First Drive after building, Major shake

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Calipag

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WELL! I was on my way home with the Dart. This is the first long drive since we built her and had her aligned. The build consisted of, swapping the drive line and rear from a 74 Dart. Changing our 1970 from a /6 manual drum car, 7 1/4 rear SBP to a V8, power disc, 8 1/4 BBP car. I used all the factory items from the donor car engine, trans, driveshaft and rear.
The engine is a fresh rebuild, I just serviced the trans (new filter and fluid) and rear prior to installation. It has all new tires, and a new factory rubber front end part with a fresh alignment. I replaced both front caliber and brakes and rear brakes and 1 wheel cylinder on the passenger side.

The car drove great on the side streets, alignment was great and the car was running well.
Then I jump on the freeway and get up to 50-55 and everything is good for a while then I get this terrible vibration through the whole car. It shook as if I had a flat, and I actually thought I may be losing the driveshaft. I pulled off the freeway to the nearest parking lot and checked over the car. Everything seemed the way it should be. I convinced myself that it was the road and started on my way again. The car ran fine, steering fine everything seemed good. After driving for awhile it did it again. I pulled to the shoulder and waited and then continued on. I got off the freeway and took side streets home the rest of the way. The car seemed fine on the side street even after getting up to 45-50.
 
This is VERY disturbing. Vibrations usually are not intermittent. That is usually they come on at certain speeds, certain gears, certain engine RPM. This might be something, loose wheel, improper wheel fit to hub (such as wheel with too small center bore not centering properly on hub) I don't know. Something loose, allowing a "shimmy" situation

I WOULD NOT DRIVE this until you can do an in -depth look at things. Try different wheels/ tires a pair at a time.
 
Brakes. Had a ranger do it last fall. Owner used the parking brake and it hung up. Causing a drum to go out of round when it got hot. It did get very hot.
 
Did you redo the front wheel bearing sets? It could be wheel bearings. If you set them to tight. Once everything heats up and starts expanding they start grabbing at the races.

And check your lug nut torque.
 
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My vote is out of balance tire and /or bad shock .

1. Out of balance tire, slow enough the out of balance is not sufficient to produce vibration. Fast enough and things get to bouncing.

2. Bad shock, at speed everything is fine til the tire hits a large enough bump to get it to bouncing and hits its harmonic frequency and amplifies.

3. Alignment off, yes it was just done but it might not be right. My 67 dart has a shimmy at 40 to 45 everything is in acceptable shape but I'm sure the alignment is off. Above or below the speed and it drives great, no pull good road feel.
 
Another thought.. do you know the other car drive train didn't do this too?
 
Bad tires sometimes do this when they begin to separate.
 
If its not the tires , the only other thing it could be is a bent drive shaft. I had a similar vibration only at highway speeds . The rear view mirror was useless because it was vibrating so much. It took a wile to figure it out. My Driveshaft came from a 70 duster in a junkyard . I took it and installed on my barracuda without getting it re balanced or checked out. I finally had enough took it out to bring to the drive line shop so they can measure the correct length for a new shaft. The tech takes my old driveshaft , rolled it on the ground . Then we saw the beg bend in the tube. Problem solved
 
Not enuff + Caster, causing "shopping cart" wheel shimmy.
Prob set to factory specs. for bias tires.
Check the alignment setting from the alignment shop, if the caster is near "0", or negative -
Try having the alignment set to attached chart for radial tires.

alignment-specifications.gif


Bad tire/balance, with bad shock is viable, - brakes - not so much.
 
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My vote is out of balance tire and /or bad shock .

1. Out of balance tire, slow enough the out of balance is not sufficient to produce vibration. Fast enough and things get to bouncing.

2. Bad shock, at speed everything is fine til the tire hits a large enough bump to get it to bouncing and hits its harmonic frequency and amplifies.

3. Alignment off, yes it was just done but it might not be right. My 67 dart has a shimmy at 40 to 45 everything is in acceptable shape but I'm sure the alignment is off. Above or below the speed and it drives great, no pull good road feel.

Brand new tires with balance and new shocks all the way around. The rear springs are the only items not replaced. I did use the original factory torsion bars.
The alignment guy that I took it to is a area expert for classic and custom cars.
 
Did you redo the front wheel bearing sets? It could be wheel bearings. If you set them to tight. Once everything heats up and starts expanding they start grabbing at the races.

And check your lug nut torque.
This is something I'm going to check. I did have all of that apart and didn't thing of the front bearings.
 
Brand new tires with balance and new shocks all the way around. The rear springs are the only items not replaced. I did use the original factory torsion bars.
The alignment guy that I took it to is a area expert for classic and custom cars.

He may be an expert, but what are the alignment specs? Did he give you a print out?
 
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