69 280SL 4spd to Auto

[MnSL]

I’m going to be replacing the 4spd on my car with an automatic.  I know this is not an easy swap; but I plan on doing it to allow easier driving for my better half (nasty commute). 
It is a good time to do the swap as my car is in restoration and almost at the “put it back together” stage”.  (BTW - I will be keeping all the 4spd parts to sell with the car when that time comes if the next owner wants to return it to original factory condition.)

I’ve done some searching on the forum and have put together a quick list of items or procedures needed:

1.   Get a donor car
2.   Swap flywheel (use correct donor year to avoid balance problems)
3.   Swap pedal assembly along with related hydraulics, lines, clips, etc.
4.   Purchase or make new front driveshaft
5.   Swap shifter and linkages (bits and pieces are sedan, others are strictly W113)
6.   Use correct length flywheel bolts
7.   Purchase or find correct length speedo cable
8.   Misc wiring: Back-up lights, neutral safety features, kickdown and possibly some engine idling interfaces

I would really like to use a torque converter transmission (TC) rather than the K4A025 fluid coupled (FC) transmission. 

Questions:
A. How much more difficult is the swap with a TC rather than FC transmission?
B. What are the best sedan donor cars to use for FC or TC transmissions?
C. Does anyone know if a “How To” manual exists on the forum for the swap?
D. Have I forgotten anything?

Thanks for the help!

[Benz Dr.]

You will need small stuff you might not even consider.
Tunnel carpet
Throttle body with switch
Dowell pin on crank shaft is a different lenght
You will need to remove the pilot bearing on the crank end
I would consider changing the front wiring harness to conform with an auto trans set up.
Contanst speed solenoid.
You will also need a kick down switch and cable for the neutral switch.
You will need a rad with a trans cooler and the lines that run from the trans to the rad.
Banjo bolt for modulator vacuum line
Small brackets to hold lines in place found on auto cars

  Most of these change overs don't work all that well because of patched in wiring which is why you might connsider changing that too.

[Richard Madison]

I guess you have considered completing the restoration then selling the car and finding an auto car...most Pagodas for sale in the US are auto tranny cars and they are available in various price ranges.

Even if the modified car has all the manual parts, it's quit a job to reverse the mod. I suspect some potential buyers will walk away.

Richard N, NYC

[drmb]

I have just completed a change from manual to auto on a 1970 280sl,had a 71 108 as donor fitted cooler in radiator lower tank,cooler pipes,flywheel,shortened front of driveshaft and rebalanced,removed pedal box then fitted shorter bolt for brake pedal mount,fitted 108 speedo cable,vacuum pipe,kickdown switch.Interrupted wire to starter solenoid and put back via inhibitor switch,also included wires for reverse lamps.The auto box is the k4c025 type so did not have to add idle switch on throttle body or constant speed solenoid.Biggest challenge is shifter rod,connecting early type shifter ( back to front shift pattern)to later type auto.inverted lever on side of auto and made up linkage in between.I have pattern of correct shape and ratio,cut and bound carpet of centre console.About four days work,now everything works and drives perfectly.

[MnSL]

Benz Dr.
Thanks for the list of items.  There are quite a few small parts to worry about.

280SL71
Yup.  Thought of the restore, sell and buy.  But this car has a special place in the family (don't they all!<g>).  I'm hoping it can stay in the family for generations.  You're right about the buyers.  Anything I do to the car beyond factory has the possibility of reducing the pool of buyers.  I'll have to live with that...or put it back together as it came from the factory to get top dollar.

drmb
Wahoo!  A success story!!  Do you have a write up or photos of the swap?  If you don't mind, maybe we can chat in a couple months after I find a donor car.  So the 108 was a good donor?  I'll start looking for a transplant patient.

For what it’s worth: I've built German-based racecars doing engine and transmission swaps.  Wiring is always fun!!  This project will hopefully be similar to other projects I've done using donor cars.

Thanks everyone for the counsel and advice.  Much appreciated!!

[GGR]

I'm going to convert my '71 280SL from auto to manual one of these days. So all what you need will be available. When do you need it?

[MnSL]

GGR

Wow.  What an offer!  Thank you.
No hurry actually.  I'll send a PM so we can discuss.

Mark

[mirkwood]

I'm going to convert my '71 280SL from auto to manual one of these days. So all what you need will be available. When do you need it?

Hi Gael,when did you get the SL ?  Five speeder again? Cheers! Ron B.

[GGR]

Hi Ron,

I got the car last January at an estate sale. 80.000 original miles, no rust, but in need of body work. Runs great. Will most seemingly fit a Getrag 5 speed in it.

Cheers

Gael