Author Topic: Question about Shifting Problems with my 300SD  (Read 338 times)

avantbenz

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Question about Shifting Problems with my 300SD
« on: 13 October 2018, 08:30 PM »
I'm trying to diagnose an issue I'm having during shifting.

It doesn't seem like a serious issue and I've found a workaround but I'd like to get everything running well *without* applying my workaround.

The issue: If I start the car, put it in 'D', and drive she shifts fine. When I stop at a stop light or stop sign and put my foot on the brake long enough to come to a complete stop and then press the accelerator pedal it seems like the transmission slips. It feels like she's starting in 2nd gear but not really - there is a total lack of power. My workaround is that whenever I come to a complete stop I move the shifter from 'D' to neutral and then back again into 'D' and then proceed to drive with no issues.

Any ideas? Is it a vacuum issue? Throttle lingage issue? I just want to know what I should tackle first because it seems like adjusting the transmission shift points is a big deal. Also, I checked my transmission fluid and it seems like it's at the proper level although it looks a little dirty. I'll probably end up changing it and the filter soon but I don't know if this would actually have anything to do with the issue I'm experiencing.
Daily Driving 'Patience' ~ 1980 300SD

Diesel 617

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Re: Question about Shifting Problems with my 300SD
« Reply #1 on: 13 October 2018, 10:25 PM »
Hopefully others will chime in

First make sure you have the proper fluid level, it is unconventional and your need a ruler and mm conversion. Avoid getting any fibers whatsoever in the trans fluid or on the dipstick. Use a piece of cardboard or leather to wipe the dipstick see this procedure to check: https://handbook.w116.org/Maintenance/MY72/120.pdf The 78-80 300sd 722.120 transmission is W4B-025

Does the kickdown switch work? https://www.youtube.com/watch?v=nzBBHwX41mY and https://www.peachparts.com/shopforum/diesel-discussion/367833-order-troubleshooting-kick-down-switch.html

Do the RPMs/engine rev high then shift into gear i.e flaring? If so adjust the vacuum going to the trans: http://www.peachparts.com/Wikka/Trans722VacMod see post 51 and read the next two the Technical Data Manaual should have the correct spec as the FSM does not.
1980 300SD Worn out Engine
1979 280SE Euro Spec Import Crank Windows and Cloth Seats, needs head rebuild, and WUR rebuild
1979 300CD


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https://www.ebay.com/usr/vintagepartsandstuff/

daantjie

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Re: Question about Shifting Problems with my 300SD
« Reply #2 on: 13 October 2018, 11:20 PM »
Yup always start simple. Pan drop to check the sludge/debris situation. Then new Mann filter and good Dex III fluid. Measuring hot fluid level is critical to having a trans shift well.
Daniel
1977 450 SEL 6.9 - Astralsilber

Diesel 617

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Re: Question about Shifting Problems with my 300SD
« Reply #3 on: 13 October 2018, 11:55 PM »
Yup always start simple. Pan drop to check the sludge/debris situation. Then new Mann filter and good Dex III fluid. Measuring hot fluid level is critical to having a trans shift well.
On the note of trans fluid in the states Valvoline Dex/merc Max Life Fluid is what your after (red bottle), it meets the Mercedes specs
1980 300SD Worn out Engine
1979 280SE Euro Spec Import Crank Windows and Cloth Seats, needs head rebuild, and WUR rebuild
1979 300CD


Inventory of w116 Parts
https://www.ebay.com/usr/vintagepartsandstuff/

gavin116

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Re: Question about Shifting Problems with my 300SD
« Reply #4 on: 16 October 2018, 06:45 AM »
Sorry posted answer on wrong thread...
« Last Edit: 16 October 2018, 07:08 AM by gavin116 »

avantbenz

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Re: Question about Shifting Problems with my 300SD
« Reply #5 on: 06 July 2019, 11:53 PM »
Dropped transmission pan and noticed no debris (yay!), popped in a new filter, changed transmission fluid using Diesel 617's recommendation, and she's shifting smoother but the problem persists. I'll probably update my custom project thread on the details - posting link here for ease of navigation: https://forum.w116.org/test-drive/the-patience-project-my-1980-300sd/msg142897/#msg142897

Next step - test kick down switch and see if I can adjust the vacuum. But first, gotta adjust my valves and replace my shift bushings (not sure if they're bad, doing it preemptively).
Daily Driving 'Patience' ~ 1980 300SD

OLDGOLD

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Re: Question about Shifting Problems with my 300SD
« Reply #6 on: 07 July 2019, 07:06 PM »
This is a long shot, but check your overboost protection device switching valve and your banjo bolt on the back of the manifold to make sure it’s clear. Ya never know!