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post #1 of (permalink) Old 09-26-2003, 07:30 AM
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shimmy and shake

Hi. My 77 Silverado likes to shake like an earthquake on the highway. It has a 3" lift. I just had new tires put on, and alignment done. I was thinking maybe u-joints? I just got the truck and I have a lot to figure out on it.

BTW, what's the diff between a squarebore and spreadbore intake? I have an Edelbrock intake, but it appears to be the OEM Rochester Quadrajet carb. I am thinking of replacing the carb, it doesn't like to start real smooth and I would like more power. Any suggestions?

Thanks!!

77 Silverado
Mods so far:
Skyjacker steering stabilizer
lame seat covers.
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post #2 of (permalink) Old 09-26-2003, 08:36 AM
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Re: shimmy and shake

What kind of shake? Do you feel it in the seat of your pants or in the steering wheel?

What kind of tires? How well are your tires balanced? Have you tried swapping the front tires for the rear?


A spreadbore intake has the secondary ports sticking out towards the heads more than the primaries. Squarebore intakes have four holes of equal size. Or at least there is no flare. Go on Edelbrock's website and you'll see what I mean.

Squarebore:


Spreadbore:
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post #3 of (permalink) Old 09-26-2003, 09:20 AM
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Re: shimmy and shake

Well, it only happens at highway speed, 60 to 70 or so. And it's the whole freakin truck shakin'. I have not tried swapping tires, the fronts are new and balanced. The rears are relatively new and they do have weights. I had to buy the same type of tire as the rears for the front or a shop would not put them on (liability they say). Pep Boys futura's, 31x11.50 15's. Not a swamper tread, mildly aggressive I guess.

It seems to be worse when I am on the throttle, that's why I though U-joints.

Thanks for the info about the intakes. I think a Rochester Quad needs the spreadbore style. I will check. I would like to go with a Holley I think.
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post #4 of (permalink) Old 09-26-2003, 09:47 AM
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Re: shimmy and shake

Get the old ones balanced and have them look to see if the tire is out of round.

There's a good chance it's a universal joint or it's a driveline angle problem. I have a severe driveline angle problem which creates a vibration at 72mph.

Why did someone put 31x11.50s on there and lift it? You can fit them without lifting.

Quadrajets, Carter AFBs.... all require spreadbore. It's just the Demons, new Edelbrocks, and almost all Holleys that use squarebore. I guess the theory is that somehow four little holes flow more air than two little holes and two big holes.
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post #5 of (permalink) Old 09-27-2003, 11:49 AM
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Re: shimmy and shake

Okay, I will have the rear tires checked for balance. I picked up some u-joints since they are a cheap fix and will install them if it ever quits freakin' raining here. The ones on there look old, truck has 125k on it.

I think the truck was lifted before the tires were purchased. It must have had some larger tires on it. I bought it of some kid with no cash, so I figure that's why the small tires.

what kind of angle should I have? Maybe it needs shimmed or something.

I would kinda like to get rid of the lift, as I use the truck mostly to haul stuff while I am remodeling my house, and it would be easier access to the bed. What would I need to do to get rid of a suspension lift?

hey, thanks for the great advice. I am getting addicted to this board already.

77 Chevy
post #6 of (permalink) Old 09-27-2003, 04:57 PM
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Re: shimmy and shake

Your pinion shaft and your crankshaft should be parallel with each other.

In other words, not like this:


Does it have blocks on the back? If so, then you just need stock front springs and remove the rear blocks. If it was cheaply lifted chances are the person ran without a raised steering arm.
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post #7 of (permalink) Old 09-27-2003, 06:21 PM
 
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Re: shimmy and shake

He means pinion shaft and 'prop'shaft. I wonder if maybe your propshaft is bent slightly anywhere. I know I accidently high centered on some hard dirt and bent (ever so slightly) my driveshaft... That was a pain to diagnose. I actually had to put the thing up in the air at my local muffler man and have the guy put it in drive to see the offset motion of the shaft... That made my whole truck go to and fro... and maybe a little fore and aft!

Driveline angle is definatly another thing to look into. With just 3" blocks under my springs in the rear I developed a nice vibration from the misalignment of the pinion (also wreaked havoc on my poor pinion bearings!) Good luck to you, hope you have good luck with it!


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post #8 of (permalink) Old 09-30-2003, 05:06 AM
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Re: shimmy and shake

Allrighty, I changed the both of the u-joints on the rear shaft and had the rear wheels balanced. The shop told me that both the rear rims are out of round, so that might be a factor. I have not gotten to open it up on the highway since, but it does seem smoother already.

Pinion shaft and prop shaft? I am gonna have to look these up. I know driveshaft. I assume the pinion shaft is the short one that sticks out of the rear axle. By parallel I assume he means forming a straight line.

Regarding the lift kit. If I remove the rear blocks, will I need new u-clamps? The spring would just sit on the axle then? Would I need to change the front springs? What is this I hear about "flipping" the springs?

I looked at the steering rod to the box, it does not seem to be modified.

Thanks fellas. Learing more everyday, I just might have to keep this thing.
post #9 of (permalink) Old 09-30-2003, 08:26 AM
 
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Re: shimmy and shake

I bet the wheels out of round would be your biggest problem. They're aren't going to balance right if they are out of round, along with the fact that the rim will shake.
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post #10 of (permalink) Old 10-01-2003, 08:17 PM
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Re: shimmy and shake

no he meant pinion and CRANKSHAFT ...... lining the pinion up with the drive or prop shaft will cause harmonic vibrations and shorten the life of the u joints and pinion bearings there is an accepted tolerance of apr. 15 degrees ..... optionally you can point the pinion up and match angles with the front u joint but this is only for extreme lift and short wheelbase
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