Replace W123 Shifter with W124 or other
 

The Motivation:
One thing that bothers me about our '82 300TD is that it does not have the brake pedal interlock feature of more modern cars. The reason it bothers me enough to consider doing something about it is our toddler. He loves to play in and around the cars. Most of the time we remember to set the parking brake; but, he's a clever kid, and someday, he'll be strong enough to pull the park brake release.

The Idea:
Replace the stock W123 shifter with one that has a brake pedal interlock, such as one from a W124. Has anyone ever done this? Are the transmissions the same/similar enough? Anybody got a better idea?

I wouldn't bother it is probably a phase - all of ours have grown out of playing in cars now. It took about two years for each of our children to grow out of it. If you're really worried I'd buy or make some chocks.

I'm nearly forty years old and I haven't grown out of that phase. We've also got another on the way, so, I think I'll bother. I have wheel chocks. They aren't any better than the parking brake, and are a lot more inconvenient.

I have never heard of someone doing this, and I can't imagine it's practical.

You would have to change both the shifter assembly and the steering column lock mechanism. The former is doubtful, the latter more so, seeing as the shifters aren't even compatible between first and second generation w126, let alone cars designed 20 or so years apart. The openings probably aren't even close in size and shape.

If it's that much of a concern, why not just keep the car locked up and off bounds?

This just came to me: Around here they sell parking stops for driveways that look like asphalt that are just high enough to stop a slow-moving tire, but low enough to be driven over easily under power. They are meant to aid in parking position for the spatially challenged, but I imagine you could install them so that you drive over them to park, then they would prevent roll-back once the tire was on the other side. Just an idea.

Granted, there are a lot of things that are more practical than driving a thirty year old car. It would be more practical to sell the TD and buy a Jetta. But, we like the TD.
I'd be satisfied to stop at retrofitting the brake interlock, and leave the steering column alone. This would make it so that he or the dogs can't kick the thing out of park inadvertently. And, so that he can't intentionally take it out of park until he's a bit older.
Are you speaking from experience, or merely sniping the idea? There are many parts that can be fitted from other models. The shifter in my W210 looks remarkably similar to the W123. It is in the same relative position to the driver, both have a knob, PRNDSL vs PRND1234, etc. I have no doubt that it is possible. The questions are which cars are the best candidates to get a donor shifter, and how much modification/fabrication is needed.
Do you have children?
Thanks, that's a little better than a chock, but doesn't solve the problem for places other than my own driveway.

All the above comments aside, maybe children shouldn't be allowed to "play" inside of two ton pieces of machinery. We wouldn't let our children "play" on a forklift or tractor, would we? (Hopefully not)

The W124 is a cable mechanism in the flooring and dashboard and is more complicated than a simple shift lever assembly interchange, which is also questionable considering the two are different chassis altogether.

There is an '87 300TD available in the US market if keeping your toddler out of the car is not an option. Then again, I think the shift lever locking mechanism started in 1990...

Yes, thank you for that scolding, you condescending [censored censored censored]. You've been a great help! This isn't needed so that we may choose to neglect our parental responsibilities; but rather to have the same level of safety that we've come to appreciate from our other vehicles.
Do you ever go camping?
Do you shop for groceries?
Do you wash your cars?
If you stoop so low as to participate in any of the above, do you include your children? We do. Times are hard here; we've had to let the butler and the nanny go, and the gardener refuses to do our grocery shopping or mind small children. So, in addition to letting the kid help wash the car, he may also from time to time, be left unsupervised for a brief moment. There's also the chance that he might climb the back yard fence, sneak out through an unlocked door, etc. Perhaps your children are unable to manage such a feat, but mine seems quite clever and curious in that respect. Even if you reckon that your own children are exceptionally dim-witted, consider the fact that my dog has managed to dislodge the shifter on at least one occasion that I can recall.
Can you imagine no other reason why every car manufactured in the last two decades has such a feature?

For the rest of you, can we just assume that I've decided that it is a good idea (worth considering). I'm quite happy to have constructive feedback as to what sort of real problems one might encounter.

I'd love it if someone knows of another model that has a compatible shifter with the interlock feature.

Just found this thread where someone has had the same idea, just not with a W123. http://www.peachparts.com/shopforum/diesel-discussion/296365-retrofit-brake-pedal-shift-interlock-1987-w124.html

As I recall, the interlock came to be because licensed adults couldn't be bothered to check that the car was in P or N before engaging the starter, nor apply the brakes when starting the engine as a matter of habit.

Whatever the incidence of knocking a shift lever out of P, it wasn't enough impetus of the DOT to take action.

You might get creative with an electric door lock solenoid that extends to corral the shift lever in P. Already MB brake lights (and the horn) don't work with the key out (why???). Hmm... unless you can fashion a ratchet mechanism, you might have to apply the brakes to get into P as well. Which leads to...

You need the key switch component to ensure the shift lever is in P before removing the key. Otherwise you lock the door but leave the window open.

Your head is in the right place child proofing the car but there are other ways kids can get themselves into trouble. There are far too many reports of kids getting stuck in a hot car and being unwittingly abducted when the car is stolen to name a couple.

Sixto
87 300D

http://www.nhtsa.gov/Vehicle+Safety/Formal+Agreement+Reached+on+Brake+Transmission+System+Interlock+(BTSI)
I'm sure there are plenty of good and not so good reasons for the BTSI interlock, one of them appears to be to stop little ones from knocking a car out of Park.

It's pretty obvious that some people have no clue as to how resourceful and relentless little ones can be. I've been thinking about the same concern - I have 3 boys from age 2 to almost 7 that are massively intrigued with cars, engines, keys, and switches. The oldest figured out how to unlock the interior doors of our house before age 2. (from the key side) Its not always as simple as "just not letting them lay with a 2 ton car." Could always make something like a "club" that mechanically locks the shfter I guess? Like a simple wood or aluminum plate with a slot in it that slides into the shifter then drops down into the console so it can't slide back...

It took 16 years to enhance key in to shift with brake on to shift? In 2032 they'll add brake on to turn the key :)

Sixto
87 300D

[waiting for moderators to raise a card at me] You underestimate forum membership. I'm sure the hands that ably keep these cars running are older versions of the hands that got into cars and knocked shift levers out of park. The message is whether or not I know kids, I know how dangerous it is to leave a kid unattended in a car. It seems a difference of opinion as to whether you secure your house with a deadbolt, an alarm, a Glock or some combination.

Sixto
87 300D

Tubularfab, if I can't find a setup from another chassis that is close enough to make work, I'm also looking at various electric solenoids that are made for this purpose. Haven't found one I like yet though.

This one looks like it might bolt right up. MERCEDES BENZ 92-96 BROWN LEATHER GEAR SHIFTER SHIFT | eBay

Would like to find the brake pedal assy too.

Good grief, why can't people just answer a technical question without interjecting their opinions about ancillary issues?