Don't neglect this maintenance – transmissions are expensive to replace
Performance Gain:
Long-life transmission
Complementary Modification:
Oil change
This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your Porsche Boxster. The book contains 312 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 950+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Boxster owner's collection. The book is currently available and in stock now. See The Official Book Website for more details.
Check out some other sample projects from the book:
Replacing your oil is easy - Porsche knows that this needs to be performed once about every 3000-5000 miles, and designed the car that way. On the other hand, changing the tranny fluid is not an easy task, and you can probably bet that the previous owner of your car did not perform this task when they owned it.
What are the symptoms of low automatic transmission fluid? I experienced this with a car I purchased with a known transmission problem: when the car was stopped suddenly via the brakes and then the accelerator was immediately pressed, the transmission would slip, and then slam into gear, lurching the car forward. Not really a good sign, but I had a strong suspicion that the transmission was low on fluid. Why did I suspect this? A thorough inspection of the car showed the remnants of significant leakage of transmission fluid.
What causes this symptom with the transmission? Well, when you slam on the brakes, all of the fluid in the transmission flows to the front of the car and away from the fluid pickup, which is located towards the rear of the transmission. With the fluid at the front of the car, the transmission loses fluid for a very short while. Automatic transmissions use the fluid both as a hydraulic fluid and a coolant - they won't work if there isn't any fluid running through them. After the car has stopped, and the fluid has moved back towards the pickup, the transmission began to work normally. If the transmission has the proper levels of fluid, then this condition would not occur. Needless to say, after I replaced the transmission fluid and checked the levels, the problem disappeared. The previous owner had let it run down about 2 quarts low (the Boxster transmission takes about 9 quarts). Driving for any more time with the transmission in this state would have led to substantial damage, and could have resulted in a wrecked tranny (replacement cost $2500 or so).
Okay, enough background on the automatic transmission. The first step in replacing your fluid is to jack up your car so that you can reach the underside of the transmission (see Pelican Technical Article: Jacking Up and Lifting the Boxster on Jack Stands). It is very important that the car be level - don't jack up just the front or rear of the car, make sure that it is as level in the air as it is on the ground. The reason for this is that you will be checking the transmission fluid by removing a drain plug and checking the fluid level. If the car is not level, then you will not achieve an accurate reading. Also elevate the car with the rear tailpipe sticking way outside the entrance of your garage: you will be running the car while it's on the jack stands in order to top off the fluid.
With the car elevated in the air, you should be able to see the rear transmission pan cover (see Figure 1). You need to remove this cover, and the two aluminum support bars on either side of the car. You may have to also remove the plastic cover towards the front of the car in order to remove the two aluminum support bars. Wear safety glasses when you're under the car as you never know what small piece of dirt may fall into your eye.
The next step is to remove all of the existing fluid from the main transmission sump. There is a drain plug on the bottom of the sump that can be used to empty most of the fluid contained inside. Remove the drain plug and let the fluid flow out into a container. Your container should be able to hold at least three gallons (about 12 liters) of fluid. Once the fluid is empty, replace the drain plug. This plug should be tightened to 40 Nm (29 ft-lb).
Now you will proceed to remove the sump from the bottom of the transmission. You need to remove the sump so that you can replace the transmission filter, clean the sump magnet, and also remove all of the extra fluid that may be trapped inside. You remove the sump by removing each of the small torx bolts that attach it to the bottom of the transmission. Once those are out, you should simply be able to pull on the sump cover and it should fall off. Be aware that there will still be some transmission fluid in the sump that can spill out if you're not careful.
Plastic cat litter boxes make excellent containers for catching fluid in these types of situations. They are wide and large enough to prevent you from making quite a mess on your garage floor. Turn your attention now to the sumps and clean them out. Then, remove the transmission filter from the bottom of the transmission.
What type of fluid do you use in your automatic transmission? The Boxster requires a special type of fluid that you cannot easily find in most auto parts stores. The Porsche part number for the transmission fluid is 999-917-545-00, but is almost $35 a liter. The Boxster also can use off-the-shelf Esso LT 71141, or Pentosin ATF-1, both available along with gasket/filter kits from PelicanParts.com. I would avoid using any other type of fluid in your transmission. Also, use the same fluid for the entire replacement process - mixing and matching different types of transmission fluid can cause your transmission to fail.
With the new filter in place, you will now reinstall the lower sump. No need to fill it with fluid - simply bolt it up into place. Torque each bolt to 11 Nm (8 ft-lb), and use a criss-cross pattern as shown in Figure 6. Now it's time to fill the sump with fluid. Using a hand pump attached to the bottle of transmission fluid, thread the hose up into the filler hole and through one of the access holes in the side of the filler baffle (Figure 5). Fill up the transmission sump until fluid starts to significantly run out of the filler hole. A few drips can be expected when the fluid runs down the side of the hose: when the fluid level is at the top of the filler, it will start to exit the filler hole rapidly. Replace the filler plug and tighten it hand-tight.
At this point, you are ready to start the car. Keep in mind that the transmission fluid can only be checked when the transmission temperature is within a semi-narrow range. This temperature range is 85°-100° F (30°-40° C). You will need to start the car and let it warm up before you can check the levels. Depending upon the outside temperature, it may take up to 45 minutes for it to reach this temperature. Check the temperature of the fluid by using one of those handy infrared laser thermometers. Years ago, these used to cost thousands of dollars, but nowadays, you can pick one up for about $50.
You will be running the car while it is up and on jack stands. This can be dangerous if the car is not secure on the jack stands - check them again before you continue. You will also be running the car for an extended length of time while it warms up and you will need to make sure that you perform this outside (on level ground), or funnel the exhaust gases out of the tail pipe and out of your garage. I used a long, flexible aluminum tube that I purchased from the hardware store that is typically used for venting gas dryers out to the atmosphere (see Figure 8). If you clamp this tightly to the end of your tailpipe, and run the other end out of your garage with the garage door open, you should be able to safely have the car idle inside the garage. Also make sure that you use an electronic carbon monoxide monitor inside your garage (also available from most hardware stores) as an added measure for safety.
Climb into the car, place your foot on the brake and start it. If you hear anything amiss, or encounter any unusual problems, then shut off the car immediately. It should start and idle normally. You will need to let the transmission warm up until it is in the operating range indicated above. Note that this will make the bottom of the sump feel warm to the touch - not hot. Use your infrared thermometer to periodically check the temperature. Again, it should take between 10-45 minutes depending upon the outside temperature to heat the transmission to this level, if the car is simply idling.
With the car at the proper temperature, remove the filler plug and begin filling the transmission again. It's okay to use your finger to gently stick the hose attached to your pump up inside the transmission. At this time, the fluid should be warm to the touch. Be careful not to burn yourself on the catalytic converters, headers, or the muffler that is merely inches away. When the fluid begins to empty out of the filler hole, replace the filler plug again, and tighten it hand-tight.
Now, sit inside the car, apply the brake pedal, and slowly shift the transmission through reverse, and first and second gear, using the manual shift lever. Leave the car in each gear for about 10 seconds. Repeat this twice, move underneath the car again, and remove the fill plug from the bottom side of the transmission. With the engine still running, top off the transmission once more until fluid comes out of the fill hole. Replace the fill plug, using a new sealing o-ring. This plug should be torqued to 80 Nm (59 ft-lb)
That's about all there is to it. When you've topped off the fluid, lower the car down off of the jack stands and take it for a short drive. If all is well, you shouldn't notice any difference in performance or operation. If you were having problems with the transmission slamming into gear, then these issues should be gone by now. One last thing to note, the automatic transmission also has a built-in differential which requires standard gear oil. Check and fill your gear oil as per the instructions in Pelican Technical Article: Differential / Manual Transmission Fluid Change.
Figure 1
In order to gain access to the bottom transmission sump, you will need to remove the rear transmission pan cover and the aluminum support bars on either side. The pan cover is held on with two screws in the rear (green arrows), two more up front (yellow arrow), and also shares some screws with the aluminum support bars (red arrows). Once the cover and bars are removed, then you will need to drop down the rear sway bar. Simply remove the bolts that fasten the sway bar and bushing to the chassis (blue arrows in inset photo).
I recommend that you start the draining process only when the car is cold. When the car is warm, a lot of the transmission fluid will be trapped within the transmission itself. When the car is cold, almost all of the transmission fluid has seeped out, and is trapped in the lower sump. Note that this is opposite from the procedure for changing the oil - where you should empty it when the engine is hot. That is because the engine oil is thinnest and flows best when it's hot. The transmission fluid has a totally different viscosity. Working on the car when it's cold also assures that you will not be burned by hot exhaust, transmission or engine parts. The green arrow shows the transmission filler plug, and the inset photo shows the 17mm hex socket required to remove the transmission drain plug.
Using a lint-free cloth, carefully wipe down the inside of the sump (I used KimWipes, available from PelicanParts.com). You want to use a lint-free cloth, because tiny cloth fibers left in your transmission sump can clog the transmission and filter. The sump needs to be clean, spotless, and look brand new, as shown on the right. Make sure that you remove any remaining gasket material from the edge of the sump cover. A new transmission sump gasket has been lined up with the holes, and the assembly is ready for installation back onto the transmission. In the upper left, the new transmission filter is displayed. You should always use a new o-ring on the transmission filler plug, as shown in the middle left photo. Pay close attention to the magnet in the bottom of the sump (shown on the lower left). You should be able to simply pluck this magnet from the bottom of the sump and clean it.
The transmission fluid filter is a large canister that is attached to the bottom of the transmission, and needs to be removed and replaced. Remove the bolts that attach it to the bottom of the transmission and carefully pull off the filter. Discard it in the trash. Check the mounting surfaces where the sumps attach to the transmission, and remove any excess gasket material that may have been left there. When you reinstall the filter into the transmission, use the same bolts that you just removed. These bolts should be torqued to a very light 6 Nm (4.5 ft-lb). The inset photo shows the new filter installed in place.
Getting the hose into the sump area so that you can fill the transmission can be a bit tricky if you're not aware of where the hose is supposed to go. This photo shows the hose threaded up the bottom of the filler hole, and sticking out into the transmission sump. When the sump is installed back onto the transmission, you will need to feed the hose up the filler hole and through the openings in this baffle attachment.
With the sump installed, tighten the bolts according to the following pattern. These bolts require very little torque: only 11 Nm (8 ft-lbs). Be sure to clean off any dirt or debris that may be on the screws prior to reinstalling them.
You will need to use a transmission fluid pump which you can find at almost any local auto parts store in order to fill the sump. The pump works just like one of those pumps in your bathroom that pumps out liquid soap. The transmission fluid should be pumped into the bottom of the sump through the transmission fill hole. Remove the plug, place one end of the pump into a bottle of transmission fluid, and start pumping. Pump fluid into the filler hole until fluid begins to run out rapidly. Clean up the small spill (be sure to use a large oil drip tray during this process), then replace the fill plug, only slightly tighter than hand-tight (you will be removing it again shortly when you recheck the levels).
Carbon monoxide is dangerous, and although today's modern cars don't emit too much of it, you can still kill off some brain cells by breathing it in. Play it safe and route the exhaust from your tailpipe out of your garage area. Use a standard dryer vent hose and plug the sides of the tailpipe if you happen to feel exhaust escaping.
The infrared thermometer is one of those whiz-bang devices that never ceases to amaze me. Years ago, these used to cost thousands of dollars, but nowadays, you can pick one up for a mere $50. Monitor the temperature of the transmission sump by pointing the thermometer at the bottom of the metal sump in the center. Don't take the measurements from the sides, as the catalytic converter is nearby and will tend to heat the sump a bit more in that area, leading to false readings.
Comments: Hello, the problem i am having is so strange. Each time i use reverse on my tip tronic, in my 97 Boxster, it will work fine at lower speeds, at around 8 to 10 mph it will act like you have just applied the brakes. No strange noise, just stops the car. Other than that it performs perfect. THANKS SO MUCH.
May 18, 2012
rey
Comments: Hi Wayne...I wanna know if i will be using a 17 hex socket to unscrew the atf filler screw of my boxster 99 tranny..i want to top it up. can i do it without even remving the tranny cover?
April 13, 2012
ST
Comments: Hello Wayne:
I finally completed this project and I now have a whine coming on when I am in the fifth gear. Also the ABS indicator came on and it appears that the rear right wheel does not rotate under acceleration it seems like its stuck, but will rotate when I give it a push. I used a Mechanics stethoscope and cant hear any noise coming from inside the transmission...
Any ideas what could be wrong?
Also, I must add the following. i rear right CV boot is torn ii Rear Left CV joint is probably bad as I can hear a clunk. iii I also hear loud clicking noise when going from reverse to Park.
Car is a boxster S 2001
December 14, 2011
Followup from the Pelican Staff: Yes, I think you have answered your own question here - it sounds like the CV joints may be bad. They tend to wear out very quickly when the boot tears. Either that, or the differential carrier bearings in the transmission, but those are more unlikely to be the problem. - Wayne at Pelican Parts
ST
Comments: Thanks for your reply Wayne. After reading several forums, it appears that it is best not to get the entire fluid changed because the existing fluid contains particles of clutch, gear, etc... So changing it in its entirety will lead to slippage.... Especially so because my car is an 01 with 82K miles and has never had the atf fluid replaced...... Do you think this assessment is correct? Thanks a million!
February 23, 2011
Followup from the Pelican Staff: Interesting question. I've heard both schools of thought. Some people claim that changing the fluid makes it too "slippery" and then causes problems with the automatic transmission. I have heard anecdotal stories about this happening on some of the BMW transmissions (which are finicky), but not the Boxster transmissions. Porsche (and BMW) don't even like the transmissions to be serviced, claiming "lifetime fluid" has been installed. In my opinion, the problems that people have seen with their transmissions after changing the fluid (which are rare), may be coincidence and/or their transmissions were on their way out anyways. I think changing the fluid as described in the article is a good way to go, and a complete flush of the unit (two or more changes) is probably not necessary. - Wayne at Pelican Parts
ST
Comments: Hello Wayne: I am not sure how many quarts litres of ATF fluid to order. The order page says order 3.5 litres, however the capacity of the tiptronic tranny seems to be 9 quarts. In your reply below, you seem to refer to BMW... I am referring to a 2001 Boxster S 986.
February 22, 2011
Followup from the Pelican Staff: Sorry, I got confused! :) The first comment below is correct - I would get 5 quarts to be safe, but if you want to flush the whole thing out, you would have to do it twice, which would be about 10 quarts (but only if you did the change twice). - Wayne at Pelican Parts
Dinh
Comments: Wayne - Just want to be clear before ordering. I am still confused about how many liters of transmission needed. Your article said 9 quarts and the comment below to Jeffrey you said 3.5 liters about 3.5 quarts. All I want to do is replacing transmission filter and gasket etc. just like your article described. So buying 4 quarts is enough? Thank your for your time.
December 13, 2010
Followup from the Pelican Staff: BMW used several different models of transmissions on this car, so it really depends upon which one you have in your car. The fluid used is typically printed on a tab on the side of the transmission - it's standard transmission fluid that you can get at any auto parts store. I would probably buy five quarts and then use the wife's car to run out and get some more if it's not enough! :) - Wayne at Pelican Parts
Jeffrey
Comments: Wayne the article doesn't state how much fluid you need to do the change I have read at different sites on the net I need 7 liters also another site claims 9 and another said 6. Since I have to order this fluid ti would be nice to know how much is needed for the change. How much actually drains out and needs to be replaced. Thanks
June 29, 2010
Followup from the Pelican Staff: The manual I have says that the filling capacity for a fluid change is 3.5 liters. However, the manual also says total fluid capacity for the transmission and the torque converter is 9 liters. So, if you want to be completely thorough and try to get all of the fluid changed, then it would seem that you would need to change the fluid, drive the car 10 miles, and then repeat this twice (change the fluid a total of 3 times). The factory doesn't state to do this however. - Wayne at Pelican Parts
Check out some other sample projects from the book:
