scott863

I have an '81 US 928 with automatic trans. Dr. Bob (what a great guy!) discovered my transmission was leaking fluid after I left him a sample on his spotless garage floor. I used uv dye for trans fluid and traced the leaks to cracked rubber hoses running to the cooler.

I had the hoses replaced using the original fittings at a great little hose shop in Glendale. I replaced filter, drained the converter, and jacked the front of the car up to do a "poorman's line flush" with the help of gravity. The old fluid was pretty tired, but no metal shavings.

I've checked the level on level ground (it looks level), with the car running, cycled through the gears. I didn't have the emergency brake on I don't think. When I check the level, should the car be in Park or Neutral? The trans shifts into neutral and Reverse normally, but it is delayed to go into the drive gears.

I hope someone has some ideas, before I did the fluid change, it drove fine, never slipped.

Drewster67

The car should be at operating temperature and in Neutral. What fluid are you using?

scott863

I used what the manual states, got it from local Mercedes Parts store.

Bill Ball

Well, since you just did a fluid change, you have a pretty good idea what the problem is.

Check the fluid level again. The car is VERY sensitive to level. 4 or 5 ounces can make the difference between slipping and not slipping. It can be hard to get the level right. Make sure you are using the correct marks with the car warm after a good ride. The level must be between the two upper marks. The difference between them is about 6 ounces. Either park or neutral are OK, car running. It does not need to be neutral.

The 928 AT uses Dexron type ATF. The current versions are backwards compatible. You didn't need to get it from an MB parts store. What did they sell you?

scott863

I know I didn't need to get it from MB parts store, I happened to be there picking something up, so it made sense to get it there. It is the Dexron formulation.

I haven't been entirely certain about those marks. I've been using the notches that are in the metal piece that the reservoir is mounted to. Am I using the incorrect one? Based on the porsche service manuals it seemed, but I wasn't so certain about those metal notches being correct, the notches seem rather imprecise for a Porsche.

Mrmerlin

there should be marks on the plastic tank, IIRC

Bill Ball

If it's not to the top of the notch when hot, put a bit more in.

Mrmerlin

once again Bil with the perfect picture, You rock Bill!

scott863

Thank you guys, that's an enormous help. I do have a couple other questions, how do I warm it up if I can't drive it? What's circulating the fluid through the hoses and pipes to the trans cooler and back? Is like braking and cooling systems where there can be air pockets trapped in lines making it look full, but not really be full?

Thank you so much

Bill Ball

I would check the cold level right after your start the car and make sure it is above the cold minimum line. Once that is good, see if it will drive. If not, there is something else wrong. Note the fluid level with the car not running is not useful.

It will warm up just sitting idling as the trans fluid circulates through the radiator. You just don't want to run the car too long with the fluid low. Might you have done that when filling? You should put in the fluid initially with the engine off, until the reservoir stays full. Then briefly run the engine to pump that out of the reservoir. Just 4-5 seconds is enough. Add more fluid until the reservoir is full again, with the motor off. Repeat. In the later trans, which takes 8-9 quarts on refill, I can only get 4-5 in initially before the reservoir begins to overflow. Then I can get another 3/4ths to 1 quart at a time after each motor start. I don't run the motor more than a few seconds until I get to 8 quarts, then I just let it idle after putting it through the gears and top off versus the hot marks once it is hot. That can take a while. I drive the car for 8-10 miles and check again with the motor running.

My car will shift very strangely and even free-wheel in some gears if it is below the hot minimum by even a smidge. Not necessarily right away, but at some point within a few days after a fluid change. 4 more ounces and the car drives perfectly.

scott863

Thank you so much for taking the time to share this with me. I don't think I ever cranked the engine to circulate it more than once. I will do the cold start check first.

scott863

no luck. Jacked the back up, got it perfectly level, was low cold and hot. Filled it up while it was running, would cycle through the gears, it would not take any more, probably put in 1/3 of a quart. Reverse and neutral shift well, reverse works fine. when I put it into D or lower gears, there's a hum now, and it will creep forward, but nothing more than that. I am at a loss now.

Shark Attack

I didnt have time to read the whole thread, sorry. But here is my $.02. My 82 had the 3 speed tranny and had the same exact problem. I had what I thought was a minor hose leak up at the tranny cooler. I fixed that and all the tranny problems went away. Weird, yes. I would have never thought such a small leak would have made such a pressure differance.

Bill Ball

I'll bump this. Hopefully Steve Cattaneo will see it and have some other suggestions. I was banking on fluid level, since it happened immediately after a fluid change and it was fine after the prior hose change. Beyond that, you need more expert input and Steve is The Man. I'm not sure what would impair just all forward gears. I think it involves the B2 brake band in the later tranny but not yours, and beyond that I'm not sure what happened here and what to do next.

BTW, what brand fluid did the store sell you and which Dexron version is it? It must be Dexron II or III compatible. I think all the newer versions (up to VI?) are backwwads compatible, but maybe we should verify what you got.

scott863

Bill I bought Dex Merc III. The vibrating in drive gear concerns me.