[Steam Roller]

I was at a car show this past weekend and they had a portable dyno machine. I watched a late model Camaro (not my car) that was modified do a pull on the dyno, once it reached top end RPM the driveshaft broke with a big bang and lots of clanking noise then lots of metal pieces came flying off the rear and side of the car, most of the pieces were probably the u-joint etc. I was about 10 feet away including many other spectators, no one was hurt. After seeing this I decided not to have my pro street camaro car dynoed not because I was afraid of the car breaking but was concerned if the dyno machine or operator could have contributed to the break. I heard several stories from the car would have broken anyway on the street by beating on it to possibly the dyno machine hesitating and causing the break.

Can anyone tell me if it’s possible for the machine or operator to cause extra stress and break a drive train? I also was told to be careful of operators cheating with the ambient temperature setting on the computer which can inflate horsepower numbers.

Thanks

[tresi]

Running a car on a chassis dyno makes the rear end run somewhat hotter due to the lack of air flow over it. I doubt that had much to do with it. Sometime the driveshaft will turn more rpm than it will turn on the track due to the fact that the car doesn't have to overcome the air resistance.
Had he drove the car the same speed for the same length of time on the road the drive shaft probably would have broke anyway. The damage to the car would have been worse had it happened with the car moving 100 mph or so, if he didn't wreak.

[M&M CUSTOM]

Originally Posted by tresi

Sometime the driveshaft will turn more rpm than it will turn on the track due to the fact that the car doesn't have to overcome the air resistance.

HUH???
The driveshaft will only turn as fast as the rear tires multiplied by the gear ratio, no more, no less. Until it, or the universal joints break.

Originally Posted by tresi

Had he drove the car the same speed for the same length of time on the road the drive shaft probably would have broke anyway.

I would be willing to bet the driveshaft would NOT have lasted as long on the road if the driver has been willing to give the car the full throttle like on the chassis dyno. I would also be willing to bet that the driver was level headed enough to not give the car a full throttle beating on the street.

A chassis dyno should not put any more stress on a car and it's parts than a ¼ mile dragstrip pass.

[73oldsman]

Luckily no one was hurt in that one! Also, maybe luckier is the fact that it broke on the dyno and not on the highway while cruising @ 70 mph!

[johnsongrass1]

Originally Posted by tresi

Running a car on a chassis dyno makes the rear end run somewhat hotter due to the lack of air flow over it. I doubt that had much to do with it. Sometime the driveshaft will turn more rpm than it will turn on the track due to the fact that the car doesn't have to overcome the air resistance.
Had he drove the car the same speed for the same length of time on the road the drive shaft probably would have broke anyway. The damage to the car would have been worse had it happened with the car moving 100 mph or so, if he didn't wreak.

I think he meant he ment the wind resisteance would have slowed the car some. Preventing the engine and driveshaft rpm from reaching the critical level.

I knew of a racer who driveshaft broke and the end attached to the tranny whiped around and torn him open from foot to arm pit. His gut's were literly hangin out and he was holding them is his lap with broken a right arm and right leg in several places. Driveshaft's are not to be toyed with. They will hurt you. Often without warning.

A few months ago a dirt driver died when someone elses shaft was chucked.
The driver pulled over agianst the front stretch wall, head on with reasonable force. The track crew found him dead with the driveshaft of another car laying at his feet. It had hit him in the head. Killing him instantly. How bad would that make you feel?

[baddbob]

[QUOTE=johnsongrass1]
I knew of a racer who driveshaft broke and the end attached to the tranny whiped around and torn him open from foot to arm pit. His gut's were literly hangin out and he was holding them is his lap with broken a right arm and right leg in several places. Driveshaft's are not to be toyed with. They will hurt you. Often without warning.
QUOTE]


Would a front loop have avoided this? Man, that's a gruesom example.

[johnsongrass1]

Ball spline transmission without a carbon drivshaft.