I posted these on benzworld awhile back, but I figured I'd post them here for anyone who didn't see them. The late w126 brakes are noticeably larger(I did a quick search for dimensions,but no luck and little time) and do bolt right on to the w123 spindles. There had been a lot of talk about the compatibility, but I couldn't find anybody who had actually done it.So I just bought all the stuff and bolted it on.You would need calipers, rotors and backing plates(and wheels to clear them of course. I ordered mine for 1991 560 sec.W123 brake hoses work fine.This baby is still under construction so I can't tell you how much better they are than stock.My only other recent concern is the ability for the w123 master cylinder to push the extra volume.The w126 has a different master cylinder,so that may be an option.I'll let you guys know what I end up doing.This is the never ending project and has to be put on hold for a few months,but here are the brake pics. OK, heres one, the rest are 150kb and my photo editor just froze up :evil: maybe tomorrow.

There is a '90 300SEL in the junk yard with slotted rotors, but I dont think I can use them because my 14" wheels will not clear. Does the fact that the later W126s had a diffrent wheel offset come in to play?

Any side by side comparison of the W123 and late w126 brake rotors?

ForcedInduction Wrote:Any side by side comparison of the W123 and late w126 brake rotors?

I may pull the ones in the yard even if they won't fit my wheels. If I do I'll post a side-by-side

You should spend the extra few bucks and put the r107 calipers on there. Good to hear its a straight bolt on. What size tires and any feedback on the offset?

I use the late W126 15" wheels so I know the brakes will fit.

No problems with tire wear or bearings so I bet the offset is not an issue.

winmutt Wrote:You should spend the extra few bucks and put the r107 calipers on there.

Do those bolt on as well? 4 piston calipers would be very nice.

It looks like there is no way a R107 master cylinder will work with a W123 without custom brake lines. So, how would we control the brake bias so we don't just lock the rear wheels every time we hit the brakes?

I think there are special valves for just that puropse.

The information I had showed that nothing was needed on the MBC for the 4 pots, I do not believe the overall volume difference is tha big between 2 pot and 4 pot.

I am 99% sure the r107 4 pots are the same as used on a variety of Volvos and BMW's that I saw at the yard today. I tried some mixing and matching to see if they fit, but alas all are made for bigger spindles. I did pick up the 560SE brakes and will be mounting those soon with the new sway bar.

*if* you have the time and energy, and if you pull the spindles you can do ABS as well.

Could one just fab/modify the caliper mounts to fit the 4-pot to one's existing brake set-up? I'm running a W126 so I've already got the bigger set-up.

Telecommbrkr Wrote:Could one just fab/modify the caliper mounts to fit the 4-pot to one's existing brake set-up? I'm running a W126 so I've already got the bigger set-up.

Its a bolt on upgrade afaik.

I would assume then that I only have Gen1 as I have the original 14" 'Bunts' on my W126. If this is the case I would need rotors and calipers from newer W126? I have '82 & '85 300SD's

MTUPower Wrote:Several weeks with the new brakes and I like them very much. Easy bolt on and well worth it.

Yup today I got to use them for a real emergency brake for the first time, I am def doing this on wifes car.

Too bad it's impossible to find 15" steelies and hubcaps.

Guess I'll have to stick with the early W126 brakes.

A quick word on this, its a good idea to get a 15" spare or one that clears.

MTUPower Wrote:It's been several months now and I have to say that this is super upgrade mod- it's a must for performance.

Even for normal driving, I am going to do this on the wifes wagon in the near future.

Still haven't found a compatible 15" spare.

I would do it, but I don't want to loose my hubcaps.

There is a '79 450SLC in the junkyard here, but alas, it has the two piston brakes and not 4 piston. :cry:

Anything else of interest I should grab from it?

ForcedInduction Wrote:There is a '79 450SLC in the junkyard here, but alas, it has the two piston brakes and not 4 piston. :cry:

Anything else of interest I should grab from it?

You goin to do the upgrade? I would think that would be the same as the first gen 126. The 4 pots were rare afaik.

If I'm going to upgrade, its going to be to 2nd gen.

I've got all the big parts from an 87 420SEL to do a GenII "Big Brake" upgrade. I only need to order wheel seals and brake hoses.
The GenII is 300mm outside diameter vs GenI's 278mm. The 22mm difference is mostly in pad surface area.

Will the entire hub bolt on or should I transfer the rotor to my existing hub?

Works either way. The 2nd gen will have ABS support .

I just have the hub, I didn't need the spindle.

Today I got a set of nearly new rotors, hubs and calipers from a 1990 420SEL for $76.

I'm not sure if I want to keep the other set and put it on the 240 or sell the good calipers for funds towards the 300's toys. If anyone wants the calipers, make an offer.

I just finished the install of mine today... 1989 420SEL spindles, powdercoated 'performance gold', good condition rotors, new calipers... I did run into a problem though: after taking out the grease seals and banging out the bearing races, I realized my new bearing/seal kits were for the wrong size...(smaller) maybe different because of the ABS? (the tone ring limiting the size of the bearing and seal set?)... only thing I can think of... luckily, my 123 hubs and seals/bearings were still in good shape so I swapped them over to the larger vented rotors...

heres what I noticed:

spindles are totally interchangeable between 123 and 126... with the late 126 spindles and hubs you have the option of upgrading to ABS (I have some old sensors installed to plug the holes on mine..will do a full upgrade at a later date)
the 123 solid rotors are ~11" diameter
the early 126 vented rotors are ~11" (I think)
the late 126 vented rotors are ~12"
apparently all of the differences are in the calipers (and hubs/spindles for ABS as mentioned above)

ill prolly think of more in the morning after I get a few hours of 'rest'

also installed my vogtlands, 16" rims (and 225/50 series tires) and full suspension rebuild this weekend... still havent gotten the rear subframe mounts to seat all the way...anyone know a trick?

(06-15-2009 04:54 AM)SurfRodder Wrote:  apparently all of the differences are in the calipers (and hubs/spindles for ABS as mentioned above)

ill prolly think of more in the morning after I get a few hours of 'rest'

And the back plates.

Good to know its bolt-in. I just need seals, brake hoses and tires for my 15" wheels.

I did not replace the grease seal and am using the abs hubs. Good to know they are different.

(06-15-2009 09:08 PM)winmutt Wrote:  Good to know they are different.

yeah, wish I had paid attention to that... I'll be getting some slotted rotors eventually anyway, so Ill put my ABS hubs back in then... the toolboxes over at Kragen and Autozone kept trying to tell my dad (who went to get the seals while I was still working on the front springs) that the part number was the same for both cars... i think he just got pissed off and gave up on them. Anyway, I am definitely impressed with the overall feel of the larger brakes, I will be putting in some low dust pads when I get the new rotors to keep the dirt off my new rims...

What year is the gen difference in 126's, is the '86 a gen 1? I like the idea of getting rebuilt calipers insted of used ones as well as new rotors, I will build new flex brake lines to complete the job. So what do I need to put the 4 piston 12" brakes on my '84 300CD, is there a rear brake option we could upgrade to?

(08-21-2009 10:40 AM)Motorhead Wrote:  What year is the gen difference in 126's, is the '86 a gen 1?

GenI= 81-85
GenII= 86-91.

Quote:I like the idea of getting rebuilt calipers insted of used ones as well as new rotors

I priced it out around $300 to do the GenII brake conversion using nearly all new/rebuilt parts. Calipers, rotors, hoses and wheel seals new, only using used back plates.

Quote:So what do I need to put the 4 piston 12" brakes on my '84 300CD

Get the calipers. As long as the rotors are the right diameter, R107 4-pots should fit right on. I doubt it would be worth the investment on top of the GenII brakes unless you intend to do a lot of road/rally/autox racing.

Quote:is there a rear brake option we could upgrade to?

From what I've seen, the W123, W116, W126 and R107 all use the same 11" rear brakes.

So if I use the '86 420 rotors, calipers and backing plates, then that would give me vented rotors 1"dia bigger. I think for my pile I don't need any more brake for the front, is there any rear brake bolt on for the 123?

Nothing for the rear, not really needed. If you are interested you might want to check out some of the later model boosters as well, they appear to have a greater volume. One of the dream jobs on my list is ABS still.

(08-21-2009 10:40 AM)Motorhead Wrote:  What year is the gen difference in 126's, is the '86 a gen 1? I like the idea of getting rebuilt calipers insted of used ones as well as new rotors, I will build new flex brake lines to complete the job. So what do I need to put the 4 piston 12" brakes on my '84 300CD, is there a rear brake option we could upgrade to?

---

Motorhead, We all are dreamers here, love struck I guess, and my dream is to have a 300CD someday. So in the meantime hows about some pics of your CD. With the windows down its got to be the coolest drive on the road. With the mods you are gona have the performance and style. Best of luck!

The Gen-II brake upgrade is done! Thanks to Tom Judd for use of his shop and his time helping.

All the parts were from a 1990 420SEL. The backplates and calipers fit exactly to the 300D spindle and I bolted the rotors to the stock 300D hubs. The only major car change needed was the 15" wheels. It definitely stops much quicker and the rotors aren't nearly as hot after the 70mph "panic stop" test. Pictures will be added later, I left my camera in the 240 and Tom will e-mail the ones he took.

(01-12-2010 01:08 AM)ForcedInduction Wrote:  The Gen-II brake upgrade is done! Thanks to Tom Judd for use of his shop and his time helping.

All the parts were from a 1990 420SEL. The backplates and calipers fit exactly to the 300D spindle and I bolted the rotors to the stock 300D hubs. The only major car change needed was the 15" wheels. It definitely stops much quicker and the rotors aren't nearly as hot after the 70mph "panic stop" test. Pictures will be added later, I left my camera in the 240 and Tom will e-mail the ones he took.

I am of the opinion that a better booster can be had for this setup. The later models had a doubled chamber looking booster.

(01-12-2010 01:08 AM)ForcedInduction Wrote:  The Gen-II brake upgrade is done! Thanks to Tom Judd for use of his shop and his time helping.

All the parts were from a 1990 420SEL. The backplates and calipers fit exactly to the 300D spindle and I bolted the rotors to the stock 300D hubs. The only major car change needed was the 15" wheels. It definitely stops much quicker and the rotors aren't nearly as hot after the 70mph "panic stop" test. Pictures will be added later, I left my camera in the 240 and Tom will e-mail the ones he took.

What about those pics Forced?


So the r107 calipers should bolt right on? Even with the 15inch upgrade? Has anyone done this?

(09-29-2010 03:49 PM)garage Wrote:  What about those pics Forced?

He never sent them.

RE r107, I believe the early version will not latter (most importantly I dont think the 4 pots will). Ask in w126 forums at bw.

i'm going to be putting the gen 2 w126 fronts on my 240D. got the calipers from the junkyard for $17 each! going to rebuild them and use new rotors.

in case anyone is interested here is a photo. top caliper is gen 2 w126, bottom is w123 ('81 240D).


edit: i think i made a flub. 15" wheels required in order to clear the gen 2 fronts? PISS. i guess i'll just try bolting the caliper on to see what the deal is.

Yes 15" wheels are required.

This also applies to a w116. I put these on my 80 300sd. They came off a 91 420sel iirc.
Get the backing plate as they are bigger and have a air scoop too.

Top is w116 stock rotor. Bottom is 2nd gen w126. Thickness is obvious.

Again top w116 bottom w126 the dia is obviously larger


I've been driving on this setup for a few weeks now and I live up in the mountains. At first they felt the same till I got the pads bedded in and I noticed once they are warm they bite alot harder and I yet have to fade them out. I do notice I can lock up a front easily now with alot less pedal effort.


Edit: I did have to reuse my brake lines as the 126 lines didn't match up on the car side.