Driveline vibration

[Riceburner]

Hey guys, After rebuilding my gearbox recently I now have a vibration at 100kph and above, below that things are fine. I have the RT diff mount with the GM poly mount, the vibration was non existant before the gearbox swap although the gearbox rubber was completely stuffed. I have changed the gearbox, fitted a new gearbox rubber mount, and a kameari crossmember. I did a cut n shut on my original gearbox crossmember to make it work with the new box, The vibration was worse with this DIY mount, the Kameari mount has improved things about 50%.  I have checked all uni's, they seem fine and there was no issue until the box was changed.

 

 

I know the RT mount drops the nose of the diff as it's designed for V8 conversions, I did shave it a little to fit over the nose of the diff better but maybe not enough. I'm thinking maybe it hasn't been a problem before due to the state of the old/stuffed gearbox rubber?

 

 

[44014]

If the universal joint do not have the same deflection angle you will get vibrations and will also wear your uni's out faster.

Amagine a sine wave one starts at the bottom one starts at the top .

If one sine wave has a different acceleration and deceleration speed then the other they dont cancel each others imbalance out .

Hope I have confused you enough .

But yes it will be your increases diff angle causing it .

[nizm0zed]

quick way to check your driveline angle, put your car up on stands, make sure the rear wheels are supported so your suspension is at ride height.

Take your tailshaft off and download a digital level app for your phone.

http://www.lifehacker.com.au/2011/04/a-list-of-free-spirit-level-apps-for-your-mobile-mobile/

Measure the angle along the vertical axis on the backside of the tailshaft and the front flange of the diff.

Your angles should be opposite but equal to one another.

 

 

If you have changed your gearbox crossmember you may have inadvertently moved the nose of the diff up or down, altering the angle.

[NZeder]

I know when we install the RT type diff mount we cut the shit out of it so we can still use the stock lower mount and bracket. This way we know the diff is in the factory position - Nissan engineers spent a lot of time $$ to get that right so why would we change it for the same setup???

 

To day we don't use the GM mount but I purchased some of energy suspension jeep chassis bump stops that we cut down and enlarge the holes (don't line up with the stock diff bolt holes - close but a bit of elongating required) we have it set so as the stock mounts bolts up this bump stop is just touching the RT bracket over the top of the diff. This limits/controls the nose lift better than the stock strap but works in the same manor so the diff is in the factory location using a factory bracket and mount.

 

We do also replace the stock mount with the more $$$ and stiffer/stonger version from Kameari.

[620Z]

Refer to the Subject "Gearbox" under V8 Conversion. What I did might fix your problems?

[Riceburner]

Thanks for the suggestions guys. I'll fit my old solid diff mount in to see if it fixes the issue, if it does I'll go the the factory rubber mount and use the RT mount with a bush to stop the diff going upwards.

[nizm0zed]

Measure your angles while you have it all apart, best to cover all bases while your there.

[Scoota G]

Don't forget that the tailshaft is one of the most neglected areas of any driveline. For a couple of hundred dollars i would get it balanced. Modifying cars is like squeezing a balloon, the weak areas show up when you make other areas stronger. I just put a shift kit in the V8 Zed and it made all the clunks clunkier!

[Riceburner]

Checked the alignment between the gearbox and diff, I only used a spirit level on the end of them both, but according to this the diff nose was pointing downwards compared to the box.

 

I removed the red energy suspension GM bush, I fitted the black urethane stepped 'snubber' that also came with the RT mount and my old billet aluminium diff mount. I trimmed the black urethane snubber so there was only three steps left and this was slightly compressed with the billet mount all tightened up. I'll swap the billet mount out for a genuine rubber style shortly, but not from Nissan Australia as they are $165    Test drive, problem solved 

 

I had trimmed the Red urethane mount so it matched the shape of the diff nose when first installed, obviously it's not enough for my setup with all new mounts, previously it seemed fine but the gearbox mount has been stuffed since it was fitted.

 

Thanks for the help guys!

[luvemfast]

Good to hear Gareth 

[NZeder]

Result and I bet you had to hack the crap out of the GM mount to get the right total height