A friend just bought a project 300D - an '84 Euro W123 4-door, non-turbo, manual HVAC, automatic. The tranny upshifts with a bang in every gear.
The vacuum pump works well enough to operate the power-brake. The small vacuum lines were all messed up by the PO. I reconnected two so he can now shut it off with the key. The automatic still upshifts with a bang.
Thing is, I see no vacuum cam or switch mounted to the accelerator linkage on the valve-cover, and no vacuum line going down to the tranny. I do see a cable. Does this regulate shifts with vacuum or a cable?
Thanks.

Happy Motoring, Mark D.

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DrDKW

Hey there Mark.

I'm no mechanic, but there should be both a linkage and a vacuum.

I had a similar situation when I recently bought my w123. I bought a whole bag of Y connectors and rubber line from Mercedes Source and replaced as much as I could inside the engine bay. 15mins later, it shifted like butter.

Good luck!

Hard upshifts are a good sign. My 83 300SD gave a firm kick on each and every upshift for 18 years and 305K miles. Perfectly normal. Do nothing to it but change transmission fluid every 30K miles. Piece of cake.




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https://www.youtube.com/watch?v=oJhR7nex47w&ab_channel=Metallica

Sorry, i had to

Hard upshifts mean that your vac is not bleeding down when you apply the throttle (called WOT wide open throttle) or maybe you just need to adjust the modulator a few clicks for a gentler upshift. I think counterclockwise is the adjustment. You might just try a slight adjustment to the modulator for grins.

https://jenniskens.livedsl.nl/Technical/Tips/Files/Mercedes%20722.4%20adjustment%20guide.pdf

If you are missing equipment in the engine bay, check factory service manual for correct diagrams of connections and EPC for part numbers. Then, a trip to the junkyard

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*** I can unlock your Becker 754/780/1492, add aux/bluetooth...

Don't know about the Euro models but on mine in the vacuum line coming off of the main line there is a plaice inserted restricted fitting in the ling going to the vacuum valve on the Fuel Injection Pump and that line goes down to the vacuum modulator.
The other line that is there which on mine is black is a vent line and is not connected to anything and should not be plugged off.

If you have the little vacuum valves on the top of the Valve Cover those can be a source of a vacuum leak or the levers can be worn allowing the valves t pop further out then they are supposed to.

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84 300D, 82 Volvo 244Gl Diesel

Just make sure to use the FSM for the Euro model.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Thanks for the link! That's a great source of info. Even if your trans is operating fine, it's great to look over this type of information. It's good for familiarization of parts and procedures.

There are also a lot of related links in the text. Cheers!

I'm OK with 'firm', but not so violent, it feels like the rear-end or driveshaft is going to blow up!

Happy Motoring, Mark

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DrDKW

Maybe there's worn bushings starting with the engine mounts, all the way back?

Get it Up on a lift and have the suspension and undercarriage inspected. Pay particular note of the transmission mount AND rear differential mountings. Check for worn CV joints. Rear bearings wear...too.

Then, report back with your observations and findings...



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Car is an '84 Euro, 300D non-turbo. So no ALDA and no EGR vacuum valve or cam on the valve-cover throttle linkage.
Engine does have a twin EGR valve & block attached at the front of the intake/exhaust manifolds that appear to have been aftermarket, installed by the importer, and at one time connected to an electric solenoid vacuum-valve. But all EGR vacuum plumbing had already been disconnected and plugged.

Between the information and diagrams I found here, and in one of my W123 FSManuals it looks like I need vacuum from the big brake-booster line, to the injection-pump tranny control-valve, then from there, down to the vacuum modulator on the tranny. Also shows a dump or vent line from the injection-pump control-valve to inside the passenger compartment. The cable mainly adjusts the timing of the shifts, but not the harshness.

I may go back to my friend's next week to fiddle around some more. I got his engine to shut off with the key and now he's bugging me about the power-locks.
I told him the power locks can wait. They aren't threatening to blow drive-train parts from the bottom of the car!

Happy Motoring, Mark

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DrDKW

So what kind of up-shifts should I expect with NO vacuum connected to the modulator?

Mark D.

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DrDKW

I have no doubt there's worn bushings, mounts etc.... But for now the only vacuum systems connected and running are the power-brake and the engine shut-off. Weather permitting, I hope to get under her next Thursday.

Mark D.

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DrDKW

Mark ;

You're dealing with the typical D.P.O./D.P.M. issues, just keep chipping away at it and soon it'll be shifting well if firmly .

A !BANG! upon upshift is bad, I imagine once you get the I.P. vacuum control valve connected and adjusted, it'll get better .

Do that before adjusting the modulator .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better