Vented Disk Upgrade

[Julian8key]

When I got my 912 which had a 1970 911T engine the brake discs were poor and needed to be replaced and the calipers overhauled.

I don’t have any pictures of the build as I did this about 15 years ago and have had no problems since.

Looking at replacement discs I found Powerstop vented were good value, and the difference between the calipers on solid and vented brakes was the Caliper width, Ate seemed to used a spacer between the two caliper halves so I set about working out how to do this.

Disk installation was not 100% straight forward and I had to work our a few workaround to get everything to line up.

Front Brakes

The key issue here is the Seal between the two halves.

Finding the same seal for sale was not possible and it is not recommended that calipers are split. I had to do this to get the piston out and noted the size and shape of the seal between the two halves.

I found a similar seal was available from RS Components part 128-861 a Viton O Ring, the material is important due to the fluid it is sealing.

The one selected was of a similar size to the original but not identical, it just needed to be installed with its specification, the key being the amount of crush.

The disks are approx. 8mm thicker than standard, to make all eight spacers (front and rear) were made from the same piece of 30mm x 8mm mild steel bar.

To accommodate the O ring in the spacer I bought a 10.5mm end mill with a 5mm pilot. Key here is to have a flat bottom to the hole, the tool (Picture one) was relatively expensive compared to the other materials.

I then marked out the bar with the holes for the bolts and the brake fluid gallery. I then drilled the gallery hole at 5mm and the bolt holes at 8mm.
The last thing I did was drill the O ring recess, the depth on this is
critical, I used a cheap pillar drill to do this so spent a lot of time making sure everything was level before setting the depth of cut to 2.3 mm, I had to measure this often to avoid going too deep. You can use and o-ring calculator these days.

Once I had made the spacers were I needed longer bolts and a 911S brake pin set to enable the caliper to be returned to the car.

The discs were a direct bolt on.

Rear Brakes

The rear brakes presented different challenges the calipers were straight forward as the is no internal fluid gallery, so all was required was the spacer.

The rear discs I used were for a later model about 1970 these had a deeper cross section to accommodate wider rear brake shoes for the hand brake, something I discovered during assembly, I am not aware of vented discs being available for the 1965 model which has these narrower shoes.

I obtained the later model handbrake shoes and install kits, the retaining pins I believe are longer. I also had to get a 10mm wheel spacer turned down to allow the brake drum and disc to ‘stand off’ further from the face of the wheel hub. This is shown in the pic below. (pic three)

The final thing I had to do was offset the calliper slightly to allow the disk to rotate without fouling, I think the offset out was not quite enough, maybe 11 mm is better, I shimmed the calliper on its mount using 1mm washers

Since the upgrade I have done approx. 6000 miles with no issues.

[Eljimberino]

Hi

Great write up thank you

What year is your 912?