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Old December 17th 2010, 03:48
djmatio djmatio is offline
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944T brembo brakes on vw - which master cylinder size?

Hi,

I'm jumping back into my VW rebuild project and need to purchase a new master cylinder for my '72 super to use with the rebuilt porsche 944 turbo brembos calipers front and rear. Reading Lanner's article on vdubengineering.com lead me to try the stock 19mm MC. Looking on Mamotorworks.com it seems they have a 20.6mm master cylinder they say is for bug that "upgrade" to discs. Putting aside that my bug isn't quite what they have in mind when they say discs, is there any reason I should NOT purchase this 20.6mm master cylinder instead of the 19mm MC? Is bigger better in this case or should I stick with 19mm stock?

The newer 20.6mm MC is actually $10 less. Given the expense of this project, that hardly seems to matter at this point though. Right now I have no master cylinder and need to choose.

Thanks,

Matt
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Old December 17th 2010, 07:31
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Xellex Xellex is offline
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as far as I can tell, it's not about bigger and better when it comes to matching the MC to the caliper piston volume. All the threads around here lean towards the stock bug MC for the Brembo 944 calipers.
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Old December 17th 2010, 08:36
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evilC evilC is offline
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The 19/19mm dual master cylinder as standard in the bug should be up to the job. You will find that the minimal clearance between pad and disc of about 0.014" will give a result for the amount of pedal movement. There is a lot of nonsense/B******t talked about 'upgrading' m/cs, the only upgrade I know of for an m/c is the quality of construction not the size.
The 20.6mm m/c will give the following:
17 1/2% less pedal travel than a standard bug m/c
17 1/2% greater pedal effort than a bug m/c
(all due to its 17 1/2% bigger piston area)
You can easily calculate the expected pedal travel knowing the clearance and the total piston size in the calipers and m/c. Allow 5mm travel for a properly set up clearance on the piston rod. The calc will only give you the amount of movement until the pad touches the disc thereafter it is subject to whatever pads you use and the temperature of that pad (amount of squish). Very hot pads near to their working limit can compress dramatically.

Clive
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Old December 19th 2010, 22:44
flat flat is offline
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Stock 19mm dual circuit.

Lanner
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