I recently had a T56 installed in my 5.0L XH XR8 ute

If I had any vibrations before, I didn't notice them.

Sometimes in 4th gear @ 60km/h you can feel a very slight vibration under load (1800-2100rpm), then after this RPM it's fine.

Entering a freeway, up it in 5th gear - VERY noticeable up to 110km/h. Change to 6th and cruise at 1550rpm, no vibration...

Change back to 5th to overtake - Vibration!! If I can manage to coast at the vibration speed, it does not go away (still in gear). Hold clutch in and it stops....

This points me to the engine? But trying to simulate this when not on the freeway is impossible. The mechanic that put the box in said everything is fine (the vibration is minimal normally), but I know it never used to be there and is hence pissing me off. Especially after forking out for a T56!!

I have had pinion angle adjusted 4 times, which DID reduce vibration.

My next step was to install a 2-piece driveshaft (long wheelbase). Mal Wood seems to think this will fix most vibration problems.

But thinking more about it, could it be the harmonic balancer? The engine has around 90k kms on it. The balancer does not vibrate or move when free revving. The problem is only under load!

I'm pulling my hair out trying to come up with ideas. BTW new uni's were fitted when box went in.

Any help greatly appreciated!

Maybe try getting the drive shaft balanced. As all ready suggested to you a two piece drive shaft would definitely help reduce any vibration if it is caused by the drive shaft.

Other than that have you had your wheels balanced? Might sound like a simple solution but it doesn't take much to buckle a wheel these days and slight buckle or imbalance can give a similar vibration.

Also look at the balancer on the motor. It could have moved or expired. My auto did this due to a collapsed harmonic balancer.

Brett

Wheels have been balanced, and re-checked.

I will def go with new 2-piece, but thing that worries me is vibration stops when you hold clutch in

If the balancer looks fine when free-revving, how can you tell if it need replacing? Is there any special tests you can do, or is it best to put car on a dyno (so it's under load)?

Is it a constant vibration or does it come in "waves" for lack of a better word?

I had a similar issue when my Auto was in converter lock up which is essentially the same as having the clutch out, and between 1700-2100rpm only I would get a heavy vibration that would come in "waves" about 4 or 5 seconds between each other.

It was a lean condition due to an incorrectly positional Cam Sync Sensor made significantly worse when the Oxygen sensors decided to stop working correctly and wasn't richening up the mix properly to compensate for the Cam sensor which had always been out from factory.

I am aware you have a dizzy and not a cam sync sensor, but it may be worth just replacing your oxygen sensors if it hasn't been done recently. I know I spent $1200 on my transmission before I discovered the problem was a $60 sensor.

It wont be the balancer if the vibration stops when the clutch is in.
Check the RPM you are doing at the speed you are doing when the vibration occurs.
Then free rev the car to the same RPM and hold it there.
If it still vibrates the drama is something in the engine but if it doesnt start looking at the driveline.

Check the tailshaft for balance.

Thanks for the replies...

Have tried free revving engine to where it usually vibrates, but under free revving it's fine.

I had never had an issue with this engine/ute until new gearbox went in.

The only change was gearbox and original tailshaft went back in (previous I was running custom shaft due to having a T5z box)

I am just awaiting fitment of new 2-piece shaft, so will update once it's in.

If that fails, will check sensors, and re-check balancer. Forgot to mention have checked plugs and installed new leads as well - no change.