[Healeys] Drum to disc conversion - master cylinder change and a few questions

[Alan Seigrist]

Phil -

If you are going through that process, I would definitely get a Wilwood
dual master, this is much safer - if you have a hydraulic failure in the
front or back, the brakes will still work and you will be able to drive
home comparatively safely.

I don't know the weight balance between the front and back of your car, but
generally speaking if you put discs up front, you won't need to worry about
locking up the rear... drums usually take more effort to lock up than
discs.  You can put the discs on up front first, drive it a bit, and then
determine if the balance is right, then adjust if needed.  It's all about
the equipment on your car and the weight balance from front to back.

Also with discs, it's worthwhile to consider getting a brake servo, which
will make driving more pleasurable and give you better braking with
regular driving.

Best,

Alan

On Tue, Jan 17, 2023 at 10:26 AM Philip Fish <prcfish at gmail.com> wrote:

> Hi all,
> I'm a long time Healey owner having had my BT7 for over 30 years.
>
> Recently I had a complete failure of a brake front drum (photos below) on
> my 1956 Jensen 541 (a 4ltr Austin powered contemporary of the Healey) resulting
> in a total loss of my brakes. Not an experience I want to go through
> again. As a result I am looking to do a drum to disc conversion using
> predominantly Healey parts
>
> My car uses several components in common with the BN1, in particular it
> uses the same king pin/swivel axle set up. I have pretty much go the parts
> needed for the conversion (Denis Welsh Heavy Duty swing axles, AH 3000
> steel wheel BTC101 hubs, taper bearings, disks and hub adapters etc) but I
> have some concerns about what changes I might need to make to the rest of
> the hydraulic system, particularly what changes I will need to make (if
> any) to the master cylinder and rear wheel cylinders.
>
> I was wondering what the list subscribers have done to the MC and rear
> wheel cylinders when you've converted the front drums to disks on your
> early cars. I believe that the front calipers need higher pressures
> (900psi) to operate than compared to the rear drums (400 psi) and was
> wondering if I need to fit some for of brake balance valve to stop the
> rears locking up before the fronts. Do you change the bore of the rear
> wheel cylinders when doing a conversion as an alternative? I have also read
> on the web that there may be a check valve in the MC which I might have to
> remove. Apparently with a drum brake set up the check valve retains some
> residual pressure after braking to prevent any air getting into the wheel
> cylinders, but with a disk brake set up this could cause brake drag.
>
> I would hate to do the conversion only to have worse brakes than my twin
> trailing shoe front drums that I have now.
>
> Currently I have two 5/8" wheel cylinders on the rear, four 1 1/4" wheel
> cylinders on the front and a 3/4" master cylinder with a pretty small
> reservoir. The system also incorporates a Lockheed 3:1 brake servo.
>
> Any advice would be appreciated.
>
> Phil
>
> https://joc.org.uk/jensen-models/541-series/
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