Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) ARP4 rear brake calipers

As most of you know, the ARP4 is fitted with rear disc brakes and the handbrake operation is poor. It has been suggested that changing the rear pads for ones with a softer material might help the handbrake efficiency, but before I can do that, I need to know what car the rear calipers were originally from.

My uneducated guess would be a Sierra, maybe a Cosworth? Can anyone confirm that or have an idea of their original use?

If not, I will have to slink off to a dealer and get them to find out for me.

I seem to recall that the calipers were Mulfab. Simon will know for sure.

Does this look familiar?

http://www.mulfab.co.uk/our-products/29/brakes/rear-brakes

If you do manage to fit softer rear pads and the they work as you say, might not the normal front to back braking ratio also change? Perhaps with a tendency to lock sooner at the rear?

In terms of brake pad material, the term 'soft' is rather a misnomer. It really refers to the pads tempurature range and friction level. Hard pads = higher temperature range; soft equals lower.

I would doubt seriously that changing the pads will have any impact whatsoever on the effectiveness of the handbrake.

I am not familiar with the rear brake setup on the ARP4 but when I converted to rear disc brakes on my Plus Eight in 1990, I modified the handbrake 'tree' to increase the leverage and effectiveness. It rise to a state of 'just about legal'.

I agree with you, David.

It's the clamping ratio that is important and only mechanical leverage will supply this.

The issue with using the same pads as parking brakes is that the pads cool and thus shrink, lessening any original leverage applied. I assume the ARP4 calliper uses the same pads..?

Steve, I'm not sure of the calipers fitted to the ARP4 but mine are Sierra/Granada spec two-pot calipers.

What about the COF between the 2 materials?

Ok, how will that affect the clamping ratio, then..? Intrigued, now..

Someone on here has tried a softer compound rear pads and reported the handbrake as being more effective with no adverse other effects. I can't remember who it was now though .

Later - this one..

Originally Posted By hARPpy chappie
Personally I haven't got a clue what a 'handbrake cable compensator' is or were to find a 'rivnut' but I am able to report that the handbrake issue on my ARP4 was eventually resolved by the simple expedient of fitting softer brake pads. The handbrake now passes the MOT test. Nice. Thanks to Krazy Horse as ever.

PaulJ KH will be able to give you a part number I would have thought.

It won’t but its not only about clamp force/ratio.