My cube van has been having vibrations like driving on a rumble strip. At low speeds the vibration frequency is low and increases as the speed increases. The strange thing is that it only starts happening after driving with the vehicle at highway speeds for an hour. If I accelerate or apply torque to speed up the vibrations almost disappear. If I release the accelerator, the vibrations disappear. The vibrations are worst when I maintain the speed. I thought it was the U joints but the dealer checked them and said they were fine, no play in them. I've only got 110000km and it's a 2011.
Can U joints still be a problem even if there is no play in them?

 

I had that happen with an AWD Astro. It turned out to be a bushing in an output housing where a drive shaft entered a transfer case. The vibration was caused by the splined end of a drive shaft was allowed to wobble. This could be your issue, just at the transmission instead of a transfer case.

 

I never thought of the spline on the transmission end. It makes perfect sense when the torque is on the splines hold it in place. I'll have to get my dealer to take a look at it this week. Thanks.

 

Well brought it into the dealer this week to finally have it checked out as I couldn't pin point the source of the problem. It turns out that the problem was with the torque converter. The truck only has 117,000KM on it. I've never had to change a torque converter in any of my previous service vans, and we ran them well over 200,000KM. I hope this helps others who may have this noise or similar problem. Oh and be ready to pay over $ 2,000 for the repairs.

 

what was wrong with it?

 

Trans work is never cheap.

 

They couldn't tell me what was wrong with it because they don't open them up. They just change them. They couldn't (or wouldn't) say if this is a common problem or not but if they decided to change out the torque converter it must be because they've had the issue before. I do carry a lot of weight in it as it is my mobile workspace, and most of my customers are in town so I do a lot of stop and goes. That might explain the reason for the premature failure. To be convinced that they had fixed it, I drove the next day for about an hour on the highway to see if any vibrations would be heard and all is fine. I'm still perplexed as to how the torque converter, being on the input side of the tranny, can create a very noisy vibration, that varies with the speed not rpm, on the output side of the tranny.

 

The torque converter takes the place of a clutch. Half of it turns with the motor, and the other half turns with the wheels.

 

I understand that it replaces the clutch but the input side of the tranny is not at the same speed as the output side of the tranny. Inside the torque converter the turbine doesn't turn at the same speed as the drive shaft until it reaches top gear highway speeds. There are gears in between. I should stop thinking about it and just accept that it is repaired. I like to analyse things too much, thank you for the conversations.

 

That depends on the gear. In a classic 4 speed automatic, 3rd gear is typically 1:1. Input=Output.
Also, around 50 mph and once tranny fluid reaches operating temperature, the torque converter mechanically locks. At that point everything, engine + TC + tranny are all rotating at the same speed.