Modifying rear caliper to fit Csi?

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Percy

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I have a seized rear caliper on my 72 Csi. Neither compressed air nor a vice seem to have any effect on it - yet. While looking in my garage for spares and rebuild kits, I discovered a set of Ate calipers for an early 7 series that are new old stock in the box. The problem with using these calipers is obvious lack of clearance for the Csi's vented rotor. These calipers are wider than those found on the E3's (I have a set of those too).

I have been contemplating splitting the new calipers and inserting what appears to be the spacer from the original Csi calipers into the 7 series calipers, but that requires splitting each caliper and reusing the caliper fasteners and o-rings. I have split calipers in the past without any particular problems, but that could have been sheer luck considering the fasteners are supposedly torque-to-yield. This leads me to the main reason for my post. The opening in the Csi calipers are approximately 11 mm wider than the 7 series calipers. The calipers appear to have some sort of bolsters, the purpose of which, seems unclear but hardly critical to the structural integrity of the caliper. Has anyone ever ground off these bolsters so that a too tight caliper might be used with a vented rotor?

As it stands now, I haven't decided which route I might take, splitting or grinding and am not thrilled with either. Nevertheless, if someone has pioneered either approach I would love to hear about it!


One last thought, do any other cars including different BMWs use the same caliper? Over the years I have encountered an awful lot of Volvo's, Mercedes and Porsches that seem to use the same or a very similar ATE rear caliper setup although until now, I have never taken enough of an interest to measure them.

Thanks in advance.
 
Why not unbolt the rotor and the caliper from the body, then put them in some rubber-eating concoction? That should erode and/or destroy the seals keeping the brake pistons in place. Worst case, it would let you take a hammer and give the caliper or the rotor a good whack to try and dislodge the pair.
 
Thank you for your replies

Bill Riblett said:
E-12 based 6 series used the same calipers. Walloth und Nesch may have the bolts and seals if you start disassembling calipers. They are in Germany. Don't know where you are. If you are in the US, you could try contacting Carl Nelson: www.bimmerdoc.com
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Thank you both for your replies.

I have looked more closely at the 7 series calipers and determined that grinding (as easy as it might seem) is a waste of time. The bolsters likely protect and guide worn pads when they are extended. Further, even with grinding, there seems little room left for the "meat" of any new pads. I would like to reduce unsprung weight but for some reason, grinding the pads down to bare minimum is not particularly appealing. :lol:

I now recall being told by a parts "specialist" that one year of the 7series E23 Euro model used the same Csi calipers. Whether this was accurate or not, it is obvious the calipers he sold me (years ago) will not work and I am probably going to merely split them and add the spacers from the original calipers.

For what its worth, BR is partially correct that some of the early 77-81 E24's use the same rear calipers (34211119211). Some of the models used a solid rear rotor while others use the vented rear rotor found on the 3.0cs/i models. My limited research indicates that most of the models used a solid rotor; however, a 1978 633Csi North American model seems to be the same as the 3.0csi: http://www.realoem.com/bmw/showparts.do?model=5233&mospid=47204&btnr=34_0067&hg=34&fg=10 but that is still no guarantee of getting the correct caliper. :roll:

Many thanks
 
A few years ago, when I needed new rear calliprs, I could not find rebuilt ones, but at that time the new ones from BMW weren' all that expensive - $250/pair?

Unfortunately, parts prices have risen dramatically in the past year or so and they may be a lot more now.
 
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