I'm not done yet with buck-shotting my high speed vibrations (60-70 and then over 80) issue with my 79 blue Calais. I get a fine vibration sometimes yes, sometimes no at these speeds. It's annoying in comparing the ride to my 79 Brougham. Granted the Brougham has 61,xxx miles on it and the Calais has (probably) cracked the 200,000 original miles barrier, I still think I can do better. Here's what's been done:

* Rebuilt Transmission - the prior 200R4 was tired after 22 years and had a destroyed tail-shaft. I now have a superbly rebuilt 200R4 in there thanks to leads from C/O to go with Extreme Automatics in Ohio. Great people, great unit.
* New Yukon pinion yoke. (Also, NO more differential leaks, the new yoke and new cover gasket have sealed that up nicely.)
* Tires are ok, new Hankooks.

Next Stop: I found a shop here in SC that will re-balance my driveshaft and if it's no good, build me another one.

If that doesn't help I guess I will just have to live with it, this is a high mileage car and perhaps this just comes with the turf. The front end on this car has been completely rebuilt, so I'm hoping I can really rule that out as the cause.

 

Years ago I changed out the universal joints on my ‘80 and got a vibration as a result. More than likely I didn’t clock the yoke to its original orientation with the shaft. I had a local shop balance the driveshaft and that settled the issue. Hopefully it takes care of your vibration too!

 

I would swap out the engine mounts if they are original. These motors move around way more than people realize, which can result in odd driveline angles or some contact between the body and driveline.

 

Vibration Analyzers exist that attach to the axle or whatever. I have seen at least one video on YouTube and all the guess work is eliminated. Finding a shop who has a good one and knows how to use it would be key. Bernie Thompson on YouTube is an expert:

 

All good info, thanx. The motor mounts were changed when the 260 was rebuilt in 1992, but agreed, that in and of itself was a long, long time ago.

 

I've had shops not balance tires correctly try a differnt shop..

also you didn't say if you have stock wheels/tire size.. Custom aluminum wheels are some times hard to balance correctly..

 

I've seen collapsed mounts (engine, trans, body, subframe, even exhaust mounts) cause a vibration, or maybe more properly "feel" like a vibration when they lose their ability to dampen the normal engine or chassis noise. I once had a improperly installed tailpipe hanger give me fits. The steering wheel had a slight vibration that drove me nuts. Turns out the tailpipe hanger failed and was metal on metal, that was just enough to put a harmonic through the chassis...

 

Try reclocking the converter 120 degrees. Try flipping the driveshaft 180 degrees. What kind of wheels are on the car? If they are stamped steel, make sure the tire shop uses the lug centric adapters instead of the cone adapters. Check the engine and transmission mounts. If they are oily or soft replace them.

 

Thanks all, I will give this all a try. I have the factory SSIII wheels with 205-75-14's on the car.

 

I didn't see where you changed the U joints. Quite often a vibration us a failing U joint. Make sure the Yoke wasn't overtightened on the differental, should turn very easily, with little resistance. Another thing to check is the tire balance, maybe lost a weight or weren't balanced correctly?

 

I've been advised by a (somewhat) local shop that my driveshaft is out of balance and also is warped but repairable.

And from the Overkill Department, not only am I getting it fixed, equipped with NOS universals, but I also put in an order for an aluminum driveshaft for the car. All should be ready for me to pick up today. I decided to get an alum shaft for the car since one day, maybe soon, I will be getting a 350 for this car so I figure what the heck. For the time being though, I'm sure it will mate up well with my rebuilt 200R4 purchased from Extreme Automatics earlier this year, my 3:08 gears, and my fire breathing 105 hp 260 wheezer.

 

Glad you got the vibration issue figured out, and a new aluminum driveshaft is a nice upgrade!

So, what’s the plans on the soon to be 350 powered Calais? Going stock rebuild or stock appearing modified, or…….?

Don’t be too hard on the little 260, they were far better than some of the other options of the day. The 260 that came in my ‘80 was rock solid reliable and would take the highways at 75-80 just fine. My 350 upgrade was a result of the guys I hung around with that drove Chevelles and Novas! lol

 

After picking up both driveshafts yesterday I noted the alum shaft is a good inch thicker or so. This may be too wide for my existing exhaust pipe but we'll see. If it is I will just hold it aside for when I install a true dual exhaust equipped with the crossmember that will enable the pipes to be tucked under the car better.

I would like to look into a stock 1979 350 R motor built to 79 H/O specs. I have alot of the parts already so this would be the way to go.

 

I actually had 2.5" dual exhaust with a compact X pipe routed under the single hump on my 88 Cutlass. The pipes would be close with a bigger than the factory match stick 7.5" driveshaft. If you get a 79 350, the heads should be crack checked. There were cracks causing noise on a 79 350's 3A heads from Delta 88 on the G body site. Build a 76 350 and pretend it is a 79 350🤫.

 

You may notice with the aluminum shaft that your car picks up some acceleration due to all the drag you're eliminating from the stock one.

I swapped out to an aluminum shaft on my '72 and it was noticeable right from the first pull.

 

A 76 350 painted blue, good concept indeed.........

ANY acceleration pick-up coming out of my 260 wheezer would be greatly well received. I', going to make the attempt on this install tomorrow morning. One way or another, by this time tomorrow the car will be back on the road.

 

Aluminum driveshaft is in, no issues at all with clearances, and no more high speed (up to 72) vibrations, looks like we have a winner. Carolina Driveline comes through with a great driveshaft build!

 

Good deal, Gene, glad that worked out! 👍

 

Thanks, it's been a bit of a long road with this car, in paying attention to the others, this one was not being taken care of as it should have been. Not so anymore, it's back up to snuff and is ready to drive anywhere.