VIBRATION!!! I FOUND IT!!!!!!

[RECHRGD]

Yep, it's gonna be fun driving at 175mph all the time.  Now I've just gotta get some brakes that will stop it in time so as not to run any red lights.

[Cooter]

Great news, Bob. So, now I'm curious how this can happen. Is the balancing method those guys used incorrect? Is it balanced until installed?

 think because the OD trans  turns the drive shaft much faster than it would be with a normal trans , so needs to be more accurately balanced

The overdrive make it spin slower, or so I thought.

No, the driveshaft as stated above spins EXACTLY the same RPM's as before, it's juts doing it at a MUCH higher speed now in over drive....

@ 60 MPH, with 3:23 gears, and a 727 in High gear, the engine RPM is something like 2600....
In OVERDRIVE, the SAME Combination is spinning the engine at 2600 @ 88 MPH now @ .68 Overdriven ratio...


So, an overdrive doesn't slow down the speed of the driveshaft, it slows down the DRIVE gear coming into the Transmission...EXample: Big gear driving a little gear...2.76:1 gears...

Little gear driving a big gear =4.88:1 Gears....

Only the Drive unit (Engine) Rpm is reduced...

[FastbackJon]

Good news Bob. I had a similar vibration felt in my seat in my driveshaft of the red '66 Charger at 70 mph or 3,000 RPM in 3rd gear (727), which is about the worst place to have it when you're on the freeway where the limit is 70. I took it to Watts downtown and they got most of it out. My stock driveshaft (no GV) was slightly curved. How that happens, I don't know.

[FJMG]

GV says that it is very common to have to "fine tune" the driveshaft after it is installed.  Why?  I can't answer that one.  It just seems to me that I had to unbalance it to make it smooth out.

Glad you solved it but let me get this straight  , you took a perfectly balanced D/S and put it out of balance to reduce the vibration?  Sounds like the 440 6-pak crank with external balance to compensate for the rods. Cheaper to balance externally than redesign the entire rotating assembly. I guess cheaper to play with D/S than to build a perfectly balance G/V unit in the first place?

[ottawamerc]

Hey not to bring up an old thread but I was wondering did any of your guys cars have any transmission rear seals leak? at the slip yoke. I've installed 2 new seals and had the shop install a new tail shaft bushing but yet I still have the vibration issue too. I have tried many of the solutions mentioned in this thread except the pipe clamps. RECHRGED do you still have the clamps on and are you still vibration free?

Scott

[mauve66]

he never did post pics of the installation with the clamps............. and he has a LIFT......................

[RECHRGD]

Once I found the sweet spots with the clamps, dimes and pennies, I marked the spots and cut the worm gear off the clamps.  I took the worm gear and loose change required at the front and back of the DS to my driveline guy.  He weighed them and welded the appropriate weights at the areas I marked on the DS.  The result has been a 90% improvement.  I can still feel it a little but mostly only slowly accelerating or going up hill.  I've been able to live with it at this level, I'm thinking of going to an aluminum DS.  I'm thinking that the less rotating mass should take care of it once and for all....

[flyinlow]

 

[ottawamerc]

Ya but did you have oil leaks around your seal during the issue? mines leaking again

Scott

[RECHRGD]

Ya but did you have oil leaks around your seal during the issue? mines leaking again

Scott

No leaks.......

[elacruze]

I think I may have mentioned this somewhere else, but we had a race car a few years ago with a driveline vibration. Balancing the shaft etc. did no good. Eventually, we discovered that the rear yoke was so far out of balance that it shook the whole assembly-of course, that piece wasn't balanced with the rest of it. It was a high-quality brand name piece, but we found it took about 4 ounces of grinding to balance it. You wouldn't have thought it could be so bad by looking at it. Also, don't discount the possibility that the u-joint bores may not be perfectly aligned with the spline axis-if you have your shaft balanced, have them put a dial indicator on the tube to see how far out of center it may be.

Driveshaft dynamics are very complicated.

[ws23rt]

GV says that it is very common to have to "fine tune" the driveshaft after it is installed.  Why?  I can't answer that one.  It just seems to me that I had to unbalance it to make it smooth out.

Glad you solved it but let me get this straight  , you took a perfectly balanced D/S and put it out of balance to reduce the vibration?  Sounds like the 440 6-pak crank with external balance to compensate for the rods. Cheaper to balance externally than redesign the entire rotating assembly. I guess cheaper to play with D/S than to build a perfectly balance G/V unit in the first place?

Good news after all this time to get it running smooth but I agree that the G/V unit must have something inside out of balance or off axis. The spec. of the internal parts may meet design but balance could have been something not called out on a fab drawing.

The little experience I've had with vibration analysis tells me the unit can be spun up to various speeds and analysis equipment can locate and identify type of vibriation

Being back on the road again is great but the mystery remains.

[elacruze]

Many with GV overdrive have a vibration in overdrive. I have a very slight (not worth chasing) 30-50mph vibration in 1:1 which goes away entirely in overdrive. <shrug>

[MSRacing89]

Many with GV overdrive have a vibration in overdrive. I have a very slight (not worth chasing) 30-50mph vibration in 1:1 which goes away entirely in overdrive. <shrug>

I have one also with my GV unit.  Lots of work with the angles to make it tolerable.  There is still a slight hum between 67-70 mph.  We have all deducted here that the short driveshaft in combination with the extra weight hanging just does not make for an easy remedy. 

I would say to anyone, spend the extra money on an aluminum or carbon fiber shaft.

[MrSnicks]

Why not go super-light and get a carbon fiber driveshaft?

Patrick