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Brake Bias/Combination Questions
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? |
#2
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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/ |
#3
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I second the thanks for a great piece of research, Dave.
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Dean Albrecht "Lead, follow, or better yet, get out of the way!"E500 owners motto |
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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.
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#5
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Quote:
But in the end it will be very cool to have a 107 with a V12, 5 speed trans, Big brakes, ESP, BAS.
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To see my 129 parts for sale visit: http://stores.ebay.com/The-Mercedes-SL-Store John Roncallo |
#6
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SL600 Brake M/C
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.
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Dean Albrecht "Lead, follow, or better yet, get out of the way!"E500 owners motto |
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Quote:
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.
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To see my 129 parts for sale visit: http://stores.ebay.com/The-Mercedes-SL-Store John Roncallo |
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