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MX5 brake master cylinder pushrod
Slimy38 - 16/1/18 at 10:15 PM

Hi all, I have another question around the MX5 master cylinder. The various braking options all mention removing the brake servo, and using a rounded off bolt to operate the master cylinder. But if I compare this with the newly purchased clutch cylinder, I can see the clutch cylinder has a retained pushrod to operate the master cylinder.

This makes me wonder whether I'm missing something for the brake MC, with it just being a rounded bolt pushing on a piston. There's no retention, no circlip, rubber boot or anything that would keep the bolt in place on the piston. There's the brake pedal movement limiter, but is it permitted to have a pushrod that is not fixed to the MC?

Am I reading too much into it, is it safe to just have a pushrod 'in place' on the MC, and retained by nothing more than the pedal range?

ianhurley20 - 16/1/18 at 10:55 PM

Sorry - don't know what your earlier questions were and not really answering this one

I kept everything as it came out of the MX5 including the servo. It all works a treat!

WallerZero - 17/1/18 at 09:10 AM

I have rounded bolts for pushrods on my Zero for both clutch and brake. Never had any issues once set up right. Pedal travel has kept them in and working for 4 years no problems

JAG - 17/1/18 at 10:12 AM

Pedal travel and circumstance will keep the handmade pushrod in place.

BUT if it falls out - you have no brakes!

I'm a Professional Engineer and that's not a risk I would be prepared to take with my life or worse still with the life of my passenger.

I fitted a Servo on my car and it works very well.

If you insist on removing the Servo then create a mechanism to retain the pushrod in the master cylinder

Like this....



[Edited on 17/1/18 by JAG]

Slimy38 - 17/1/18 at 01:59 PM

quote:
Originally posted by JAG
Pedal travel and circumstance will keep the handmade pushrod in place.

BUT if it falls out - you have no brakes!

I'm a Professional Engineer and that's not a risk I would be prepared to take with my life or worse still with the life of my passenger.

I fitted a Servo on my car and it works very well.

If you insist on removing the Servo then create a mechanism to retain the pushrod in the master cylinder

Like this....



[Edited on 17/1/18 by JAG]


My thoughts exactly, I was thinking it only takes a small amount of wear on some component to allow the pushrod to drop out. I'm definitely a belt and braces person!

I like the retaining washer idea though, I did think it wouldn't have to be overly complex. The plunger at the moment comes up to the circlip so I'll have to see what I can do without compromising the return position.