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Bad vibrations (Part 2!)

I studied that link a good bit last night during my Google search, along with a whole mess of others. It would seem that because my pinion angle is the same but opposite of my tailshaft angle at rest, that at speed or under load it could easily be way off. Most of my reading pointed me in the direction of 3-5 degrees of axle windup with a low HP car and street tires running regular leafs. Therefore I believe I need an additional 4° or so of negative angle to compensate for the wind up.

I will order the 4° shims this AM. Hopefully I can have them installed by Friday, because I am taking it to a show that's 3hrs away and don't wanna vibrate all the way there!
 
Dave145 said:
I studied that link a good bit last night during my Google search, along with a whole mess of others. It would seem that because my pinion angle is the same but opposite of my tailshaft angle at rest, that at speed or under load it could easily be way off. Most of my reading pointed me in the direction of 3-5 degrees of axle windup with a low HP car and street tires running regular leafs. Therefore I believe I need an additional 4° or so of negative angle to compensate for the wind up.

I will order the 4° shims this AM. Hopefully I can have them installed by Friday, because I am taking it to a show that's 3hrs away and don't wanna vibrate all the way there!
Click to expand...
Good luck! I think you will succeed and be much happier.
 
Your 4* shim coupled with your .7* difference should net you 4.7* down from the trans output shaft. You might get some 3* shims too. So you can fine tune it.
 
My vote is for pinion angle being the issue. I would suggest a "free" test.
Grab 3-4 friends and have them pile in, then go for a drive. Get it up to highway speeds and record the start (and stop?) of the vibration.
If the vibrations changes the pinion angle is off. There is no "perfect" setting. But I generally end up between 3-6 degrees down on the pinion in relation to the transmission output. But remember - it's the differential between the two, not the actual number that matters.
 
Well I'm back with bad news. The shims didn't change the vibration at all. It's exactly the same. However, 4 hours in this rolling blender gave me plenty of play time with this issue. Here's what I found:

It starts at 65-67mph. Slight shudder in the floor. By 70-72, the whole car is bouncing around. The fenders and hood are shaking. The antenna is shaking. It's so bad that the headlights even shake! Accelerating momentarily pauses it, until you let it cruise for a few seconds, then it comes right back. 75-80-85-90 it feels the same. It doesn't get much worse than it is at 70. It vibrates regardless of if it's in 2nd gear, 3rd gear or neutral. Turns and bumps have no effect on it whatsoever. I also noticed a loud thumping sound kind of like a helicopter propeller spinning noise that starts down at 55. There's no vibration at 55, just the noise. As the cars speed increases, the noise does as well. It sounds like a failing/ failed front u joint, however both u joints are brand new and we're installed by the shop that built my driveshaft.
 
Hmmm, I know my first attempt at shimming yielded no results but once I got it right it stopped. The degree of vibration and noises has me :realcrazy:. My driveline vibration didn't shake or rattle the car just an uncomfortable vibration? The noise sounds like the differential, might address it first then go from there. Do you have any friends with a rear you could borrow? Bent axle is possible as mentioned but the noise almost has to be the differential.
 
It's a very distinct noise. Kind of like (whump, whump, whump). It's a very course vibration that as I said shakes the entire car. Doesn't matter if it's at 2500rpms or 3500 RPMs, this thing shakes! It feels like the vibration is centered underneath the front seat. I don't know anyone that would let me borrow an axle for this thing unfortunately.
.I just stuffed wheel bearings in this thing last July. Pulled the axle shafts, cut the old bearings off, and pressed the new ones on. I don't recall feeling or seeing a bad shaft at that point though...
 
I just re read your initial post on this thread and was wondering about your new driveshaft. You had one built to eliminate the trunion joint. Just a thought about that.........If the builder didn't get that plate centered exact, it wouldn't take much to get a driveshaft wobble. Another issue could be the transmission tail shaft bearing. If you can put the rear axle on stands to get the wheels off of the ground, you could test it at those speeds you mentioned. You could visually look at the front U joint to see if there is any wobble there at high speed. Since you said the vibration feels centered under the driver seat make me suspect the front joint area. Also, if you still have all the shudder on the jack stands you will have eliminated the front suspension from being the problem. Maybe even remove the rear wheels to see if that affects anything. Just don't do what I did when I tested mine with the wheels off. I let up on the throttle too fast and blew both of the dampener springs off of the rear drums because it slowed the drive line down too fast.
 
Is there any way it's the tailshaft bushing in trans? My bushing was bad and at 3000/3200 rpm it would really rattle.
 
I had the new driveshaft made because I wanted to replace my old shaft with the trunnion joint on it. At that time I figured that the driveshaft was the vibration issue, however that clearly wasn't it at all.

The last time I had it on stands and ran it up to speed (with the wheels on), I can't say I saw anything winky going on under there. The front U-joint itself appeared to be true, as did the rear joint. The shaft didn't really move much at all, even while running at 70mph on stands.

I've always been told that if the tailshaft bushing was worn that it would be pissing fluid out the tailshaft and I'd be able to wiggle the tailshaft around in the bushing sitting still, which is why I never put much thought into it until now.
 
Mine is a slip yoke, but had .015 clearance and was noisy. It leaked some but not pissing. Reason it crapped out was driveshaft was to short, which isn't your problem. If you can move the trunnion flange on trans up and down .015 you might look there. I put in a correct length driveshaft before buying the $135 tool to change it, it still rattled.
tb1.jpg
 
I crawled underneath the car today after we got back to our hotel from the show. I can't wiggle anything at all. Both the tailshaft and the rear end pinion are rock solid. Now the car has begun vibrating all the time at 65 and is noticeable. At all speeds below 65 I just hear the helicopter sound that increases and decreses with speed.

For shits and grins I flipped the driveshaft over this morning at the pinion to see if that would change anything. It did not.

I also tried driving it at 50mph listening to the noise to determine it's source. It still sounds like front u joint region to me. I tried speeding up to 60 and coasting down, and the noise followed in both directions.
 
Put the old drive shaft back in and see if it does it still.
 
I can try that, but I'd be willing to bet that it still will. The trunnion joint on it had a good amount of slop in it, which was part of why it was replaced.
 
It’s one of 3 things, now that you’ve tried the shims.
1. Driveshaft is totally out of balance.
2. Tailshaft bushing is shot.
3. Pinion preload has backed off.
 
Well since the noise seems to be eminating from the center of the car, I really have to wonder about that tailshaft bushing.

I took some measurements today before the show started in regards to the motor/trans/rear end positioning as well. The trans is biased toward the drivers side of the car by what I'd guess to be between 1-1.5". The rear end is biased towards the passenger side by 1/2". The trans measurement I kinda just eyeballed, and the rear end measurement I took between the outer sidewall edge of the tire and the fender lip. I don't know if the pumpkin would be shifted to the passenger side (indicating both axle shafts are the same length and the rear end is just slid over), or if the pumpkin is actually centered and the axle shafts are indeed 2 different lengths. Both the rear end pinion and the trans tailshaft weep fluid as well.
 
Tried looking in my mopar for a service manual for 64, none. I'm not up to speed on trunnion tailshafts. Is there a bushing or a ball bearing back there?
 
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