Many folks have trouble with the aftermarket `silver painted' clutch slave cylinders. After some use, or if left standing for weeks, they suck air in past the cup seal and it won't bleed out.
Reason is these cylinders are missing the cup spreader which was in all the genuine cylinders.
p/no is 17H7540, it is now NLA.
I have just made one from HDPE plastic, if anybody wants to make some too, here is a poor sketch.
Sorry, got no CAD on the Macbook and the PC is now dead, RIP.

[edit] If there was enough demand for these I could get them made in quantity on a CNC lathe, it's just not worth moulding them unless making zillions.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Mini Spares UK sell AP clutch slave cylinders (GSY110) that have the correct cup expander
The rubber parts in their cylinders also last longer
AP Cooper S caliper kits (GRK5006) from MS last 12 months of serious racing in Group N before needing replacing. Other ones are lucky to last one race meeting before turning to cardboard!

The cup seal in these slave cylinders is a common 7/8" one. I have bought good ones in the past from my local brake shop.
I agree many aftermarket seals are rubbish now.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Hi Kev

Any chance you could post a pic of the finished article

Thanks

Bernard

I took pics today with my old 4MP Pentax. Both pics look like crap as the part is black and closeup focus is poor, even on macro. I tried my 8MP phone and it was no better.
I will take some more tomorrow with my Fuji, of both the new part and white delrin? original.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Here ya go- sorry for the pic quality.
The sketch showed 3 holes, I did 4 because it's easier to do on the mill.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Well, Laingy came round today and he fitted this new one I made into his aftermarket `silver' clutch slave cylinder.
There is now no lost motion at top of pedal stroke; whereas before, the pedal went down well over an inch before you could feel pressure as the seal lips sealed the bore.

Minispares' genuine slave cylinder (with the original spreader in) may be 2x the price of their cheapo silver one without, but if you need a new cylinder, I'd say it's worth it.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Caparo (AP Braking) has a comprehensive catalogue of genuine brake parts for Minis, etc (pages 49, et al). This gives you the part numbers to be looking out for)

Cheers

AP only lists the whole slave cylinder, and the seal kit.

I have machined a few spare plastic spreaders now.
I'm not going into quantity production, but if anyone here needs one to improve their aftermarket cylinder, PM me for details.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

That doesn't surprise me at all. If you have a genuine slave cylinder it will include the seal spreader, right? If you need to re-seal a genuine slave cylinder, you won't need to replace the seal spreader.

Just done and acquired myself a genuine NOS one offa eBay!

Cheers

Just acquired a Drmini special. Thanks Kevin

Received a couple today - look good, Thanks Kevin

Gidday Kev

I dug up this post from last year.. is there any reason not to make one of these out of teflon? I have *just* enough left to make one of these for the new slave cylinder I just bought... I've been using a pre-XF Falcon one (smaller bore, more travel), but it's too stiff for the kids to use.

I don't know how I'll go making a tool to machine out the locater groove for the spring (3.7mm x 13mm) - does it need to be there? will it still work if I bore out the centre and make it a neat fit over the spring, maybe even keep the aluminium locator thingy that's in there?

I drew it in solidworks - one of your dimensions didn't work though 39.16 degrees instead of 45 - not sure where I've gone wrong



cheers
Simon

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did I tell you that I won a trophy?

I would use a hard plastic for stability and ease of machining. I use HDPE as I keep it in stock for making wiper escutcheons. Delrin or similar is fine too.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.