Transmission Fluid Problem on 928 S4

Hi,

I recently purchased a Porsche 928 S4 which had been in storage for four years. 

It has not been driven yet other than to go onto a transport and then up on a ramp. The automatic shift was stiff, so my mechanic checked the Transmission Fluid and he said there was none in there (visual check in the reservoir). He added about 2 litres and checked the automatic shift and this was now smoother through the changes.

Is it normal for a car left standing for a long time, for the Transmission Fluid to disappear. As there is no obvious signs of leakage.
 

No. ATF doesn't just disappear. However, the capacity for ATF in the transmission reservoir is less than the transmission holds. When the engine is turned off, ATF begins to return to the reservoir from different parts of the transmission. The longer the transmission sits idle, more ATF is trying to return to the reservoir. If the reservoir cap does not seal, ATF will leak from the cap onto the ground. 

In addition, your transmission could have been low on ATF from the outset. The engine must be running and warm to correctly check the level of ATF at the reservoir. Some folks don't follow that requirement, and therefore shortchange the amount of ATF needed.

I will have to check with the previous owner (who stored it for 4 years) to see if there were any leaks.

GKEJ,

If it were me,  I'd completely replace the ATF and filter in this transmission (I've owned and been driving automatic 928's for nearly all of the past 25 years).    Dexron was the original fluid, it used to be sold by Pep Boys as Proline Dexron III, but it is now hard to find, as Pep Boys has stopped selling retail products..  Greg Brown (owner Precision Motors, 928 specialty shop in Anaheim area) says it is the best fluid on the market for these transmissions.   Here's a link to nearly the only seller in the US:     

Edited PS:    Do a search for 'Proline Dexron III' on Ebay.   The link wouldn't post on this 928 OC system.

Be sure to read up on all you can find about the way to purge and replace the fluid, and how to get the proper amount into the transmission pan.   Lots to learn if this is your first 928.   Congratulations, they are great cars if well maintained.

Gary Knox
'95  928 GTS

Hi Gary, thanks for the steer on Pep Boys Proline Dextrin III. Found their website, unfortunately they don't ship anymore as you indicated.

Found some on the America eBay site, just need to check how easy it will be to ship to the UK.

I have read that mixing transmission fluids is not recommended, so research on purging necessary. Lots to learn. 

Since you are in Europe, there may be another source for Dexron III ATF there.   I'd suggest a good search, including shops specializing in servicing cars from the 80's and 90's.  Might be best to focus on those who service Mercedes from that era, as the  928 transmission was made by Mercedes and used in their 5.0 and 5.6 liter cars (and maybe other MB's as well)..

There is also some recent discussion on Rennlist 928 Forum that the Fram Dexron III may be the same as the Pro Line. It is labeled the same by Advance Auto and Walmart in the USA.

Gary