I did a search but can't find a specific answer.

Will a lightweight friction disc put less stress on the syncros ?

The way I understand things (which could be very wrong) the main shaft and friction disc are the only rotating items that need to match the transmisssion speed when shifting. The disc has quite a bit of polar momentum, it would be easier to change the rpm of a lighter one, thus less wear and tear on the syncros.

 

Your theory seems basically correct (after mentally following the path through the transmission). There's a few other components that really don't contribute significantly to the rotational momentum of the input shaft, and aren't worth considering. Ya, I'd buy your theory

So now here comes the question that really matters: Do you know of a specific disc that's as durable as the stock disc yet measurably lighter?

Keep in mind here that just as with the engine side (lighter FW & PP), there's a point where the benefit of mass reduction is diminished by other problems. So how much lighter are we talking?

 

I don't have a specific disc in mind, but with the materials available today, it should be possible to have a light weight and durable product. What I don't have is a feel for the gains realized.

Has anyone noticed improved shifting with a light aftermarket disc?

 

To my knowlege there isn't a disc out there that's marketed as a 'lighter' disc.
With respect to performance - pound for pound you would realize a much greater net gain in the removal of mass from the flywheel, in that you can remove a lot more mass from the flywheel, and from a greater moment arm (relative to the disc).
Additionally, there's not a lot of profit potential in a disc relative to the profit that can be realized from a flyhweel.
Nevertheless, the minimal gains would probably be outweighed by the potential for smoother shifting.

 

I notice you have a MY04. I think it would be more economic to simply just run what you have (the stock clutch) After it wears out in 3-4 years, (depending on how good you are to your clutch) with all the knowledge you will learn in 1 year on this website, you will have a better idea.

 

whoops, repost

 

My focus is not to lighten the car to gain hp/wt, but to allow the transmission to shift easier/ faster. I don't intend to replace my clutch till it wears out. I typically get >60K miles on a clutch.

My question was more of a theoretical one, from the standpoint of how much less mass the synchros would have to deal with, and would this be a measureable benefit.

 

The disk is already so light that I don't think there would be any difference at all. The input shaft is considerably heavier the the clutch disk.

Members on this board have reported performance benifits with a lighter flywheel. (comptech, toda) The rpm's will drop slightly faster upon taking foot off the throttle during shifting. That just means you would shift quicker.

 

The question still remains.

Grinding when shifting occurs when you engage the gear prior to the synchro matching the rpm (up or down) of the main shaft and clutch to the transmission rpm. The friction disc plays a role in this because of the relative large diameter and considerable polar momentum (compared to the mainshaft).

My gut feel says that reducing that weight will also reduce grinding gears and allowing faster shifts because the synchronizer rings will be more efficient.

 

Ok, this is the first I have heard about a grinding issue in this thread, so I will try another angle. I have talked to a small number MY04 owners and they say that the MY04 shifts smoother then the previous MY's.

You could try performing a thorough flush and bleed and see if that helps. I have a MY03 and I have absolutely no problem's shifting. It seems to shift easier and faster from 6 thousand rpm's and higher.

This is the first grind issue I have heard with a MY04. Other than performing a thorough flush and bleed, I really don't know what to tell you.

As far as a lighter clutch disk, there just may be a lighter one out there, but I can guarantee you that the engagement characteristics will be nowhere near what they are now. In other words, you might not like the characteristics of a "race" clutch disk.

Basically, if you want better performance, you want to shift faster, (speed shift) go with a lighter flywheel such as a comptech for one. Members on this board have reported that the "STOCK" clutch disk works very well with an aftermarket pressure plate such as the ACT along with a lighter aftermarket flywheel.

I don't have hard documented evidence, but I don't believe that replacing the OEM clutch disk will help your MY04 shift any better as my MY03 has a stock clutch disk and I can slice through gears like butter.