Hello,

I was just curious with all of the various MB transmission dipsticks available if there was the possibility that they weren't all exactly the same.

It has only happened twice ever, but on those occasions the car has held the start-out gear too long and hard shifted into the next gear. Both times were after just backing out of a driveway, once when the transmission was cold and once when it was hot.

I have read a thread where a very similar issue was described but unfortunately no one ever posted their conclusion (frustrating). The most commonly suggested cause was low transmission fluid. The first time it did the "slip" thing I checked the fluid after I got back home. It read 81 C using my infrared thermometer and the fluid was touching the top full line. Perfect right? However, the last time I did a drain and fill it took less to fill it than what came out, and it was shifting perfect before. Should I just add a couple hundred CC and see if it stops?

Thanks

 

Mine has had a habit of doing the same "hold" then hard shift that you speak of since I've owned it. Did it on the fluid that came with the car, the fluid that Mercedes put in it (that was a solid 1/3 of a quart more than what I just put in it on the next fluid change based on the what the dipstick told me was full).

 

So, it did it with 1/3 quart above full and it also does it at what your current dipstick says is "full"?

In other words, the fluid level made no difference for this particular symptom?

 

I have always found my Merc stick to be accurate.

Put the car in sport mode and I be the hard shifts will disappear.

It is related to a fault in one of the valves in the tranny and the higher shift points in performance will allow it to shift properly.

It should not hurt the robust XJR tranny to run it in sport mode all the time, I always run mine like that, plus you get 1st gear instead of starting off in 2nd.
Vector

 

Yes, mine has done it on occasion for 55k, doesn't matter if it is in sport mode or not, fresh fluid or not, overfilled or not. As Vector said it is a fairly common fault that is usually attributed to valve pressure.

 

Mine does it too! It's most likely when the engine was hot, I park for a few minutes, then set off again.

Using sport mode definitely helps. Please note that when this transmission in used in Mercedes cars, our sport mode is the default, and the Mercedes snow mode is our standard. So using sport mode all the time is unlikely to cause harm as that is what Mercedes vehicles do anyway.

I changed the transmission fluid and filter, and it didn't make any difference. However, after 85K miles, the fluid was in an absolutely disgusting state - with a thick layer of black sludge at the bottom of the pan. This cannot be good for the transmission. I would recommend 50K mile intervals (which I believe is the updated manufacturer advice).

 

I would tend to agree with that plus mine does it more when I don't really accelerate a ton, just get up to speed in say a parking lot.

 

What they said, and I would like to know the physics claimed by those who think being +/- a 1/2 qt of transmission fluid causes problems.

 

Well, a few hundred more miles and it hasn't done it again. I didn't adjust the fluid level since it seems perfect already.

I just can't drive it in sport mode all the time.

I don't like sport mode. It always seems like the engine RPM is unnecessarily high. Regular mode is so smooth and quiet, and if I put my foot in it it's still very fast! I just love the non-sport mode. I guess I'm getting old, lol.

 

It will happen again, bad valve, common problem.

Sport mode took a little getting used to, especially all the torque available when starting off in 1st instead of 2nd.

I find that if I ease back on the throttle at the right time, the car will shift in sport mode a little earlier, if you keep the hammer down it will continue up and shift at a much higher RPM.

The reality is that after driving in sport mode only for about a year now, I don't even notice that it is on. I just am careful with the throttle on starts and help it with upshifts.

As was said, our normal is "snow mode" on some other cars with this tranny so it can be a very nice way to use all the power the XJR offers us.
Vector