If you decide you AREN'T going to do it, let me know where the parts car is. I have a 73 1800 ES auto that I would like to convert.

Mattb has covered much of what you need to know. Before you buy, you should find out what type of transmission is in the 1800E. If it's an M41, you are good to go, but some 1800s had an M410 transmission, which was also used in the 164 and is not a direct fit in a 140.

I believe you will find that the front half of the driveshaft comes in several different lengths, depending on what transmission was used. Finding one for an overdrive 140 can be tough. Only the front half differs---all rear halves are the same, other than diameter and flange size, between the center bearing and the rear end. If you can avoid it, you don't want to mix and match driveshaft halves---you can run into problems with balance and vibrations. Better to get a complete shaft from a donor car.

If you buy the whole 1800E for parts, be aware that the front crossmember assembly and rear axle are in much demand among 122 owners, as swapping them is the easiest and best way to put four disc brakes on a 122.

I'd start by doing a search for auto->manual conversion here on the board.. has been discussed in lenth...

Quick run down though, you'll need:

Clutch pedal, cable, (preferably a complete pedal box), crossmember (or do some fabrication on yours), driveshaft (or have one fabricated.. you might get lucky and find that your auto driveshaft will work)...

Of course, you'll have to either use the 1800e engine, or swap flywheel for flex plate.

You'll need to do the wiring.. come up with a overdrive switch. Maybe a relay...

Since your 142 is an E, it should have the same size driveshaft flanges as the 1800.. but do double check.

Since you'd have the 1800e tranny (linkage cover).. you'd either have to modify the crossmember to use that shift linkage, or find a earier transmission cover and 'wobble stick'. If you go for the latter option, you'll have to drill/tap that new cover to accept the 4th gear sensor switch.

In all.. it would be a lot easier if you were to start with a 140 as your donor car.... as it would have about everything you need. but that won't necessarily be easy to find.

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-Matt I ♥ my ♂