Vibration Question

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colonelpowers
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* REQUIRED* Type and Year of Model Ts owned: 1926 Tudor
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Vibration Question

Post by colonelpowers » Wed Apr 07, 2021 11:03 am

On my 27 Tudor, I have a vibration that I am hoping to diagnose. Moments after you first shift into high and only for a few seconds I have an awful vibration that rattles the whole car but as I accelerate it quickly goes away. It doesn't seem to have anything to do with the shifting itself because whenever I slow down to a similar speed with the car still in high the vibration returns but goes away as soon as I accelerate again. The vibration is also present at the top end of the speed (usually going down hill). The car pulls hills without issue and has plenty of power. It doesn't vibrate under a load, just at these specific times.

Any ideas?

Thanks and God Bless,

Joshua A. Powers


Norman Kling
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Re: Vibration Question

Post by Norman Kling » Wed Apr 07, 2021 11:23 am

It is possible it might be "harmonic vibration" At certain speeds an engine tends to vibrate. Lower or higher speeds it does not. The only correction for that condition would be to disassemble the entire engine and transmission and balance all the parts.
Another possibility would be fuel mixture at idle. When you first shift, the engine is idling, but when you increase the throttle, you open the air flow through the main body of the carburetor. When the throttle is closed you are using the idle passages. Also when you are going downhill, you close the throttle and again drawing fuel mixture through the idle passage.
Norm

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Oldav8tor
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Re: Vibration Question

Post by Oldav8tor » Wed Apr 07, 2021 11:52 am

Sounds like my car.... Driving a T is seems like it's missing a gear between low and high. My solution is to speed up a bit more before shifting to high. I also noticed when I switched from a 11 tooth pinion to a 10 tooth that the speed range where that happens narrows.
1917 Touring
1946 Aeronca Champ
1952 Willys M38a1 Jeep (sold 2023)
1953 Ford Jubilee Tractor


speedytinc
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Re: Vibration Question

Post by speedytinc » Wed Apr 07, 2021 12:52 pm

I had a similar situation i assumed to be a harmonic.
Accelerating on the freeway. @ about 53mph wouldnt go any faster & vibrated horribly. I found that retarding spark & slowly abvancing, I could get past this rough spot to get to 60. (this is a 100% balanced everything motor.)
After breaking the crank. (mint shermike - surebreak) I put in a scat crank. I still get a harmonic vibration. Now @ 58mph. That works better.
When i am in a hurry 55 is a comfortable speed.
Try the retard trick @ hi speed.


katy
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Re: Vibration Question

Post by katy » Wed Apr 07, 2021 12:59 pm

It sounds like the spark may be too far advanced, have you tried adjusting (retarding) the spark when you shift?

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Henry K. Lee
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Re: Vibration Question

Post by Henry K. Lee » Wed Apr 07, 2021 1:11 pm

Sometimes your clutch dogs hang up too causing a similar condition.

Hank


TXGOAT2
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Re: Vibration Question

Post by TXGOAT2 » Wed Apr 07, 2021 1:23 pm

A bad U-joint or loose driveshaft bushings could cause that. So could a dry U-joint. Loose bolts anywhere in the driveline, loose or damaged pulleys, loose motor mounts, loose rear hubs, problems in the transmission, and more could cause it. From here, I'm best-guessing it could be an issue relating to the U-joint or loose bolts holding the U-joint ball housing together. If you can duplicate the vibration by varying the engine speed with the clutch disengaged and the car standing still, it would suggest an internal problem with the engine/transmission or a loose motor mount.


kmatt2
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Re: Vibration Question

Post by kmatt2 » Wed Apr 07, 2021 1:59 pm

Your vibration happens when the car is driving the engine, on the low to high gear change, on the high to low gear change, and going down hills. This could be caused by drive shaft fore & aft movement, the ring gear negative load pushes the pinion forward a little on the shift or down hill load. On a level road try slowing down more gradually to the low gear change. On the low to high up shift try accelerating a little slower. Make sure to retard the spark for the up shift and then advance the spark on acceleration. Does this change the vibration any ? If it does then the problem could be in the drive shaft. The modern type drive shaft spool, ( fun products type ) deals with movement better, but the stock T system works ok if it is in good condition.


Jerry VanOoteghem
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Re: Vibration Question

Post by Jerry VanOoteghem » Wed Apr 07, 2021 6:32 pm

Do you have the side bolts & wood blocks in your engine mounts? Many times, the lack of them can cause big vibrations.

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Barry Loucks
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Re: Vibration Question

Post by Barry Loucks » Wed Apr 07, 2021 8:22 pm

Bad U-joint? They cause vibration upon deceleration in a more modern conveyance?


John Dow
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Re: Vibration Question

Post by John Dow » Mon Nov 29, 2021 5:15 pm

Do I really need the vibration dampening mounting blocks? I'm installing a newly rebuilt engine & transmission which has had all components carefully balanced and the crank replaced with a Scat Crank. The blocks are a pain to install and I'd just like to omit them. Your thoughts please.


Jack Putnam, in Ohio
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Re: Vibration Question

Post by Jack Putnam, in Ohio » Mon Nov 29, 2021 5:28 pm

Put the blocks in. Henry did it for a reason. He could have save $$$. He didn't because they were needed.


speedytinc
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Re: Vibration Question

Post by speedytinc » Mon Nov 29, 2021 5:46 pm

Upper bolts go in first. I have been using longer bolts & adding a radius rod spring to tension, but not ridgidize the mount.
Block top notch clears the heads,
Trim the blocks enough to slide in easy. Consult T1 on tightening.(or not tight??)


Norman Kling
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Re: Vibration Question

Post by Norman Kling » Mon Nov 29, 2021 9:47 pm

Those blocks avoid side sway of the crankcase. The upper two bolts are tight which holds the ears to the frame, so any sway will work the metal and fatigue will set in breaking the ears off. The blocks will prevent this.
Norm


Norman Kling
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Re: Vibration Question

Post by Norman Kling » Mon Nov 29, 2021 9:49 pm

Have you compared this T to others. They all have some vibration when the engine is going slow. If you rev a bit more in low before you shift, does it still vibrate in high? I wish I could diagnose it in person, but hard to do so on line without experiencing personally.
Norm


MichaelPawelek
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Re: Vibration Question

Post by MichaelPawelek » Mon Nov 29, 2021 9:53 pm

All three Model T’s I have owned have had a vibration at a certain rpm range though I do not know exactly what rpm it is/was. It has never been bad and generally only noticed in “blurry” rear view mirrors. All three have had holes drilled in the flywheels for balance but no other parts were balanced in the rebuild process.

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Jugster
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Re: Vibration Question

Post by Jugster » Mon Nov 29, 2021 11:57 pm

Every Model T I've driven behaves that way. The car needs an intermediate gear between low and high, but of course doesn't have it. Make a habit of accelerating gently until you're out of that pesky vibration range.


DickC
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Re: Vibration Question

Post by DickC » Tue Nov 30, 2021 4:23 am

Experience tells me that you have a bad U-joint.


DickC
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Re: Vibration Question

Post by DickC » Thu Dec 02, 2021 3:33 am

I forgot to add in my response, please when you find the problem tell us what it is/was. We don't learn if we are not told. Thanks!!

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