I can explain as much as you want to hear, though it’s probably best to ask specific questions to get any particulars you’re looking for. What started as a “I wonder if this would work?” snowballed into weeks of reading and searching to gather information and then the parts needed to make it happen. This didn't occur totally in a vacuum, I have needed the advice & info from Bill, Gerry, and Jason Hurst to get this far.
In a nutshell, from about 2000 - 2006 or so, higher level Mercedes used a Brembo-sourced, fixed 4-piston front caliper with 40 mm & 44 mm bores to equalize pad wear. As discussed earlier, the steel / aluminum construction allowed them to place a larger rotor inside a given wheel. The calipers can be found on most every model depending on year - but never on base models – always at least one or two engine options up. They were used with rotors ranging from 312 mm to 345 mm in diameter, depending on what wheel size they were to be coupled with. There are subtle differences among each, depending on chassis and rotor size (both thickness & diameter), so it pays to really search the web before purchasing a set. To illustrate how subtle this can be, refer back to the photos of the 8-piston calipers posted earlier in this thread. They can appear to be all the same, but if you look closely at the abutment brackets, there are actually 2 very similar styles. These are intended for use with 360 mm rotors, but there are others where the caliper is spaced out to clear a 390 mm disc. Even the M-B specific forums are unclear or have information posted that is accepted as fact, but is incorrect.
As of the 2010 model year, Maserati still used this caliper design on Quattroportes, the only other manufacturer I’ve found that does. M-B has since moved to a newer - cost reduced, it appears - Brembo caliper of the same construction, but only using 2 bolts to retain the housing to the bridge. This new design can also be found on current SRT-level Chrysler products.
The conversion was done the same as most every other one has been performed: Drill & tap the dust shield mounting holes to a 7/16”-20 thread and slice off the ways for the factory calipers. A set of adapter brackets were then fabricated to mate the new caliper to the modified spindles. I did retain the spindle seal dust shield by trimming a pair of 9C1 pieces down to clear the adapters. The rotor is a regular C6 Z51 front disc, 340 x 32 mm, redrilled for the 5 on 5” bolt pattern and the center bore has been opened up to mate with the larger register. The hubs are just regular B-body units with the rotor cut off and the longer Dorman studs installed.
Spindle with adapters:
I chose the ML-series SUV specific calipers, as they are meant to be used with a 345 x 32 mm rotor, and the banjo bolt bosses most closely match the B-car configuration. Some of the sedan calipers have an elongated mounting boss that looked to be asking for troubles like pinched brake lines or contact with other suspension components. As the ML calipers are intended to be mounted in the leading position, and they needed to be trailing for the wagon, I had to disassemble them and swap parts side to side to get the correct combination of piston location and bleeder screw orientation.
Refinished calipers:
A couple things to be aware of: the calipers do clear the SS wheel, even with the 340 mm rotor, but are closer than I hoped. The Corvette rotor is readily available and inexpensive, but it is narrower through the pad contact area than the Mercedes rotors are, therefore I wasn’t able to push the caliper down over the rotor any further without the pad running off the wear surface on the inside. M-B specs the same pad for all diameter rotors, and widens the rotor contact area to compensate for the radius mismatches. As it is, the pads use up every bit of the Corvette wear surface top-to-bottom, so the room for error in adapter design is very slight, and it took two tries to get the brackets just right.
First attempt at M-B brackets below one of RPM's Corvette brake brackets:
The M-B caliper use a 10M-1.0 thread for the banjo bolts, same as PBR uses for the SS/9C1 rear calipers. I purchased a pair of those bolts intending to use them to mate the lines to the calipers, which would have worked with the factory lines, but the Goodridge Impala lines I had are thinner and required yet another trip to the machine shop to shorten the bolts before they could be used.
If I did this again I might choose a caliper off of a sedan rather than the ML. The curvature of the ML calipers is such that they are closest to the wheel at the ends, I haven’t done much more looking, but a switch to a caliper intended for a smaller wheel might improve clearances even further. The ML calipers use a 14M-2.0 threaded mounting bolt - not a readily available size in socket head configuration, so the spindles needed more material removed for socket clearance than I would have liked. The sedan calipers use a 12 mm fastener that would have been easier to locate in the preferred style. Additional searching through a rotor catalog might reveal a better choice than the Z51 part, perhaps one that would allow the caliper to be pushed more towards the spindle. As Mercedes are a 5 on 112 mm pattern it’s probably a bit of a stretch to get a 5 on 5 inch hub inside an M-B specific rotor
I’ve simplified a lot of work down to a few paragraphs, but that should still give a pretty good idea of what was done.
- J
