722.118 transmission removal and replacement - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 11-02-2011, 12:20 PM Thread Starter
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Date registered: May 2010
Vehicle: 1979 300TD 1983 300TD Turbo
Location: Langley, BC, Canada
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722.118 transmission removal and replacement

Model: 1979 300TD. This transmission is not vacuum controlled.
This was not a difficult task and neither did it require fancy equipment. I did the job out in the street with little to no help.
Tools needed:
1 13/16” (46mm) open ended wrench from your local pawn shop for $15 to undo the drive shaft nut.
Lo-ong extensions for your socket set. I managed to get a 3/8” set of three extenders for $25. The guy at the tool store knew exactly why I needed them. No need for a ½” set if you don’t have one.
8mm Allen and 10mm Allen fittings
13, 17, 19 mm wrenches and sockets
Piles of softwood blocks for supporting and lowering transmission.
Bottle jack
I find cardboard the most comfortable thing to lie on under a car and have plenty of it.
Eye protection.
Parts needed:
Filter and gasket kit
End clips for the shift link rod
Nylon bushings for the shift link rod
Crush washers for the dipstick hollow bolt, cooler lines, torque converter plug.
New flex hoses for cooling lines if you are uncertain if they were ever replaced.
Driveshaft centering bushing at the front of the driveshaft may also be replaced at this time.
Transmission o-ring and torque converter seal if considered necessary for the replacement transmission.
These are my notes based on my experience as a first time, rank amateur. I used the Haynes manual and various tips that I picked up from helpful people.
1. Raise the rear of the vehicle. You will need to rotate the driveshaft when it comes to undoing the driveshaft flex plate. Undo the 46mm (1 13/16”) lock nut on the drive shaft to give it room to collapse enough for the front flex plate to be removed and the transmission eventually to slide back. I was bearing against the parking brake which was enough because not a lot of torque was required to undo the nut.
2. Remove the exhaust pipe support bracket. Make a drawing because the way the pieces fit together is quite a puzzle.
3. Support the transmission by a bottle jack just rearward of the exhaust pipe support bracket, so that you can undo the transmission mount support to work behind it.
4. Undo the transmission support bracket and transmission mount (as one piece) from the transmission by undoing the 19mm bolt at the top, and then the four 17mm bolts to the frame. Doing this will now expose the flex plate for easy removal. This bracket will go on and come off a few times during the entire job.
5. Mark the spots on the flex plate where the drive axle and the transmission are fixed. Undo the flex plate. My bolts took an 8mm Allen on the rearward side and a 17mm wrench on the engine side. The washers of the bolts are always found against the flex plate. I let the 17 wrench rest against the frame and used a breaker bar (aluminium mountain bike handlebars) on my good old 3/8 socket wrench.
6. Bolt the support bracket back on again to be able to drop the rear of the car and put the front on jackstands for the final job of removing the trans.
7. Undo everything attaching to the transmission. The speedo cable needs the locking bolt to be fully extracted and then given an enthusiastic tug to come out.
Unclip the shifter link rod, and the control pressure link on the passenger side, which needs its 10mm locking bolt fully extracted. Don’t forget the electrical fittings which may need a cleanup.
Undo the 2 rearmost and 2 forward 4mm Allen bolts attaching the cooler lines to the engine. It is not necessary to do the middle ones unless you want to, and for that one would need a 10” long 4mm Allen key or you’d have to move the exhaust pipe out of the way. To move the cooler lines out of the way of the trans that is about to come down, undo their forward flex lines (19 and 17mm wrenches). Replace them with your new ones when you bolt everything together.
8. Undo the 6 13mm bolts of the torque converter, which can be reached by opening a plastic cover forward of the torque converter housing. I cranked the engine using a wrench on the power steering nut to make the 3 pairs of bolts appear in their turn. They weren’t torqued on very tightly.
9. Now for the main bolts.
a. Drop the trans as far as it can for you to get to all the bolts. I began by loosening very slightly all the easily accessible bolts. For undoing the top starter bolt, those long extenders and articulating knuckle come in handy. I used only the universal knuckle and the Allen head on about 5 ft of extenders. I used a shortish breaker extension on my Craftsman 3/8 socket wrench and after some reasonable force they came undone. I did not anticipate that undoing the starter was included in the package. If I had had more time I would have opened up and checked the starter, but I now know how to unbolt it for next time.
10. Depending on where you are doing the job, you can now build a scaffold of boards to support the trans from this time until it comes out.
11. Have a go at those top bolts. The left hand one I could undo from not too far back. Get a hand in there and ease the socket in while pushing gently from the far end. My extender setup was a shallow 17mm socket, behind it a 2” extender, then the universal knuckle, and then the 4-5 ft extenders. The right hand bolt had to be attacked from further back.
12. At this point I tightened the lower four bolts a little, and supported the trans on my cradle. Undo the last bolts and separate the transmission. I had a terrible time getting mine apart because the torque converter had fused with the flywheel. Eventually I had to kick the transmission away from the motor. Then pull out board after board in your scaffold until the trans is on the ground. I did this out in the street and there was no need to jack up the vehicle to great heights. Drag your prey to the garage and remove the torque converter. I had reasonably fresh ATF in it and did not see the need to drain it.
13. This would be a good time to change out the centering bushing on the front third of the drive shaft, but be sure to mark the position where it slides on the rear section, with some white paint. To knock out the the old bushing I used a ½” pipe resting on a piece of wood, and then slid the shaft down onto it with considerable force. Haynes is a bit optimistic in their instructions. Insert the new bushing by holding the old one against it and giving it some enthusiastic blows with a hammer.
14. I greased my flywheel and cleaned all mating surfaces for the bell housing. My torque converter flex plate was in a fine condition.
15. Install the torque converter onto the new transmission. There are good instructions for this at How to Install a Torque Converter
16. Before installing the new transmission you want to more or less line up the holes on the torque converter with the holes on the flex plate. Now line up the new transmission with the engine by patiently working boards under it until it is lined up. I leave it up to you to figure out how you are going to manage this. Bottle jack and wife helped as well. When it is more or less lined up by eye, draw it in using the starter bolts and the bolt on the driver’s side that takes a nut. Be ever so careful not to force anything or strip the recesses on the engine side. Check constantly whether your torque converter is able to spin freely. That way you know that it was properly installed.
17. Work in the other bolts keeping to torque specifications. For good measure, I bought some new bolts with longer thread for the bottom two.
18. With the transmission fully lowered at the rear, you can now install the top bolts and the starter bolts. It helps to seat the bolts by hand working your arm in from just forward of the bell housing. This didn’t take long at all.
19. Connect up the cooler lines and their flex lines. Bolt them down onto the motor and connect their banjo fittings with new crush washers. Do the same for the dipstick.
20. Connect up all the fittings on the trans. The control pressure bar has to be prised off its ball joint using a stubby flat screwdriver before the fitting can be worked onto the trans. This is the ball found on the engine side (see Haynes p 149). Give it some grease before clipping it back on.
21. Push the torque converter forward to engage the flywheel and bolt it on. I used the smallest ratchet to work those 6 13mm bolts back on because I am paranoid about stripping anything. I will check them for tightness from time to time.
22. Check all trans to engine bolts for the correct tightness. Make sure the ground wire is bolted back on as well as the bracket securing the speedo cable.
23. All that now remain are the flex plate, the support bracket, the exhaust pipe bracket and anything else I have forgotten to mention. Don’t forget to fill up with red juice (4.8 l)
24. You will not believe your joy at finishing this job successfully.
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post #2 of 3 (permalink) Old 11-02-2011, 04:39 PM
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Welcome aboard!

You'll most likely to find answers to your queries in the w123 section.
Transmission issues have most likely been covered and you'll also find diagrams.

Here's the link:
W123 E,CE,D,CD,TD,TE Class - Benzworld.org - Mercedes-Benz Discussion Forum

Good luck!
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post #3 of 3 (permalink) Old 11-04-2011, 02:05 AM
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