FRporscheman

Is there an animation for beating a dead horse? Insert it here.

I know there's been a lot of discussion in the past about the various lightweight flywheels available, including the factory Porsche 944 S2 setup. I just wanted to share my experience and my thoughts on this, having just did a conversion myself. Please don't ask me why I decided to convert to a 944S2 fw and tt - it's a long story and I'll start another thread.

The 968 in question is a '93 6-speed with 230k miles. The pinion bearing issue never occurred to this car, and the tranny shifts silky smooth in every gear. The TT bearings were bad, but not too bad. They would only grumble gently at that certain rpm. The motor mounts are fairly new and the engine did not vibrate much at all before this saga started.

I took out the entire flywheel/clutch assembly, bellhousing, and TT. I installed a 944S2 flywheel (resurfaced), relined 944S2 clutch disc (new friction surfaces and new springs), used 944S2 PP (resurfaced), new 944S2 release bearing, new pilot bearing, good used 944 NA clutch fork, good used 944 NA fork shaft, new fork needle bearings, 944 NA bellhousing (needed to grind small area around ref sensor to mount 944S2 style sensor bracket), and finally, a 951 torque tube rebuilt with new delrin bushings and new 6006zz vxb bearings.

The only thing I would have done differently in the entire setup is to have used a 944S2 torque tube. The S2 torque tube has a slot cut into it (like the 968 TT) which supposedly damps vibrations. Other TTs lack this slot.

I took it on a few test drives, and the vibrations were intolerable. Not only did it actually annoy me with the vibration sensation, the real problem was that it worried me that it might wear something out or shake bolts loose, or maybe crack a bracket or something. I was especially worried for the oil pickup tube, which as we all know is already susceptible to cracking from vibrations.

At this point I ordered the 944S2 front damper pulley (aka harmonic balancer). I figured this was the key to making my car as smooth as the factory 944S2s were. I just bolted it on today, and it definitely makes a difference. I'd say at least 75% of the vibrations are gone. It's very hard to really quantify the amount of vibrations at all, let alone any quantified before/after measurements. But my arsoscope measures less vibrations.

This could be in my head, but I think there are still some vibrations. The only thing that's left is that slot in the TT which I don't have. The vibrations now are definitely tolerable, and not dangerous at all - it's hardly an issue. But I just didn't want to neglect anything while addressing this whole vibration issue. I certainly won't take out the TT just to fix a minor vibration so I think I'm going to leave it how it is now. I'm happy with it but I just wanted to report that this setup is not as smooth as a 968 TT with a 968 flywheel.

But after months of the car sitting (I just refused to drive it and risk a broken pickup), I'm happy with it now and I can finally add to those 230k miles.

EDIT 8/26/09
I just wanted to add that I eventually found that coincidentally my BS belt skipped a few teeth around the same time I did this swap, so all the extra vibrations were caused by that. Now, with a correctly set BS belt, S2 flywheel, and S2 damper pulley, the car is 100% as smooth as it ever was, perhaps even smoother.

Thom

Interesting feedback, thanks for sharing.

Whenever I've been in a 968 it always felt lightly smoother than my S2.
However I found the difference so small small in terms of smoothness and overall comfort that "upgrading" an S2 with a DMF wouldn't be worth it IMO.

Also, and for what it's worth, I doubt you would get rid of the remaining vibrations by just swapping the 951 TT with an S2 TT.

One combination that would be interesting to try now is a 968 with the S2 vibration damper to see if it cuts vibrations even further.

PorscheDude1

I plan on installing a Fidanza, Design 1 racing clutch disk (has dampening springs in the center as opposed to the solid 968 disk) and S2 harmonic damper in the near future.

Here is the beatin down horse pic.

FRporscheman

It's definitely not worth it to convert an S2 to a DMF. Unless you already have the 968 TT and you are already changing the clutch, and you really really like the easy clutch change of the 968.

I forgot to mention that performance gains with the LWFW were insignificant, even before adding the weighty damper pulley.

chilibluepepper

Arash - do you have a picture of the slot(s) on the S2 Torque tube? I am aware it has one, but I have not actually seen it, and would like to know the location and dimensions. I am doing a 968 engine w/951 TT and S2 transaxle swap into my 951 chassis. I have the S2 Harmonic balancer, and would consider also slotting the TT before the car is completely assembled. Maybe slotting is the final to cancelling the last bit of vibrations.

RajDatta

Arash, I wouldn't get too worked up about slots. They had them in the early cars and the later cars didn't have them.
Raj

300guy

Neat stuff.

I also have the S2 pullley, Fidanza 968 flywheel and the entire rotating/reciprocating assembly was balanced when I rebuild the engine.

Result: Vibration at 3200-3400 during deceleration is significant and embarrassing. I believe that my torque tube needs rebuilding as I can hear the worn bearings with the clutch out when idling, and my S2 pulley was used.

I found that a large source of my rattling was heat shields touching the factory resonator, but there is still too much for my liking. The rattling make my passenger look at me like somethings wrong with the car.

I'm considering installing a 928 torque tube damper when I rebuild the torque tube, but its a shot in the dark. I'm also considering installing a fluid harmonic balancer between the transmission and the torque tube (on the clamp that connects the two)... but haven't thought that one all the way through yet.

FRporscheman

I would love more information on this "928 TT damper".

The slot is in the bottom of the torque tube, about 2 inches from the front, to about 20 inches from the front. It almost looks like a similar slot could be made with an angle grinder. But like Raj said it's a very minor detail that probably makes little/no difference.

User 41221

How fresh are the motor and tranny mounts, and at what rpm range are you feeling the vibration? If they weren't factory parts, that vibration you were experiencing might have pushed them beyond their limits and could cause the vibration you are feeling, especially if it goes away at higher rpm levels.

And yes, I am still jealous of your avatar... lol

User 41221

How fresh are the motor and tranny mounts, and at what rpm range are you feeling the vibration? If they weren't factory parts, that vibration you were experiencing might have pushed them beyond their limits and could cause the new vibration you are feeling, especially if it goes away at higher rpm levels.

And yes, I am still jealous of your avatar... lol

Mike O

I'm very interested in the results of this build. I have the Fidanza with a solid clutch disc and no damper. The only complaint I have is the "nuts in a coffee can" ratttle that occurs under very low torque. Very low like at speeds below 30 mph and letting of the gas to slow down. It irritates me so I push in the clutch and it goes away. I believe the theory that all of this noise is coming from the gear box due to rapid torque reversal that causes the gears to chatter. I haven't been able to convince myself that a harmonic dampener on the other end of the drive line will help so I have not experimented with it.

RajDatta

Harmonic balancer will not cure your coffee can rattle. It will still be there.
Raj

PorscheDude1

I am hoping the Design1 Racing sprung clutch disk inconjuction with the damper will eliminate 75% of the noise.

Honestly, any noise really will not bother me. It is not a luxuary car.

Mike O

LOL! Mine's not either! Raj - Didn't think it would but I like to get all of the experimental results I can

RajDatta

Been there, done that

Raj