87 300D bowden cable - PeachParts Mercedes-Benz Forum

Mike_Hawk · #1 05-15-2007, 09:44 PM

I want to try and adjust my bowden cable, but don't know where it is and how to adjust it.

Brian Carlton · #2 05-15-2007, 09:47 PM

Look below the oil filter housing and slightly forward of it. There will be a bracket with a white plastic nut. Turn the nut toward you to increase tension on the cable and delay the shifts. Turn the nut away from you to loosen the tension and create earlier shifts.

Mike_Hawk · #3 05-15-2007, 10:34 PM

Is there a picture available highlighting it?

Mike_Hawk · #4 05-16-2007, 02:46 PM

BTW, I don't see a white plastic nut.

Would it be where that small rubber boot is, but on the other side of the bracket?

gsxr · #5 05-16-2007, 05:53 PM

Why do you want to adjust it? What is the problem/symptom?

Mike_Hawk · #6 05-16-2007, 06:01 PM

Quote:

Originally Posted by gsxr

Why do you want to adjust it? What is the problem/symptom?

Hard shifting. Very annoying and is getting painful since I do a lot of city driving.

gsxr · #7 05-16-2007, 06:05 PM

Ah. That's not a Bowden adjustment. You have a vacuum leak. You'll need to trace the vacuum line going to the tranny and look for leaks, cracked rubber fittings, etc. This is very common. Fix the vacuum problem and the tranny should shift like butter.

gsxr · #8 05-16-2007, 06:06 PM

BTW - since you own a 1987 300D, check out this article if you haven't seen it yet:

http://www.w124performance.com/docs/mb/articles/124.1x3_buying_tips.txt

Mike_Hawk · #9 05-16-2007, 07:08 PM

Quote:

Originally Posted by gsxr

Ah. That's not a Bowden adjustment. You have a vacuum leak. You'll need to trace the vacuum line going to the tranny and look for leaks, cracked rubber fittings, etc. This is very common. Fix the vacuum problem and the tranny should shift like butter.

That's actually my first course of action but at this moment money's too tight to invest in a Mityvac. Due to that, I wanted to try a cheap fix first.

When I go to diagnose the vacuum, what line(s) do u recommend for testing?

babymog · #10 05-17-2007, 12:11 AM

If you can't check with a mityvac, look the lines over with your hands and eyes.
Follow the line out of the elbow on the side if the IP, that is the vacuum modulator that controls vacuum to the trans, also the lines from the blue saucer-thing, lines to the IP, just look for cracking Tees/elbows/etc. and lines hanging free, you might find it.

Adjusting the Bowden cable will just change the shift points, not the harshness as was mentioned.

Mike_Hawk · #11 05-17-2007, 03:12 AM

Quote:

Originally Posted by babymog

Follow the line out of the elbow on the side if the IP, that is the vacuum modulator that controls vacuum to the trans...

That vacuum modulator is adjustable, right? Is it like adjusting a distributor on a gas engine (release screw, rotate unit accordingly, and tighten screw)?

I did happen to find a line that was disconnected! I also had 2ft of vacuum hose and went to town replacing some loose fittings. I found a cracked rubber vacuum hose nearby the belt and where that big tube connects (brake master cylinder?), right under the fat upper radiator hose.

The overall shifting seems to have relaxed a bit, but the 1-2 and 2-1 shifts are still hard with a "thunk".

babymog · #12 05-17-2007, 10:06 AM

If you're getting close, you might be finished with the transmission, the modulator would be the last thing I'd adjust (yes it adjusts as you observed).

I've found that on all three of my '87s, the ALDA was soft, needed a turn-and-a-half out to bring the off-boost power up.

What that did, besides giving me more power/response from idle and low RPMs, was change the pedal position vs the power output of the engine, essentially bringing the shifting pressures in line with with the power, and shift quality at part-throttle improved significantly.

Mike_Hawk · #13 05-17-2007, 12:52 PM

What are the procedures and guidelines for adjusting the vacuum modulator?

gsxr · #14 05-18-2007, 11:53 AM

The vacuum modulator on the tranny is adjusted so it doesn't flare at WOT shifts. All part-throttle shifts are adjusted via the vacuum signals. I would mess with the modulator on the tranny as a last resort - you don't start there. The rubber cap pops off, the little T-handle inside comes out slightly & turns to adjust pressure. I wouldn't adjust more than 1/2 turn at a time though.

1) If the ALDA is virgin, this could be a big problem. Do a search and adjust 1.5 turns CCW. This makes a huge difference in shift quality.

2) The vacuum control valve (VCV) on the side of the injection pump also needs to be adjusted per the factory procedure - loosen the 2 bolts, have someone press the accelerator pedal to the floor, tighten the bolts. The end. It almost always ends up in the middle of the slotted adjustment range. DO NOT try to tweak shifts soft/firm with the VCV! It doesn't work, the results are often worse.

3) When was the last fluid & filter change? Usually by 20-25kmi, I notice shifts getting firmer. After the fluid & filter change (including draining the converter), the shifts would go back to normal (nice and soft at part throttle). If you're at 25k or more, I'd do this first. I'd recommend Mobil-1 ATF as well - this also helps.

Mike_Hawk · #15 05-18-2007, 03:25 PM

Quote:

Originally Posted by gsxr

...The rubber cap pops off, the little T-handle inside comes out slightly & turns to adjust pressure. I wouldn't adjust more than 1/2 turn at a time though...

...2) The vacuum control valve (VCV) on the side of the injection pump also needs to be adjusted per the factory procedure - loosen the 2 bolts, have someone press the accelerator pedal to the floor, tighten the bolts. The end. It almost always ends up in the middle of the slotted adjustment range...

...3) When was the last fluid & filter change?...

Is that rubber cap located on the tranny itself? If so, is it easily accessible?

I did the VCV procedure and it went all the way to the right of the top slot (turned CCW). I set it at that. Is that normal?

Last tranny fluid change was less than 1k ago, though I didn't change the filter or drain the torque converter. I forget what brand it was, but it was a red bottle and had Max Life on it and was for older transmissions. It's widely available. How is the torque converter drained and refilled?