Downshifting; Transmission Vacuum
 

It seems that there is a vacuum leak of some sort (I am pretty sure) with my transmission.

I have a 1995 C280 with the 4 speed auto. Car has 130,000 miles on it, and still drives like a dream. Trans. maintenances have been performed between 10-25k miles consistently. Everything is great with the transmission, albeit the progressing Reverse engagement delay.

When accelerating from a stop, all shifts are normal.
But then if I want to speed up, the car won't downshift unless I engage kick-down.
Let me give you an exaple:
If I'm cruising along at 40 mph, and I push the gas so that the trans will downshift to 3rd gear, the transmission won't downshift (will stay accelerating in 4th gear). I will push the gas to WOT, and it still won't downshift. But if I then engage kickdown, it will downshift to 2nd gear and take off.

The kick-down is fine, it's just the vacuum pressure in the trans. If I hit the gas all the way (no kick-down) down and do it fast, it will sometimes downshift to 3rd gear properly. However, if I push it slowly, it won't downshift.

I hope this was the least bit understandable!
Thanks!

David,

I'm very new to this group, and you've been very active for awhile, so I know you're far more knowledgable about these things than I; however I have searched and read lots of previous postings about transmission problems such as the ones you're now experiencing. The advice that has been repeatedly given in response to these problems usually involves either adjustments to the Bowden Cable or adjusting/replacing a bad shift modulator.

Of course, your tranny could be dieing a slow death, but you don't have THAT many miles on her yet. (After all, the first 100,000 miles is considered the break-in period for these cars, isn't it:D ).

Good luck!

I think David's already an expert on Bowden cable adjustment. I suppose you are going to need something like a MityVac - just saw it on sale for $42. Might pick one up myself since it can also do brake bleeding. You'll want the one with the pressure gauge like this one:
MityVac Pro