention 1948 Plymouth with an older resto to a 350/350 combo? Fortunately, there is a good driveshaft place 20 minutes away. So, Pull driveshaft and take to them for a balance and u-joint switch.
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Old 02-28-2019, 07:18 PM
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I lifted the car and was checking things out in preparation for pulling the driveshaft when I discovered that the TH350 mounting pad was destroyed! The rubber had totally separated from the metal base. I located and installed a replacement and will be driving this weekend to see if this was the cause of the vibration. Fingers crossed. By the way, the top u-joint has been replaced, however the rear u-joint appears to be very rusty- so I might just replace it anyway.
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