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Discussion Starter #1 (Edited)
I need help figuring out what a sound from the drivetrain on my 1991 MR2 turbo is.

Please ignore ideas that may be related to the engine, brakes, suspension, gearbox clutch and wheels. I've examined this problem enough to know it is a drivetrain issue.

The sound is a metallic clanking/clacking/clicking noise (more like a "thump" than bad engine valves ticking, yet still metallic) that seems to appear once every time the wheel rotates. The sound is coming from the rear at the driver side.

When very slight throttle is applied, as in simply maintaining 50 MPH on the highway with no acceleration or deceleration, the sound is usually not present. However, immediately as I lift off the throttle and the car slowly decelerates, the sound will appear. Applying throttle again to catch up to 50 MPH again will again make it disappear.

Sometimes the car needs to be driven for approximately 20-30 minutes before the sound will appear at all. However, sometimes the sound will be there almost right from the start. I don't know why this is, maybe related to temperature changes.

The car can also be put under hard load on a dyno without the sound appearing at all, but these dyno pulls are only for short periods of time.

What is this sound? Any ideas are appreciated, but what I'd like most of all would be simply a suggestion for what I should look at first. I.e. with a sound like this one, statistically speaking, what part is worn or broken and how do I confirm this before buying a new part or parts?
 

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The drivetrain includes clutch, gearbox/differential, and axles.

I would encourage you to consider all ideas and double check stuff, because if you are 100% certain it is a drivetrain problem but it isn't the transmission (unless by gearbox you are excluding the differential / final drive) or clutch, the only things left are axles so you might as well check them without posting a thread for additional ideas. :p

Can you replicate the sound by raising the vehicle on jackstands and rotating the wheels with the engine off / transmission in neutral?
 

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Like JLee said, sounds like a bum axle most likely, if everything else you've said is to be taken at face value.

Also like JLee said, don't discount everything else unless you're 100% sure and have triple-checked it yourself and had another person double-check that. Such stories I have...
 

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Discussion Starter #4 (Edited)
The drivetrain includes clutch, gearbox/differential, and axles.

I would encourage you to consider all ideas and double check stuff, because if you are 100% certain it is a drivetrain problem but it isn't the transmission (unless by gearbox you are excluding the differential / final drive) or clutch, the only things left are axles so you might as well check them without posting a thread for additional ideas. :p

Can you replicate the sound by raising the vehicle on jackstands and rotating the wheels with the engine off / transmission in neutral?
Sorry about that, you're right of course. The gearbox has been overhauled and the clutch has been replaced, but the sound appears even when the car is in neutral and coasting, regardless of the clutch being engaged or not. I am excluding the differential/final drive when I say gearbox, I should have been more specific, forgive me.

When I have the car on jackstands and twist the wheel forwards and backwards (in neutral with no hand brake) I can hear a sound that is quite similar to the sound I'm talking about. I'm not sure if it is normal for it to make a sound when doing that.

Just rotating the wheel freely does not produce any sound.

I've also tried to twist the wheel from side to side on both axis, there is no play that I can feel.
 

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Discussion Starter #7
Replace the axle(s) and see!

When was the last time your car got axles? What condition are the boots in? What does the grease inside the CV joint look like?
I have no information for how old the axles are.

The boots appear to be fine, the rubber does not appear worn or to have any cracks or tears. I have not checked the grease inside the CV joint, I can try to do that but I will probably need to read up on how to do it first. I'm only a beginner.
 

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Could be a wheel bearing. I had one go once that appeared fine, other than making a rhythmic "clicking" noise. On disassemble, I found two small pits in the bearing race.
 

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From your description I'd guess its a worn CV joint. A good upgrade is to replace with stronger cages using a kit from CRW or ATS. Search on this as there are some videos and pics in forum on how to do .

Jim
 
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