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#1
06-21-2018, 03:14 PM
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S-Class SL-Class Brake Master Cylinder for W124
Hi Everyone,
I was wondering if someone could tell me if the brake master cylinder from an S or SL Class (say an R129) can be used for a W124? Would it be a direct fit? Would there be any benefits to doing that? Would the calipers and assembly need to also be changed, etc... I have a 1995 W124 and am about to order a new master cylinder and noticed that the heavier model master cylinders look pretty much the same except for an additional orifice that can be plugged up. I'm wondering if there might be any benefits to getting the larger bore master cylinder. Thank you! 
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#2
06-21-2018, 04:12 PM
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tfb:
Numbers are important. What are the bore diameters of each? Are either of them stepped, and if so the diameters?
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#3
06-21-2018, 04:49 PM
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Master cylinders are sized in relationship to caliper size and to a lesser extent brake booster power / manual brakes. With a stepped bore, front to rear brake balance can be altered by changing one bore size.
Many times the master cylinder pattern is the same across models or even across makes as auto makers generally use outside vendors ( Like ATE , Girling, Lucas, Bendix ) making swapping possible. Brake line location is usually different across models so some fab work will be needed. Early R129 cars have a master cylinder mounted valve that is somehow tied into the ABS, I've never researched it. The real question is what problem are you trying to solve? Using a MC from a heavier car won't necessarily make the brakes work better. If you are able to lock up the wheels / get the ABS to cycle under braking, the car has strong enough brakes. ( As long as there isn't a parts failure that causes only one wheel to lock )
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#4
06-21-2018, 05:06 PM
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Quote:
The larger booster/master cylinder pairs from the 400E/500E is shared across W126/R107 after 1983, R129s except the V12s, W140 V8s, and the 190E Evo II. Here's a table: I've personally paired a 300SE master cylinder/brake booster set to my 4 piston 400E brakes on my 190E chassis. It was a direct fit/upgrade. I wouldn't just change the master cylinder or the brake booster alone. I would match them up together. So if you wanted to replace the master cylinder with a larger one, go ahead and get the booster with it.
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#5
06-21-2018, 05:19 PM
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Thank you for the thoughtful replies.
I have a 1993 300SL with the the four piston setup, and a 1995 E300D with the two piston floating caliper design. And it just seems to me that for the W124 cars with the diesel engines, the stock brakes are on the weak side compared their higher performance siblings. Maybe due to the heavy diesel engine... After 292K miles it's time for a new master cylinder. Was just wondering if it would be an upgrade to use the 1" piston instead of the 15/16". But w/o changing the calipers (and disks + wheels to go with it), it looks like maybe not much of an improvement.
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#6
06-21-2018, 05:42 PM
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Quote:
An increase in the diameter of the M/C piston in the pushrod circuit (front brakes) would result in an increase in the required pedal force to achieve the same braking force.
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#7
06-21-2018, 07:59 PM
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Quote:
See the caliper section here https://www.motor.com/magazine-summary/performance-perspectives-july-2008/ Floating calipers have a piston or pistons only on one side of the caliper. I doubt the E300D has a floating caliper, it probably has a fixed caliper with a single piston on each side. Quote:
The on your E300D , only " fix" may be to use larger rotors / calipers and proper MC from a late R124 SL600 but this would be more work. I've had my 97 SL320 on a couple of time trial track days and can easily cook / fade the brakes. The car slows / stops fine on the street but multiple race track brake applications take their toll as the R129 " Sport Licht " Is only semi sporty and at 4,100 Lb makes a mockery of light.
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