Serious vibs

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mygtsissweet

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Ok my gts 340 auto 727 with 373 rear I think. Problem is at 80 mph it starts to feel bad vibration and cannot drive through it. Drive shaft? Rear end? Any ideas? T I A.
 
Have you checked the u- joints, wheels balanced, driveshaft balance ? Have you changed anything recently? Is it a new vibration? You need to give more information for these guys to try to troubleshoot it over cyberspace.
 
coloradohill said:
Have you checked the u- joints, wheels balanced, driveshaft balance ? Have you changed anything recently? Is it a new vibration? You need to give more information for these guys to try to troubleshoot it over cyberspace.
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We put in electronic ignition recently. When I say bad vibration I mean it feels like something is gonna blowup from driveshaft back with a loss of power cannot drive thru it.
 
Out of balance tires come in at around 55 mph.

Wider tires on back vs front?


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mygtsissweet said:
We put in electronic ignition recently. When I say bad vibration I mean it feels like something is gonna blowup from driveshaft back with a loss of power cannot drive thru it.
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Put your points distributor back in and give it a go again.

Process of Elimination, get it back to the state where it was running good.


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if you have ever driven a car that is missing on a few cylinders it could shake you out of the seat. Having no drivability issues from 0 to 80 would make me more inclined to believe it would be u joints, rear end or very bad tire balance. If this just happened immediately after the ignition change I would retract that last statement. More information would be good.
 
mygtsissweet said:
Ok my gts 340 auto 727 with 373 rear I think. Problem is at 80 mph it starts to feel bad vibration and cannot drive through it. Drive shaft? Rear end? Any ideas? T I A.
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I wonder if a really bad transmission mount could be the cause
 
mygtsissweet said:
Ok my gts 340 auto 727 with 373 rear I think. Problem is at 80 mph it starts to feel bad vibration and cannot drive through it. Drive shaft? Rear end? Any ideas? T I A.
Click to expand...
Does it do it when in neutral and you rev the engine to the same rpm as when you have the problem at 80 mph? If it does then it can be ignition and carb related.
 
With a 26'' tire at 80 your in the 4k rpm range. If it doesn't happen in 1st or 2nd gear or free revving in that area, i'd suspect it's a issue in the pumpkin. My buds 70' Cuda did the exact same thing and it was the pinion shaft/gears starting to come apart in his 4.56 geared 8.75.
 
Make sure your leaf spring U-bolts are not overtightened. Per the MP Chassis Manual, "Overtightening can cause spring friction, which will produce a "booming" noise inside the car."

I once had a 66 Dart that "boomed" at say 50 mph or so. I have always wondered since if that was the cause.
 
mygtsissweet said:
Was never running good
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1) U-joint(s) shot/grooved trunnions/caps(s) binding.
2) Damaged/imbalanced prop shaft, or wrong driveline angle.
3) Damaged/deformed/worn front yoke, same for rear+ loose nut/bad bearing on pinion. Bad diff/bearings/axle bearings or adjustment.
4) Check rad fan, particularly a clutch type, a bent blade will cause a vibe & not track linear w/rpm....& will fracture the pump shaft if You keep running it up high.
5) Ignition mis/crossfire, check for fine carbon tracking/ionized dust/moisture in the cap, rotor condition.
W/O seeing/hearing/feeling what You're experiencing, those are the best starting points & order I can give You.
 
So it's always run like this? If you want help, you need to answer some questions and stop being so vague. We need answers and more info if you want help. We're not gonna pull teeth here.
 
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