The Forgotten On

Alright, So on with the saga of the poorly shifting transmission.

I've replace the modulator and the rear vacuum hose with cloth covered rubber hose (same as factory) as posted in my last thread here: https://rennlist.com/forums/928-foru...r-on-a-s4.html

It is basically impossible to pinch that stuff shut so I doubt that is why. I also verified that chunk of line was clear by blowing air through it without much trouble.

Since then I've tested the vacuum at the modulator and there is none when testing from the modulator end of the line with the engine running.

I pumped the mity vac and it held perfect vacuum which made me think the aftermarket vacuum tree had a check valve pointing in the wrong direction. I remove a line and it does not. I could feel vacuum from it.

So now I think I have a completely clogged vacuum line on my hands.

Does anyone have a preferred way of unclogging the line? I've read brake cleaner works well, and so does carb cleaner (that one is harsh on rubber lines so it's a no go).

C531XHO

So to be clear you think you have a blockage in the steel section? If so seems odd. Blocked with what? I can imagine rubber sections collapsing/pinching if not retained. If it were me I would run a temp rubber line the whole way and see if there is any change.

Mrmerlin

well you can isolate the hard line you will have to remove/move the heat shields to do it has any work been done on the TT?
if so maybe the metal line is pinched.
at this point it might be a better idea to get some of the hard plastic vacuum line and run it to the trans if you cant figure out a solution

The Forgotten On

No work has been done on the torque tube under my care. Some trans work was done about 15 years ago on it that required the trans to be removed.

At least that is what I can deduce from the history I got with the car. No mention of rough shifting after that. That owner kept very good records and always had it serviced immediately if something went wrong .

The trans was never touched after that outside of fluid changes.

I'm gonna try using a piece of weed wacker line through the trans end of the line and then blowing it out with brake kleen on the engine side. I'll see if that helps. I got this idea from the Mercedes forums and Speedtoys.

If not I'll run a new plastic line back to the modulator like you said.

I did bend the hard line about 1 inch away from whatever it follows on top of the trans to hook the soft line to it but it went right back to where it was after on its own so I doubt the metal line pinched itself shut.

What is odd is that it is a perfect blockage and can hold a perfect vacuum. I'd assume a kink would at least let some air past it.

The Forgotten On

Well, I finally got around to unclogging the line only to find out I pushed the front vacuum line off when using weed wacker line in the hard line

Great, I thought, This is the line that many say is a pain to replace compared to the rear. Oh how wrong I was.

It was a cakewalk compared to the rear one and took all of 5 minutes, if that, to stick on a new silicone vacuum hose. 1 cat downpipe heatshield removed and access was good with a set of long pliers and a screwdriver to prop the hardline.

I discovered the clog though when I removed the old vacuum hard line though. It snapped right where it collapsed. It was a low temp PU plastic or similar (melts under 240F) and it just melted closed. Silicone melts at over 400 so I should be fine lol.


I'm glad to finally have this behind me and should now have a transmission that doesn't kick me in the back during low load shifts.