W210 Transmission Fill Cap
 

I feel stupid here but, for some reason, can't get my transmission fill cap to snap back on after doing a transmission service. When I removed the cap I broke off the red tab and pushed the stem through with a small screwdriver and the cap came right off. When I try to replace it with a new tab it will not snap down. It seems like I'm missing something. The cap just slides right back off - the tab not engaging anything. The notch in the tab looks like it should engage the flange on the fill tube but is too far away.
What am I missing?

The red tab is a one-time deal. You need to purchase a new red tab to get the cap back on. It gets broken in the removal and you need a new one to resecure the cap.

I would appreciate another try. As I said, when I try to replace with new tab the cap doesn't want to engage.
Thanks.

I have never found a need to replace mine. The cap is pretty snug on there and now that I have the dipstick tool, I will likely check the fluid level at least at every service.

Len

My Cap doesn't fit tight at all. In fact, I'm sure it would fall off due to vibration, etc., if not mechanically attached with the lock tab. I am puzzled. Can anyone give me some guidance?

Does your cap still have the rubber O ring on it? That's what makes mine fit so tightly.

Len

No, I don't have an O ring. I guess it would fit on the plastic snout on the cap and go inside the transmission fill tube. There is no groove for an O ring. That would help and I will see if I have one to fit it. I would still like to know why I can't get it to latch into place.

Look down the tube with a light. The o-ring may be in there.
If so, pull out and put back on cap.
Dr.D

I found an O ring in my collection that worked. Now the cap fits snugly enough that I am comfortable just stabbing it onto the fill tube. There was no O ring in the fill tube. Either it was never there or was lost when I removed the cap. I am still very interested in why my cap won't latch onto the fill tube with a new lock tab. Any thoughts??