Caliper piston diameter w124 + r129


300E 24v / 300CE 24v – 295×22 dics

Top piston: 42mm
Bottom piston: 38mm

E300 / E320 – disc size 294x25mm

Top Piston: 42mm
Bottom piston: 38mm

500E and SL500 – disc size 300×28

Top piston: 42mm
Bottom piston: 38mm

600SL and supposedly 500SL 94-98 – disc size 320×30

Top piston: 42mm
Bottom piston: 38mm


Regular sedan w124- disc size 258×9 solid

Piston: 35mm

s124 / w124 wagon + SL500 to 1998(?) disc size 278×9 solid

Piston: 38mm

s124 320TE w124 disc size 278×20 vented

Piston: 38mm

Master Cylinder + brakebooster w124 + r129

pushrod circuit is for front wheels, and floating for rearwheels

w124 regular 5+6 cylinder + w123(?)

Piston diameter (pushrod): 15/16″
Piston diameter (floating): 3/4″
Piston stroke (pushrod): 17mm
Piston stroke (floating: 15mm

Booster type: Single
Boost factor: 3.85

w124 Long Wheelbase + w201.029, w201.034

Piston diameter (pushrod): 15/16″
Piston diameter (floating): 3/4″
Piston stroke (pushrod): 17mm
Piston stroke (floating: 15mm

Booster type: Double
Boost factor: 4.5

w124 V8 (except Euro 124.036 500E) + r129 (except 129.076 600SL)

Piston diameter (pushrod): 1″
Piston diameter (floating): 3/4″
Piston stroke (pushrod): 17mm
Piston stroke (floating: 15mm

Booster type: Double
Boost factor: 5.6

Euro 500E w124 + 600SL

Piston diameter (pushrod): 1-1/16″
Piston diameter (floating): 1″ or 13/16″
Piston stroke (pushrod): 19mm
Piston stroke (floating: 13mm

Booster type: Double
Boost factor: 5.6


The difference between the Master-cylinder of a normal 5-6 cylinder w124 and the 500SL (400E and 500E USA, not Euro 500E) is that the diameter of the pistons is increased from 15/16″ to 1″ and kept the same in the rear.
This incease the braking-power of the front wheels compared to the rear, they have also accompanied this tad more larger diameter of the MasterCylinder with an increase in Brakebooster from 3.85 to 5.6 (or 4.5 to 5.6 if we look at the sportier w201 and Lang w124)

What to choose depends a bit on what setup you want on the car, and what types of pistons you install.
The 500SL had non-vented discs in the rear and is more front heavy, so the promotion of front braking power might make sence,  if you only upgrade the front that makes sence, whereas if you upgrade to 500E front brakes and 320E vented rear discs, i would suggest you stick with the stock w124 mastercylinder, especially if you have a rear-end heavy car.

I run stock w201+w124 Mastercylinder+ 300E 24V discs (same piston diameters as 500E but lacking 5mm in disc diameter) and 320E rear vented in the rear, and that was quite balanced, where if having a heavier engine than the m103 (like a v8) or lightened in the rear, one might be better of with a 500SL master cylinder.

Rotor R107 560SL

r107 560SL front brakedisc

Rotor W126 1st Gen


w126 gen1 front brakedisc


Rotor W126 2nd Gen


w126 gen2 front brakedisc



w124 brakes vented rear from a m104 touring (s124) 278x20mm
Ventilated rear discs w124

w124 brakes front 295x22mm 4-pot from a 300CE/300E 24v 3.0
ATE number 39 and 40

5 thoughts on “Brakes – system, and part specs”

  1. Hi

    Your tech support is great !

    I bought a 1982 280CE i wanna built with better performance. If I follow your indications, Gen 2 W126 rotors won’t fit 560SL calipers : too thick. Is it right ?


    1. i dont think the calipers would be a straight fit on the hub/front anyhow, but the diameter is another issue.
      w126gen2 calipers for 300mm discs wouldnt be supper efficient on 284mm r107 discs,

      Regarding thickness i would dare run the calipers on the r107 discs, aslong as you have new/good brakepads, the decreese in thickness, 27mm to 22mm (total of 5mm = 2.5mm/brakepad)

      new brakepads is a lot thicker than 2.5mm,and if it was a problem you wouldnt be able to run totaly worn out brakepads.
      althou, dont go for wornout discs.

      its might be possible, i would probably not do it anyhow, due to disc thickness difference.

  2. Hello,
    I have a quick question (or two). I have a ’75 w114 (280) and I was told that the 88 560sl front brakes would fit my car (spindle swap). I can’t find anything on the internet to back this up. My hope is to upgrade the stock brakes and possibly an LSD swap with mid 3.xx gears to support a mild (400hp) LSx swap i am planning. Is this a viable option for me? I would like to find a set of Penta s to fit the front brakes (16″?) as well. Any help or advise would be greatly appreciated.
    If I am posting this question in the wrong place, I apologize. I couldn’t find a generic email or “contact us” spot.


    1. Hello there, no problem, we answer anywhere that works.

      The w115 and w123/w126 doesnt share the same front spindels, but the r107 and w114/w115 do share the same front end construction (double wishbone) in the earlier models atleast,

      i havent looked into this myself, and there doesnt seem to be a lot of other that have either.
      thats the best stuff i found, but the w126 he suggest for brakes have the calipers at the rear of the hub, while the w114/w115 have them at the front, hence – you would need to swap sides, left to right and right to left, to be able to properly bleed them…

      regarding differential, the 3.27 and 3.06/3.07 came with LSD, but with your build, a quaife diff might be a valid option, any housing from w116 or w126 would work on your car. and Quaife sells kits that supposedly work good with these houses. (if you cant find a stock LSD diff)

      il email you, and we can continue from there.

  3. My 124 Yr 1997 needs brake booster replacement. Lucas No 004 430 1630 was original BUT OEM offers 03.7760-2702.4. So I dare not order ,as maybe it is wrong one. Can you please advise. Thank You very much

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