Hello all -- I've been trying to rid my car of a rather nasty 2-3 shift flare (not present under very light or very heavy throttle) in my 82 300D turbo. 3-4 will also flare on occasion, but not frequently.

I've been following this guide, posted elsewhere on the forum: http://transmission.articles.mbz.org/adjust/

I've found that vacuum at the brake booster line is 21-22 in., but that it drops to around 18 in. when attached to the regulator valve on the injection pump. If I disconnect this valve (and plug the feed line) I've got the same shifting conditions but with 22 in. of vacuum. The valve is not adjusted properly yet; there is at least 1mm gap between the stop pin and the lever at full throttle. Also, the switchover valve levers are worn out.

Is the regulator valve shot? Or can I adjust it back within spec? And does the bad switchover valve (on the camshaft/valve cover) affect this?

I'd like to at least start with full vacuum at idle.

Thanks for any input.

Look on the mbz.org site for an article on the K1 spring kit. It's a repair kit Mercedes offers to replace a spring in the valve body to reduce 2-3 flare. It's $10-$15 from the dealer.

Russ M

Wish I'd known about that K1 spring upgrade while I was doing my B2 piston... Now I'll have to drop the pan and go through another gallon transmission fluid...

Ah, hadn't heard about that. I'll definitely look into that K1 repair.

Any advice as to whether the regulating valve on the IP is shot? After reading another shifting article (on the mbz.org site), it seems that some feel 15-20 in. of vacuum is fine at the main booster line, lower than the 20-23 in. I was shooting for -- and could get if it weren't for the valve.

I'd like to try adjustments first, as I really hate working under the thing while it drips ATF all over me...

If it is flaring, and you wish to attempt adjustments to the vacuum system to compensate, you need to reduce vacuum to the transmission.

You could do a very crude test to see if you might benefit from tinkering:

Disconnect the vacuum to the transmission and drive it. See if the flaring is eliminated. If it is, and the shifts are too hard, then you need to see if you can modulate the vacuum to the trans by adjusting the vacuum control valve.

Also, the adjustment of the Bowden cable can affect the sensitivity to flare.
IIRC, if it shifts a bit later, it is less likely to flare, but, I haven't tried it personally.

Well, I'm pretty sure you shouldn't see vacuum as high as 20 inches...it's been awhile since I tinkered with the valve. Somewhere around 17 with the throttle link 10mm from the stop pin on the valve sounds about right (but that's a rough guess). There's a little adjusting disk that fits on the stop pin that assists with this adjustment. As the throttle is increased, of course, vacuum falls off toward zero.

I recall a thread in the archives by DIY guru boostnbenz that thoroughly addresses the issue of wear to the vacuum control valve. I'd chip in more, but he's clearly better versed in the issue than I am.

One thing to keep in mind, though: when you adjust the vacuum, you affect the firmness of ALL shifts, not just the 2-3. If you're only getting a flare in one shift, do you really want to make, say, the 1-2 shift harsher in order to "fix" the 2-3? That said, I know a guy who drove his W123s with the vacuum line to the shift modulator disconnected. He's got a 19-inch neck though, and is probably less susceptible to whiplash than other folks.

Russ M

Oops, forgot this...

Here's the part number for the K1 transmission spring kit: 126 270 44 77. Mercedes calls it a "thrust pin," but it comes with three springs and a couple plungers. Again, mbz.org has a nice writeup on installation.

Russ M

That is way too high. Should be around 6" hg with the throttle at that position.

Ehhh, right you are. I shouldn't have thrown a wild-assed guess out there. Acy, the adjusting routine is in this article http://transmission.articles.mbz.org/adjust/
including the spec of 5.5 to 6.5 hg with the lever on the vcv 10mm from the stop pin.

Thanks for keeping me honest, tangofox.

Russ M

Appreciate the replies. I think I'll give the K1 kit a shot -- looks fairly easy to do. No sense adjusting the thing, finding it still acts up, and then having to readjust it after the K1 kit goes in.

You might want to try some trans-x first. I have used it on other vehicles with success. You put it in and then drive for about 500 miles before it starts to work. But it does work.