[Healeys] Disk brake conversion

Michael Salter michaelsalter at gmail.com
Mon Aug 29 12:31:27 MDT 2016

Hi Ross,
Before going any further I would recommend assessing what you have.
If you are not intending to use a brake servo then best to model your new
system on that of the pre BJ8 disc brake system.
Is the total piston area of the calipers that you have chosen larger or
smaller than that of the the Girling 14 calipers that those cars used. I
forget the diameter of the pistons in those calipers, it may be 1.4", but
I'm sure someone on the list will have that info.
If the piston *area* is similar say within 10% then they should be
satisfactory with the 5/8" bore master cyl  used in those cars although the
1" rear cylinders of the 100/6 may have resulted in excessive rear braking.
 *BUT* a change from 1" (0.79 sq. in) to 5/8" (0.30 sq. in), i.e less that
40% area, IS SERIOUS OVERKILL and should definitely have moved the bias to
the front.
You need to do the calculations before changing things..
Michael S
BN1 #174

On Mon, Aug 29, 2016 at 11:47 AM, Ross <rvmaylor at shaw.ca> wrote:

> Gentlemen
> I have installed a front disk brake conversion on my 58 BN6. The brake kit
> was supplied with the uprated calipers, which use the larger BJ8 pads
> (vendor description).
> The system was bled and the pedal firm. Initial drives indicate very
> little front brake support.
> The next recommended move was to replace the rear drum brake wheel
> cylinders, from 1” to 5/8”. That was done with no recognizable improvement.
> The next move is to switch out the master cylinder from ¾”  to 5/8” as per
> the non-servo disk brake BN7.
> In this case should the push rod length be changed as well to get
> increased fluid into the front disks?
> Or is a proportioning valve a better way to go?
> Regards
> Ross Maylor
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*If you can't fix it with a hammer, you've got an electrical problem.*
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