Electric handbrake conversion

As I’m sure most AK owners will attest to, the handbrake is about as much use as a chocolate teapot!

So after three years of motoring (and parking it on the gears), it’s time for an MOT. I spent a good half day adjusting the handbrake shoes and cables and had the brakes at least biting. Then, having dropped the car and giving the handbrake lever one last yank to test my handiwork, the connector on the end of the handbrake cable snapped off. Joy.

Having read lots on the forum I decided it was time for the electric handbrake conversion.

Big thanks to AK Charlie, Highlander and others for working all this out, I’m by no means taking any credit for their ingenuity but thought I’d do a write up to describe a retrofit, just in case it’s useful for someone else.

Parts:

  • 1no 40 x 40 stainless steel (304) 90deg angle section, 5mm thick, 1m long
  • 2no 40 x 40 angle section, 30mm long (as above)
  • Actuator kit from Hollins. 100mm stroke, 800N, 12V. (Just say it’s for a cobra and Paul will send the right kit)
  • Double pole latching switch (I used this double pole, latching Savage switch from CBS)
  • 5m of 4core 12A cable
  • 5m of 2core 12A cable
  • Nuts and bolts:
    • 2no. M8 25mm to fix the 1m angle iron (spanning piece) to the chassis
    • 2no. M8 25mm to fix the small brackets to the spanning piece
    • 1no. M8 Xmm high tensile 12.9 grade to fix the lever arm extension to the lever arm
    • 1no. M6 Xmm high tensile 12.9 grade to fix the actuator to the spanning bracket
    • 1no. M6 Xmm high tensile 12.9 grade to fix the actuator arm to the lever extension
  • Some decent drill bits to get through the stainless (m42 grade bits recommended)

Here’s what you do…

  • Check which solenoid you have. I had planned it all for the LAS unit, but actually had the LA1 unit which is slightly different and has m6 bolt mounts not m8
  • Take off the old handbrake cable connector from the lever under the boot (tricky!) and from the handbrake lever in the cockpit
  • Remove the old handbrake cable
  • Make a new connecting bracket for the lever.
    • Make 2no 50x30x4mm plates.
    • 8.5mm hole centred and 12mm I’m from the edge
    • 6mm hole centred and 10mm in from the edge
Lever connections
  • Test fit these connectors onto the lever arm, space with m8 washers to allow the actuator head to fit between, use high tensile 12.9 grade bolts for these connections
  • The actuator has m6 connections (check your actuator, other options from Hollins have m8 connections)
  • Temporarily clamp the 1m section of angle iron to the chassis, spacing slightly off the grp section of the boot to avoid squeaks. I’ll refer to this as the spanning bracket
Spanning bracket clamped to chassis
  • There is a small amount of play in the connection to lever arm, so line the actuator up with the arm so it is on pushing on the pivot side of the arm and then also 90deg to the new spanning bracket
Actuator pushing on pivot side of lever, not off the end
  • With the actuator perpendicular to the spanning bracket and temporarily bolted to the lever arm, offer up one of the 30mm angle brackets to a few mm from the edge of the actuator body. Make sure the bottom of the 30mm bracket is on the back of the spanning bracket such that the force of the pushing motion from the actuator is braced by the 30mm bracket and not pushed sideways
  • Mark the edge of the 30mm bracket on the on spanning bracket
  • Mark the position of the holes required to bolt the spanning bracket to the chassis
  • Remove the spanning bracket and take it to your drill press
  • Drill 8mm holes either end of the spanning bracket to allow you to bolt it to the chassis with m8 bolts
  • Measure the gap required to fit the actuator housing between the two 30mm brackets and then mark the position of the second bracket
  • Drill 8mm holes through the centres of the two 30mm brackets to bolt them to the spanning bracket and then 6mm holes in the other face of the 30mm bracket for the bolt to secure the rear of the actuator – measure these on each bracket and try to get them to line up as much as possible when the two brackets are facing each other
  • Mark the position of the centre of the 8mm holes when in position on the spanning bracket, then drill 8mm holes to match in the spanning bracket
  • Bolt the 30mm brackets to the spanning bracket
  • Test fit the spanning bracket and temporarily connect the actuator to the brackets
  • Check the actuator is reasonably perpendicular, adjust position of spanning bracket if required
  • Clamp spanning bracket and mark centre points of 8mm holes on chassis
  • Remove spanning bracket, drill with 6.8mm drill bit and tap with m8 course tap
  • Bolt spanning bracket to chassis
  • Bolt actuator to bracket with 12.9 high tensile bolt XXmm long
Temporary setup to test fit
With high tensile bolts

Next comes the wiring. It’s all pretty simple and only requires a permanent 12V, ignition switched 12V, Ground, three connection to the two way switch and then the feed to the actuator.

DIAGRAM

I installed fitted the circuit board on the bulkhead to the right of the fuse boxes which made the wiring pretty simple. The only difficult bit was running the two core cable in split conduit down through the transmission tunnel to the actuator.

After finishing the wiring… I spent about 2 hours fault finding with a multimeter, including taking the actuator mack off the car and running it on a bench 12V supply. I eventually tracked down the fault to a dodgy connector on the actuator, they are pretty rubbish and I’d recommend changing to something a little better (you don’t want your handbrake getting stuck on when you’re out and about!).

It was a little worrying cutting a new switch into the dash, but going gently did the trick. I carefully drilled the centre point from the back of the dash with a 2mm drill bit, once through the fibreglass I gently pushed into the back of the leather to mark the centre point. Then with a sharp Stanley blade I cut a cross through the centre point that was slightly smaller than the diameter of the switch. Then the scar bit, from the back I used a hole saw to cut the correct diameter opening in the fibreglass. Test fitting the switch with the leather being pushed back through the hole I had to open up the hole in the fibreglass a little with the Dremel until the flange could be comfortable pushed through the hole.

I decided to locate the switch in a position that would make it difficult to accidentally press it well driving!

It has noticeably better performance than the previous cable setup. I recently had it tested for the MOT and it achieved 15% effort, just shy of the 16% requirement. This was with the pot in the default position. I’ll be turning it up a bit for the retest shortly.

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