Can the Tiptronic ATF get contaminated with diff lube? - 986 Forum - The Community for Porsche Boxster & Cayman Owners

I have seen a 0740 code in my 2000 S Tiptronic, which is identifying a problem with the lock up clutch on the torque converter (I think). It has been suggested to me that one possible cause is that the Tip fluid could be contaminated by diff gear oil and that high mileage Boxsters are succeptible to this. I can see how contaminated fluid might affect anything in the tranny with a clutch but it seems more likely to me that any cross contamination would go the other direction and you'd see ATF in the diff. I guess a lab analysis would clear this up once and for all but I thought I'd ask whether anybody has real world experience with contaminated ATF. The shop manual seems to indicate it could happen if you pulled one of the axles without draining the diff first. Can it also happen if you had seals leaking on both the diff and the tranny? I'm probably going to get the Tip serviced and fluid replaced with new and I hope it puts the 0740 code to rest.

I think the Automatic in the Boxster S is a derivative of the ZF 5HP19, which is found in a good number of Audi's. We've found the torque converter clutches wear out often in these, particularly in applications of 250hp and above. It's a wise first step to replace the fluid - and the filter, and see if it fixes the problem, but I think you'll likely end up replacing the torque converter. As far as the diff fluid mixing with the transmission fluid - it is possible through the seal which seperates the diff from the transmission body - but it's unlikely. Have whichever shop checks it check the fluid level first - if it's overfilled, you might have mixing. If not, you don't.

Thanks for the info. I took the car to the local Porsche shop yesterday and they're going to perform a fluid service on general principles. I told them to go ahead and take a sample of the fluid for lab analysis if they thought it was worth it and I would pay the extra. Question about the failure mode of the torque converter - if the lockup clutch fails will the car leave me stranded on the side of the road? My inclination on my new-to-me 100k mile Boxster is to drive it until it totally fails. Right now the car drives fine once it warms up - nice firm shifts and solid lock up. Maybe I'll be lucky and the service alone will correct it but if it doens't is there any harm or risk from driving it with a weak torque converter?

If the failure is similar to what we usually see, you won't notice much of anything, except maybe slightly higher revs when the clutch really wears out. The torque converter will operate normally as a viscous coupling, but it won't lock up when in the highest gear. We've never seen one really hurt anything. I'd make sure the shop you're using is replacing the fluid filter as well - Audi and VW don't have a service interval for the fluid and filter, and it's just crazy. Normally when we replace the fluid it's as black as used motor oil, and the new, clean fluid is the color of honey!

Thanks for the info. I'm probably going to drive it a while and leave it alone unless it gets a lot worse. The shop still has the car so I don't know what to think right now.

I picked my car up from the shop yesterday, without a Tiptronic service. The mechanic pulled the fill plug and got a chance to see and smell the fluid. He said it was not contaminated with diff lube in the same way he's seen in a different car. He recommended I think twice about a full service because he couldn't recreate the 0740 code and the car acted normally in his view. I was still inclined to go ahead and do it but he told me it would cost over $500 to pull the pan and replace the fluid. That's a lot of money and I'm thinking I could do it myself and save $350. The only thing that worries me a little about DIY is removing the braces and pan that have to come off to reach the pan itself.

Go to Pelican Parts and read the DIY on how to do the service. You will need 9 liters of of ATF fluid, the kit, torque wrench, Torx sockets and a digital in-fared thermometer. You will need to put your boxster on stands and be sure it's fairly level. Good Luck...I did mine and it took about 2 1/2 hours. The pan is the easiest part.....