Chasing Annoying Vibration

[gmorris]

I've been chasing an annoying vibration on my '69 Chevelle for a long time now. I was completely convinced it was driveshaft angle related and just bought and installed a new aluminum driveshaft with front CV joint from the driveshaft shop and the vibe is still there! While chasing this I have replaced the big block with an LS3 so that eliminates the clutch and flywheel etc, replaced the tremec 5 speed with a 4l60e so that eliminates trans issues, replaced the driveshaft and am running 1º rear working angle and front cv to eliminate that, had the wheels/tires checked and rebalanced plus rear wheel pads cut down to eliminate the chamfer and ensure they are fully centering on the hub flange all with no effect. I think it's down to rear end/axle issues now. The vibe is a constant rythmic pulsing anytime I'm over about 70mph. Could a slightly bent axle cause that? It's a new moser 12 bolt with trutrack and 33 spine axles.

[andrewb70]

Axles turn at (driveshaft RPM/axle ratio), in other words, much slower. Can you feel it in the seat like a buzz? Does the rear view mirror go fuzzy? I would check the runout of the rear yoke.

Andrew

[gmorris]

It's a pulsing rhythmic vibe that starts at about 70 and gets much worse as you go up from there. It definitely makes the rear view fuzzy and you feel it through the whole car but definitely coming from the rear. Since breaking my back I can't feel my feet or ass but from memory you can feel it through the seat as well.

Good idea on the yoke...has to be something between the driveshaft and ground because that's all that hasn't changed. It will piss me off it is is the yoke since it was all brand new and set up by moser and has been there since day 1. I just assumed it was driveshaft related all along. I realise the axles turn slower but as speed increases so do they so it's still possibly axle related.

[andrewb70]

Gary,

Yes, the axles do speed up with speed, but they still turn substantially slower than the driveshaft. Vibration related to wheels, bearings, or axles tend to manifest itself as more of a thump...thump...thump...as opposed to a buzz...Clear as mud? LOL

When I installed my CV driveshaft, I also installed a new billet pinion yoke from Mark Williams. This was part of my problem, as was the front working angle, which is about 6 degrees (with the CV that doesn't matter).

Andrew

[TheJDMan]

It sounds like I have the same high frequency vibration at 70 and above and it only occurs in 5th and 6th gear. How does one accurately check the runout of the pinion yoke? would you locate off the drive shaft tube? My center section is a refurbished surplus NASCAR unit I purchased from Roush Racing and it came with a billet yoke while the driveshaft was purchased new from Strange. My U-joint working angles have been adjusted from one extreme to the opposite within my adjustment limits and the vibration has changed but never completely disappeared. I have come very close to ordering one of those CV drive shafts but like Gary I'm concerned that it won't eliminate the problem. Does anyone have a good procedure for checking the pinion yoke runout?

[andrewb70]

G-Force Transmission makes a pinion run-out checking tool, but it only works with yokes that use a 1350 size u-joint and it is fairly expensive (around $300 as I recall).

When I checked mine, I used a dial indicator and went off the u-joint caps as the reference point. I put the plunger on the cap and found the low spot, set the dial to zero, then compared that to the low spot on the opposite cap. Not sure if that is a legit way to do it, but that's what I did.

Andrew

[bryant]

just a long shot but if you over tighten the u joint straps, it will distort the u joint cap pinching the rollers. this usually causes early failure of the u joint but may be able to cause a vibration.

[FlyDoc]

going off the over tightening possibility, you could be getting the vibration from early stages of wheel bearings going bad.

[TheJDMan]

In my case the vibration is not in the wheels or axles it is a much higher frequency and from the description Gary's vibration sounds the same.