I been reading a lot of threads on the usage of M calipers on the rear for 5 lug conversion, found the mention of using 5mm washer / spacer between the caliper and mounting bosses to space for the early 911 vented ( 20 mm thick ) rotor, but no real mention of this being the total thickness needed or if it is 5mm PLUS the splash shield mounting bracket , which would add it's thickness to the overall dimension.
If someone with more knowledge of this setup would enlighten me , I would appreciate it.
Thanks...

Jaxdream

I don't know if I am more knowledgeable but I just installed M calipers on my 75 chassis. I used 1/2 SAE flat washers as spacers. I ended up using 2 per mount hole to get the caliper centered on the 20mm 911 rotor. Car not running yet so no real world feedback but visually it looks correct.

If I were doing that, I'd at least use FLAT washers with the hole the appropriate diameter for the bolt.

The Cap'n

I used the washers on mine, sized to the bolt. Two per bolt. I am using vented rotors. I also bought longer bolts as I felt I wanted it threaded all the way.
Van914

Thanks, this is helpful , but I was wondering about the most ideal dimension , as washers are sometimes inconsistant in uniform thickness , although SAE washers are more consistant. I suppose I'm looking for the magic number / dimention that would center the caliper over the rotor best. I read in some earlier threads that the dimension that others went with was 5mm , but no mention if this was achieved using the splash shield bracket in conjuction with another spacer or simply spacer (s ) to add up to 5mm , if that is the magic number .
Thanks I'll get some sae 1/2 in washers and measure them , I do want to use metric if at all possible .

Jaxdream

ah! no no I have 2 1/2" washers too and though it does not rub bad it is NOT centered....i wish I knew the exact dim's as it will make an aWfUl noise when warm and pulling into my garage.....

I used a piece of flat bar and drilled two holes 3 inches apart, instead of washers.

Iwas planning on using a piece of flat stock also , just wanted to find out the desired thickness to center the caliper over the rotor and thread the sides that can extend slightly past the bolts to attach the splash shield.

What thickness bar did you use??? If you don't mind adding it to the thread.

Jaxdream

yes please....?

OOPPPSSS wrong , my bad !!!!!

Mybe Eric Shea will chime in as in the threads I have read that he commented on it was he that specified the 5mm spec , but wasn't alluded to as to if the splash guard bracket was part of the dimension or not, so .......the mystery continues.

Jaxdream