View Full Version : Strange rattle/vibration sound

05-07-2017, 08:26 AM
Late last year I noticed when accelerating moderately from a stop or stepping on the gas once the car was warm hard I would hear a loud rattling/vibrating sound from underneath the car. Yesterday driving to the show it was pretty pronounced but typically only when I was "under load" accelerating up a hill or into to the wind (which was really strong at times).

For example, running at 60-62 mph up Blewett Pass I was between 2900 and 3000 rpm. If I stepped on the gas to accelerate even a little I could hear the noise. When I got back into town at a stop if I slowly stepped on the gas to accelerate no problem. But, a little more pressure and here's the noise again. Definitely not quiet either if I can hear it over 60 mph above the drone of the mufflers. I can actually replicate it sitting still with my foot hard on the brake and revving the motor. As I pulled into the shop last night the noise seem to come from the drive line tunnel, but other times it sounded like right under my seat. Really confusing to try and pinpoint (of course, a second person will be needed to figure it out).

My dad and brother thought possibly it's an exhaust vibration. Acceleration is fine, in fact, no problems there at all. I've checked clearance and hangers for the exhaust and everything seems fine. I do have a slight vibration still over 65 so am wondering if maybe it could be drive shaft related.

What other ideas do you have to check? As I said it's irritatingly loud but doesn't seem to affect the running of the car.

Jeff W
05-07-2017, 12:34 PM
The E-brake equalizer arm lives in that area and mounts to the transmission brackets. Maybe something is twisting when the Tories applied hitting your floor pan... nice that it makes the noise when stationary. Hard when you need to strap a buddy to the fender while at speed.:ROTFLMAO:

04-23-2018, 12:10 PM
Ok, so update and looking for some tips/advice for a novice on the best way to check.

I took the Falcon out again this morning. The rattle/noise has been more persistent at slow speeds, especially when accelerating after turning right. However, this morning I also had a lot of drivetrain vibration on accelerating. The transmission seemed to shift gears well enough but there was this shaking from underneath (it seems) on acceleration. It diminished around 50 mph when cruising but any time I pressed on the gas you could feel it again.

My neighbor and I suspect the u-joints are bad. I'm not sure if they were ever replaced when the car was rebuilt. I'm assuming they were. The rear of the car is on jack stands right now.

1) What is the proper way to check the u-joints?

I've got the rear on jack stands. Car is in park. Driveshaft rotates a little side to side on rotation and the wheels move before they stop because of the transmission in park, I assume. On the rear, in tying to manipulate the shaft up and down or side to side there's no movement.

On the front there is a slight amount of movement up and down - not much but definitely not tight like the rear joint. Could this make that vibrating noise since it's at the transmission?

2) Where are folks getting their replacement ones?

Finally, if not the u-joints what else would cause that vibration/shudder - torque converter?

04-24-2018, 07:57 AM
A couple of photos - front and rear view of the driveshaft. The fact that the vibration is more pronounced at lower speeds has me confused.

04-24-2018, 10:55 PM
Hey Scott. If the U-joints are even slightly bound-up you'll get vibration. Maybe even more-so than if they are a little sloppy worn-out.

The only real way to check them is to pull the drive-line out and give them a feel. The front one you just need to pivot the yoke in its two directions to see if it is smooth and not too tight or too loose. Sort of the same with the rear, except the two caps will need to be rotated individually. That said, you may not feel or notice a failure that might be evident only when the car is under load, so I would suggest having them replaced. At $15 a piece (give or take), no point guessing. Whether you do them yourself or you take the shaft somewhere to have them replaced - that's not something I know how best to suggest. You can probably see DIY videos on YouTube if you wanna give it a go.