Master cylinder question

Baikal Bimmer

Baikal Bimmer

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Hi all,
Quick question, I have a 72 Csi with the thin style booster, will the master cylinder from a 1977 e24 work?
 
I have a strong suspicion that the master cylinder from a '77 E24 will interchange with a 72csi. See e.g., part no 34311102812. https://www.realoem.com/bmw/enUS/pa...0CSi&mg=34&sg=25&diagId=34_0857&q=34311102812

Naturally, I would want to make a quick comparison between the MC currently fitted to your car with the new replacement. I can't visualize any obvious dimensional differences. The only difference that comes to mind may be the size of the two ports at the top of the MC receiving the reservoir fluid. The newer MCs had a larger opening which is addressed by different sized rubber grommets.

The fact that you mentioned the "thin style" booster, raises another question. I am not aware of a thin style booster originally fitted to a csi. If you are currently using a non-original thinner booster, it probably necessitated moving the brake lines to accommodate the different positioning of the master cylinder (closer to the firewall) caused by the thinner booster. Should this be the case, the replacement MC, should fit. When you reference the thinner booster, I suspect that you are referring to the booster originally found on the 2800 Cs model or the booster fitted to the 2002tii.
 
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The pancake booster was replaced in April of 72 and CSi production commenced in 1971. You may be correct about the MC grommets being a different size. The 22.2mm MC was used with the fatter booster but it should work just fine with a pancake style booster as well.
 
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