Strange Droning Noise

[Grey]

Hi everyone, I was wandering if anybody could give me some insight as to a very strange droning noise that is very LOUD heard in cabin. The drone sounds very bad and it only happens in 2nd, 3rd and 4th gears under load (does not happen in 1st or 5th gear). To add, it only happens from 2000rpm-2300rpm (very narrow rev range). The more I push the gas pedal under load, the more louder the sound is.

Some background information:

I recently purchased an R34 GTT to find out that it had a stagea RB25DET NEO engine in it (same engine, different sump, different mounts etc). The car has an R33 turbo internals in an R34 turbo gearbox. The clutch according to a mechanic at Chaser's Eastside, is a heavy duty either single or twin plated exedy / 5zigen clutch. Also, the clutch makes a metal on metal sound when depressed but I was told it is normal for heavy duty clutches to make those noises because of the lack of dampers in their design compared to the stock clutch.

Now the clutch itself bites hard and is not slipping. It revs smoothly and nicely at higher RPMs, but at lower RPMs its a clunky and not very smooth. I've taken it to 4 different mechanics with varying experience and no one seems to have any idea what the issue is. They all seem to point me towards a drivetrain issue. I'm thinking it's probably the clutch but I need some ideas as to what and why this noise is happening. It's EXTREMELY ANNOYING!

I've ruled out it being an exhaust issue, so could it possibly be that the rubbers on the engine mounts are worn out giving the clunk noise? OR possibly the fact that the engine swap was not done properly and mounts were not installed correctly giving a bad vibration?

Additionally, when I am cruising in 3rd / 4th / 5th gear and I lightly tap the throttle gently or hold the throttle down at 5-10%, I hear a "clunk" "clunk" "clunk" noise along with a bit of bogging as if the car is getting gassed then nothing, gassed then nothing with clunking noises.....

These problems have been making my life suck as I have forked a lot of money on this car and it still has these issues.

Ideas / help / recommendations are highly welcome, thank you.

[Duncan]

Hi mate, that is quite a series of questions/comments there, it would help if you can be more specific about exactly what you want feedback on.

Generally a twin plate clutch does have more bite/ is less progressive to use....there is a reason they are not fitted by the factory. So basically, that is something to learn to live with.

A clutch issue cannot be affected by revs, because once it is fully engaged it is either working (ie gripping) or slipping. So if you say it is not slipping then there is nothing further to look for with the clutch.

The clunking noise when first going under power is likely to be a worn or misaligned diff centre, or stuffed Cvs (or maybe uni-joints) in the tailshaft. I am surprised none of the mechanics diagnosed that because it is quite common. The fix is to replace or recondition the tailshaft, or if it is the diff it may just be able to be adjusted. Nothing should clunk when you put your foot down, it is the sound of something moving when it should already be fully engaged.

Finally, the drone is a lot harder (I'm assuming it is driveline not engine or exhaust). It could also be a diff problem (eg low on oil, or orn), or a gearbox problem, or even just noisey tyres. If it gets better or worse when turning a corner it might also be a wheel bearing. Hard to more specific than that without more clues

[Grey]

Definitely not noisy tyres or low on oil as I just had a major service done on it using the best oils. I will get a 5th mechanic to have a look at the problem soon and I'll tell him what you have said to see what he thinks. Hopefully I can sort this out without forking big money out. Thanks for the insight. If I ever get this fixed ill post up what is wrong with it.

Edited April 10, 2013 by Grey