We used the 15 inch alloys that were on the w126 car (88 420SEL). I am not sure the proper term for that style of wheel.

We ended up using the master cylinder from an 82 SD parts car that I had stashed from years ago and a power booster from a 79 300D that I guess I am turning into a parts car now, unless I can figure out how to transplant the m/c and booster from the 420 sel.
I really don't think the m/c swap is possible... unless we transfer all the anti-lock equiptment .
The booster from the w126 (420sel) has the bolt pattern different for the w123 master cylinder.

The hardware up front such as backing plates, calipers and rotors fit perfect though, and was so easy I would do it again on my 80 TD wagon when I wear out all the 14" tires around here.
I don't think it is possible to swap the m/c or booster setup from a second gen w126 car to a w123 car. I was kinda desperate for a booster and really wanted to use the dual pod setup so I looked at it fairly close but I could be wrong. I stopped short of removing those parts cause I don't think it will work, but would love to hear from anyone that might have succeeded at it and how it was done. I know of a few people on here that talked about doing it but I don't think anyone has swapped the antilock equiptment.?

since the rotors came from a used car, they may be warped also... pull those rotors and replace them with new, and the pulsing should vanish.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Hello, I guess I neglected to point out that we did the brake upgrade and still had the pulsing in the exact same way, which is what prompted me to check further into the master cylinder. It was actually a toss up between checking the back rotors or the m/c and I just guessed on the m/c cause the rear brakes looked outward to be working fine.

Now, After changing the m/c and the booster all seems good... so that would rule out my thinking that we had warped rotors from a panic stop in this past winter. Oh well, wanted the bigger brakes anyways.
Maybe that panic stop this past winter is where we blew the seal out the back of the m/c causing the fluid to leak into the booster. It was very cold that day.

We discovered this m/c /booster problem with help from this forum... we decided before taking any lines off we would remove the bolts holding the m/c to the booster and shine a light into the booster.... that is when we found the booster to be half full of brake fluid.
We changed the m/c and booster at the same time as mentioned so I cannot say for sure what was causing the pulsing. I can't imagine that the booster was working very well with it being half full of fluid. I am not exactly certain how the booster works for sure other than it is a big diaphragm for vacuum to assist. I guess the fluid half way up would decrease it's vacuum capacity by half ??

The other thing I should point out is that she brought the car home one day last summer saying that the brake pedal went to the floor briefly and then everything was good again for the rest of her trip that day. I looked at it and added a bit of fluid, but nowhere near the amount that was found in that booster. I checked the rubber lines and the rear p/s looked a bit wet so we ordered new rubber lines. Before installing the ridiculously priced new lines... I looked more carefully at where this old line was leaking and decided that it was close to the connector to the steel line, so I tightened that connector...sprayed it with brake cleaner... dried it off and took it for a test drive. It was a bit spongy but the connector and line were dry...so we bled all wheels and it was good again until the panic stop this past winter where the pulsing started.

This is what has me stumped is how did all that fluid get in the booster without me knowing about it.? Is it possible for these m/c to develop a leak and then seal themselves back up? That one time last summer after the pedal to the floor when I added the wee bit of fluid is the only time I touched the brakes since we got the car until now. The brakes have always seemed good up until her incident with the pedal going to the floor last summer and then the panic stop this past winter when the pulsing started.
I am thinking that maybe we got the car with an unknown bad or on it's way out m/c and even the previous owner did'nt know himself. When the car was purchased I was given what appears to be conclusive bills from the mechanic from the previous owner and nothing for brake service to indicate anything. (maybe part of the problem= no brake service)

I should also mention that the lock on the rear hatch has stopped disengaging fully when the doors are unlocked. We send one of the kids over the back seat to unlock it all the way. I believe this started around the time the pulsing started, so could this be related or do I just need to spray some lubricant on it. I am starting to wonder if some brake fluid has found it's way into the vacuum system back there via that booster being so full of fluid. Do I need to open up the vacuum pump to make sure it is not full of brake fluid as well now?

I have read about these master cylinders not taking well to the brake pedal being depressed too far. When she had the pedal go down to the floor last summer did she perhaps do something to the seals inside the m/c? I would'nt think it to take so long for it to show itself as a problem. We drove the rest of last summer and half the past winter and it was fine until the pulsing. Sorry I am so long winded.

Found the cause of the brake shudder on the 85' Will post some pics when the batteries are charged for the camera. Unbelievable rear rotor wear on the inside of the rotor....could'nt see it until the rotors were removed. The face outward looks normal and I could turn the rear wheels easily by hand. I have actual metal peeling off the inside of the rotors. Definately not a smooth surface. I am Very happy to have taken them off now. Thanks VS tech for the suggestion. I figured the fronts were fine since there was no pulsing in the steering wheel. So I checked the rears with my finger behind the rotor.