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^ that is a semi solid transmission mount and adds a lot of interior cabin noise. I have this with LWFW and RS motor mount. The gear whine(like a race car) and LWFW marbles noises are very much present. Looking to go back to a stock setup with function first inserts for added stability.
I don't understand this quote : "your transaxle popping out of gear"
Which transaxle ? The RWD transmission has no transaxle anymore, that's the point.
If it means that the gear engaged might pop out, this could also be related to a bad setting of the gear lever linkage : its is a well known issue that lead some guys to rebuilt a gearbox which had nothing wrong, juste a bad setting of the linkage.
Anyway, I can understand the mount being on right side instead of being in the front would provide a different holding of the gearbox but on full torque load, engine and gearbox are supposed to twist a little. When the longitudinal tube is in place, it would mean the whole transmission would twist : engine+gearbox+tube+transaxle (front diff)
But I wonder where the 9&10 mounts, specific to the C4, are going. Anyone has a photo with parts in place ?
9&10 are to support the front diff on the front suspension crossmember, can just see it to the bottom right of this pic:
This effectively supports the middle of the gearbox at the other end of the car due to the stuffiness of the prop shaft - very little twist is possible with this all correctly fitted.
"your transaxle popping out of gear" was their words not mine, I suspect they meant that running without the prop shaft or any additional support can allow the whole system to move about enough to cause problems with the shifter mechanism.
With the prop shaft out the way its quite apparent that the single right side C4 tranny mount will not provide adequate support as the front of the gearbox gets kinda floppy.
All I'm trying to do is point out the fact that this c4-c2 mod is asking parts to deal with forces they were not designed for - look at how robust and considered the C2 mount is in comparison.
For a track car like Jacks the last thing you want is the whole engine and gearbox moving around while you are driving, cant be long until the rear engine mount surrenders somehow.
I'm pretty sure you could let the longitudinal slave cylinder tied up somewhere, you would then still benefit of the rear axle locking differential by PDAS.
The PDAS would keep "locking" the longitudinal diff without knowing it's not active anymore.
Maybe if the cylinder is removed and the line correctly closed, it would work as well, but maybe not. I think I'll try everything without removing it at first.
That's exactly what is is being done, only the slave cylinder for the centre diff is being removed, the one for the rear diff is left in situ and the PDAS should apply it.
If thats the plan then I think there will be problems with engine and gearbox stability.
The C4 gearbox mount is designed to be used with the torque tube and not as a standalone gearbox support. It only connects to one side of the gearbox and will not provide adequate support if the torque tube is not present.
As per the link in my post the 993TT boys have had to deal with this issue when converting to RWD, from that page:
"When AWD components are removed from a 993 turbo or C4, you are left with a mono-directional mount at the front of your transmission. This mount was not designed to handle engine torque on it’s own and introduces a variety of undesirable behaviors, such as your transaxle popping out of gear under hard acceleration or deceleration."
Not considered it as an issue...I'll look into this but even though the mount goes to the side of the front of the box rather than the very front I can't see that it would necessarily cause an issue, particularly with RS mounts for the engine. The 993 had a slightly different mount which I believe was softer. However we will double check this
Yep I've seen welded up diffs before.. but not a specific collar. Also no detail here on whether it was used in a 964 or how the PDAS was working with the rear diff?
Great work Jack, I like the video,
can't wait to hear your impressions driving it ,
Are you confidente the limited split differential would work with the master cylinder in place ?
could you describe how ,
Yep I've seen welded up diffs before.. but not a specific collar. Also no detail here on whether it was used in a 964 or how the PDAS was working with the rear diff?
Great work Jack, I like the video,
can't wait to hear your impressions driving it ,
Are you confidente the limited split differential would work with the master cylinder in place ?
could you describe how ,
There are two hydraulic lines going to the back of the car operated by the PDAS. One feeds a slave actuator which activates the centre diff, this has been removed and the line blanked off with a bleed nipple (might find a more elegant solution eventually but this is fine in terms of function). The other line goes to the rear diff and has been left in place. The PDAS will still think it is actuating the centre diff by pushing pressure down the hydraulic line to the centre diff, it has no sensor to tell it it is no longer working. In the same way it should still try and actuate the rear LSD when it detects slip, however since the line is in place this should work. .......in theory! Don't think anyone else has tried this so we will see but no reason it should not work.
Actually, the PDAS blocks the diffs most of the time above a small speed, except when braking : it then releases pressure on slave cylinders.
That is why it is highly NOT recommended to enter a curve with a C4 without having the foot at least slightly on the brake pedal.
;-)
That is definitely not my understanding about how the PDAS works Manu.. it is true that if the PDAS has engaged and you dab the brake that will release the lock on the diffs but it will not simply engage them at all times above a slow speed> It engages them when it detects that there is slip in one of the wheels.. just as a mechanical LSD would do on the rear diff.
08-02-2017, 07:21 AM
