Vibration under acceleration

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Jun 20, 2006 | 04:14 PM

71-Triple Blk

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Heel & Toe

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Vibration under acceleration

Hey guys I am very new to the forum but I am hoping that someone can help me. I just picked up a 71' roadster at Bloomington and I have a vibration during acceleration. It happens about 2000 RPM on upward and increases with engine load. It is not the transmission or shafts because it will do it in neutral. It is a 350cid with a Th400 by the way. I am about ready to change the motor mounts but the motor doesn't have excessive movement that you would expect from a worn or broken motor mount. Can you tell me more on the harmonic balancer and the correct one to use for this late 71'? I read an earlier post that stated a different set of timing marks from 70' to 71' which could mean that the timing could be missing. Nonetheless, how do I tell if the balancer is correct and good? Also what else could be my issue?

Thanks,

Brian

Jun 20, 2006 | 04:33 PM

Les

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From: Sierra Foothills CA

Have you checked to see if your fan bolts are tight? Also, check the bolts that mount the bellhousing to the engine. I've personally seen both of these cause a vibration like you're talking about. If you start replacing parts & then find out it was something simple like this you probably won't be too happy. Good luck.

Jun 20, 2006 | 09:50 PM

71-Triple Blk

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Heel & Toe

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Thanks for the advice - I actually have electric cooling fans but I will check the bell housing bolts. Would lock washers be a fix?

Thanks again!

Brian

Jun 21, 2006 | 10:47 PM

71-Triple Blk

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Heel & Toe

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Tried the Bell Housing bolts and no luck

I tried the bell housing bolts and they were tight. A posting today mentioned the water pump as the cause of the issue - is there any way to diagnose the vibration instead of swaping parts?

Any help is appreciated!

Brian

Jun 22, 2006 | 05:09 AM

Les

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From: Sierra Foothills CA

Two things come to mind-

You can grab the pulley attached to the water pump & attempt to wiggle it side to side & up and down. If you get significant wobble, which you should be able to see and/or hear, your bearings are worn.
Or you could disconnect the belt for the water pump, start the engine briefly, & see if the vibration has gone away.

Jun 29, 2006 | 11:36 PM

71-Triple Blk

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Heel & Toe

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Bringing Closure to this mess for future issues

A small victory - I got rid of the terrible vibration with a $11 transmission mount. He has a solid mount with no rubber - I guess they are for really hi-performance engines that dont care about the ride. Quite smooth now - took her out and laid into it - second gear scratch and it is quite impressive...

Thanks for your help.

Brian

Jun 29, 2006 | 11:42 PM

roger55

Burning Brakes

Joined: Jun 2006

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From: San Angelo TX

I've seen this problem before a few times with an out-of-balance pressure plate but never with an automatic.
However, my feeling is that it is the torque converter. It would do it in neutral if it was this.
Anyone ever seen this before?

Never mind. I was writing this as you were posting your fix.

Last edited by roger55; Jun 29, 2006 at 11:44 PM.