- Engine/Trans (measured at the front pulley with a square). 0.6 degrees UP
- Rear Pinion (measured by putting straight edge along back of pinion). 2.7 degrees UP
If this was your starting measurement. I would make the engine 3 degrees down, with your 2.7 degrees up. The reason I say this is I find anything over 3 degrees on the motor is too much and makes it harder to balance. Universal joints flex around 3 degrees at the max, or so. Just my 2 cents worth.
Key thing here is I did NOT level the car. So the only details that really can be determined here is the difference between them. I can state with all probability that the nose of the car was pointed down when I took those measurements.
Yeah, it's the ONLY part on this whole damn driveline I haven't replaced. My father-in-law mentioned the same thing. What I don't understand is how that could cause a vibration. It makes sense to me that it could cause crabwalking or wear in tires, but a vibration? I'm not arguing that it is not the issue, I'm just saying that it does not seem "logical" to me to be causing the problem. Can you expand on why you mentioned this?
Maybe connected here, maybe not - but I've always wondered about that whole "phasing" thing
with the rear u-joint/driveshaft/pinion?
I mean....
When we're working on a car that's probably close to new/original and we need to take the driveshaft
out, it's pretty common to mark both the shaft and the pinion so that you put it back in the same
orientation, right?
So....what do you do with this situation with a setup that's definitely not as built?
Third members get replaced. Driveshafts get removed, sometimes for years - or swapped.
There's obviously only two ways to put the rear u-joint into the pinion yoke, but does it matter which
way you do it in such situations?
Does it even matter in the grand scheme of things?
It's a good question. As you state, parts are swapped all the time. I guess, when there is a problem, people just need to go back to the basics of driveline angles?
Put it on a level 4 post drive on and measure the driveline and pinion angles properly. Then adjust to match the wisdom provided here.
Agree. The only problem is I don't have access to a 4 post lift - only 2 post lifts. The best I can do is use jack stands or other means to get the car up while resting the car on its wheels/ suspension.
Another point to consider...
"When accelerating slowly, no issue. When accelerating hard, there is constant hard vibration"
When accelerating hard the yoke of the differential rises... Changing the pinion angle...
As Moes mentioned 3 degrees is the preferred max angle on a U joint... But honestly thats more to do with maximizing U joint life.. They actually work okay up to about 6-7 degrees.. The fact the vibration worsens when on the gas shows the yoke has to go lower to improve the situation...
View attachment 1277908
Yeah, and that's why I had high hopes when I added the 2 degree shims to shim the pinion down.
Here's my 2 cents worth based on personal experience today in my A100.
My truck has been sitting around for a w=few weeks and not moved....so it gets 'flat spots' on the tires. After travelling at 50-60mph down the highway for about 5 miles or so, the vibration goes away. It would have gone sooner possibly if I had over-inflated the tires before setting off this morning.
I used to get the same with my GTX, mainly because it didn't get driven often enough.
Thanks, but I have swapped the entire wheel and tire combo from my 70 with no change to the problem.
combined with this:
- I had a slightly bent axle. I bought two new axles from Dr. Diff and installed them. No change to the vibration.
I think WileERobby may be correct. How did you get a "slightly bent axle"? But it was replaced in into the same rear axle housing? I have seen a couple of 8-3/4 Mopar rear ends that had tweaked housings.
I recently had a similar "frum,,frum,,frum..."noise issue with my wife's Ford Explorer. Drove me crazy, because all of the wheel bearings had been replaced within the last couple of years. Well, I discovered that one had failed, and the left rear wheel was not running true. The rear wheel/tire was apparently "scrubbing" ever so slightly at highway speed. I replaced the bearing assembly and the problem went away.
Yeah, I have no idea how the axle got a .010" bend in it. On the other hand, I have now replaced it with brand new axles from Dr. Diff (with new bearings by the way), and still have the same vibration. So it can't be the bearings and it seems my slightly bent axle wasn't an issue either. Maybe it was that way from the factory?
Brake rotors
Tire balance
Wheel bearing.
Shocks and or springs.
Brake rotors, tire balance and wheel bearings have already been tried.
I have not replaced shocks of rear leaf springs, but I'm not sure how those could cause this type of vibration?
