Have you verified the driveshaft ends are aligned properly with the shaft and each other?

You might consider a larger diameter driveshaft.

We've been trying to find a similar vibration in my dad's car for about a year. Last week it was making a horrible broken rear end sound after he won the race lol. Pulled the 3rd member out and the pinion gear is about to explode, every tooth is chipped,cracked and coming apart. Don't know if that's the vibration yet, but hoping so. These mystery vibrations are pain in the ass to find. Good luck

quote:

Originally posted by Brktracer:
Have you verified the driveshaft ends are aligned properly with the shaft and each other?

You might consider a larger diameter driveshaft.

They have been checked and are correct. I had a new 1350 end installed 2 weeks ago on the trans side to match new Strange hardened yoke. (I didn't want to use an adapter u-joint) I also verified the rear u-joint has no slop side to side and is captured properly by the Moroso u-joint caps. It is a 3" or 3.5" (I don't remember)

engine and trans mounted solid ?

Im going through the same thing..1965 Impala been a race cars since the early 70s..The driveshaft is 61 inches long center to center..I had the driveshaft shortened a half inch as i first thought it was to long..Went to the track and serious vibrating around 5500 rpm...Had the driveshaft rebalanced put ride height on a lift (stand under rear to get to ride height) and still vibrated..Changed the 5.57 rear gear to a 5.14 as it had shook a pinion shim out..Then had new driveshaft made (went to 3.5 diameter instead of 3 inch) and 4600-5500 it shakes like crazy..The driveshaft looks to be whipping when videoing it..Kinda lost...
Mark Williams and other "race" driveshaft companies say that the only shaft that they can guarantee that wont shake is a carbon fiber shaft due to its length and it spinning outside the "critical speed"....Thinking about doing a aluminum driveshaft being they are much thicker...I could have almost afforded the carbon driveshaft from what i have spent already lol..

Tom: I'm sure you have run across this (MW tech article), but just in case you haven't maybe it will help.

At the point you're at, it would be real interesting to try a different center section if you have a 9" or remove the carrier if a Dana or 12 bolt and run things up to speed with only the driveshaft and pinion to see if it vibrates. Maybe those are ways to narrow down the problem?

At a minimum, maybe make iterative steps to narrow down the problem area. For example:
1. remove rear wheels and run up to speed on stands to see if it vibrates.
2. remove axles and run up to speed
3. remove carrier and run up to speed
4. etc.

Trying to think outside the box...

quote:

Originally posted by 68TSCAMARO:
engine and trans mounted solid ?

It vibrated with Moroso mounts and with the new engine and mid-plate.

quote:

Originally posted by Brktracer:
Tom: I'm sure you have run across this (MW tech article), but just in case you haven't maybe it will help.

At the point you're at, it would be real interesting to try a different center section if you have a 9" or remove the carrier if a Dana or 12 bolt and run things up to speed with only the driveshaft and pinion to see if it vibrates. Maybe those are ways to narrow down the problem?

At a minimum, maybe make iterative steps to narrow down the problem area. For example:
1. remove rear wheels and run up to speed on stands to see if it vibrates.
2. remove axles and run up to speed
3. remove carrier and run up to speed
4. etc.

Trying to think outside the box...

Re-scaled the car over the winter and changed the pinion angle. (ladder bar car) The engine is at 0, the pinion is down 2 degrees.

Borrowing a set of rear wheels for this weekend.

have you tried increasing the driveline angle

Tom, I have a go-pro mount to go under your car that will shoot the shaft, pinion etc. if you wanna try that.

quote:

Originally posted by 68TSCAMARO:
have you tried increasing the driveline angle

Yes, had up to 5 degrees with the bars, 7 when I ran leaf springs on the car.

quote:

Originally posted by Ron Gusack:
Tom, I have a go-pro mount to go under your car that will shoot the shaft, pinion etc. if you wanna try that.

If the new borrowed wheels don't fix it, I will take you up on this offer.

Is it during all of high gear? This an 1/8 or 1/4 mile car?

I played with pinion angle on my ladder bad setup once, boy did I screw that up! I made a SEVERE vibration around the 1000ft to the start of the traps, then went-away. Would come back on decel for a bit.

I changed it again, was perfect on the track, then BAD going to/from the lanes!

I finally learned the proper way to do it, been 100% perfect ever since!

As many say, take the driveshaft out and stick it in your trailer when you do this, all it will do is cause you confusion!

Angle finder on the balancer or lower pulley, then on the flats of the pinion, see what the difference is.

In my car the engine/trans points down, some people are lucky and they are flat. I could not raise my trans up anymore, too close to the tunnel, and I couldn't lower my engine (easily), so I worked around it all.

My pinion is about 1* UP to get me 3* to 4* negative overall. When I set the pinion to -5* thinking this is what I needed, I about shook the fillings out of my teeth!

You are taking driveshaft angle and pinion angle into account when calculating the actual driveline angle right ?

So I borrowed my wheels back to test with. I had lent to my buddy to use. Same old vibration with different wheels and tires.

Only thing left that hasn't been rebuilt is the rear with 25 year old spool and axles. I pulled the rear housing, we're going to shorten it 1" on each side and stuff it with new bearings and such.

Going to re-do the front end alignment over the winter, re-scale and set up the suspension on the car, possibly put my bigger engine in it too.

If that doesn't fix it, I'll strip it and throw it out in the woods behind the house to make a cat house out of it.

I would suggest a new driveshaft in a 3.5" dia from a company that builds race specific shafts. I willing to bet the 3" shaft is to small and is flexing in the middle for a short time.

While you have the rear end apart I would check the side runout on the spool.

quote:

Originally posted by Crisco:
I would suggest a new driveshaft in a 3.5" dia from a company that builds race specific shafts. I willing to bet the 3" shaft is to small and is flexing in the middle for a short time.

I would have to re-mount and lower the engine for it to fit. I have the back of the trans as high as it will go to level the engine. Not much clearance for a larger driveshaft.

quote:

Originally posted by NFC:
While you have the rear end apart I would check the side runout on the spool.

Good advice, was on the list of things to check. Going to put the axles on the lathe and check them too while its apart. I checked them in the car as best I could but it doesn't hurt to double, triple check things.

Hey Tom, didn't you just win "King of the Track" at Mason Dixon with that lucky vibration? leave it in there!!....Just kidding, Congrats!!