Hope I can find some advice here to steer me in the right direction.
1970 Challenger, everything is either new or rebuilt. 340 833OD, I have a new strange 60 rear end and driveshaft.
I get a horrible shudder/vibration just as I let off on the gas. Happens mostly in 4th gear on the highway. Happens in other gears too but definetly most noticeable in 4th. If Im cruising at 70mph, pull out to pass someone touch about 80mph then let off the throttle I get this vibration. It almost sounds like the trans is "freewheeling" if that makes sense, resonates throughout the whole car with a buzzing vibration. But if I keep on the gas just a touch it will not do it. Also if I depress the clutch during this, it still occurs and no change is noticed. Im going to pull/inspect the driveshaft and u-joint stomorrow, otherwise What do I look for next? Driveline angles?? Car shifts fine otherwise. Thanks for the help!

When you pull the driveshaft check how much end play you have into the trans. EDIT check angles too

U-joint or missing clip on rear joint?

check your ex. pipes,i had the same prob. it was the exaust.

Make sure your pinion nut is tight.

Pretty sure it is the pinion angle, use some wedges to change it and see if they fix the vibs. If they do I would suggest rewelding the spring perches to get you the right pinion angle.

Ive already got a 3 degree shim from dr. diff.

Im going to measure angles again just to be sure.
The car has the "made in mexico" leaf springs and sits alot lower than stock. But I like the stance and wanna figure out this vibe.

Talked to Cass about this before I put the shims in. Let me double check my measurements and report back.

Oh I looked at my driveshaft and I have at least 1" of shiney slip yoke showing out the trans, is that ok?

Normally you would want the car full of fuel and ready to drive, you slide the stock Mopar tranny yoke in all the way and slide it back out about .750, 3/4 of a inch, and then have the driveshaft built that long so it has at least 3/4 inch forward movement and similar backwards movement when installed Most of the stock 727 and standard 833 tranny yokes (not the tiny ones like the 904 and some 833 O.D. have ) have around three inches of splines inside them, measure yours and shoot for the middle of the travel at static ride height

70 440 4 speed challenger, had the same vibration, had my driveshaft balanced, solved the problem.
jess

Just went out to check my angles......now let me make sure I am doing this right, sorry I know this has been beaten to death here....

I have a digital angle finder.
Car is on the ground, level surface. Full tank of gas. Ready to drive.

I zero my angle finder on the the ground
Therefor my pinion angle and trans output angle are relative to the ground, correct?

If so, these are the measurements I got (relative to the ground "zero")

rear pinion angle is 8.6 degrees up!
transmission ouput is 1.3 degrees down.

Doesnt this seem way off? Or maybe herein lies the problem? Did I put my angle shims in backwards??

Pinion should angle down about 2-3 degrees so that is at neAR ZERO DEGREES UNDER ACCELERATION/LOAD OR parallel TO THE TRANS OUTPUT SHAFT. I GOT WORK GLOVES ON. sorry for the caps .

Ok I have verified that the shims I installed are orientated so the fat part of the wedge is at the rear end of the perch (back of the car) so looks like that is installed ok. I still font understand how the perches are so far off? Dr diff helped me out ordering this whole rear end, if I take out the shims that's over 10 degrees pinion up?
I am still unsure I am taking these angle measurement correctly

If the trans output shaft is 1 deg down from horizontle and the driveshaft is 2 deg down from horizontle then the front ujoint (the important piece here) is 1 deg down since it is 1 deg "further" down than the trans shaft. The shaft will be 2 deg down from horizontle also on the other (pinion) end & you would want the pinion ~5 deg down from horizontle as it will rise ~2 deg on accell to only be 3 deg down from horizontle and since the shaft is 2 deg down from horizontle the rear ujoint (the other important piece) in effect is 1 deg "up" from the pinion. On accell the front ujoint being 1 deg (further) down than the trans and the rear ujoint is 1 deg (further) up than the pinion (which rises 2 deg) means they are parallel in different planes. You measure angles to ground to see what angles you have on the angle finder but its the angles of the ujoint (shaft) to the front yoke (trans) and the angle of the rear ujoint (shaft) to the pinion that count (& cause the problems if they ain't right) as in too much angle. How much the pinion rises depends on power/strip/street/daily driver etc. Messure your angles & post em. Have the car level side to side and end to end for accuracy

Check the bell housing bolts. My barracuda started off like yours, and got worse as they backed off more. Took me a year to post my troubles, and Rapid Robert figured it out in two seconds. That guy lives up to his screen name......

Checked the bellhouse bolts, all seemed tight although I squeezed about an 1/8 turn of out em.


all right did my angles...heres how it looks.

zero'd digital angle finder on shop floor.

drive shaft angle= 2 degrees down ( slopes down from trans to diff)

trans output= 1.3 degrees down

diff yoke= 8.6 degrees up

The front ujoint is .7 deg down and the rear ujoint is 6.6 deg down. Not good. I would put the fat part of the perch shims to the rear to rotate the pinion down to where it is closer to 2.7 deg down from horizontle (which makes the rear ujoint .7 up) plus a bit further down from that to account for the pinion rise. 2 deg addit'l sticks in my head but that might be for hot accell and not a DD so check on that. but yes the pinion is way too high. when done check the angles again & you want more than .7 deg difference in the front ujoint to trans & depending on what you end up with after adding the angled perches you might want to add another pair of OE shims on the bottom of the trans to raise it some to increase that angle (want more than .7 diff). I ain't sure if you can lower the pinion that much (that you need) with angled perches & you definitely might want to raise the trans to reduce the change needed. Holler when you can. EDIT for now I'd put the angled perches in (thick to rear) & see what that does for the vibration

I am considering just pulling the rear out and re-locating the perches. That way I can ditch the shims too. I already have the 3 degree shims installed and dont want to piggy back another set on top of those.

SO, Would I roll the perches back about 10-12degrees?