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Tandem master cylinder issue
sdh2903 - 3/9/16 at 12:50 PM

So, I'm currently building a westfield and using their tandem brake master cylinder. After connecting it up and trying the pedal it didn't feel right, it felt as though it was binding and the pedal didn't return. I checked the clevis wasn't catching on the pedal all was free and clear.

So I disassembled the cylinder this morning. I have a couple of queries which I'll get to.

Circlip removed and I was expecting the plunger to reveal itself under spring pressure but no it needed a tap then pulling out.



The first seal has a small nick out of it, no sign of the missing bit in the cylinder. Other seal was fine.





Now heres where I am a little confused. According to pictures and other info I've read there should be a second spring at the end of the plunger? Ie furthest away from pedal end. The part you can see in the pics below, ive pressed in and it's smooth but there's no spring return? It just stays depressed? Surely this would never work? Or am I being a bit thick?





Due to the nicked seal I will be getting in touch with the factory anyway but I'd like to be sure and not make myself sound like a pleb so any input gratefully received regarding the non return issue.

Steve

Dick Axtell - 3/9/16 at 07:55 PM

quote:
Originally posted by sdh2903


Now heres where I am a little confused. According to pictures and other info I've read there should be a second spring at the end of the plunger? Ie furthest away from pedal end. The part you can see in the pics below, ive pressed in and it's smooth but there's no spring return? It just stays depressed? Surely this would never work? Or am I being a bit thick? Steve


A dual-circuit master cyl usally has 2 pistons (or plungers). The example shown in your 3rd pic, is a primary piston, which sits closest to the brake pedal's input rod.. There should be a secondary piston, which sits at the end of the mcyl bore furthest away from the input rod end.

There should be (has to be) another spring fitted to the end of the secondary piston, in order to return the whole piston train to its unoperated position.

Was there definitely no such return spring?

sdh2903 - 3/9/16 at 08:07 PM

I haven't been able to remove the second plunger. In the pics showing the hollow cylinder you can see the end of the second plunger. I pressed it with the end of an artist brush and it moved to the end of the cylinder and stopped. No return at all. After tapping it on the bench it moved back a little. No spring pressure at all.

Every build diagram of a tandem cylinder I've found has a second spring. I will be giving westfield a call Monday.