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Vibration, Now What?
Calling all Cobra gurus,
I just got my car back from the shop. Though I went in for a pesky oil leak, I came out with a rebuilt/ballanced driveshaft, new rear main seal, King Cobra HD clutch and Billet Steel flywheel. I do like the feel of the new clutch, but I swear that the car is vibrating more than it did prior to the shop visit. I picked out the flywheel myself and it is the same 50 oz weight as the one we took off. When I pour on the steam, it just feels like there is more vibration than before. The engine is ballanced and blueprinted (using the old flywheel), would changing an equal weight flywheel matter? Could being on a lift for two days have an effect? I carried the drive shaft to one of the highly-regarded driveshaft specialty shops for the rebuild, so I'm guessing it's ok. But the ride seems a tad rougher going down the road if I push in the clutch and roll at low RPM. Am I just imagining this? I really don't think so. Love to hear some speculation from experience. Thanks, TR:CRY: |
Rotate the driveshaft 180 degrees. This sometimes makes a big difference.
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TR,
You may want to check the pinion angle. Roscoe |
Thanks Jeff.
Roscoe, Could a bad angle have been the root cause of yoke problem? The car only has 4,500 miles on it, the last 2 ,800 I put on it myself with no abuse. The original tires look brand new. No noticable tread wear. Doesn't this seem a bit early to have to replace a yoke and universal joint? The drive shaft had no weights tacked to it when I brought it to the shop, but had two on it when I picked it up. |
Put it on a frame lift, crank it up and idle in first gear, you or someone look and see if there is any out of round in the drive shaft?. Assuming it was vibrating from day one?. Tires?.
I used BIG MOE, out by six flags, stay away from DRIVE LINE SERVICE. |
Perry, it didn't vibrate before I had the work done, but the fact that the yoke was in such bad shape in do few miles tells me something must not be right. Drive Line is who did the work. They were recommended by a couple of folks as good. I trust you had a bad experience? The shaft went from having no ballast to having a fair amount when Drive Line was finished. I was expecting a smoother ride and got the opposite. Smell a rat?
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Tony, after the second re-do by DLS on a
fairlane, I gave up!!. I would still do the lift check with some RPM. |
You mentioned a 50 in/oz flywheel. All 351W's use a 28 in/oz flywheel. 5.0 motors from about 83 or 84 up use the 50 in/oz flywheel. If you have the wrong one, the motor will vibrate.
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Jack,
The original flywheel was a 50oz unit as well. That is the flywheel that was put in the engine by Southern Automotive. Bill told me a 50oz was correct. T |
Tony, seems to me that it must be related to what you changed. I would start with ruling out the driveshaft.
Pathenry, I will take your advice when I need to custom fabricate a driveshaft for my streetrod. |
Well, Southern Automotive certainly isn't known for putting the wrong parts in their engines. A 50 in/oz flywheel (and the crank damper as well) would have had to be balanced this way by Southern for a reason. More often than not, an engine shop will try to balance it internally and not require offbalanced flywheels and crank dampers to get it balanced. Costs a little more, but the engine runs smoother.
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Perry,
Is the driveshaft wobble always noticable to the eye? Is it obvious when it isn't balanced correctly? Tony |
It sounds like a driveshaft problem, but you can isolate the engine and drivetrain quite simply. :rolleyes:
Do you feel the vibration when the car is stationary and you rev the engine? I noticed a thread where someone finally found their vibration. Two of the spark plug wires were switched! A consistant misfire could feel the same way. |
With the car on the lift and a little rpm, you can see/trace down any vibration
problems. See if it persists with the wheels removed?. |
Is it definitely a vibration, or is it a shuddering clutch? Often, a clutch won't have bedded itself against the flywheel for a few hundred miles. Most clutch companies advise against accelerating hard for a few hundred miles.
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Thanks guys. The engine is cammed up to the point that it vibrates the car pretty well, especially at idle (1K RPM). I've taken the car up to 60 mph or so and thrown it into neutral in an attempt to isolate the shaft from the engine. I still feel some vibration. I'm leaning more towards the rebuilt driveshaft. The whole driveshaft assembly is only about 18" long. Could the adding of the balancing weights have a noticable effect on the ride with regards to vibration? Perry has me worried a bit in that it looks like the same guys did a job for him and never got it right. Changing a shaft is so easy compared to replacing the flywheel, I think I should convince myself that the shaft is not contributing to the problem. Everyone agree?
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I agree. What about the answer to Bob Putnam's question? Is the car vibrating when you rev it in neutral at a standstill? Clutch in and clutch out?
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While driving down the road, push the clutch in. This will tell you if it'e engine speed related or vehicle speed related. If it's engine speed related, it should do it with the car at a standstill. Slowly bring the revs up in a steady fashion, smooth or vibratory?
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The clutch feels pretty solid with regards to grip. After talking to Alan at Unique and Lewis at Southern Automotive, it sounds like my problem is likely centered around the fact that my new flywheel and clutch assembly were not balanced prior to installation. I noticed that some material had been removed from the original flywheel in a couple of spots (probably done by Lewis during the original build). I can only surmise that a light little car with a thundering engine won't mask even slight imbalances.
Just goes to show you, only trust your snake to the experts. I don't see enough of this stuff to know the difference between "average wear" and "got to be replaced". |
Re: Vibration, Now What?
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