High speed shimmy help

Reply Subscribe

Thread Tools

Search this Thread

Nov 25, 2001 | 05:28 PM

78shortbox

Thread Starter

New User

Joined: Nov 2001

Posts: 8

Likes: 0

From: Columbus US

High speed shimmy help

I am looking for some info on what all to look for on my 1978 4x4 when driving down the road. The truck has 192,000 miles on it and is running a 351. The truck runs find down the road up till about 50 mph, anything above that and the truck rattles and shimmies pretty bad. The previous owner who was the original owner of the truck just put on a new sway bar setup last year and he claims this helped the steering out quite a bit. The tires are radials and are about 50% tread, and they are not mudder tires, they look to be a fairly decent street radial.
What all should I look for or fix?

Thanks,
Tom

Nov 25, 2001 | 06:32 PM

otto

Posting Guru

Joined: Dec 2000

Posts: 1,686

Likes: 1

From: Racine WI

High speed shimmy help

Bent wheel or or possibly out of balance wheel, in Mississippi this happens alot "when you get mud in your tires"

Seriously the a buddy and me were out galavanting in his 79 F-150 4x4 and we got a flat so we threw the spare on there and we going to continue on our way once we hit the road it was awful doing anything over maybe 35-40 the truck would shake violently and rattle, It seriously scared me be riding in this truck at 40 mph and we were on the turnpike so he was trying to do the 55 speed limit, Man I was scared

Anyway we get home and he asks his brother about the spare tire he donated to his cause and he "says that wheel is really bent thats why I took it off my truck" so he got the old tire fixed drove like a dream again

Just a suggestion on something to check, also check the radius rod bushings

Nov 26, 2001 | 11:35 AM

brents

Senior User

Joined: Apr 2001

Posts: 321

Likes: 1

High speed shimmy help

Hi,

I would have a look to see if there is an idler arm or center link that is "worn" in the steering linkage.

Is there any slack in the steering box?

-Brents

Nov 26, 2001 | 11:46 AM

dfisher1

Posting Guru

Joined: Jul 2001

Posts: 1,613

Likes: 2

From: Gainesville, FL

High speed shimmy help

78,
Tire balance is most probable. Does the shimmy come and go on a steady tempo, fading in and out? That means you have two tires out of balance. Does the stearing wheel shake in your hand? If so, it's your front tire/tires. Does your brake pedal pulse? Then your drums could be out of balance. If the steering wheel shakes when applying brakes then your rotors are out of balance. Does it shake only when you let off the gas? Probably a U-joint or slightly bent driveshaft. A two piece dirveshaft out of phase will give the same symptom. How big are your tires? The bigger the worse the problem. The 4 x 4s had steering dampers on the drag link. Is yours any good? Is it leaking Oil? Detach it and look for a blown shock. Just a few suggestions.
Good Luck, Have Fun,
KingFisher

Nov 26, 2001 | 05:01 PM

Chuck P.

Elder User

Joined: Jun 1999

Posts: 861

Likes: 0

From: SE PA

High speed shimmy help

In addition to the above, I would have someone turn the wheels slowly and gently back and forth, do the visual of everything under there. If nothing is obvious, then I'd have to ask you, "Ever replaced the bushings if the front?" If not, I really think this is a lot of your problem. How's the steering stabilizer? Most 78-79's in the swb 4x configuration came with them stock, this may be gettin' a little lazy and won't help. Wheel bearings are next, if you raise the wheels off the ground, grab the tire top and bottom and see if you have any play-if you do, look behind to make sure it isn't a ball joint going, if there isn't any play there, then look at the wheel bearings. Most of my problems on a '79 swb 4x have been in one or more of these areas over the years. If I recall any other wear problem areas, I'll post 'em.

Nov 27, 2001 | 05:21 AM

georgiafordman78

Senior User

Joined: Nov 2001

Posts: 144

Likes: 1

From: Savannah US

High speed shimmy help

Maybe an out-of-round tire, bent wheel, wheel balance, or a loose front end. If the shakin happens at a certain speed then disappears after you go faster it may be bad shocks. Is the tread on your tires "choppy"? If so its from lack of rotation or bad shocks. Maybe u-joint or driveshaft too. Be more specific on where the shake comes from, at what speeds, if it goes away at higher speeds, and if your on the gas or off it...

Nov 27, 2001 | 06:59 AM

78shortbox

Thread Starter

New User

Joined: Nov 2001

Posts: 8

Likes: 0

From: Columbus US

High speed shimmy help

Thanks for all the help. The shimmy gets pretty bad around 55 mph and worse if you go faster. I have checked several of the problems from all the replies and I am pretty sure it is the U joints. They are very sloppy, and clunck pretty bad when you let off of the gas.
I will start with them first and replace them.
Thanks,
Tom