Sign of Impending Failure for W140 5-Speed Automatic? - PeachParts Mercedes-Benz Forum

Western140 · #1 04-21-2006, 05:33 AM

Hi, I replaced my 126 last year with a beautiful 1994 Black Pearl S320. It has 121,000 miles on it, it drives perfectly, and the only things I've replaced so far are a coolant temperature sensor, and the blower regulator.

Recently though, there has been a hesitation when the transmission is shifting from 2nd to 3rd. It will go to neutral for just a split second and rev up maybe 100-150 RPM before it grabs 3rd. This was happening only when it was cold, and then only sometimes, but in the last few days it seems to be doing it all the time. All the other shifts are fine, and there doesn't appear to be any slippage while in gear. Is this the first sign of needing a rebuild? Also, I had a transmission service about 9 months ago.

I was hoping this would be the first car I've owned NOT to need a new transmission about a year after I purchased. I've spent countless thousands replacing trannys on two Saab 9000 turbos and then rebuilding the one on my old 300SEL. I guess it's my used car curse.

Ferdman · #2 04-21-2006, 06:49 AM

When was the transmission filter and fluid changed last? If you don't know or don't have service records for your S320 I'd start there.

G-Benz · #3 04-21-2006, 10:35 AM

I don't know what transmission you have, but the W126 and W124s share the 722.6 (I think) version. There is a known issue with what is callled a 2-3 shift flare...i.e., hesitates between shifts between 2nd and 3rd, noticeably around 1500-2000 rpm.

The fix is a $15 part known as a K1 kit. The OEM spring and seals in the K1 valve get weak and are slow to transfer fluid pressure (hence the "flare"). The repair is a stiffer spring that is included in the kit, and those here that have done the install claim it erases the problem. I have the same flare, and I think this weekend I will finally do the install.

It can be done w/o removing the transmission, and except for having to drain the fluid and drop the tranny pan for access to the K1 valve, I believe it's a 1/2 hour job.

Ali Al-Chalabi · #4 04-21-2006, 12:19 PM

It's the 722.5 tranny. Similar to the 722.4 but with an overdrive gear added.

Western140 · #5 04-21-2006, 02:25 PM

I looked through my manual and it doesn't say anywhere which transmission (722.5 or 722.6) I have. So if it's the 722.5, does that same problem with the 2-3 shift flare occur, and can it be fixed with the K1 kit that G-Benz was talking about? It would be great if the problem is that simple.

KenP · #6 04-22-2006, 06:55 AM

According to the Mercedes literature I have, the 722.6 transmission first appeared in the W140 in 1996.
Hope this helps.