924Board.org

[Mkol]

i have a 1979na, im trying to rebuild the ATE master cylinder but struggling to find a source for the kit, mine is a 23mm bore which is strange as from what i understand that year would have been 19mm from the factory.

all of the motor factor sites online throw up the 19mm kits when i tap in my reg number.

i only really need new seals so can i just by something generic with 23mm seals? i believe the part number for the cylinder is: 477 611 017 A

[Beartooth]

I looked around a little bit for one for my car a while back, but didn't see anything out there. Obviously mine's a year newer and a 931, but it does have a 23mm bore. I didn't dig much because mine had some corrosion in the bore, so it may not have been rebuildable anyway. That kind of thing shows up on ebay now and then, but otherwise, it seems like they're out of production and probably not coming back. Too few people bother to rebuild them (sadly), and even a lot of remans on that kind of thing are disappearing in favor of cheap new replacements. One possibility would be to buy a kit for another ATE master cylinder from the same era with a 23mm bore - you might luck out and be able to use the rubber pieces at least. Another option might be to take it to a parts store and see if you can match up a workable replacement (probably something VW, but who knows).
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1980 931 diamond in the rough

[Mkol]

[Beartooth]

I'm not sure on the bore either; maybe that was a change from the early 924s. RockAuto will usually give you bore sizes on brake parts if the manufacturer lists one, and I'm seeing 13/16 (20.6mm) and 20mm there for the '79 and earlier 924s. But RockAuto can be dodgy on the 924 and other lower-production and European models. I should probably verify mine is 23mm; I'm mostly going off what I've seen quoted.

Anyway, it'd be good to know if there's a kit that'll work. One thing I've gathered is that - bore size aside - there were several changes to the master cylinder over the years that were just moving the lines and pressure switches around. So, with a little work, interchangeability is a lot better than on paper. It's too bad it's not like an old Ford or Chevy where you probably didn't need to even know the model, or at worst there were three or four master cylinders, each of which would bolt into around a million cars. But it looks like that casting was used quite a few different places. Lots of VWs with what looks similar, but mostly 19/20mm bores. It does look like Mercedes used a similar 23mm MC in the early 70s, but also hard to find... Maybe that 23mm bore is an oddball.
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1980 931 diamond in the rough

[Goldwolf]

Where did you see that the Dorman MC would work? I might need one too. The ATE one does exist but they are pricey.
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1981 Weissach Edition #179

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