Firstfives.org

I thought '79 to '81 e12, e24 front brakes were all the same. Part numbers are, autopartswarehouse.com sells the same rebuilt calipers, pads, springs, clips for pre '82 5's and 6's.

So I mount one caliper, to see the rotor is off to one side. Two sets of rotors measure the same. Two sets of front hubs on the struts are the same. Four Ate caliper halves, pistons, look the same.

But the bridge pieces between the caliper halves, one set is 1/4 inch thinner than the other. Not sanded down, that way from the factory. I think the four bolts holding the caliper halves together are longer, shorter.

Any knowledgeable comments ? I thought fronts were 5,6 series mix and match. Now, thinner bridge shims vs. 1/4 inch thicker makes the piston travel to the disc different, more less.

Weird.

Update for nobody interested:

I assume the 1/4" thicker caliper spacers worked, as the car always stopped without any problem. I just wish I'd noticed the rotor position between the caliper halves before disassembly. Far as I can tell it had to be off center, causing the outside pistons to extend further than the inside to contact the rotor.

The inside caliper half is fixed by being bolted to the strut. The inside rotor surface is fixed, by being a constant part dimension being bolted to a standard wheel hub.

As the caliper spacer width is the variable, wider than what is correct is what moves the outside caliper half away from the rotor, to not be centered.

Wonder where the thicker spacers came from ?

The M535i uses the same caliper halfs but thicker spacers to allow for vented rotors. Don't quote me on this but it's something I recall investigating years ago when I was looking for a brake upgrade. In the end I ditched the extremely heavy calipers for bigger aluminium E38 calipers + bigger rotors.

I've not looked under my 528 to compare rotors, now that you mention it, not vented, probably.

Still, my main concern, observation on the 633 vented rotors, is the thicker caliper spacer puts the outside pads 1/4 inch further away from the rotor.

From 30 years of go kart disc brake building, never was a disc not centered between the pistons/pads.

Mill the spacers down and you're golden.

I did something similar to the e38 calipers I'm using on my e30.

Oh nervana, that I had a shop with a milling machine. And a hoist, welder, spray booth, and four employees.

I put the fat spacers, clips, pins in a bag for the estate sale. Maybe if I run across an article someday about how, or if, those pieces ever worked. With the inside caliper half bolted to the strut tabs and the wheel hub flange allowing only one size rotor to bolt to it, the thicker spacers and parts were never more than a way to make the rotor not be centered in the caliper.