V6 transmission whine - Alfa Romeo Forum
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V6 transmission whine

My 98 reg 166 3.0 V6 with the 6 speed manual has a transmission whine, that sounds little bit like a straight-cut gear set. As the problem is present through all 6 gears, I'm guessing it must be a problem with the diff.

Would it be a false economy to try and source a 2nd hand diff, or complete gearbox to rob the diff from? I know most members would probably suggest Q2ing it, but I don't need an LSD. But I would consider it if was deemed bad sense to fit a 2nd hand diff, and if a new OE item was comparable in price to a Q2 (I genuinely have no idea how much a new OE diff costs).

I really need to strike the right balance between doing this cost effectively, but doing it right. It's going to be an expensive job either way, I appreciate that.

And I suppose the most important question is, should I really be concerned by this? I've read that diff failures seem to be common on V6 models, and I realise they can fail spectacularly. But I don't drive my 166 hard, nor does it do great mileage.
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I was in the same predicament a few months ago and got a 6 speed from a 2.5 V6 from autolusso much cheaper than a 3l box. The box was £250 delivered to my local garage, they fitted it for about £350. For normal driving it feels no different but when driving hard I notice you do need to change gear slightly sooner, in theory acceleration is faster due to the shorter gear ratios.

With the LSD fitted the box would have cost over £800 which i just could not justify.

Everyone on here will tell you that LSD upgrade is essential but a highly regarded Alfa specialist told me that he finds the 3.0l not as prone to diff failure as people say but its the higher powered 3.2l that really do need up rated diff and hence didnít recommended q2 as essential for me.

Hope this helps, I suggest you giving autolusso a call to discuss options for your car, they are always very helpful!

Good luck!
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The 6 speeder isn't a great DIY gearbox due to having to get the main bearing pre-loads right.

The diff itself only has plain bearings in it, and they only do any work when you are turning, so likely not that.

If it's a main crownwheel/pinion problem, then if you swapped out the crownwheel, that's easy enough, but you also need to swap the pinion as well...and that's part of the output shaft which then gets you into the whole bearing pre-load adjustment deal which is prety specialist.

Could be diff bearings which is a DIY proposition or a relatively cheap repair, as long as it's not led to CWP wear as well.

A Q2 is a nice thing to have, but if the box is coming apart anyway, it's easy to inspect the diff and see if the pin is escaping.

The limited experience I have with the 6 speeder was an Alfa refurb from a GTA. You could see where the casing had been welded up after the diff fell apart! The diff in it was a new one, but I fitted a Q2 anyway as I was looking for the handling benefits more than anything and had grand ideas that my supercharged 12V motor would produce enough torque to trouble a stock diff.

Another thought - if it is purely rev-related and not road speed related, then it is likely going to be input shaft bearings.

HTH
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