Shimmy in Rear of 64 C20

[64tantruck]

I have a shimmy at about 45-50mph. Smooths bout above 55 mph +/-
Truck is a 64 frame with 78 rear 3/4 ton axle and air bags. Ive been underneath everything is tight. I have rotated wheels and had them re-balanced. Again nothing up till 40-45mph then smooths right out abouve 55mph As my kids put it "it feels like the truck is wiggling it's but"
Staying close to home most of the time dont go up in the highway much because of gearing. 65mph= 2900 RPM.
So its mostly a cruising truck, we dont race it at all.
350ci with TH350 tranny and 3:73 rear gear. 28 inch tall tires.

Thanks,
glenn

[LuckyLightning]

I had a similar problem once. Check to see if your drive shaft is properly balanced.

[Ol Blue K20]

Bad tire or bent rim

[chevyrestoguy]

Check your:
Driveshaft (u-joints, damage, etc)
Carrier bearing (see if the rubber has separated from the steel)
Pinion angle
Axle bearing
Check for bent axle

[forestb]

I find that a shimmy in the rear is usually caused by too much alcohol, really good music or both.

[old cool]

My truck has developed a vibration at lower speeds. It also makes a raspy whirring type sound under truck as I drive along buildings or curbs. It also vibrates as I slow down and down shift. Problem starts at about 10 mph and vibrates to about 35 mph (also as I'm slowing from 35 to 10). I feel like its coming from front, as it acts like tire imbalance. Don't think so, hence, not putting out any cash till I get other things checked. Today, I heard a clunk coming from rear on some take-offs.
My point, a young fella at parts store said his truck is doing the exact same thing and he said it was U-joints.
Start with the simple and move forward. All of the above make sense. I don't think anyone mentioned bad tire belt.

[forestb]

This might sound to obvious but make sure all your lug nuts are tight. I had a wheel come off on the freeway because I couldn't figure out why my truck was shimmying. (thank God no one or thing was heart)

[64tantruck]

Thanks to all for the responses. Wheels are good.
Going to pull driveshaft and check joints
And possibly have it balanced.

Glenn

[old cool]

Hey tan truck. Did u ever get to bottom of shimmy problem?

[padresag]

it is only the front wheels that can shimmy. the rest are just vibrations.
so did this just happen after you changed the rear end or all of a sudden?
. possible tire separation.
ron

[old cool]

Hey Ron
If your asking me, I can report no rear bearing work yet due to finances though I did change rear u joint. Did some inexpensive vacuum corrections, timing and carb adjustments. i may have a weakening brake booster (hose to back of booster under dash sounds of air but not loud). shimmy is in front so im hoping its just balance. Tires are a few years old but only have 2k miles. I did see where po put a small yellow on hub and also on wheel stud. New hub may be out of round.

[HemiChallenger71]

Just to throw it out there; my uncle had a nagging vibration from the rear of his astro van (this was years ago). Turned out there were no weights on the new drums after he re-did the rear brakes.

[padresag]

Originally Posted by old cool

Hey Ron
If your asking me, I can report no rear bearing work yet due to finances though I did change rear u joint. Did some inexpensive vacuum corrections, timing and carb adjustments. i may have a weakening brake booster (hose to back of booster under dash sounds of air but not loud). shimmy is in front so im hoping its just balance. Tires are a few years old but only have 2k miles. I did see where po put a small yellow on hub and also on wheel stud. New hub may be out of round.

sounds like a centre support on d/shaft if you have a 2 piece d/shaft.
back to o/p and you, I have had separations on 2 different sets of tires that looked good but I also had for a few years. ! set I had 3 separations on a 5,000 mi round trip(7:50 x 16) and the other was 2 separation on a set of 33 x 12.5 x 15 Hankooks. bought both sets new. another thing that can give one a funny ride is mixing bias and radials on the same vehicle
ron

[64tantruck]

Still trying to identify this. However I have been spending a lot of time on my wife's 61 apache 10 project truck. Now that winter is here. I'll jack up the 64 and pull the drive shaft. It is the two piece style with a center support. I guess that is a common failure. Not building this one my self (bought it mostly done) I'm not sure how the PO did the install. Thanks for the info, once solved ill post my finding to hopefully help others

64tantruck (Glenn)