***Solved***-Rotating Knocking Sound on Acceleration

[gtd65]

Our trusty 240SX SE (Auto) has developed an intermittent noise under acceleration when in gear.

If the car is revved in neutral, there is no knocking sound.

The noise only appears when pushing on the gas pedal and I'm assuming it might be transmission related but everything is shifting properly?

One bit of background info is that the gas tank was recently changed and I'm wondering if this could be part of the dis-assembly and perhaps incorrect re-assembly?

Any ideas?

[Jagstang]

It could very well be your axle(s). Go to your rear end, and check the axles for any damage, torn boot, etc. Also, check and see if the bolts and nuts are tight.

[Jagstang]

Oh, and if the axles seem fine and tight, try checking the differential. If the differential is A-OK, move towards the U joint bushings on the driveshaft. If U joints seem fine (and you have the stock POS 2 piece design), check the center carrier bearing. If all that seems fine, then it may be your transmission. But keep the expensive/harder to diagnose piece for last.

[gtd65]

The noise appears to be coming from somewhere to the front of the driver and passenger seats. When I sit in the car I'd guess the sound was coming from somewhere in the center of the car between the engine and transmission shifter area.

My GF was in the car with me the other day and she thought it was coming from the drivers side..go figure...

I have noticed a pattern, when the car is cooler/cold the noise isn't there. Only after the car has warmed up do you hear the noise.

I should really get underneath but the car was given the once over by the local Tuffy oil change place. They reported that the tension rod bushings were worn, I'd have expected they went right over the car for anything obvious while pimping for extra work.

Car shifts perfectly, no matter the noise levels.

[gtd65]

Oh, and if the axles seem fine and tight, try checking the differential. If the differential is A-OK, move towards the U joint bushings on the driveshaft. If U joints seem fine (and you have the stock POS 2 piece design), check the center carrier bearing. If all that seems fine, then it may be your transmission. But keep the expensive/harder to diagnose piece for last.

Would UJ's make noise only under pressure?

Carrier bearing might be likely but I'll try to get a chance to inspect over the weekend.

[gtd65]

Well so much for checking over the weekend...

I finally got under the car today - went in from the front side first - no sign of anything unusual.

Went in from the rear (ooh err Mrs!) and didn't see anything unusual at all - looked at the carrier bearing - it appeared as it should when it left the factory to be honest.

I then ran my hands round the drive-shaft (ooh err Mrs! x 2) closest to the diff. I noticed that there was a slight projection that interfered very slightly with the hand-brake cable..which in turn transfers the impact to the metal shielding under the car...hmmm.

So in summary the driveshaft was basically turning and whacking the handbrake cable making a heck of a weird noise.

I've pushed the cable back (roughly) into position but couldn't get one run exactly into the correct position for the provided clip. That will be tackled another day of course.

I read numerous posts about people having problems after removing the rear ends - I'm wondering now if it was simply the handbrake cables that were the problem for most folks as it's not really that obvious from underneath?

This problem resulted when I had the gas tank swapped due to a crack on the passenger side. The guys obviously didn't do a thorough job on reassembly, as I've already fixed a disconnected fule tank hose that gave wildly fluctuating gas gauge readings and an exhaust hanger did not have the pipe on it!

Overall, I'm bloody relieved it wasn't anything worn out or damaged as this car has been very well looked after in the 12 years that we've had it