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Disc Brake Conversion

Bugeye Sprites never came from the factory with disc brakes, although the Healeys did offer a conversion kit that they used on their racing Sprites. These conversion kits are now very rare and expensive, but there are newer alternatives that work just as well. The most common is to use the brake setup from a later Sprite or Midget, which is essentially a drop in replacement.

The conversion has 3 sections:

  1. Replace or rebore your master cylinder with one with a 3/4" bore. These can come from a later Spridget or the Bugeye one can be rebored.
  2. Replace the Bugeye rear drums with the later style ones.
  3. Replace the front spindles with the disc brake ones.

When I pulled the motor from the 1974 Midget I used as the donor for the motor I also grabbed all the bits needed for the brake conversion. These pieces were all rebuilt and installed on the Tunebug. Here are the pieces you need:

Rear

  • Rear brake backing plates
  • Rear brake internals (pads, springs, slave cylinders, etc.)

Front

  • Everything between the shock absorber arm and the A-arm (entire spindle and caliper/dust shield).
  • If the donor car uses the later steering rack, you will reuse the Bugeye steering arms. Otherwise you can use the ones from the donor.

1. Master cylinder

I had my master cylinder rebored for the use of the disc brakes. At the same time it was cadmium plated -- looks fantastic! Had it done through Gerard's Garage. Gerard's a real Sprite guy, and had the proper bits remanufactured for the master cylinders. I've no connection, just a happy customer.

2. Rear brakes

Next up were the new backing plates. More cleaning and degreasing, then some paint and all was ready for assembly. I reused the old washer and circlip for the slave cylinders, and with the help of some photos from the BCF was able to get all the brake bits in their proper places.


Painted backing plates

Once all the parts were cleaned and painted it was time to install all the pieces. Things went together pretty simply


Everything installed

One thing did come up here -- the old parking brake rods are too short to be used with the later style backing plates. The later plates sit at a bit of an angle from where the original ones sat, so the old rods don't work. The solution is to cut the rod in half, thread each with a die, and use a coupler nut to join the two. Makes the length adjustable and works great. Thanks to the late Frank Clarici for this tip.


Rod cut in half


Threading the rods


All done with the threading


The two rod ends joined with the coupler nut


Everything stalled and ready to go

I went back later on and added a few jamb nuts and some blue locktite after the coupler came loose and the rods separated. Well worth doing.

3. Front brakes and suspension

The first steps here were to grab the parts from the donor car, and clean everything up. I took off everything from the steering arms to the A-arms. The A-arms and kingpins were rebuilt by World Wide Imports, and rebuilt disc brake calipers were sourced from there as well.

Next came a thorough cleaning of all of the bits, and a bit of painting. The brake dust shields and spring perches were painted, as were the steering arms from the Bugeye (these get reused).


Dust shield and spring perch painted


Steering arm installed

First up was to reinstall the A-arms and disc brake spindles. All went together simply enough. The disc brake pieces install in essentially the same way as the drum brake pieces. I replaced all my lines with new ones during the restoration, but the hard brake lines are the same for drum or disc front brakes so there is no need to replace them if they are in good shape. You will need the disc brake flexible lines.


A-arms installed


Hubs installed


Calipers on

A quick note on installing the calipers: while each caliper may physically fit on either side, they are handed and must go on the proper side. The bleeder screw needs to be positioned at the top of the caliper so it will bleed properly.


Flexible lines connected

Simple enough, and everything here just bolts right on. Last step is to bleed out the lines and off you go. The new discs are a good match for the uprated engine, and should hold up well for some spirited mountain driving.

Final Thoughts

  • The biggest tip is to make sure you grab all the bits you need from your donor car. You'll at least need the rear backing plates, and everything between the shock arm and A-arm. To be sure, I took the shock and A-arm as well so I knew that I had all the pieces.
  • You'll probably want to grab the steering arms from the donor as well, just in case. I even took the tie rod ends. Didn't need either for my particular conversion, but they're easy to grab while you're in there.
  • The only big modifications will be to re-sleeve the master cylinder and extend the parking brake rods.
  • You will also need to bend the rear brake pipes just a bit so that they will meet up with the slave cylinders, which are in a slightly different place on the later backing plates.
  • Don't cheap on any of these bits. Your brakes and suspension are a system that much work right all the time. This was a place where I choose to have the sub-systems rebuilt by a professional: Peter Caldwell with World Wide Imports rebuilt the calipers and A-arms, and Gerard's Garage did the master cylinder. The rear brake innards were all new from Moss Motors.