Harmonic Vibration

[Frankenchevy]

Just got thru reading your post. Isn't the L31 a small block? The photo in post #69 shows a flex plate with a huge weight as seen on external balance 400 or 454 engines. Just a thought

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I dunno. If you look at post #64, it’s what summit lists for sbc with 1-piece rms. Weight looked the same as the one hays sent me as well, that I swapped it for. They could both have an incorrect catalog, I suppose.

 

[Poppy 87]

I'm using Tapatalk right now so I can't see the picture you referred. I still think that weight is huge! Perhaps search for an image of a GM flex plate for the L31?

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[Frankenchevy]

I'm using Tapatalk right now so I can't see the picture you referred. I still think that weight is huge! Perhaps search for an image of a GM flex plate for the L31?
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I looked at rock auto and it looks the same. if I’m not mistaken, it’s the same size as the one on my 327 that’s as smooth as a sewing machine. I’ll look in the morning, but I’m 99% positive.

 

[bucket]

All the later small blocks with a 1-piece rear seal had that big weight on the flexplate. It's also a smaller bolt pattern so they can't be mixed up with the earlier ones.

 

[Termite_Delight]

All the later small blocks with a 1-piece rear seal had that big weight on the flexplate. It's also a smaller bolt pattern so they can't be mixed up with the earlier ones.

4.3's use the same flexplate as well.

 

[gotyourgoat]

I put these American Racing wheels on because the powder coaters wanted just as much to powder coat my steelies. I’ll probably powder coat my steelies and put them back on when I get new tires because I like the look better.

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Have you tried swapping to this other set of wheels and seeing if the vibration changes?

 

[Frankenchevy]

The other tires are pretty old. I don’t really want to drive freeway speed on four old tires that have sat out in the sun/elements. Maybe I can get the steelies coated and mount up some new tires as an experiment.

From the couple of rotations and rebalances, the vibration seems to be coming from the same area. However, whenever I’ve had a tire balance issue, the vibe is a consistent cadence at a certain speed. This vibe comes in and out and will change cadence all while maintaining the same speed on the same bit of road. I’m not saying the tire/wheel balance isn’t a possibility, just that it doesn’t feel like any tire balance issue I’ve ever experienced.

 

[Frankenchevy]

The steels are hub centric and the ARs are light centric. That might make a difference, but tons of people are running ARs on squares...

 

[SquareRoot]

The other tires are pretty old. I don’t really want to drive freeway speed on four old tires that have sat out in the sun/elements. Maybe I can get the steelies coated and mount up some new tires as an experiment.

From the couple of rotations and rebalances, the vibration seems to be coming from the same area. However, whenever I’ve had a tire balance issue, the vibe is a consistent cadence at a certain speed. This vibe comes in and out and will change cadence all while maintaining the same speed on the same bit of road. I’m not saying the tire/wheel balance isn’t a possibility, just that it doesn’t feel like any tire balance issue I’ve ever experienced.

Exact same feeling mine has at about 55 and up. Please figure this out so I don't have to spend anymore money on mine.

 

[Frankenchevy]

Exact same feeling mine has at about 55 and up. Please figure this out so I don't have to spend anymore money on mine.

Lol, I’m on it!

Does yours have an NP208? I’m wondering about the chain tension...

@bucket , does the truck that you experienced this in have a 208?

 

[yevgenievich]

Mine has similar vibration with 241, which is similar to 208 Seems like transfer case is in common. Or it's something in the suspension

 

[SquareRoot]

Yep. 350/208, cucv axles

 

[Blue Ox]

My impression is tires. A small imbalance or eccentricity among the tires that are minor by themselves but go in and out of phase because of minor differences in tire diameter so they either cancel or harmonize to make the vibration randomly come and go.

Just a thought. Worth everything you paid for it.

 

[SquareRoot]

I'll be swapping the trans and t-case over the next few months. Out with the 400/208, in with the 4500/205. If that don't fix it then a new set of tires and wheels will follow. If that don't fix it well....I'm out of luck. Everything in the drivetrain has been replaced with new from bumper to bumper.

 

[Snoots]

Hey @Frankenchevy,

Do you notice this vibration at the same RPM when parked?
If only when driving, then after driving feel the hubs. If any hub feels hotter you likely have a bad bearing.
And, refresh my memory, what engine do you have?