Rebuilding the brake system on my 6.3 and more specifically the rear calipers. As the picture depicts, I am unsure how the piston is supposed to be positioned
In the socket. Anyone have a clue
* notice the step I'm pointing to
Felix - important one. W109 300SEL 6.3 rear caliper has handbrake mechanism in the piston bore. the step / notch in piston face must sit at 6 o'clock looking from wheel side.
If its even 15 degrees out, handbrake cam wont retract and pads drag.
Red rubber grease on pressure seal. white silicone is ok for dust boot only. insert piston with notch at 6 o'clock, push home, make sure it didnt spin. if it spins, rotation arrestor pin in bore is damaged.
Fit dust boot, handbrake cam, check cam moves 20-25 degrees with no bind.
6.3 brakes are not the place to guess. workshop manual 42-100 has 14 pages. PM if you need PDF.
Adding to Billy: the W109 6.3 rear caliper rebuild kit is Mercedes-Benz part number 000 586 14 56. Contains both pistons, both pressure seals, both dust boots, both handbrake cam o-rings, and the correct fastener kit. Mercedes-Benz Classic Centre Stuttgart still stocks it at €380 the kit ($615 landed). McStarparts has it at $540 in stock.
Do not source aftermarket rebuild kits for the 6.3 brakes. The seal material has to be IIR (butyl) to be compatible with the original Castrol GT LMA brake fluid the system was designed around. Aftermarket kits often supply EPDM seals which will swell in the original fluid within 18 months.
Billy, Hugo - step at 6 o'clock confirmed.. genuine MB kit ordered from McStarparts.PDF of workshop manual section 42-100 recieved via PM Billy - extraordinary detail. Cheers..
Felix. The 6.3 rear caliper piston positioning is fiddly. Wear gloves and bring towels. Theres always more oil than you expect when you crack the line. If you want a hand let me know, im in Sutherland Sunday mornings until 11.