Does anyone know what causes hard down and up shifting on a 1982 300sd. adjusting the vacuum modulator is out of the equasion as well as lines hooked up improperly. It just started happening suddenly today.

One of the lines most likely is plugged or partially plugged.

Cheers,

Bill

Thanks Bill


Cheers.

Or became unplugged. Check for a loose vacuum line in the area of your last maintenance.

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Sam

84 300SD 350K+ miles ( Blue Belle )

I have the same problem. it started after i replaced my motor mounts... i checked all the lines ans they look fine... one did get unpluged but it was the only unpluged line i found... so i pluged it in and no help. it still shifts like i'm droping the clutch (if it were a stick) I also have a rough idle... could these problems be connected? they started at the same time.

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Yup, sure could be. Wish I could tell you exactly where to look. I don't have much experience with vacuum trouble shooting.

It should be mentioned that the rubber connectors at junction points should be checked, if not replaced. I replaced the connectors on my TD because they were getting age cracks allowing a little air into the system.

Cheers,

Bill

I checked my connections again and cleaned the lines where there was a little blockage and still no improvement. I do have a theory though. Recently I have been adjusting the modulator on the bottom of the trans to take the sharpness out of the up shifts. It was chirping wildly into second and third had quite a bit of whiplash. Is it possible that because there was buildup in the lines my adjustments were affected by that. Then maybe over time the buildup grew to a blockage that made my shifting al wonky.And then when I cleaned them my adjustments would still be out because there was more vacuum available. In short do you think adjusting the modulator further would be the answer of am I in danger of hurting the trans.

I would check your vacuum pods for the climate control, if they are leaking, you will have rough shifting. If that's not it, make sure your alda is still sealed up, that will also cause rough shifting.

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87 300D - Running on Veggie oil; 260,000 plus miles; Original #14 head

From going through this myself and from what I have read here, MB uses vacuum a little differently. It is used more to smooth the shift along with the modulator. The reason is the modulator is adjusted for a certain pump pressure then vacuum is applied, depending on the IP linkage position, to smooth the shift. Try this link to help explain:http://articles.mbz.org/transmission/adjust/

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Sam

84 300SD 350K+ miles ( Blue Belle )

I have read through the link blue posted and found the first half fairly easy to follow.But when I get to the modulator adjustment I found myself at a loss partially because I've never used a mighty vac and secondly because I have no Idea if I'm supposed to be checking how much vac the modulator holds when vac is supplied at idle and full throttle or something totally different allthogether.And how much vac it's supposed to hold in these two instances if this is the proper procedure. Another interesting thing about my transmission shifts is that not only are they hard going up ond down, they are also early at about 3100 into second and 4100 into 3rd. I tried to adjust the bowden cable and the only thing it does is allow me to make my shifts earlier with the proper adjusting.If I try to turn the adjusting nut out or ccw it max's out at 3100 going into 2nd. Could this be linked. At this point I have my modulator turned ccw further than I think it should be turned in efforts to take some of the harshness out of my shifts and that really worries me.If someone can help I would really appreciate it.

I have an 83 300SD. I am always interested in reading about the auto trans in these models because mine shifts hard from 1-2 and flares from 2-3 and sometimes 3-4. The symptoms are not as severe after the car is good and warmed up. I've see alda mentioned a few times. What's an alda?

Thanks,

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Sunny PA
79 240D
83 300SD

In laymans terms the alda regulates how much fuel the injection pump sends to the engine. On my 1982 300sd it sits atop the injection pump. It's square in shape about 3 by 3 inches with a black cap on top of it. If you pop the black cap off the top of it you can adjust the amount of fuel given to the engine(via a set screw underneath the cap) . If you are looking to attempt this you should do some reading first. Remember and I can't stress this enough, don't turn it to far if you do the set screw will break, rendering the alda useless.While adjusting the screw if you feel resistance do not go any further. Believe me I'm suffering from this very result.BTW there are few places to buy a replacement alda if you break it and they aren't all that cheap! Oh yeah and one more thing... BE CAREFUL!!!

You coulda tweeked your boden cable. If it.s a little to tight it will want to over rev then shift hard. loosen it just a little an see. J

Adrenlin 500,

From your post, I am unclear which step you are stuck on. Can you give me a number?

Are you unsure of something with your mightyvac?

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Sam

84 300SD 350K+ miles ( Blue Belle )

Sorry for the confusion Blue, when I got to the part where I was supposed to be checking the vac at the modulator I wasn't sure how much Hg I was supposed to be getting. Or really how I was supposed to be checking the modulator at all in regards to vacuum.Fortunetly I figured the culprit though, there was a blockage right in front of where the fuse box is, and I was getting 0 vac. Anyway If you happen to know how much vac an 82 300sd is supposed to get at the modulator that would be good info to have. Due to the vac problem last week I did alot of messing with it and I'm sure it's out. Another thing i'm having a hard time with is getting my rpm's to shift past 3100 into 2nd.Any Ideas?