[chevellefreek]

my driveshaft is hitting my floor boards right above the u-joint where the trans and drive shaft meet do you guys think it could be a bad you joint ? how can i check if the u-joints bad

1970 chevelle
1967 chevelle

 

[Bret]

Unless your u-joint is totaly wasted, I dont think it is a u-joint problem. Do you hear the contact of the drive shaft to the floor? Does it happen over bumps, more often or worse when the car is loaded with more people or loaded trunk? Or just under heavy load?
I had the same problem with my 71, only happened when loaded and hitting large bumps/dips. I't turned out to be a driveshaft length problem. The driveshaft was bottoming into the trans when the rear suspension compressed and causing the trans to lift at the tail shaft and allow the u-joint area of the driveshaft to hit the body under the floor.
I would check the trans mount and see if it isn't broken or saturated with oil. Also check the drive shaft slip yoke depth into the trans, measure the amount of the driveshaft yoke that isnt into the trans. The distance from the tail shaft seal surface and the end of the round portion that slpis into the trans. You should have a minimum of 1.5 to 2 inches of exposed shaft. If that makes any sense.
Hope that helps, let us know what you find.

 

[aukai]

I changed my body bushings when my billet yoke was hitting.

 

[Guest]

1.5 to 2 inches of exposed shaft

I think that is a bit much, 1 inch would be just fine through the entire travel of the rear. Some of the shafts are only 4 inches to start with and having 50% of it hanging in the breeze kind of defeats the purpose.

 

[chevellefreek]

i thought it was the trans mount too. so i changed it and it only made it worse. i changed the front 4 boudy mounts too. it always hits even if im the only one in the car. i added some stuff to the motor like new carb, intake, headers and new exhaust. when i ran it again it was fine but i floored it to so the difference with all the upgrades. shortly after that i heard the knocking above the center console. the knocking is slow when i let the car idol in drive but when i hit the gas it hits faster and louder as i accelerate. any tips on checking for a bad u-joint would be great.

 

[phocksphyre]

the knocking is slow when i let the car idol but when i hit the gas it hits faster and louder.

Just to be clear, does the noise vary with vehicle speed or engine speed? If it varies with engine speed, not vehicle speed, it isn't a u-joint problem.
John

 

[chevellefreek]

its only when the car is moving when its on park or nuetral their is no knock .as i go faster the knock gose faster . when i installed the new trans mount i noticed where it was hitting cause the undercoating was completely removed. it was right above the u-joint where the trans tail & drive shaft meet . do you think i can jack the car up from the rear and put the car in drive to so more of whats going on. or put it in nuetral and see if the drive shaft has play

 

[chevellefreek]

its only when the car is moving. when its in park or nuetral their is no knock. as i go faster the knock gets faster . when i installed the new trans mount i noticed where it was hitting cause the undercoating was completely removed. it was right above the u-joint where the trans tail & drive shaft meet . do you think i can jack the car up from the rear and put the car in drive to so more of whats going on. or put it in nuetral and see if the drive shaft has play

12

 

[Jim Mac]

jack the car up in the rear, block the front wheels. put some safety stands under the car, put the car in neutral and you can grab the drive shaft and turn it by hand. if you see or feel any play the ujoint is toast. Is it possible that one or both of your engine mounts are torn up? If the engine mount is worn or completely trashed, I imagine it could lower the front of the motor and tip the back of the tranny far up enough to make the driveshaft hit the floorboard. Did you have to remove the engine mount bolts to install the headers? could you have possbly left it loose and maybe it fell out? Just a few ideas. jim

 

[chevellefreek]

with the car jacked up and in nuetral is the drive shaft supposed to move by hand ? and should it wiggle and if it dose wiggle dose that mean its shot