Brent 89-GT

Steve, You must have mis-read my post. Tom Charlesworth claimed he had broken two driveshafts on AUTOMATIC equipped cars. He claimed it was the shock of a high rpm one-two shift that caused it, hence the one-two shift is programmed to occur at 4500 rpm in Auto cars.

That would make the manual cars much stronger, as I have been unable to break my driveshaft even with repeated high rpm clutch drops and speed shifts.That is certainly more abuse than any factory auto shift.

The question remains to the automatic trans S4 owners....is this normal? I just find it strange that Porsche would have to program in a shift point to baby the driveshaft when an obviously much stronger part existed in the manual cars. Is it the third bearing in the torque tube?

2V4V

Brent,

One of the many reasons drag race guys use an auto trans is that they are easier on the drivetrain (one of the many).

I have a GTS (28.18) a/t in my '84 which (currently) puts out ~ 275 HP at the rears (pretty close to many factory 5 L cars). I have shifted at 6K rpms from 1 to 2 more than a few times. Nothing breaks. I have used 928 a/t boxes with far more HP than any factory car, have yet to see or hear of this problem anywhere else (without serious, deliberate abuse), on any 928, manual or auto.

Part of the beauty of an auto box is the relative lack of shock to the driveline during shifts. As you have observed, a hard clutch shift will induce a far greater momentary load, esp if not well-executed.

If this guy is breaking driveshafts, he has a different issue with the trans set-up. There's a world of possibilities, I'd love to see the driveshafts, and how/where they failed. But it's not that the 928 motor has soooo much TQ.

Greg

tuk_928

Good thread.

Steve or anyone...can you please tell me what "TV Cable" stands for here? I'd love to tweak the shift points on my s4's A/T as it seems to shift way too low in the rpm range for my liking...never gets close to redline even at WOT.

Thanks,
Tim

Brent 89-GT

Well Greg, I would have to agree with you. The reason I brought it up was because Mr.Charlesworth, a PCA national tech advisor stated so in the current issue of Panorama. I find it to be a crazy assertion myself and can not imagine how a max rpm auto shift in a stock 928 could possibly cause damage like he suggested. Further, I can not imagine that Porsche would send their top of the line model out the door with such a glaring weakness.I am still a little baffled as to why the car is set up to shift so early in the power band from the factory. It just seems so un-Porschelike. Ipersonally would have been bummed had I bought an auto car and found this out. Thank goodness I was adiment about the five speed

Erik - Denmark

Tim,
You have 3 cables to the gas regulator
1. One to the accelerator pedal
2. One to the Tempostat
3. One to the automatic transmission - That is this one - This has to be adjusted without slake - Disconnect this at the ball point, pull slighly in the cable and adjust the length so the head align to the ball and mount it.
There is a good instruction in the shop manual
Mark the starting position, so you can find back, if something’s goes wrong - Best to the adjustment in small steps of f.ex. one turn, and test and so one
Good luck
Erik in Denmark

Steve Cattaneo

Brent,
I totally agree with you that the manual drive shaft with its three support bearings would be stronger then the automatic with only two support bearings. But as to the transmission its self, the automatics can absorb and transfer more torque then a manual. Even with the automatic drive shaft being weaker I doubt the cause of failure was a 1st to 2nd shift at 4500RPM


The US autos were set up to shift at 4500/4800 RPMs for fuel economy. It is not hard to raise the full throttle up shifts. A simple adjustment on the valve body will do it.

Tim,


TV means throttle valve, a shift timing valve controlled by a cable on the engine. Make it tighter and the up shifts will be later to a point.

SteveM928

I think it was this board where it was mentioned before, but did anybody ever figure out how to adjust the A/T to downshift into first gear at a higher speed? Once you're above about 20mph, it won't shift back down to first anymore if you floor it, and acceleration is relatively sluggish at that speed in second gear.

Tony

OK....
To get a first gear start is a NO BRAINER, you dont need an electronic box to do it. Select "2" or put your foot down in D. With the cable adjusted properly or just on the tight side it WILL go to 1st.

What is needed IMHO is a way to drop the tranny into first gear at a slightly higher speed. The biggest achilles heal in this car is entering a corner at appx 15 -20..in 2nd gear....exit the turn foot to the floor and NOTHING! It feels like my 3yr old can pass me on his bike! The tach just slowly winds up until its time for 3rd. It takes an eternity.

With the selector in "2" , a down shift to 1st at 20 mph or a selectable speed, would be very cool!