Effect of wet clutch degradation and ATF

[SuperSalad]

Experimental characterization of the sliding friction of a
degrading wet friction clutch

I thought this was interesting because the reasoning was unexpected for me. It isn't that the fluid or the friction materials themselves "wear out" but that as time goes on, the porous friction material loses its ability to evacuate the ATF from its pores and this is what reduces its coefficient of friction; and not by a small amount.

I know I'm paraphrasing and trying to simplify it, but that was the basic gist I got from the paper. Does anyone else have a different interpretation of the results?

 

[Lolvoguy]

is there a TL;DR version available?

 

[69GTX]

Synchronizer operation on T5 manual transmission

I found this article a few days ago on a Mustang site. They say pretty much the same thing. The T5 has similar characteristics of the later T56 offered up in so many GM vehicles from 1993-2008?

For a manual trans, it's a battle between optimizing synchronizer life vs. gear/bearing life. What typically fails first? I would lean towards the synchronizers, especially the earlier versions which had cellulose lined friction rings, plastic shift forks, and brass or aluminum shift parts instead of steel. The synchronizer linings on early T56's are very similar to automatic transmission clutch surfaces. So in a way, a T56 (others) are a combo of manual and automatic transmission parts. And I think the OP's article link can apply to both automatic and manual transmissions, especially those manual transmissions spec'd for ATF.

Can one single fluid to all 3 jobs perfectly or even adequately? Tremec T56 engineers and quite a few transmission shops/builders still stick with the ATF recipe rather than a stronger MTL. For a TKO Tremec recommends an MTL/synchromesh. There's little doubt that the wrong lubricant in a manual transmission designed for ATF can degrade synchronizer operations far earlier than expected. An over-abundance of EP/AW and other additives would seem capable of "clogging" up or glazing over the rough surface of the clutch friction material.

 

[MolaKule]

Quote:
Based on the observation it is evident that the degraded friction surface has lost its porosity.

Thus, the ability of the degraded friction surface to evacuate the lubricant from the interface deteriorates, suggesting that the friction torque occurring in the clutch is predominantly controlled by the lubricant.


And this why the friction modifier in the ATF should have a stable chemistry.