Differences between 1st Generation and 2nd Generation W126
 

After much searching, I never saw a concrete answer to the differences between these two runs of the W126. So, for that matter, I would like to create a solid thread to leave for the W126 enthusiast.

Here are the basics:
1st Generation W126 ranges from 1981 to 1985, included.
2nd Generation W126 ranges from 1986 to 1991, included.

I have filled in some of these already, but I would like to have the moderator(s) compile everything down here in the following categories:

Seats (7-pleated design on 1st, big-pleated leather from 1989 on in 2nd).
-Underdash plastic key holder and rolltop console box in 2nd. (Standard on models with passenger side airbag, option on all others)


EXTERIOR
-Longer wheelbase (+L) models available in 2nd.
-Bumper design (vent design in the front).
-Lower plastic moldings (ribbed in 1st, flat in 2nd).
-Headlights (recessed in 1st, flat with plastic cover in 2nd).
-Headlight wipers (an option in 1st, standard in 2nd).
-"Bundt" wheels on 1st, 16-hole wheels on 2nd.
-Automatic heated mirrors in 2nd.
-Electric sliding sunroof in 1st, tilting and sliding in 2nd.
-Better rust-proofing from 1985 on.
-Water heated windshield with thermostat (2nd).
-Different dome light designs (seatbelt warning in 2nd).

INTERIOR
-Seats (7-pleated design on 1st, big-pleated leather on late 2nd as an option).
-Different seat motor design in 1st and 2nd.
-Airbag (option in 1st; driver's standard in 2nd, with passenger as option).
-Underdash plastic key holder and rolltop console box in 2nd (option w/airbag).
-Vinyl door panels (1st, early 2nd) and leather (2nd).
-RS seatbelts from 1985 on.
-Adjustable steering column.
-Electric headrests standard in 2nd.

DRIVETRAIN / MECHANICAL
-Differential subframe mounting configuration.
-Different window regulator styles.
-Frequency valve (1st) vs EHA valve (2nd).
-Gas: 380/500 engines (1st) vs. 300/420/560 (2nd).
-Diesel: OM617 (1st) vs OM603 (2nd, on 1986-87 and 1990-1).

BRAKING / SUSPENSION
-Smaller calipers on 1st vs. bigger ones on 2nd.
-274mm brake discs on 1st, 300mm brake discs on 2nd.
-Rear hydraulic leveling suspension in 560SEL models (2nd).
-ABS: option in 1984 and standard from 1985 on.

ELECTRIC / ELECTRONIC
-Memory seats (option in 1st, standard in 2nd).
-Deletion of radio aerial adjustment switch for 1991 only.
-Traction control (only available in the US in 1991).
-Third brake lamp, standard in the 2nd Generation.
-Low washer fluid cluster light only standard in 2nd.
-Low engine oil cluster light only standard in 2nd.
-Different Becker radios in 1st and 2nd.
-Different climate control systems in 1st and 2nd.
-Different headlight switch design (letters illuminate).
-Solid state transistor for blower motor.
-Recirculation mode in climate control.

Help me complete this list!

I think the explanation is that the model change between 123 and 124 happened at the same time as the transition of the 126 generations.

Your list seems to bear this out, the features shown on the list that are gen 1 are consistent with a 123, while the gen 2 features are consistent with a 124.

To ad to your list

Second Gen:

Standard ABS
RS seatbelts 85+
Different window regulators
They used a solid state transistor with a huge heatsink to control heater blower
300mm brakes instead of 274mm
Different automatic climate control system
Electric headrests
Automatic heated outside mirror
Letters around headlight switch illuminate
Water heated windshield with thermostat
Motorized steering column adjustment
Recirculation mode on climate control
Tilt sunroof (never ever EVER use the tilt feature)
Updated dome light with seat belt warnings

14 inch bunts on Gen 1, 15 inch 15 hole on Gen 2
Frequency valve gen 1, EHA valve Gen 2
380/500 engines gen 1, 420/560 engines gen 2
Electrically, a list as long as your arm.
Most body parts will interchange from Gen 1 to 2
Most electrical components will not interchange from Gen 1 to 2

Paul

Added! Keep them coming! :)

The brake calipers from 1st to 2nd gen do not have any more or less pistons, they are just a different size. And the rotor mounting design is the same from 1st to 2nd gen. I think you are thinking of the W124, which uses a set screw on the rotors.

My question is which body parts won't interchange?
I know the II dash with the passenger airbag won't fit in a Gen I

Jeff

I have only seen the roll top console in later 2nd generation cars with a passenger air bag in place of the dash glove box. Noticed some 6 cyl gas cars have painted rear defogger instead of thin wires in the glass.

I stand corrected! The list has been updated.

The dash will interchange if you keep the passenger air bag. The problem is you loose the glove box, or gain a glove box depending on which way you are going. The bumper is a little different but will interchange. As far as I know, all the body parts will fit. All the interior parts will fit. Please correct me if I am wrong.
You can put a gen 2 transmission in a gen 1, but not the other way because of the crank sensor.

Paul

Is it like in the W124, in which the seats are interchangeable but the seat motors are not?

What exactly is a "-Water heated windshield with thermostat (2nd)." -- I've never heard of or seen such and I'm curious.

Also -- nobody's mentioned yet (Maybe we are taking it for granted or maybe I skimmed too quickly) -- second generation is (or can be) a longer wheelbase. The back doors are longer and there is more leg room in the rear seat. (I can't sit in my own back seat in my 300SD but I can in the SDL.)

I'm not sure whether the 90/91 second generation "350SD" is the longer wheelbase or the shorter one, but anything that ends in "L" is definitely going to be longer. I think.

Don't know if this is enough difference to be worth putting on the list but the control switch to operate the sunroof got moved from the first-gen rocker switch on the console stack up to the now-conventional location on the upper dome light.

All SD's and SE's are short, and all SDL's and SEL's are long. Gen1 and Gen 2.
A far as seats, the seats are the same, the electrical is different so the motors won't directly fit but can be modified to work. The head rest are electrical on the Gen 2 but manual on the Gen 1. The headrest motors can be put in the Gen 1 seats if needed.

Paul

Made a few adjustments (One comical, the rest legitimate)

The 84+ cars have a metal plate behind the windsheild that heats up the glass where the wipers sit. Its for snow so I wonder if the first gen 126 has a serious issue with packing snow in the wiper cove.