JR HAWK 009

OK, I am trying to get down to the bottom of my high speed vibration that I have had for 3+ years and I -think- I almost have it licked. I thought it was my rims and tires but when I got a new set of rims/tires, the vibration remained exactly the same so I figured it wasn't it. I then replaced my TA with an adjustable one and set my angles correctly (was off 3+ degrees), that eliminated A LOT of it, but I still had some. I then bought an adjustable panhard bar to center my rear end and also had my u-joints replaced (with greaseables ) and my stock driveshaft balanced w/o the pinion yoke but with the tranny yoke. The guy that balanced my DS said that he had to straighten it first a little bit because the runout was out of spec. He then balanced it but his machine (some old thing) only spins at 2,000 rpm's. After he straightened it and put the new u-joints in he put it on the balancer and told me it didn't need any weight and that it was off only 1/10 inch ounce (?). He told me I would -never- feel it and that his machine is more sensitive that my car is. He deals with mainly heavy duty trucks and such. I have all poly suspension bushings as well as a double rod ended panhard bar therefore my suspension will tend to transfer driveline vibrations just a -tad- bit more than a dump truck would....lol Well, I take the shaft home and install it. Take it for a ride and it vibrates noticeably WORSE than it did previously. I then drive it back home and unbolt the shaft from the pinion yoke and rotate it 180 and bolt it back up. Take it for another ride and it is much better. I still do have a VERY tight vibration at highway speeds though but it is better than it was before I had it straightened and balanced. The vibration I have now seems to be even tighter than what I had before the balance and new u joints and seems to get tighter with increased speed. At 115mph it gets to be pretty noticeable.

Could the shaft -still- be out of balance?? How much difference does a 6, 7, 8, 9 or 10,000 rpm balance make compared to only a 2,000 rpm balance? The guy that did mine seems VERY knowledgeable, but he seems to do mainly heavy equipment shafts and hardly any sports cars. He told me that he hardly ever does an aluminum shaft and that he has to switch all his stuff over from steel in order to weld on them.

I am now thinking of taking the plunge to a carbon fiber shaft, as they are supposed to be the -best- for reducing drivetrain related vibrations. I don't drag race the car nor do I consider myself hard on the drive train (never have even done a single clutch dump or burnout), therefore my main purpose of swapping driveshafts would be to have a -very- well balanced shaft capable of spinning 7,000 - 8,000 rpm's safely and w/o vibration. I drive the car only on nice weekends and like to take small road trips with it and sometimes end up doing 90-120mph when the highway opens up enough to safely do so.

anybody have any comments or suggestions on if they think a carbon fiber driveshaft could possibly take care of my vibration...?

thanks for any help..
Paul

Injuneer

Might want to add basic info like the year of the car. You mention running a stock DS, and that it is aluminum.... so that might narrow the year down a bit.

JR HAWK 009

yeah, it's a 2000....

RAT454

Seams like you've narrowed it down to the drive line, However you might get it up on a good secure lift and run it up and see if you can tell where the vibration is comming from.

Could be a problem related to the bushing in the tail cone of the Tranny and or a drive shaft output yoke being a little worn. this would cause some Wobble that could create a harmonic vibration....

You could also have pinon issues on the differential, worn parts in it, loose bearings that cause things to do wierd things at high speed... a slightly bent axle shaft, loose bearings, out of balance rotor any number of things...
might talk with the folks at drive line specialist...

If you're sure it's the shaft, you can try the hose clamp trick, it takes alot of time and paitents..

JR HAWK 009

I looked that the tailshaft and tried to move it with no movement at all. I just had new gears installed and the pinion bearing looked good and we put in new carrier bearings already. I already checked for the bent axle, that was fine. I also went through two sets of rotors w/o any difference.

The way I look at it, if I was able to noticeably reduce the vibration by just turning the shaft 180 in the pinion yoke then it almost has to be driveshaft related.

RAT454

A bummer...
My Camaro had a vibration problem the first time I took it out and it turned out to be the pinion nut was a little loose allowing a little too much slop in,

Curious as to what you finally find out on this problem....

Tom Woods has some interesting thoughts on vibration (not sure I totally agree with him) at
http://www.4xshaft.com/index.html

I suspect you looked at this already, just throwing out thoughts here..how is the rear u joint centered into the rear yoke. Does it use tabs on the yoke to locate the joint, can the joint move up or down in the yoke before the clamps or bolt straps are installed....also how's the tranny to frame mount?

I have no experience with carbon fiber shafts.

You might look at finding someone that does high performance shafts for high speed applications online and send the shaft off to them.

The folks that balanced my shaft for the Camaro spun it up to 3000; I use 2.56 gears so my shaft speed is about 3600 at 120 mph.
What is your rpm at 120?
Theoretically you can calculate here using a 1.0 tranny gear ratio

http://www.xse.com/leres/ss/calculator.html

Just some thoughts

JR HAWK 009

I have 3.73 gears and a 295/30/18 tire. My DS is spinning at 2,000 rpm's already at only 40mph. It's spinning at 4,000 rpm's at 80mph and around 5,700 rpm's around 115mph.

I don't have the tab system. I will be looking at the tranny mount pretty soon.

BradcTA

Make sure you use rubber trans, TA, and motor mounts too...

matLT1

The factory balance spec for those driveshafts is roughy 18 gm-cm. Although he gave the results to you in in-oz's, the spec would convert to roughly .25 in-oz's. A couple of things to consider are that the shop you took it to only balanced the shaft to 2000rpm when he really should have balanced it to 3000-4000 rpm (at a higher rpm you may be out of spec). 10000 rpm wouldn't be very realistic because the shafts isn't even capable of spinning that high (exceeding critical speed).

Did the shop check the balance with the slip yoke installed? Or did he just balance the tube? Slip yokes and u-joints can cause vibrations due to centrality problems. Its also possible that the slip yoke is lose in your tailshaft and causing vibrations.

JR HAWK 009

ok, what rpm's is that 18 gm-cm spec'd at? 2,000 rpm's are way too low for my application...that's only 40mph in my car...lol

yeah, the slip yoke was installed but the pinion yoke wasn't. I just ordered a new custom made PST carbon fiber shaft with a new slip yoke and aluminum 1310 yokes. They are going to balance it at 8,000 rpm's for me.......so they say anyway. I am probably going to install a new tranny bushing as well over the winter, seeing it's not hard to do.

matLT1

I couldn't say the exact rpm for that spec but I want to say it is around 3500 rpm. Just make sure the people who are making your shaft for you send you the data sheet for your new shaft. It should have the runout at the front, middle and rear. It should also tell you the balance (gm-cm @ rpm) for both front and rear.

JR HAWK 009

Is this something that all shaft makers do?? I guess I have never heard of that, but I am checking with someone now that had a CF shaft made by PST to see if his came with a data sheet.

matLT1

It may not be automatically included, but that data should always be collected to confirm that the shaft is within specs. If you were to request the data they should have it on file.

JR HAWK 009

this is what PST emailed me when I asked them for a "data sheet"....