Horrid vibration at about 40mph

So I took my car on the freeway for the first time today and I have a horrible vibration at about 40. The vibration is bad on and off the gas. The car feels like it is going to explode. I know I have good motor mounts.

I have a 48 Ford tudor with a 350/350 combo and a 10 bolt rear.

Would I be best off having the driveshaft balanced and replace U-joints?

Any suggestions would be appreciated as I don't want to spend to much money where it isn't needed.

Thanks in advance.

 

You just gotta check all the front end and suspension stuff first. It could be a loose bolt somewhere. Bias plys? Maybe its got flat spots from sitting. Bent wheel. who knows.

 

I'd look at those ujoints first. It's unlikely but maybe a weight fell off the driveshaft.

 

Start simple, air pressure, make sure everything is tight that should be then have your tires balanced (if you haven't already) wheel alignment then move onto replacing parts

 

Is the driveshaft long enough? How's the pinion angle?

Why would you think you need to replace your new U-joints? Isn't everything new already? If not, look at all your old stuff to see if it is worn out. Could be any one of a million things.

 

Might be caster shake, check the pre-load on your front axel bearings.

Fred

 

Check everything that spins!

Look at my post about Coker tires... which ended up not being the problem!

It was a faulty brake drum!

Whoduthunk??

http://www.jalopyjournal.com/forum/showthread.php?t=786590&page=2

Sam

 

Search death wobble: http://www.jalopyjournal.com/forum/search.php?searchid=6559505

 

Lets start with, Where is the shake?

In the steering wheel = Front suspension

In the seat of your pants = Rear suspension and drive train.

Start with the wheels, and work you way into the driveshaft, do the easy stuff first.

 

Probably not that -- deth wobbel (search that !!) is a low speed shake after going over a bump --
but still pays to check your front end alignment.

 

Who made the drive shaft ? Are the U joint's out of Phase ?


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Are all the lug nuts tight?

Put the car in neutral & grab the driveshaft end, move it & check for play, on each end.

Jack each wheel barely off the ground & grab it shake right/left & top/bottom.

 

Like Millers garage says....don't waste time and money on guesses. where does the vibration originate....steering wheel shake is not drivetrain but suspension or wheels.
Feeling in seat or floorboards is drivetrain but not front suspension . Run it up on a lift and look underneath....any change without weight of car on the ground....know where to look and you'll find the problem

 

Re reading your post, I see you asked

Would I be best off having the driveshaft balanced and replace U-joints?

The way I'm reading it, you made the drive shaft, Non Drive shaft, shop build ?

I make My own, But I was in the Automotive Protype Type Biz.

.

 

driveshafts need to be straight ---lots of people build their own with good results if it is straight and in phase it is not your problem...

 

I didnt build the driveshaft. It was on the car when I got it. I had a tired out 305 in it and I swapped out a 355 over the winter. I never took it on the highway until today. The vibration is not in the front end. I jacked the car up and put it on stands.
I fired it up and the drive shaft has a wobble to it in the rear. Just fine up at the trans, about a 1/4" wobble at the rear u joint. The wobble isn't in the rearend.
After running it I took a straight edge and the driveshaft is not warped. I looked closer at the rear of the driveshaft and it looks like somebody hacked the driveshaft and rear u joint mount looks to be welded on crooked..
I also looked and it appears that I could use a driveshaft that is about an inch longer.

I called A1 driveshaft and they told me they won't add 1" to a drive shaft. The said that for an inch they would recommend a longer yoke. Either way I'm going to drop it off there Monday and see what they have to say.

 

I took video of the wobble, but can't upload it with my phone.

 

There may be a problem with the torque convertor and/or flex plate. I had a vibration problem on a car I built and finally got the vibration with the car sitting still. I replaced both but you can rotate the convertor in relation to the flex plate and see if that makes a difference. You have just installed a new engine and kept the old trans. Was the vibration present before you changed engines? Good luck !!