MTFCA Forum

My 1927 T roadster pickup has a 1920 engine/transmission and at low to moderate RPMs it is smooth, but at high RPMs it starts to have lots of vibration under no load or running down the road. What would be the first suspect? I thought maybe the rear main bearing may be worn so I pulled the oil pan. I see no way with out my little 2 year old grandsons hands and arms to get to the rear main. Also, nun of the rod caps had dippers on them. Should they? The connecting rods all looked like they had plenty of oil all the way up into the piston skirts. Phillip

Phillip I would first start looking at ignition. Plug breakdown at higher RPM's are common. Check your coils too. I had one that
drove me nuts, it was a bad plug. Sometimes loose connections at the timer, etc. Did this just start acting up?

All the Best,

Hank

Hank,
Had the coils rebuilt and adjusted by The Coil Doctor, new plugs and new New Day timer. Cleaned and tightened the plug wires and the wire under the coil box. Did not think about checking to see if missing at higher RPM. Got the truck last December and it was doing it then. Will do the ole screwdriver test on the plugs tomorrow. Thanks.
Do you have any kinfolks from Mississippi or Alabama?
Phillip

How high of RPM/Mph are you talking ?
A stock T gearing, non counterbalanced crank is going to vibrate some, say over 40mph...just sayin.

I have been dealing with the same thing for a couple of years now. My engine and trans. have been rebuilt with scat crank and all the good stuff and balanced. Same thing though smooth up to a about 38 mph then a vibration starts. I have just learned about a torque tube bushing right behind the u-joint that is a common wear item according to the model T service manual. I will be pulling my drive shaft out tomorrow, I hope, and checking that bushing and u-joint.

I also noticed that after I grease that bushing the vibration is not as bad. You may want to try that.

Phillip process of elimination for sure.

Could very well be a bushing as Scott talked about.

Just trying to assist, as others have said, some do vibrate but should not rattle the teeth out of your head. Had one have a slight leak blowing between # 1 and # 2 cylinder, no popping or spudering but had vibration.

Brought the cylinders to top dead center and applied compressed air to that cylinder checking the one next to it. It told on itself.

Hope you find it,

Hank

A good friend found his driveshaft was out of balance.....not bent or out of alignment. A new drive shaft from Chaffins corrected the problem. His original drive shaft did not seem to be machined the complete length. Some may find this hard to believe.....but it is true! Nothing else was changed......just the drive shaft. Something to consider.


Les

Phillip, not clear from your original post, this vibration at high rpm while car is in motion, is it only when in motion or also when the car is not moving?

Do your engine pan arms have wood blocks? You can get a lot of vibration if they are missing.

One way to determine whether the vibration is caused by misfiring is to note whether it occurs when pulling or while running at constant speed or when decelerating. It takes a hotter spark to ignite fuel under high compression and the compression is raised when you open the throttle. Sometimes a weak spark or a weak spark plug will misfire when pulling but continue to spark at constant speed such as running on level ground after you reach cruising speed. When it is closed, you are running on lower compression. A knock at constant speed or when closing the throttle just slightly, is usually caused by a loose connecting rod bearing. It would not be a "vibration" but a rattling sound.
Norm

I put a tack and the vibration is slight at idle (300-400 RPM) and get pretty bad getting above 700 or so. I shorted out each plug at about 700 RPMs. I did not try getting above 800 RPMs (if my tack is right) because of the bad vibration. Would miss when plug shorted out but vibration did not lessen. I am thinking magneto or something in the transmission. I will use my GPS to get MPH when the vibration starts. I think is lessens when under load. Any thoughts on the rod caps not having dippers?

Ts weren't made with rod dippers. They're not a bad idea but it depends on the dipper. I've seen some pressed-metal dippers fail.

Yeah, shouldn't be shaking at that rpm.
Don't recall you saying if there's any noise.
And I believe you said it is there while driving or sitting still. If so, I would be leaning towards the flywheel or something related.

You say "under no load", I assume that means your parked, and just revving the engine. If that is true, the issue is not with the 4th main nor the drive shaft bushings, as no power is being transmitted, past the clutch.

I suspect a transmission issue, hard to say what. But I suspect a loose part, or a highly out of balanced transmission.

Mark Nunn wrote: ↑

Tue Apr 09, 2019 8:32 am

Do your engine pan arms have wood blocks? You can get a lot of vibration if they are missing.

Phillip,

Answer Mark's question, it's a good one.



Also, try running without a fan belt. Fans can be grossly out of balance and make lots of vibration. An often overlooked source!

No wood blocks for engine mounts. Some really great suggestions. Look like it is now down to flywheel or transmission.

Phillip

Phillip wrote: ↑

Wed Apr 10, 2019 1:18 pm

No wood blocks for engine mounts. Some really great suggestions. Look like it is now down to flywheel or transmission.

Phillip

Try putting in the wood blocks and side bolts. It has ceased vibration in several cases that I'm aware of. At the very least, it's an easy thing to try. Do you know what wood blocks I'm referring to?

I do not know about the blocks you are referring to.
The motor mounts I saw are one in the front under the hand crank and one on each side. Driver side by the starter. Should there be wood blocks somewhere on this.

Yes, wood blocks should be in the frame cavity at the rear pan mounting brackets. Cannot tell from your picture taken at that angle, yours might be there. There should also be a bolt going through the side of the pan ear through the wood blocks horizontally, again, cannot see from those pictures if you have it or not.

From the pictures you posted I would rule out the left ear and front motor mount as being a cause of excessive vibration.