Hi everyone,

This is my first post... I've been lurking for a while and have read a lot of the archives, but I'm having trouble finding the answers to a couple of specific questions on my 1980 w116 300sd (seems like a bit of a rarity around here).

My transmission flares quite a bit and is just generally not quite right, so I bought a mightyvac and followed the instructions for checking the vacuum going to the modulator (using primarily info from Brian Carlton's posts). The line going to the tranny doesn't hold vacuum for long, so I'm assuming I need to get under the car and replace the vacuum cap on the modulator. However, I'm not sure what the vacuum should be at the VCV when I put the mightvac in place of the transmission line. Right now it reads about 17" at idle. This seems high, as I read in an archived post that it should be around 8." However, I'm not sure 8" is correct for a 116. Does anyone know what the correct vacuum should be here on the w116 so I can adjust the VCV properly?

Also, I'm wondering if I may have gotten a mightyvac that was bad out of the box. Are they supposed to hold vacuum when you release the handle? Mine does not... the second you release the handle, the vacuum is released. It seems like it should hold vacuum, right? I think I'll return it and get another one just in case, but from what I've read around here it seems like it should be able to build up vacuum with consecutive pumps, which right now it cannot do.

thanks for any help you guys can provide... glad to be aboard the forum. it's already helped me a lot.

- dave

I returned the first mightyvac and got another. this one holds vacuum as it should. the first one was bad out of the box.

Still don't know what vacuum should be seen at the trans in my 116 (17" now), but once I've replaced the leaking cap on the modulator I guess I'll just adjust the VCV to lower it some, maybe down to 10" or so, and see if the flaring goes away.

- dave

I tend to disregard the manual specifications for the vacuum levels for the reason that the manual was written for a brand new vehicle and a brand new transmission. When new, it may have been shifting perfectly fine with 17" vacuum at idle, however, with 200K on the clock, the clutches are no longer in new condition and less vacuum is needed to avoid flaring.

So, I would agree with your approach. Once the modulator holds vacuum, see if you can adjust the VCV to reduce vacuum to 12" or so and take it for a test drive.

Understand that the W116 may not have the capability of adjusting the VCV via a screw underneath the domed cover. You may need to adjust the linkage to the VCV to reduce it's vacuum due to the age of that system.

thanks brian, I'll report back once I've played around with the adjustment. I noticed that I have no orifices in any of those lines, either, so if I find the VCV adjustment impossible maybe I'll try an orifice in the suction line and see if that can bring it down. I'm also going to add one of those green dashpots from the later cars and see if that helps. Maybe take a shot at adjusting the modulator, too, if it comes to that (assuming the 116 has an adjustable modulator). I was sad to find that the k-1 kit won't work for me, but oh well. The car's in good shape overall and only has arouand 150k miles, so I'm sure something will work.

at any rate, I'll reply back when I've either got it fixed or have run into a brick wall.

thanks again for the reply...

- dave

hopefully this will help someone with an older VCV...

It turned out that my car's VCV did not have the removable cap. Finding this, I decided to just take the front cover of it off (removed the two screws on each side). this exposed a threaded rod with a 10mm nut and an 8mm locknut on it. I loosened the locknut and, with the engine running and the mityvac attched to the tranny output of the VCV, adjusted the 10mm nut until I had about 11" of vacuum going to the tranny. tightened the locknut, put the front cover back on the VCV, and viola... nice, firm shifts with no more flaring.

so the old VCV is actually pretty easy to adjust compared to some of the ones I've been reading about in the archives.

also, I put a vacuum dashpot in line with the supply vacuum to the VCV... not sure if it's doing much, but it sounded like it was worth a try. the part number is 000 304 02 34 and it was about 7 bucks at the dealer.

anyway, thanks to brian for the help... hopefully this info is useful to someone down the road.

- dave

__________________
1987 190d turbo, 5-spd conversion -- 146k
1973 280 -- back on the road with a euro m110
1980 300SD -- RIP - Sold for parts (lost battle with rust)

That's great news Dave.

I'm certainly unfamiliar with that VCV.

Is it possible for you to take a photo of it and post it.........we could use it for reference purposes in the future.

Many folks don't have the VCV with the domed cap that I'm familiar with.

TIA

Dave please post pictures to describe what you did?
A lot of people here with older cars and dont know what to do.
I think this same vcv was in the 80 300d.