Vibration troubles continue:
Summary: Man, oh man! I really thought I had it this time, and I was pretty excited to do this, because it represented new territory to me. The last post about pinion angles really convinced me that the pinion angle was my issue. Now, I have resolved the pinion angle issue to the best of my ability, and if I did as well as I think I did, it's good to go, but it unfortunately made very little to no difference in the vibration. The 75+ mph vibration is still there.
The theory/facts/assumptions:
The wave-tops from the last posts:
- Engine/trans angle (Reading 1 in the diagram in post #130 above) should be approximately parallel with the rear diff/pinion (Reading 3).
- The angle at each u-joint should be ~1* when you have polyurethane bushings
- Originally Engine trans measured nose-up 2.7-3*
- my driveshaft measured nose-up 1.7-2*
- my pinion measured nose-down 1.3-1.6*
- Thus pinion angle was ~3-3.6* (very bad)
- Engine/trans were out of parallel from the pinion by ~4-4.6* (very, very bad, apparently). I was sure after the previously posted video that this was my culprit
New upper control arms:
First, let me just say that while I was disappointed with the advertised pics of the Team-Z
control arms in comparison with other parts of theirs on my other black car, the actual parts look much better than the advertising pics... They're really doing themselves a disservice with those ad pics, IMO. Here's what they look like in comparison to the
BBK 'gripp' UCAs that came off of the car:
The pic may make those threads seem a bit small, but after using them and adjusting things with them, I have no concerns whatsoever. They are very stout.
Now, UPRs Pat Casey claimed that the stock
upper control arms are supposedly 9 3/8". I wouldn't know but the BBK Gripp UCAs were only 9 1/4", as best I could measure. I set the Team-Z UCA that way to assist getting them into the car. However, I still came up a bit too long:
Now, maybe the rear moved a bit to cause this on the install, but regardless, the Gripps were just not long enough and could not compensate for how much the car is lowered in the rear. Side note: lowering the rear pushes the differential nose-down, because the UCAs are shorter than the LCAs. The Team-Zs did have enough extension range to get me back to where I needed to be in the end. I was concerned before-hand that I would hit the end of the extension range and then would need to purchase adjustable LCAs, too. That was unfounded.
Here's a before/after of the gripps vs. the Team-Zs. It's a shame these will never been seen by anyone other than maybe a mechanic on a lift:
Pinion Angle adjustment:
So, after getting the new UCAs in, I re-baselined my angle measurements. Put spacers/washers under the trans bushing and achieved ~2.5* nose-up (note: don't compare this to my previous numbers as I had set a new zero on my angle cubes. I was more consistent with my measurements this time and only relative angle of the drive line components matters). Then, I set the pinion-angle to ~2.5* nose-up, and held my breath as I measured the D/S angle. My plan was to keep adjusting the engine and diff until they were parallel and the D/S was approximately 1* offset at each end. Would you believe it?! The D/S measured 1.5-1.55* nose-up on the first try! Talk about fortunate; I was thrilled! Getting the right washers to achieve the engine/trans angle was, I thought, going to be challenging and tedious. It turns out that it was pretty straightforward.
Edit: I wanted to capture this data for future consideration. According to
QA1's Website (linked):
Many drag racers adjust their pinion angle to optimize operating angles for maximum power delivery when the car is under power. The less operating angle in the u-joint, the more power will make it to the rear tires. By compensating for pinion rise in their static pinion angle, racers can minimize pinion angle during hard acceleration. Ladder-Bar and 4-link style suspensions offer a lot more control of the axle, and therefore the pinion. But drag racers will still set up the pinion angle to compensate for the rise. According to Pro Stock chassis builder, Jerry Bickel, ladderbars require ½° of pinion angle. A 4 link requires 1-2½°. Vehicles with leaf springs can require 6-7°.
So, optimally, it looks like I'd prever that both the engine-trans & Pinion be rotated to face nose-down about 1-2.5*, and to pick whichever angle creates at least 1/2 a degree of angle (according to another part of the link) between them and the D/S when it's not under load. This would give me close an optimal straight-line drivetrain under acceleration, while also giving me a vibration-free cruise. I may do this in the future, but at the moment, the current nose-up angles should still be right for clearing up my high-speed cruise vibrations.
Outcome:
I got the car out on the test drive and was immediately disappointed when I got it to 80 mph. [Edit after more drives] The vibration is still there but it is slightly better. I'm disappointed that $230 on parts and the time put into the research & work failed to resolve the overarching vibration issue. OTOH, at least I am getting things the way I know they should be, am methodically working through and eliminating all possible causes or combinations of contributing causes, and am still bound and damned determined to see it through.
Future work:
- D/S rotation: I'm going to rotate the D/S 1/4 turn at a time for
s 'n giggles to see if there's any difference, because more and more I see this issue being the claimed solution for folks, but if this cures it, I'm going back to the physics drawing board until I understand why or how this would solve a balance/vibration issue.
- D/S balance: A place nearby balances the d/s on its own, which bothers me. I really want a place that can balance the D/S with the front yoke after
@HotFox mentioned that his yoke turned out to be the issue. Nevertheless, the alternative is just to order another yoke from a trusted manufacturer.
- If those fail, I'm out of ideas that exclude tearing into the rear and replacing/resetting everything that makes sense to: flange/yoke, bearings, and redo pinion specs. And if that fails, I'm burning the car to the ground and starting over with a new, third fox!