Yet another trans shifting question - PeachParts Mercedes-Benz Forum

JEREMYC · #1 11-24-2006, 10:06 AM

Hello all. Hope everyone had a great Thansgiving. On the ole' 83 300CD, I have had some shifting issues since I have owned the car (about 6 months) Shifting from 1-2 is real hard and shifting from 2-3 and 3-4 is real soft, actually flares. By the end of a 30 minute trip, most flaring will go away. I did the bypass thing on my EGR with Brian's kit and I removed the 3-2 vacuum switch on top of the valve cover per the instructions on this site somewhere. I made sure I reconnected the vacuum lines back good. I did that Tuesday night. I noticed Wednesday afternoon on the way home that my shifting from 1-2 got a lot softer, almost flaring like the rest of the gears. I have not checked the vac line going to the trans yet nor have I hooked a vac gauge to anything yet. Can I assume that I may have gotten rid of a vac leak by removing the 3-2 valve, therefore changing the vacuum my trans modulator see's and hence changing the way it shifts? I plan on hooking a mityvac to it this weekend and seeing what idle vacuum is and then making sure it goes down to 0 on acceleration. I also plan on testing the vacuum to the trans to make sure it holds and I dont have a cracked line or a bad modulator. Am I on the right track? Anyone have any other advice?

rrgrassi · #2 11-24-2006, 10:13 AM

Check your Vacuum Control Valve also as instructed in a thread started by Firemediceric. Brian Carlton gives a great step by step troubleshooting instruction. You do have to have a miti vac to do this test, though.

JEREMYC · #3 11-24-2006, 10:50 AM

Thanks for the info. I found the post you are talking about. Pretty much describes my car. I will give it a try this weekend and report back. Thanks!

JEREMYC · #4 11-26-2006, 02:30 PM

I am in desperate need of some advice. I followed the instruction posted by Brian Carlton in response to firemediceric's trans shiftinf problem. When I hooked my vac guage up to the trans output from the VCV, at idle I had over 20 inches of vacuum. I removed the plastic dome cap from the side of the VCV and loosened the 2-sided nut and it did result in me being able to get the vacuum down to 8 inches but when i out the cap back on, it went up 2 inches. My set up is actually not the exact same as what brian described. I have the same set up as firemediceric. Under the plastic dome cap is a 2-sided nut and that is it. The screw it sits on does not have a place to put a screwdriver in order to turn it to reduce vacuum to the trans. So I took the VCV off the car and took it apart. When I turn the lever, it does not appear to put pressure on the valve that is hooked to the vacuum outlet. However, when I pumped up the mityvac while hooked to the VCV from the trans side, it would pull 15 inches of vacuum and hold. As I moved the rac, it would slowly decrease down to zero at WOT. My question is, how do I adjust my VCV if I do not have an adjusting screw. Please help!!!!!

firemediceric · #5 11-26-2006, 03:04 PM

After some trial and error, I was able to use a screw driver to push against one of the flat surfaces of the adjusting sleeve. Once I had the vac at 8" I tightened down the lock nut. It took a few tries to keep the sleeve where I wanted it while tightening the nut.

I have been reading some other posts and I have since become a little confused. The other posts call for 18"-20" of vac out of the VCV, just where mine was before adjusting it, but I can't argue with the results I got following Brian's advice. The trans seems to be shifting flawlessly now.

JEREMYC · #6 11-26-2006, 03:24 PM

After I put the VCV back on my car, it would not hold a vacuum at all when I take the supply line off and pump with the mityvac. It did hold before I took it off. I think I have a bad valve and it is leaking inside the VCV. I believe this because the vacuum goes up when I put the plastic cap back on. The vacuum should be contained inside the valve on the VCV, not throughout the VCV itself. I also hooked the mityvac directly to the trans line and it would pump up to 15 inches and hold all day. I know the modulator on the trans is good. Could I take a VCV off of a 81 300sd and use it on my car? I have an extra one on a salvage car at work I can get. After hooking everything back up, the hard shifts are back and there is no flaring. 2-3 and 3-4 are normal. 1-2 is pretty hard and I got a clunk on downshifting from 2-1 that I had never had before.

JEREMYC · #7 11-26-2006, 03:34 PM

Here is a pic of my setup. http://i97.photobucket.com/albums/l231/JEREMYC_03/MercedesPictures001-1.jpg

As you can see, there is no locknut on mine.

firemediceric · #8 11-26-2006, 07:57 PM

After removing the sleeve and then re-installing it, mine seated only as far as yours is in the pic, IIRC. After rotating it some, it seated further and allowed enough thread for the lock nut. Without the lock nut, my sleeve would vibrate off of the threaded post just from the engine vibration.

JEREMYC · #9 11-26-2006, 08:42 PM

So you were able to rotate yours? Mine had the spring like device attached to the bottom of it and would only allow it to turn o much. I could see that by turning the screw, it would put more or less tension on the sprng which pressed the valve in the controller to release the vacuum and allow it to drop down. The reason I think mine is leaking internally is because with the plastic cap off, my vacuum dropped, when I put the cap on, the vacuum would go up and only drop about 5 inches under throttle, it would never drop to zero under full throttle.
Could somone hook a guage up to there VCV and remove the cap to see if the vacuum changes? If it does not, I can assume that the vacuum valve inside the VCV is leaking into the plastic chamber. I would assume that this is not how it is supposed to be. It looked to me that the throttle position pressed the spring into a lever on the vacuum pod and used that to release vacuum and allow it to drop to 0" at WOT.

firemediceric · #10 11-27-2006, 07:59 AM

As you probably saw in my thread when I was working on this, when I removed my VCV cap and started to loosen the locking nut, my vac actually went up

. I figured I must have jarred something loose in the process of opening up the domed cap.
Once I got things adjusted as described earlier and put the cap back on, vac did not change. It remained the same with the cap on or off.
I'd go back and double check, but I'm worried that if I tear into it again I will screw something up.