I'm running a a833 Od in a 65 4dr Coronet. I've been fighting vibrations in the drive line ever since I did the swap. The drivrshaft has been back to the driveshaft guy once since he built it. I got rid of most of the vibration by replaceing the transmissin slip yoke but I'm still getting some high speed vibration, especially on deceleration, after winding it out.

How much slop should there be in the tailshaft bushing.....My trans guy was susposed to have changed it but it seems to be excessive to me.


Thanks Trysix

I think the fact that the vibes worsen on decel, points to an angularity problem between tranny, driveshaft, & rear axle. I read somewhere once, it is more important to have centerlines of trans and rear axle parallel, rather than have them pointing directly at each other.
Is the trans and driveshaft the only change made? How much can you move the slip yoke into the trans by disconnecting the d/shaft from the r. axle and pushing it forward?

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'66 Cuda 225/4spd
'66 Dart GT convertible 225/auto
'64 Dart GT 340/4spd

The slip-in yoke will have some "wiggle" to it. Is the trans yoke sticking out of the bushing more then 1 inch?

Here is a test you can try, load a bunch of heavy stuff in the trunk to flatten-out the springs, this will change the driveshaft angle and push the slip-yoke into the trans a bit more. See if that helps the vibration.
DD

I'll see if I can get car lifted up on the tires so that I can check alignment at ride level. I also can let some air out of the air shocks and load up the trunk. We have been having a lot of rain and bad weather, that's keeping the car in the garage, but I'll let you guys know when I get some results.

Thanks David/Trysix

I measured the amount of yoke extending beyond the tail shaft. ...(1.5 ")
The yoke has about 1.5" of spline free yoke ....with the amount hanging out of extension housing there is about 3" of spline in contact with the trans output shaft.
I let my air shocks down all the way which is equal to about 2 inches of body height. This put the yoke only about 1/4" father into the tail housing.
I drove it with the rear up and down and it made no difference in the vibration.
The driveshaft is almost in direct alignment with the transmission. I would be hard pressed to give you an angle but it is't much.
I would guess that 90 percent of the vibration is on deceleration at above 70 mph.



Thanks again, David/Trysix

This really sounds like a worn bushing or yoke.
Did the driveline shop balance the shaft with the slip yoke on the shaft?
You could try rotating the yoke on the u-joint 180 degrees.
The vibration could also be from a yoke that is a little to far out of the bushing, do you see any "raccoon tail" marks on the yoke surface?

Can you find a different driveshaft to swap-in and try?

DD

Thanks Again Doc,
Don't have another driveshaft....this was a custom built.I have doubts about my driveshaft people even though they have been in bussiness for many years. There are no balance weaghts on the shaft although they realigned it once.
I have since found out that most racers in the area use another shop that I didn't know existed. This shop is actually a big truck shop. My machinist recomended them and he runs a mid nine second camaro....so they will be on my option list. I have already ordered a new bushing and it'll be my first step.
Oh by the way I finally put a hard run on the new 8 3/4 posi with the 373 gear. My best time on the G Tech with the old rear was a 16.82 at 83.4 MPH . Tonights test was a 16.51 at 85.4 MPH. Some of the improvement might be cooler temperatures.


Trysix

As a consumer there are a few things you can check before you install the driveshaft. You can use a couple of v-blocks positioned at each end of the driveshaft on a relatively flat surface. I've used the trunk of a car. Then you take a magnetic base and a dial indicator and check the runout in several places along the d/s's length as you rotate the shaft by hand. I've gone one better, by making v-blocks out of sealed ball-brgs and some angle iron. Anyway, obviously the less runout the better. I'd say anything over .020" is too much and needs to be addressed one way or another.
If you want to straighten it yourself, it can be done with a good oxy-acetylene welder. Just crank the 'high side' up, use a medium tip, and heat it up. You'll see the indicator needle 'rise' as heat is applied. Then quickly remove heat and apply wet rags to quickly cool the metal back down. If properly done, the metal will shrink and actually reduce the amount of runout. It's trial and error, because there are alot of variables. This may have to be done in several locations, depending on the layout of the bend(s). This only deals with bends in the shaft, reducing runout will improve balance, all other things being equal. But final dynamic balance is another animal.
Of course, the best way, is to do all this in a lathe, with the shaft between centers, but not everyone has access to a lathe.

_________________
'66 Cuda 225/4spd
'66 Dart GT convertible 225/auto
'64 Dart GT 340/4spd

Thanks Bud,

It may be a while before I dig into this problem again..waiting for parts coming by slow boat. I'll try to remember to update you and Doc.


Trysix

Finally got the new tail shaft bushing installed ,it didn't help anything. I think I need new trans slip yoke. Anyway I have good news.
None of the driveshaft shops in my area will balance a shaft, they rely on alignment and correct runout and evidently in most cases that's good enough.....not for me.
I ran across an old Hot Rod article in a driveline and chassis publication that I hadn't looked at in years. It had a an article on how to balance a driveshaft on the car. You put the car on stands with the rear end up in the normal position. Run up to about 45 MPH in 3rd gear and mark the high(heavy) side of the shaft with chalk. Ease the chalk up to the spinning shaft (just behind the frnt Ujoint) until it just contacts the shaft. Then put two worm/screw type radiator clamps , side -by -side, 180 deg. from these marks. Run the car while stopping and moving the worms away from one another at about 1/16" intervals, until the least vibration is felt.

Mine took about ten tries to get it right but wow about 90 % of my vibration is gone. A lot of off and on up and down effort....but it's worth it.

You guys should put this one back into the old memory banks.It works.

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65 Coronet 4dr
Always being Modified

This happened many years ago in Seattle(Ballard area). Evidentally, this guy must have had a problem with his driveshaft. He had his car parked in an empty parking lot between a Schucks Auto Parts and a gas station. He had jacked the rear of his car up with a bumper jack, and had crawled underneath it to dink with it while the engine was running, tranny in gear. When the guy came in early the next morning to open up the gas station, he noticed this car up in the air with its engine running and rear tires spinning. He went over to investigate and found this guy dead underneath it in a pool of blood. There were no witnesses, but the police surmised that his long hair had gotten caught in the spinning drivehaft, dragged him into it, knocked him out, and scalped him. He bled to death.
So please be especially careful if you try to diagnose a spinning driveshaft.

_________________
'66 Cuda 225/4spd
'66 Dart GT convertible 225/auto
'64 Dart GT 340/4spd

Good job on the driveshaft rebalance job, sounds like you found a pretty good weight combo to stop the vibration.

This is a good reminder about how a 'do it yourselfer" can fix more stuff then you would think.
I recently did a "trial & error" rebalance job on a friend's 360 SB while we were doing a clutch & tranny swap. I noticed the engine vibrated and that the flywheel was not an externally balanced 360 unit, so we got some longer grade 8 pressure plate bolts and stacked some extra weight (thick wall washers) onto the assembly. Our first test made the vibration worse so we moved the weight to the opposite side and things got much better. Took one of the 3 weight stacks off and better still. We stopped there with about an 80% improvement, we could have spent all night going after the rest of the shake but had other stuff to finish-up.

I have used the same "hit & miss" rebalancing on wheels, I paint a few test weights and try them in different spots to see if I can find a "sweet spot". Be sure to mark the places you have tried the weight, as you move them. I find a tire / wheel can be in perfect balance but the brake hub / rotor it mounts to may be off weight.

This type of job takes some time but it does work and always be super careful if you are going to spin the part and watch it with the car in the air.
DD

Once, I had a 2 1/2 ton floor jack blow the seals (without warning) the car went to the ground fast.....I wasn't underneath of course.
For this job, I used four hvy. duty. jack stands and a floor jack for added insurance.....shook the car from different angles to make sure it was solid.

Point well taken.

Thanks again guys,
Trysix

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65 Coronet 4dr
Always being Modified