Aluminum driveshaft installed and now have a new problem.

[RECHRGD]

Some of you know that I have been battling a driveline vibration for years since installing a Gear Venders OD.  I narrowed it down to having to balance the driveshaft while on the car to get the smoothest operation possible.  I got it to where it was livable, but still had a little vib between 60 &70mph.  This year I decided to bite the bullet and get an aluminum driveshaft and that with less rotating mass, life would once again be good.  Took the car out for it's first drive of the season today with high expectations.  When first pulling out into the roadway I felt a little wobble from the rear but just figured it was something in the road.  I drove at highway speeds and it seemed that the vibration was now gone except for maybe a little around 75 or so.  I accelerated to over 100 at part throttle and all seemed pretty smooth.  So at this point I'm pretty happy and decide to get a little more frisky with the car.  I accelerated from 50 to 70, fairy hard but not full throttle, and felt more driveline vibration.  Not happy!  Came to a stop light and when leaving felt the wobble again.  Not happy!  I then pulled into a weigh station area that was empty to try a hard launch, but not enough to spin the tires.  I gave it about 3/4 throttle from a stop and I thought the rear end had come loose.  Really not happy!  It felt like I would imagine a car with bad wheel hop would feel like.  So nothing is different from when I put the car away last fall except for the lighter driveshaft.  The one thing I never liked, was the pinion angle I ended up with after the GV install.  I was unable to get a nose down angle on the pig and had to settle for a nose up angle.  It's been that way for years with no problem and plenty of full throttle blasts.  Could the lighter DS now have caused the pig up angle to be a problem?  Any ideas?  Unhappy Bob......

[firefighter3931]

Bob, i'm willing to bet that pinion angle is your problem. 

The fact that vibration increases under hard acceleration leads me to this conclusion. When a car is launched hard the pinion will rotate up towards the floorpan...the harder it launches, the more it rotates. 

You really should have 2* nose down of pinion angle with a factory style XHD spring....more if you're running a Super stock leaf pack.


Ron

[RECHRGD]

Thanks Ron.  It just seems strange that just a little less weight on the DS would now make a problem out of what was't a problem for years.  The problem with the gear vendors, is that it mounts at the end of the tail piece off the tranny and prevents the tinny from being adjusted up at all.  Maybe some GV owners can chime in and I can see what they've done.  In the meantime I'll go back and trailer the car home so I can use the lift in the shop to try and figure this thing out.  It's a real pain living off a gravel country road when you're into cars.....

[cdr]

also,if you have ubolts on the rear ujoint it is easy to get them to tight & it will make the joint bind up,you should use locktite & get them snug,if you have straps disregard.

[RECHRGD]

I do have the u-bolts.  Do you know what they should be torqued at?

[BSB67]

I do have the u-bolts.  Do you know what they should be torqued at?

Did you always have u bolts?  What kind?

[RECHRGD]

I do have the u-bolts.  Do you know what they should be torqued at?

Did you always have u bolts?  What kind?

Yes, I've had them from probably '99, but have never known how tight they should be.  I got them from Year One.  I know that when I was taking off the steel DS I found a couple of the nuts to be loose on the u-bolt, so I'm sure I tightened them more than before when installing the aluminum DS......

[cdr]

i tighten them just enough to flatten the lock washer & lots of blue locktite on threads.

[cdr]

i just put my alum drive shaft in,i think i am going to go with lock nuts.

[firefighter3931]

i tighten them just enough to flatten the lock washer & lots of blue locktite on threads.

Same here...but i use Nylock nuts. Tighten until the lock washer goes flat and call it good. Haven't had any loosen off yet. 

Ron

[RECHRGD]

Got the car back home and up on the lift.  The u-bolts were not really all that tight on the u-joint and it looks and feels fine.  The nice new aluminum yoke on the DS took a beating though on my launch gone bad.  It should be OK, just need to file off some rough edges.  So, it's got to be the pinion angle.  To get to a 2* down angle on the pig, as Ron suggests, I will need to get to a 2* up angle on the tranny tailpiece.  Doing that will raise the Gear Vendors unit up at least an 1 1/2".  To make that happen I will have to take off the GV unit and beat the heck out of the tunnel area of the floor to make the room.  Maybe I'll start another thread to pull in some of the guys that are running the GV's to see what they've done.

[cdr]

you need to put shims in the rear end.

http://chucker54.stores.yahoo.net/noname45.html

[cdr]

[RECHRGD]

Thanks,  I've got plenty of shims from fighting this battle previously.  The problem comes in when trying to keep the tailpiece and pig on parallel but opposite angles, as recommended.....

[cdr]

 put an adjustable pinion snubber or some caltracs to get rid of the spring wrap up you are having.

[Sublime/Sixpack]

The correct wedges under the rear spring perches should give you the 2 degrees down of the pinion in relation to the trans. output shaft. That's what you're after right?

[ottawamerc]

Ok so after a bunch of research and trial and error on this that I did last year this is what I came out with: the pinion angle needs to be equal and opposite to the tranny output right! so lets say your GV output is at 0*+1* up then your pinion needs to be 0*-2* down. (more down because of spring deflection). So if your GV fits where it is now find out what your degree is + or - then shim your pinion. I could be 100% wrong (typically are)    Also remember that the longitudinal angle must be equal, thats whats was eventually wrong with mine. A simple string pulled tight thru the motor/ transmission and pinion center line will confirm this  

Scott  

[RECHRGD]

The correct wedges under the rear spring perches should give you the 2 degrees down of the pinion in relation to the trans. output shaft. That's what you're after right?

Correct, but when the current output shaft is at 5* down from front to back the amount of change at the pig is beyond reasonable.  I'm no expert, but I'm basing my thoughts on what I've gathered on threads here and on google....,

[Bobs69]

Has the drive shaft been high speed balanced?  Gear vendors says you must do this.  If not, too bad.  Dodges don't have much of an angle up and down for the drive shaft according to them, that's why the engine is set back on one side more then the other (to make up for this).

[RECHRGD]

Has the drive shaft been high speed balanced?  Gear vendors says you must do this.  If not, too bad.  Dodges don't have much of an angle up and down for the drive shaft according to them, that's why the engine is set back on one side more then the other (to make up for this).

The driveshaft balance does not come into play with the issue I'm having.  But Wow! Now you throwing in a side to side angle into the equation.  I'm going to go pour a scotch.........

[b5blue]

Just a shot in the dark here but the lighter DS would reduce the at speed vibration but possibly offer less dead weight against axle windup?  Could lowering height of the shackles or raising the front eye bolt holes somehow correct pinion angle just enough to stop bind up?     

[RECHRGD]

Just a shot in the dark here but the lighter DS would reduce the at speed vibration but possibly offer less dead weight against axle windup?  Could lowering height of the shackles or raising the front eye bolt holes somehow correct pinion angle just enough to stop bind up?     

Maybe, I'll be looking at any and all solutions.  This was going to be my final fix after years of living with a less than perfect set-up.  I feel like just taking off the GV and using it for target practice.....

[firefighter3931]

The correct wedges under the rear spring perches should give you the 2 degrees down of the pinion in relation to the trans. output shaft. That's what you're after right?

Correct, but when the current output shaft is at 5* down from front to back the amount of change at the pig is beyond reasonable.  I'm no expert, but I'm basing my thoughts on what I've gathered on threads here and on google....,

Bob, if the output on the trans/GV is 5* down then you need to get the pinion at 7* nose down to achieve the desired 2* nose down result. 

Shim stacking may be difficult depending on where it is now ? 

There are two options the way i see it :

(1) Have custom shims/blocks made to correct the pinion angle. You will need longer u-bolts to make this work

(2) Cut the spring perches off the axle tubes and have them rewelded with the proper pinion angle adjusted into the axle housing

I'd be interested to see where your current pinion angle is at on the differential. 

If as you stated previously the pinion is pointed up...we know that the pinion angle is waaaay off and needs correction. 



Ron

[RECHRGD]

The correct wedges under the rear spring perches should give you the 2 degrees down of the pinion in relation to the trans. output shaft. That's what you're after right?

Correct, but when the current output shaft is at 5* down from front to back the amount of change at the pig is beyond reasonable.  I'm no expert, but I'm basing my thoughts on what I've gathered on threads here and on google....,

Bob, if the output on the trans/GV is 5* down then you need to get the pinion at 7* nose down to achieve the desired 2* nose down result. 

Shim stacking may be difficult depending on where it is now ? 

There are two options the way i see it :

(1) Have custom shims/blocks made to correct the pinion angle. You will need longer u-bolts to make this work

(2) Cut the spring perches off the axle tubes and have them rewelded with the proper pinion angle adjusted into the axle housing

I'd be interested to see where your current pinion angle is at on the differential. 

If as you stated previously the pinion is pointed up...we know that the pinion angle is waaaay off and needs correction. 



Ron

Thanks Ron.  I'm having second thoughts on my measurement on the tailpiece.  I got the 5* down from the oil pan rail.  But I was just out in the shop and took a vertical measurement at the end of the tailpiece and it read 90*.  If that's the case, then things are much more workable.....

[b5blue]

Just a shot in the dark here but the lighter DS would reduce the at speed vibration but possibly offer less dead weight against axle windup?  Could lowering height of the shackles or raising the front eye bolt holes somehow correct pinion angle just enough to stop bind up?     

Maybe, I'll be looking at any and all solutions.  This was going to be my final fix after years of living with a less than perfect set-up.  I feel like just taking off the GV and using it for target practice.....

I've followed your subject a long time and you have me never wanting to add G.V. at time.