Vibration at half throttle

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Model T Ford Forum: Forum 2015: Vibration at half throttle
Top of pagePrevious messageNext messageBottom of page Link to this message  By Chuck Godfrey on Tuesday, May 26, 2015 - 08:29 pm:

here is whats going on. Motor starts and runs good. parked at idle no problems. get close to half throttle it starts vibrating bad shakes the whole body.( I know half throttle sitting still is not good anyway) driving it starting out in low and speeding up no issue going from low to high no issue. high gear to half throttle vibration is back and the futher past half the worse it gets. no issues in a pull. vibration goes away when you go to nuteral and idle down from half throttle, while driving Motor is strong and runs great plenty of power for a T.
any ideas or tips on things to check


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jack Daron - Brownsburg IN on Tuesday, May 26, 2015 - 08:56 pm:

I'd lean toward checking the center main bearing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Tuesday, May 26, 2015 - 09:24 pm:

Have you checked the compression? Compression is highest with throttle open and the engine pulling hard. If you have a weak cylinder, it might idle OK and run OK at low throttle but when you run at higher throttle, it will be weak in one or more cylinders. That's where I would check first. A loose bearing would cause a rumble most noticeable when pulling, but the engine would run smoothly, just rumble a bit. Retarding the spark would also cause less rumbling in a loose main bearing.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Coiro on Tuesday, May 26, 2015 - 09:30 pm:

Yeah, I was thinking the same thing about retarding the spark.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Wednesday, May 27, 2015 - 06:26 am:

Is it something that has developed gradually while driving for months or did it suddenly appear?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem - SE Michigan on Wednesday, May 27, 2015 - 10:48 am:

Chuck,

Try running it without the fan belt on. It's amazing how an out-of-balance fan can shake a car. And yes, some original, unmodified fans are badly out of balance.

Also, are the wood blocks and/or side bolts missing from your engine mounts? The absence of either one can cause bad vibration. Also, look for a cracked or broken motor mount, also a vibration cause.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Willie K Cordes on Wednesday, May 27, 2015 - 06:18 pm:

Chuck, you are talking about a T car, not a worm drive rear end model TT truck.
A lot of TT trucks have a vibration in the drive shaft at about half throttle. A little slower or faster and the severe vibration goes away.
Some TT owners put a bearing in the center of the driveshaft to eliminate the vibration.
Just asking since it sounds like that TT problem.


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