Lotus Elan

Girling Brake Master Cylinder Replacement

PostPost by: Concrete-crusher » Thu Oct 25, 2018 6:21 pm

I know this is a similar thread but a different question , I have purchased a new Girling 0.70 Master Cylinder which arrived today , and the reseviour is small like the clutch master cylinder , does it make any difference ? Obviously if it?s unsafe I will return it

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PostPost by: UAB807F » Thu Oct 25, 2018 9:36 pm

Hmm, a good question. Thinking about it the smaller reservoir has plenty in hand to operate the brakes under normal operation so my first thoughts are that it's unusual but not unsafe.

Thinking about a larger reservoir it has a few advantages. Firstly in the event of a leak you can press the pedal more times before you run out of fluid and secondly there's more fluid so you can run your brake pads down more before you actually need to top up. I wonder if that was the main reason for more fluid capacity, to ensure safety between service intervals ? (no idea, just a guess)

Not exactly related but if you wanted a fluid level warning light system then a smaller reservoir reduces your fluid volume even more whereas a larger capacity would have more in hand.

Practically speaking, given how most cars aren't driven that many miles and unlikely to wear out brake pads between services I can't see any problem in using it. You'd have to keep an eye on pad wear/fluid level more often but otherwise the little chamber that actuates the brake system doesn't know how much fluid is above there, does it ?

But if anyone has a logical reason why it's a bad idea then it's of interest to me as well.
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PostPost by: Craven » Thu Oct 25, 2018 9:44 pm

As brake pads wear the pistons move requiring the space to be filled with extra fluid, X4 calipers, perhaps reason as clutch has just the 1. Just a guess.
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PostPost by: MarkDa » Fri Oct 26, 2018 9:01 pm

The originals must have been larger to allow for pad wear.
If you think about the volume required the clutch sized reservoir is about the same diameter as the rear pistons and total pad wear is getting on for 40mm, which would empty the reservoir.
The fronts are bigger, so you really do need the bigger pot.
Even if you kept topping up for wear when you replaced the pads you would overflow the cylinder when pushing pistons back.
Mind you I do tend to clamp the flexible and discharge fluid through bleed nipple when changing pads which mmitigates the issue.
Let's face it Chapman would have used cheaper cylinder if it would have worked.
So bottom line is send it back and get proper one.
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