Hydraulic disc

[vintage65scoot]

Hi glad you've got the piston back in good thinking using g clamp obviously piston is tight in slave cylinder just wondered if it returns ok and does not bind

[rosscla]

I fitted that backplate yesterday and bled it and it seems to work. I definitely now have a much firmer front brake than I did with the pop in one I was using previously. When it went in it actually took very little force with the G clamp, not quite like running a nut on a bolt, more like winding a clock so I think it will be OK when it beds in a bit.

I think the piston might be a little slow to retract as if it is binding a bit but I also think I might need to adjust the static pad a bit yet to get the balance just right. WIP as they say...

[warts]

The seals are designed to be square when there is no pressure, as you apply the brakes, the piston moves the pads toward the disc. The piston should not slide through the seal, but distort sideways. From squareish to sort of parallelogram with curved sides. When the pressure is released, the memory of the polymer should retract the piston sufficiently as it returns to its original shape. As the pad wears, the seal allows the piston to adjust position by slipping a bit.
Ford did a huge amount of research on this when they were having brake problems on one of the cortina's. The seal was allowing the piston to slide and then not retract properly with too much pad pressure on the disc causing excess wear, disc distortion and most important, warranty claims. Hence the dictats to not lube your seal.
They also discovered that the pad is best just touching the disc (which the dry seal ensures). There is always sufficient runout to knock the pads back.
It was always thought that there must be clearance, but their investigation discovered it wasn't the case for optimum performance/life balance. In a sort of counter intuitive way.
I still find a little brake fluid helps, as does ensuring there are adequate chamfers. I also fill the space between the seal proper and the s**t shield with high temp silicone grease, otherwise the void fills with watery crap and corrodes piston and bore.

[Innocenti225]

Hi
Any Idea what the Slave Cylinder is....as after one for a similar conversion

Cheers

[warts]

Doing this sort of reverse engineering used to be easier in the olden days, because there were paper parts lists to compare - and probably a smaller list of options in the time before you could use a CNC to have whatever you wanted made.
Now much of the info is designed to be accessed by inputting the registration number... How useful is that?

Didn't Ross say he used a Austin Metro front brake seal? You could do the same, and get the piston at the same time, if you have the capabilities to machine the bodt and back plate.
Other than that, was it Beedspeed or Chiselspeed?
Back a while ago, MB used to do a similar conversion and I think one of the Vietnam places - ScootRS?

[Innocenti225]

Cheers the Back Plate is all good and already Threaded, it is the actual Slave Part that I need the info for...The Seal & The Piston is less of a Problem...but Cheers

[warts]

As far as I have seen, the cylinder is a custom made job, rather than an adaptation of a ready made one.
If the back plate is already threaded, then if someone like MB don't want to make another, it is a relatively simple turning job to make one.

[rosscla]

Yes, the slave unit is custom made item you will not be able to buy one anywhere unless you can pick one up second hand, they're rare and increasingly sought after.

MB or Taffspeed might be able to make you a new one if you gave them the backplate to match it or a reasonably competent machine shop should be able to make you one - but I'd have thought you'd be better to go with someone who knew these conversions directly rather than have someone reinvent the wheel.