DIY W123 Transmission Diagnose and Adjustment 722.xx OM 616-617 - PeachParts Mercedes-Benz Forum

1980-300D(bio) · #1 07-12-2011, 05:48 PM

Hello,

I though that I should put together in a simple manner all I found out in the process to fix my flaring tranny. I hope this information is useful.

Please add more details, pictures, videos, etc

Its kinda pointless to mess with the tranny if the engine is not working properly.

Engine First:

-ATF level.

-Change all Filters.

-Fuel hose leaks. Upgrade Hand primer pump for a new bosch.

-Chech tank screen.

-Valve Adjustment. Check the Timing chain.

-Compression Test.

-Clean Injection System with Diesel Purge. And Or upgrade to Monarch Nozzles.

-Timing, Injection Pump

- In the case of a Turbo diesel, check your turbo for proper functionality and clean it. Use the ALDA screw to adjust for a richer air mix. Clean the "banjo" bolt.

-Oil consumption/loss.

-Linkages, are they working right? moving smoothly?

-Glow plugs, if the engine is starting rough/ smoking and gets better at Op.Temp. When changing them you may want to get rid of the carbon buid up using a "reamer":
http://www.benzworld.org/forums/w123...mer-clean.html

-Tranny additives... this is what Benzworld think:
http://www.benzworld.org/forums/w123...-good-bad.html

Vacuum:

- Replace all rubber connectors that look aged or brittle ... Its cheap, just do it all. Don't forget the most important one at the Modulator.

- Check Modulator vacuum line is holding pressure. Usually black, goes from the top of VCV to under the car and connects into the Modulator. If not, replace the line and go to the modulator itself and check if it holds vacuum .

If the modulator doesn't hold vac, the you should replace it. Although is not just swapping parts it needs to be adjusted to the right pressure and the new piece doesn't come with a thrust pin, look inside of the old one and use that part with the new one.

- Check main vacuum hose and Pump (It should read 21-25 inches of Hg). Disconnect main vac hose from brake booster and plug that end with thumb, connect mighty vac to both plastic tees (with a Y connector) that were connected to all vacuum lines. Use the MV as a gauge. This is dine with engine at idle.

-Disconnect Cruise control electric plug and then disconnect all vacuum hoses but one going in top of the VCV and tho other to the shut off valve. You are leaving out cruisecontrol, climate control, EGR and door locks.

-VCV adjustment, this is a valve that leaks vacuum in relation with the position of throttle. Its located in top of the IP and is made of a white/yellowish plastic. It can be adjusted to control when shifting happens, this is usually THE FIX. With old/worn trannys, you may have to deal with a harsh 1-2 shift to avoid flares between 2-3 and early 4th gear.

Check this link by Gregs300CD: http://www.benzworld.org/forums/w123...g-vcv-diy.html

-Reconnect & Simplify the vacuum routing. Delete EGR. Leave one of the vac lines from the main hose going directly to the VCV. Connect your MV to "other users" one by one to test for leaks. Then start connecting one by one "other users" to see if there is a leak in one of such systems. Go for a test ride with each one of them. Usually there is a leak in the Door Locks or Climate Control, if thats the case, bypass it and deal with that later.

-Someone messed with the Mod. pressure before... well, that's a tough one... regulating the Mod to specs is a real pain in the ass. But it can be done with a gauge connected to the test port, sometimes can only be read with the car running at 50mph.

Useful Diagrams:

Vacuum:

Shifting points:

Linkage:

EGR DELETE:

above, the blue painted line goes thru the firewall to leak, its open an usually black.

Thanks to all the people that helped me with advice and images, you guys rock!!

Govert · #2 01-26-2012, 06:41 PM

Quote:

Originally Posted by 1980-300D(bio)

If the modulator doesn't hold vac, the you should replace it. Although is not just swapping parts it needs to be adjusted to the right pressure and the new piece doesn't come with a thrust pin, look inside of the old one and use that part with the new one.

First try to replace the rubber O ring (722.1 transmission) or rubber cap (722.3 or 722.4 transmission). Only if you pull ATF through the modulator, you should replace it.

Quote:

Originally Posted by 1980-300D(bio)

Shifting points:

This applies to the non-vacuum diesels. For North American models up to 1980. 1980 and further had vacuum-controlled transmission.

cullennewsom · #3 10-14-2012, 01:35 PM

I got tired of that useless drawing in this thread, so I found a higher resolution version and cleaned it up a bit, while also making it a small enough filesize to be allowed on the forum. It isn't perfect but at least it is useful now.