5th Gear Vibration/Shudder

[ferni]

A while ago i took my car to Compuline in Nunawading to get the wheel alignment checked out, and see about getting a Whiteline handling kit. I went to them since they were a whiteline recomended dealer etc...

Thier alignment machine does it with the wheels rolling, only 2 at a time... they asked me if the GTR is a awd... i told them yes...so they had to drop my shaft since only 2 wheels could be on the rolling dyno alignment computer thing.

They dropped my whole tail shaft for some reason instead of my front prop, which is where it is normally done as far as i know.

They checked the alignment, spoke to me about it, told me there wasn't enough adjustment in stock arms to fix it to what i wanted/whiteline recommended and advised me i order a whiteline handling kit and front camber kit to fix it up. No problems... they put my tail shaft back in ...

Later that day driving home i notice there is a vibration/shudder coming from (i thought it was my front left at the time, but later realised it is coming from the rear)...

Only in 5th gear

starts and seems worst, most noticable at about 2800-3000rpm (~110-120kmh)

Most noticable on moderate throttle, just before boost comes on, its hard to tell if its there when boost comes on since the engine gets a bit noisier, and its hard to feel any vibration/shudder while its accelerating this hard.

It seems to be worse when i have a passenger, ie more weight?

I can only think it is my tail shaft. Since then i have had a look, and there is no markings on it to show where it was before it was taken off... they didn't mark it when taking it off?!?!? I'm under the impression thats a common practice with ANY car, let alone a performance car like the GTR... there seem to be 6 settings/places it can go back on ... there are 2 gaps where it slots in that i would assume should be dirty since its been exposed for the last x years... the way they put it back it it was clean... by lining up the 2 dirty gaps in the holes (hard to explain)... there are only 2 settings it could be... i have tried both and no luck, the shudder/vibration is there, and its pissing me off big time..

I have also had a full whitline handling kit/wheel alignment done elsewhere, and new tyres, hoping that it may have been something this could of fixed (in case it isn't the tail shaft..)

Anyone had anything similar? any ideas?

Same speed or same RPM in 4th gear is fine, smooth as a babys bottom.... only 5th gear... I don't really want to go back to them .. personal preference ...

[GTRgeoff]

Andrew

probably just a minor harmonic with that gear and rpm. Always a bit hard to tell without driving or sitting in the car so I'm just guessing. Did the wheels come off for a balance? You could have thrown a weight while driving but it's unnoticable in 4th due to other vibrations. Can the shaft go in the other way around?

I get a strange harmonic that is evident about 5 mins after starting from cold for about another 5 mins. It then dissappears altogether. I'm not driving hard at that stage so i don't worry too much. It was all fully balanced at rebuild.

[ferni]

Andrew

probably just a minor harmonic with that gear and rpm. Always a bit hard to tell without driving or sitting in the car so I'm just guessing. Did the wheels come off for a balance? You could have thrown a weight while driving but it's unnoticable in 4th due to other vibrations. Can the shaft go in the other way around?

 

I get a strange harmonic that is evident about 5 mins after starting from cold for about another 5 mins. It then dissappears altogether. I'm not driving hard at that stage so i don't worry too much. It was all fully balanced at rebuild.

I'll take you for a drive if we are both at the PI day and its not fixed by then, you're just a bit far away to come there to take you for a drive..

Wheels didn't come off - and i have since had new tyres (and wheel balance) done...

No the shaft can't go the other way around... it was the whole thing, including the uni joint in it...

[Emre]

Andrew,

The exact thing you are describing had also started in my car after my last gearbox change, quite a few months ago now.

It can't be RPM related as it only happens in 5th gear. The tailshaft speed is directly related to road speed rather than the RPM but my tailshaft has never been removed.

Did you get anything else done around the same time...?

It was really bothering me at the start, but now i am used to it. Let me know if you find out.

[ferni]

Emre - I had a clutch done a week or two earlier... but bit of a co-incedence that i noticed it the day these guys dropped my tailshaft...

I was thinking the same, can't be RPM since only 5th gear....

and i can go the same speed in 4th/3rd and not get the shudder, but i can't put the exact same load on it where it happens in 5th...

Does yours get worse if you have passengers/more weight?

[Amaru]

The same thing happened to me (coincidently not long after I got a wheel alignment done) and it was the driveshaft bearing (I cant remember the proper name for it, but if you look under the car, the driveshaft that runs from the gearbox to the rear diff is actually 2 pieces with a bearing in the middle). There is a rubber protector around it which can start wearing out and causing it to clunk/vibrate. My mechanic also said its not uncommon for the bracket which holds this up (if the rubbers ok) to come loose and fall down a bit, which will cause the same thing. Im not sure if its what is wrong with yours, but maybe check it out. Mine started out as just a small vibration and only really happened in 5th gear, and then got so bad it was clunking about and hitting the bottom of the car (my rubber wasnt worn, just the cradle had come loose) after a few weeks. It would only take you 5 mins to jump under the car and check, so maybe worth while

[GTRgeoff]

Good call Amaru. I'm going to be under the car today so will check mine also for the funny vibration I get, but it deems rpm related in mine.

Andrew, I'll see you Tuesday at the club meeting or Sat at PI and we can discuss further. A quich drive at PI will allow me to sit in the back as well and see if I can isolate the location.

[ferni]

Amaru: thanks for the ideas mate.. much appreciated. yep the shaft is 2 peices with a unijoint in the middle.... that they dropped the whole thing.... where is the rubber protector you're talking about (i will look maybe i just haven't noticed it?) I do remember a bracket holding it up, has 2 14mm bolts in it i think, i remmeber that the guys at compuline lost one of those bolts and put a new one on.. maybe something to do with that i didn't look at closely

thanks ill have to have a word to my mechanic and look closer at this.

[Emre]

Andrew,

Yep, mine is more noticable when a passanger is on board as well.

Tailshaft related problem makes the most sense as everything before the gearbox is RPM related.

Mine has been doing this noise for the last few months and it hasn't gotten noticably worse. Mind you, it doesn't see a lot of kms these days.

I will have a closer look next time the car is on a hoist as well, I think Amaru is onto something here.

[ferni]

I've tried changing hte tailshaft in 3 out of the 6 diff positions already and was starting to loose hope in that.. but i agree, hopefully Amaru is onto something here.

My car is a daily driver, freeway nearly everday so it really gets to me.