After adjusting my ALDA I began having AT issues on my 83 300cdt. I've basically fixed them by adjusting the vacuum control valve (the modulator didn't seem to affect it much, I don't think the control valve was letting out enough vacuum because there was bad flaring).
I turned the screw on the side of it out maybe 1 turn. My shifts are acceptable now, but I have a pronounced clunk going from second into first. I don't especially care about this, though I'd like to get rid of it, but is it bad for the transmission?

The transmission is fine with hard upshifts or hard downshifts. It means less wear on the clutches.

However, the driveline, including universal joints and constant velocity joints are not all that happy with sudden speed changes. They load up pretty good for a fraction of a second during the gear change.

The driver is also generally unhappy with a very quick shift, either up or down.

Mine clunked for over a year until I got down to business on the VCV. I don't think it will do any serious short-term damage but ..who knows? Try fiddling with the VCV - If memory serves you need about 10-15 inches of vacuum at the 2-1 downshift or it will clunk. I think the Brotherton article or the Penoff goes into this in detail.

Rick
Deltona FL

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)

I finally got my transmission shifting exactly like I want it , but NOT through adjusting things. In fact, I wound up moving the adjustments I had made back to about where they had originally been.

It turns out that the vacuum switchover valves in the black plastic box on top of my valve cover were the culprits, I have a picture below so you can see the horror for yourself. I hadn't realized how messed up they were when I'd looked at them before because they are about equally broken. Unfortunately, the new valves cost $50 each.

So, for those of you out there with transmission shifting problems--be it too hard, too soft, flaring, slipping, whatever--learn from my mistake and check this part first if your car is equipped with it. It is under a black plastic box (easy to remove) on top of your valve cover and you'll see five or six snaking rubber lines. Make a diagram before you take anything apart, because you won't remember it. If your switchover valves look like mine, replace them BEFORE you go cranking on the modulator or the vacuum control valve. It's a good starting point and may save you and your transmission a lot of undue stress.

Replace them by unscrewing the 4mm allen holding them down, then pulling them off the metal shaft around which they rotate. The new part from the dealer has a weird little mini shaft which didn't seem to work, I pulled it and stuck them on the old one to avoid change. Part # is 0029975336 for the whole valve, they came with new levers, I'm not sure if you can get the levers seperately, but I needed the whole assembly anyways.

Well, one vacuum problem fixed, ten more to go.

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We've had a lot of discussion reagarding these valves. On "most" vehicles, they control the EGR only. So, if you simply disconnect and plug the vacuum supply to the black box, the leaking valves can't affect the transmission shifts. I've recently done exactly that on the SD, but, haven't tested it yet because I'm in the middle of a head gasket change and a bunch of other odds and ends.

Now, on "some" vehicles, these valves also control vacuum to the transmission, and, in this specifc case, the valves should be replaced in the manner described above.

The transmission on my SDL has a hardshift but only down to 2nd or 3rd I believe. I can't remember which exactly or it may even be both. So, what does this valve look like for a 603?

Thanks
David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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