Aprilia handbrake mechanism

[davidwheeler]

Had occasion to struggle with sticking rear shoes and so contemplated the handbrake mechanism.  I had always assumed that the rollers on lower ends of the little levers connected by the rod acted equally to apply both shoes but I now see that the rear roller moves away from its shoe when the front one engages.   This seems singularly pointless!   All it can possible do is perhaps to aid in returning the mechanism to the off position by the rear shoe acting to push its roller forward and thus the front one away from its shoe.   Seems an elaborate way of doing it when a stronger spring would do the same.

[BlueSky]

David,
The hand brake mechanism shown in your photo is on back to front, but I think you are correct with your observation on how it operates.
Noel

[Scarpia]

otherwise the handbrake actuator return spring would have to overcome the residual pressure of the piston against the trailing shoe also from the foot brake. I suspect the piston would tend to set out once the handbrake takes the shoe towards the hub?

[ben]

I think your original assumption was indeed correct David. Also your photo shows the mechanism upside down rather than back to front.

When the handbrake is applied it does not rotate the little lever to which it is linked but moves it bodily foreward. This brings the roller at the bottom of the lever directly against the front shoe (ie the RH one in Noels picture) and at the same time pulls on the link which is pinned to the  top of the lever to transmit an equal force across to the other little lever. This then rocks on its fixed pivot to turn the tensile load in the rod into an outward force on the rear shoe.

To perhaps put it more simply the application of the handbrake forces apart the central pivot points of the two little levers, one being fixed to the backplate and the other being attached to the operating lever. The two little levers and the linking bar then ensure that equal and opposite forces are applied to the two shoes.

This very elegant and beautifully made system of levers gives very powerful braking and operates completely independantly from the hydraulic system.
Unfortunately however it is prone to seizures of the various pivot pins which at best leads to reduced handbrake efficiency and at worst causes the brakes to drag and even lock on completely.(Making it b*****y difficult to get the drum off to fix the problem!!) 

[BlueSky]

David's photo is upside down, but the levers with the roller ends are on the wrong way. The slightly scalloped facet should face to the outside. See the corrected photo. David I hope this brake is not fitted to your car in this condition

[simonandjuliet]

I love this kind of technical detail that is highlighted and discussed. This is one of the big draws of the Forum for me; a great resource and very helpful if we want to keep our machines working as they should .....

[davidwheeler]

Fear not, that is the spare.  It came from Ben??!!   The ones on the car are the right way round though I confess I had not noticed the wrong 'un.  Intriguing...
I also had not appreciated that the whole lever and its pivot moves forward but when you look at it closely I see what you mean.

[davidwheeler]

All the same, I think I'll take another look next time I have a day or two to spare as it did not seem to move the rear shoe at all as I recall even though all the bearings are free.

[ben]

I just wish I could remember who I got it from!

And well spotted Noel---your eyesight must be better than mine!

By-the-by I put another 200+ miles on the Aprilia today going to Goodwood to see all the lovely Fulvias.--In the SUNSHINE!!!

[BlueSky]

Not so much good eye sight, more from past experience!! I can't remember what happens when it's on the wrong way only that it causes a few problems.