Tech Tips

Checking and Replacing Transmission Fluid

Corey Jacques of The Sports Car Workshop

We recently purchased a Porsche that was in excellent cosmetic condition…very well preserved and well presented.  However, the road test was a letdown.  The car shifted miserably and when letting off the gas would experience backlash that was getting worse each trip.  A check on the lift confirmed that the transmission had much internal wear as the differential had let out a bang when suddenly accelerated or decelerated.  This kind of damage could have been the result of a rear-end accident at some point, but it also could be due to poor transmission maintenance.

            Is your Porsche kept highly polished and pampered in a nice dry environment where you don’t even drive in the rain unless necessary?  How often do you crawl under your car for the same type of loving care?  Newer cars don’t require the frequent maintenance that our older Porsche do.  It’s easy to forget that routine maintenance checks are due.  Your transmission fluid should be changed every 30,000 miles or every two years.  (Check your owner’s manual for intervals of your model, a 356 may require changes between 6,000 and 12,000 miles…and checked every 3,000 for proper level).

            The importance of the level and quality of transmission fluid is due to the fact that it directly affects the wear of the transmission.  If the fluid level is low, it can significantly accelerate wear of the synchro rings, sliders, and gears.  Once wear starts, the additional metal particles in the fluid only assist the wearing process by acting like a grinding compound.  If your transmission seems to be getting more difficult to shift smoothly, the fluid level should be one of the first items to check.  The fluid also assists in cooling the transmission.  Like engines, transmissions generate heat, and a function of the transmission fluid is to help dissipate the heat.  (Some models even have an external fluid cooler to deal with the heat generated)

            A good place to start is by checking your transmission fluid level and noting when it was last changed.  There are probably cars out there that haven’t had the level checked…let alone changed…for many years.  The process to check the level is very basic, but because it does require getting under the car, it probably doesn’t get the attention it deserves.  There are two plugs in the transmission; one to check the level and also used for filling (upper plug), while the other (lower) plug is used for draining purposes.  First you will need to remove the fill/inspection plug.  (Consult your owner’s manual for exact location of the plug.)  With the engine cold and the car on level ground, simply stick your finger in the hole and curl it downward to see if you can feel any fluid.  If you can feel fluid, the level is OK.  If not, it may require just a little to bring it back up to just below the hole.

            If you are planning on changing the fluid, have a drip pan available that is capable of holding at least five or six quarts of fluid.  Having some rags at the ready would also be a good idea…just in case!  Driving the car for a few minutes beforehand may be a good idea to warm up the transmission fluid a little so that it will flow and drain easier.  Then remove the filler plug first to check to see if the level was low to begin with, and also to vent the transmission case allowing the fluid to drain easier.  Next remove the drain (lower) plug.  Note that the drain plug is magnetic and will attract small metal particles.  You want to completely clean the plug of metal particles before replacing it in the case.  Replace the drain plug and torque to 17.6 ft/lbs.

            To refill the transmission fluid, you will need a simple hand operated transfer pump.  Most any auto parts store should sell one of these pumps to transfer the fluid from the container of fluid to the upper hole in the transmission.  Simply put the hose in the hole and pump the fluid until it just starts to drip out of the hole…then reinstall the fill plug.

            As for the type of transmission fluid, we recommend Swepco 201 Multi-Purpose Gear Lube 80/90.  Porsche enthusiasts and weekend racers alike have been very pleased with using Swepco 201 for years.  Many have commented that it has improved the operation and feel of their transmissions and helped prolong the life of the components.  My own 1985 Carrera was quite difficult to shift when I purchased it, and a simple change to Swepco made a very noticeable difference.  A transmission rebuild can be a very expensive event…not to mention the “down time” while the work is completed.  Why not avoid unpleasant surprises from your transmission…put on some old clothes and check or change your transmission fluid today!