The Dodge Challenger Message Board

When I drive at around 55 mph there is a resonating vibration. If I increase the gas the resonating time increases and if I lifht up the pedal the resonation time is around 3 seconds. Drive shaft not balanced properly or is there a possibility that the turbine (10 inch) is not balanced??

340 CID, 727 gearbox, 8 3/4 with 3.91 ratio.

Does it happen at 55 in second gear as well as drive?

If so it is speed related and not rpm related so the problem is either driveshaft, one or both UJs, pinion angle, bent axle shafts, rear wheel balance.

If in a lower gear it happens at a slower speed the problem is somewhere between the crank pulley and the torque converter.

PS

I have spent years getting rid of the vibrations in my Challenger. It used to be TERRIBLE! at 70mph it was shaking so much my hands were going numb!

I have got rid of all the vibrations now except ONE.

I too have a vibration at 55mph. It starts around 50mph and tails off at 60.

When sorting out all the other vibrations I found the biggest difference was when I altered the pinion angle.

Thanks for your comments

I had a drive around and at 20-25 mph (1 st gear) and 35 mph (2nd gear) there was some smaller continuous vibration.

when driving at 55 and putting the geat in N there was no vibration

at 75-80 it seem like the car starts to shake somewhat at the rear because there is no vibration felt on the steering wheel.

what I'm mostly worried about is that this vibration will cause some damage. I will, of course, look into the whole problem during the wintertime when the car is in storage.

So that is around 3000rpm in each gear. If it is at 55mph in top them it will be at 38mph in second and 22mph in first.

So it is engine related. The other higher speed vibration might be connected to the same thing or due to something else. So first problem first.

There are so many things that can cause this.

One of the vibration I had was due to a paint run under the back of the crank crank pulley which stopped it seating perfectly flat. A slightly out of round pulley will do that too.

So sometimes it can be a simple thing. Other problems can be harder to fix.

Sometimes the balancer can fail causing the outer part to rotate and throwing the timing marks out as well.

Is the flex plate and torque converter the correct balance for the type of crank you have?

Are any of the con rods slightly bent? Has the engine been rebuilt and not balanced? New pistons or anything?

I know that the engine has been rebuilt and it has been done by a person who knws what he is doing. I have found a couple of loose and missing bolts here and there in the chassis so I will go through the bolts on the engine, especially the ones connecting to the transmission.

I will also check the motor for vibration when it is in Neutral and a 3 000 rpm. There is an MSD ignition in the car so the original tach is not connected. I understand it needs some sort of filter before the tach can be used or connected.

I did have a look under the car. To me it visually looks like the rear axle is slighty pointing UPWARDS. I will measure the angle when I have time. Like you first suggested it looks like the biggest vibration is coming from the the incorrect pinion angle (at 60-80 mph). After I get this adjusted I have to see how much vibration is coming from the motor.

YES it should point up! I have copied and pasted the following from another thread on here.

The center line of the crankshaft and transmission output shaft must be parallel to the center line of the pinion shaft as shown in Figure 1.

You will note that there is some distance between these parallel lines. The distance is caused by the angle of the components and their distance apart.

Planning these component angles is critical. You have to set the components up so their center lines are parallel and so that the angle made THROUGH the U-joints is 3-degrees or less as shown in Figure 2.

While it is possible to run at zero degrees through the U-joints, something more than one degree and less than three degrees seems to run smoothest.

You Live and Learn

I have adjustable air shocks on the car so I will test with different pressures to see if there is any difference. And measure the settings according to your instructions

Looks like I should have checked the bolts connecting the transmision to the engine earlier when I bought the car. All were loose and 1 missing. Problem solved

Ah! That old problem. You are not alone I can tell you. A good mate of mine ended up putting his car away for a year or two because he was fed up with not being able to find the vibration problem. He took one look just a short time ago and realised straight away he had never tightened the trans bolts up the last time he had the engine out. There was a half inch gap between engine and trans at the bottom!

Glad you found the source of the problem. Happy motoring!

dave-r wrote: There was a half inch gap between engine and trans at the bottom!

You are not alone I can tell you. So true!!! Guess what? That is exatly how my engine and trans were bolted together!!!! The seller (the less honest sort of seller) said that the vibrations were caused by a worn u-joint. Call me a stupid arse if you want, because I believed him. (but that was a long time ago. I hope I am a bit less stupid nowadays....)