Driveline Vibration

[BHDave]

I noticed the other day when my speed got above about 130km/h my car developed a fairly high frequency vibration that you can actually hear as a low hum inside the cabin. Not nice or confidence inspiring.

The only recent changes since i noticed it have been an rb25 box and a 1 piece tail shaft and i've also installed some new steering rack bushes but am getting no feed back through the steering wheel so don't think thats it.

Anyway, prime suspect at this stage is the 1 piece shaft which will be coming out for a check.

A second thing i noticed when i got under the car for a look to make sure the weights hadn't come off was that the outer CV's on both drive shafts had a lot of play. Could this be the cause and it's just a bit of a fluke that it's happened now? I'll be getting them recoed anyway as it causes the car to bounce back and forth at slow speeds like it has excessive back lash (which it doesn't) and they'll break eventually with the near 300rwkw if left alone anyway.

Oh, and it's definitely speed and not rev related as i dipped the clutch to make sure when it happened.

Changed the gear box mount too as that wasn't too healthy to begin with, no effect, but the box doesn't bounce up and hit the tunnel on bumpy roads any more.

Has anyone had issues with the CV's before as it's not something i've seen in my browsing over the last few years?

[BHDave]

Pulled the drive shafts this morning and dropped them in to be recoed. The bloke reckoned they were in pretty good nick for their age, through there was some discolouration in the outer on one side due to heat.

He asked if they had been clicking (they had) as there was some minor dimpling in the outer ring of the outer CVs. So the whole clicking diff thing can be put to bed once and for all when i get them back on the car (hopefully).

Stuck the car in gear and brought the drive line up to speed (seeing as the were no driveshafts). Vibration is still there though no where near as bad with no load (or maybe driveshafts to contribute?), so the prime suspect is still the tail shaft. that can come out tomorrow and get re balanced.

Edited May 26, 2007 by BHDave

[sh@un]

These problems are notoriously hard to trace quickly

Have you eliminated the possibility of tyre/rim damage causing and this?

[Cubes]

Dave drop it back to fourth and see if its still there.

I had a box that would vibrate in fifth gear over 110km/h. Slight high frequency vibe that would wobble the center interior mirror so that everything looked slightly blurred. Couldn't really feel it.

Box eventually blew third gear dropped in another and no vibe.

[BHDave]

Have you eliminated the possibility of tyre/rim damage causing and this?

Yeah, I've already swapped the rear wheels to test it, no change.

Thanks cubes, I had considered the possibility that it was the box, but didn't want to go there at this stage I tried both 4th and 5th the first time I noticed it and it didn't seem to make a difference.

[GTS4WD]

Yes.. I too am interested in this as i have the same problem.. or perhaps is it just a skyline attribute?

It happens over about 110Km/h and is fine if there is more than about 15% - 20% throttle but bellow that it vibrates..

Edited May 29, 2007 by GTS4WD

[T04GTR]

its the tailshaft. getting the driveline angle corect is a pain. what you can do is shim up the geabox on its mount as high as it can go. and use "pinaples" in the rear cross member to tilt the front of the diff upward.

for refecance there needs to be no more than a 2 degree diferance in shaft angle between the diff and gearbox. the height can be off but the centrelines have to be within this tolerance.

[T04GTR]

i had the same issue with my dr30 (26/25box) and it made short work of the uni joints too ;(. my problem was the tunnel wasnt big enough to lift the box high enough.

or could just be a badly made shaft aswell. like my one.

[BHDave]

Got new drive shafts in, measured up to check the tail shaft angles based on daves posts and found the nose of the diff needed to come down about 3 mm and it would be dead straight, box end was spot on. So made some spacers, chucked them in, no difference

And my rear roll center adjusters are the wrong ones

And now i have to get back under the car to remove the tail shaft

[dead32]

well that just suck's. how far over the output shaft does your custom shaft sit, whilst sitting on the floor?

[T04GTR]

hang on. if the box is pointing down. the diff needs to point up the same angle.

basicly to make a paralelagram.

[BHDave]

The box is pointing straight at the diff, so the whole lot is square (to within a mm or 2). I bent my tunnel up for clearance when i was installing the box so it was sitting in the right spot. The yoke is parallel to the tail shaft which is parallel with the pinion. I don't particularly want to start messing with subframe angles just so i can get away with using a one piece shaft. I'll get the original 2 piece shaft modded before i go that far.

Anyway, i got back under and removed the shaft so it's going to have the balance looked at.

It's about 75mm dead32.

[dangerous_daveo]

What it COULD be (as it was with mine) is just dodgy unis. We had the shaft rebalanced, did nothing. Moved the box up, did nothing. Changed the wheels, same deal did nothing. Put it on the dyno under some load got under it to check, was definately the shaft.

Went back to the place that did the shaft. They then all of a sudden 'worked out' that they put the cheap uni's in. Put in the better ones, haven't had a problem since. So if everything else is hunkydory, that could be it.

[T04GTR]

yeah. posibly. i recod my gtr shaft and used a really good sticky greace. now it shudders under power. awsome :s

[BHDave]

Latest is the shaft was fine for balance but one of the unis was attached to the shaft about 25 thou off center. This has now been fixed. It goes back on the car tonight when i get home.

[BHDave]

It's back on the car, the vibration has improved a bit, it's still there but nowhere near as bad as it was. Saturday morning i'll be back under the car with a set of calipers checking again to see if anything has changed.

I knew i should have stuck with a 2 piece.....

[dangerous_daveo]

I'm still running with the uni joints themselfs. Obviously check everything else first. Or do what we did with mine, whack it on a dyno get under the car, see whats wobbleing.

Just a shame those thompson couplings arent mass production yet.