Brake Bias/Combination Questions

[veg-O-matic]

Hello,

This is my first post, so thanks for having me . I am working on a 87 300D that I am upgrading to 500E brakes. I have copied gsxr spreadsheet and refer to it religously! Thanks for putting that together! I'm not really looking for suggestions on what I should do, but I have a general concern about the brake bias, since it is so important not to lock the rears first. I am struggling to understand Mercedes logic on the 94-98 SL500 w/ 472/ESP and later Euro 500E vs the bias on the US 500E.

The 500E went from 300x28F-278x24R to 320x30F-278x24R (except Euro) correct? Now I don't see a big difference in bias, because the rears are the same and the front pads and piston diameters are the same for 300 and 320 calipers. Only the torque radius changes by about 10mm in the front, which I assume is only a small difference in brake force, but much better brake fade.

The 94-98 SL500 w/ 472/ESP and the later Euro 500E had 320x30F-300x22R correct? I see these rear calipers as a big jump from the 278x24 rears on the US 500E with much larger pads, larger pistons and the 11mm torque radius increase.

I realize that there were two piston diameters available for the rear 300x22, but either of the rear 300 calipers are larger in piston area than the 278 caliper.

So am I correct in thinking that Mercedes was able to make the 500E brake successfully with two different brake bias combos if you compare the later US vs Euro models?

[gsxr]

I believe that is all correct. Just remember that Mercedes used one master cylinder for these combos: 294f/278r, 300f/278r, 320f/278r... let's call that "stage 1" for easy reference. But Mercedes switched to a larger master cylinder for these combos: 320f/300r, 334f/300r... let's call those "stage 2".

If you're going from stock 1987 300D brakes to any "stage 1" combo, your original MC will work OK, but the pedal effort may be a tad higher than you prefer - try it and see what you think. If you want less pedal effort, then swap in the dual-diaphragm booster & "stage 1" master cylinder used on all USA model 400E/500E's.

If you're going directly to "stage 2", the pedal feel is quite likely to be softer than you want... you'll more likely to want the 400E/500E booster, with the "stage 2" MC from the SL600. The same applies if installing the "stage 2" setup on a USA 400E/500E... it will work better with the bigger MC.

For a 1987 300D, since the car is relatively light, and has the replaceable ball joint in the LCA... I would recommend the 300f/278r combination, since it's 100% bolt-in. The 320 or 334 fronts will need either R129 knuckles or the late-style LCA, which adds additional time, weight, and $$$. Don't forget that adding unsprung weight is not desireable... you want to keep that to a reasonable amount, especially if the engine's power output is not significantly increased. The 300f/278r setup should be plenty for a 3300lb car with up to about 300hp.

BTW, a current copy of my spreadsheet should always be posted here:
http://www.w124performance.com/images/W124_brakes/

[need2speed]

I second the thanks for a great piece of research, Dave.

[gsxr]

Note that the late Euro 500E setups also had a different master cylinder, with an electrical solenoid switch, that adjusted brake bias depending on variables of vehicle dynamics. So under hard cornering, it would switch to more normal bias, but in a straight line it shifted the bias more to the rear brakes. Neat stuff, but it does kind of make it difficult for us folks who are trying to retrofit newer/bigger brakes onto older cars without the electronics to control the newfangled setup.

[Roncallo]

Originally Posted by gsxr

Note that the late Euro 500E setups also had a different master cylinder, with an electrical solenoid switch, that adjusted brake bias depending on variables of vehicle dynamics. So under hard cornering, it would switch to more normal bias, but in a straight line it shifted the bias more to the rear brakes. Neat stuff, but it does kind of make it difficult for us folks who are trying to retrofit newer/bigger brakes onto older cars without the electronics to control the newfangled setup.

Yes I'm sort of backed into the corner with this. I believe I will no doubt have to install ESP on my car which also includes BAS. So I put the big brakes on from and SL600 only because I happen to have them but I have to put the 129 hubs on only because I need the 48 tooth wheels from the SL600 to run the ESP system instead of the original 96 tooth 107 hubs. Now the ESP system is integrated with BAS on my system so I will have to put that on as well. Fortunately the 129 and 107 boosters are the same P/N. So now I end up with the installing the booster and master with BAS pump as well to get it all running. This also requires modification and installation of the 129 steering knuckle.

But in the end it will be very cool to have a 107 with a V12, 5 speed trans, Big brakes, ESP, BAS.

[need2speed]

If you are in need, I have the SL600 brake master cylinder for sale, left over from my big brake project. P/N 005 430 40 01 by ATE. Shoot me a pm if interested.

[Roncallo]

Originally Posted by need2speed

If you are in need, I have the SL600 brake master cylinder for sale, left over from my big brake project. P/N 005 430 40 01 by ATE. Shoot me a pm if interested.

Well actually I have all these parts. In fact I bought the whole 1996 SL600 parts car just to make sure I would have all the parts. Turned out to be the way to go. From the car I salvaged:

Complete M120 engine with accessories.
5 speed 722.6 Trans
5 speed shifter with very cool V12 emblem
4 required computers.
2 fully required wire harnesses
2 partially required wire harnesses
Complete set of SL600 brakes
Complete set of ESP sensors and components.
2 steering knuckles.
4 16" wheels that fit on the big breaks.
And most importantly a DAS module with rear view mirror and infrared key.