Severe shake downtrack, cause?

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gregsdart

gregsdart

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When running my Dart on Friday at RockFalls raceway, the car started to shake as it went into high gear.
It is so bad i chose not to run the car again till i can figure this out. The vibration starts when i shift into high gear. It grows in intensity, then calms down gradually. The graph is of the acceleration in Gs and the rpm
Et was 8.59 at 158 mph, 2945 lb door car, 30 inch ladderbars, 4.56 dana, Torqueflite. This vibration increased a lot when the new motor with more hp went in. I plan on rechecking driveshaft, will check tires and rims for balance and runout. Any other Ideas? I have been chasing this issue for a long time!

IMG_20250803_045713619.jpg
 
Driveshaft is very short, cm by Empire? No. Worries there except i plan to check the balance
 
Crack Tailshaft housing? I guess that would leak and be obvious
 

When I had a vibration I didn't feel, but spectators could see, the ladder mounts had bent. Welding in reinforcements solved it. Fortunately, the leaf springs kept me safe.
Just a thought. I'd look at everything in the rear suspension.
 
33IMP said:
When I had a vibration I didn't feel, but spectators could see, the ladder mounts had bent. Welding in reinforcements solved it. Fortunately, the leaf springs kept me safe.
Just a thought. I'd look at everything in the rear suspension.
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sounds like you had housing floaters
 
Will be pulling the tires and wheels for rebalance, same for driveshaft. I will keep in mind the trans high gear. The issue was there before the trans was rebuilt, so it will be checked, but should be good. Thanks for all the contributions!
 
gregsdart said:
Will be pulling the tires and wheels for rebalance, same for driveshaft. I will keep in mind the trans high gear. The issue was there before the trans was rebuilt, so it will be checked, but should be good. Thanks for all the contributions!
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Yeah, I think it's just the tires. Might be that the tubes rolled if they got deflated while sitting.
 
Several Years ago a 10.0 Super Stock racer was chasing a similar issue and found nothing visual in the rear suspension. Finally did the go-pro thing as mentioned above. Revealed the threads on the pass. side front hiem were stripped and the bar was pulling out almost a inch on the top half on the run. Pretty scary! Saw this thread and thought is was worth checking out. Good luck getting it rectified.
 
Wheels and tires ,all four, checked OK, not much needed to make them spot on . Runout of both rims and tires good. Driveshaft is in the shop being checked, balanced and a billet front yoke by Sonnex. Car has ladderbars, and i just moved the axle forward as far as possible by screwing the front rod ends in as far as possible, no issues observed with any rod ends. This was done to engage the front yoke deeper.
 
gregsdart said:
Wheels and tires ,all four, checked OK, not much needed to make them spot on . Runout of both rims and tires good. Driveshaft is in the shop being checked, balanced and a billet front yoke by Sonnex. Car has ladderbars, and i just moved the axle forward as far as possible by screwing the front rod ends in as far as possible, no issues observed with any rod ends. This was done to engage the front yoke deeper.
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Just send it! Be a man:lol:
 
So looking at your G graph at the 1-2 shift. Is you shift point a touch high? It seems to drop G a good bit before the shift.
 
Never had any luck balancing a slick with a tube in it.

Ditch the tubes and coat the insides with Slime not dishwashing liquid. IMHO
 
gregsdart said:
When running my Dart on Friday at RockFalls raceway, the car started to shake as it went into high gear.
It is so bad i chose not to run the car again till i can figure this out. The vibration starts when i shift into high gear. It grows in intensity, then calms down gradually. The graph is of the acceleration in Gs and the rpm
Et was 8.59 at 158 mph, 2945 lb door car, 30 inch ladderbars, 4.56 dana, Torqueflite. This vibration increased a lot when the new motor with more hp went in. I plan on rechecking driveshaft, will check tires and rims for balance and runout. Any other Ideas? I have been chasing this issue for a long time!

View attachment 1716437630
Click to expand...

I had a pair of 16x32 slicks do that at hi speed , balance was off...
 
furrystump said:
So looking at your G graph at the 1-2 shift. Is you shift point a touch high? It seems to drop G a good bit before the shift.
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I noticed that too. Not sure, but it might be the overlap when the second gear drum changes speed?
 
Even though the heims are screwed all the way into the ladder bars check that the jam nuts are tight. I've had them work loose over time.
 
Hope the new driveshaft yoke and forward location fixes it!

If not, can you short shift it to determine if it’s speed or suspension related? Your ET will slow up, and you’ll hit that speed band later in the run. Then you can see if the shake is due to the shift and how the suspension reacts to it, or you might see it due to the speed.

Also, do you feel the shake after the 1-2? It looks your G’s rattle there too, just not for the duration that they do after the 2-3.

Last but not least, do you have a graph from the old setup since you said it did this then too, just not as bad?
 
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