Handbrake - Part 2 - Installing a Linear Particle Accelerator

The normal handbrake set-up on the AK Cobra is a cable-operated system, utilising an XJS handbrake lever in the cockpit, operating a lever mounted above the differential unit that in turn pulls on the handbrake cables connected to each rear hub.

The original AK handbrake set-up, whereby the cable simply pulled directly on the actuator lever, did appear to have a reputation for not being very efficient (based on a read of several internet forums).  AK has addressed this and modified the set-up with the cable operating the lever via a pulley set-up to provide twice the pulling power.  Improved, but still a bit touch and go come IVA / MOT test time.

AK Handbrake Modification (from AK Build Manual)

I decided to make a couple of further modifications to the system myself to improve the handbrake performance.

The first modification involves the XJS handbrake lever.  I obtained the lever from Simply Performance at the same time as my donor axles.  The photos below show the lever before and after modification...

XJS Handbrake Lever before initial modification...

...and after modification!

The second modification involved the purchase of an electronic handbrake kit from Hollin Applications Ltd.  This kit was developed for the Motability market in the UK but seems to have gained popularity with many Cobra builders over recent years. The kit includes a linear actuator, an electronic controller and a simple switch.  The controller enables the pull / push force on the actuator to be adjusted up to a maximum of 800N or 80kg in old money.  It also meets the IVA requirement of preventing the handbrake from being released unless the ignition is switched on (it does also have the problem that the handbrake can't be released if the battery goes flat - but we will cross that bridge later).  The switch is a bit basic and will do for initial testing, but it will be replaced with something to match the other interior switchgear (when I decide what that will be...)

Linear Actuator

A bracket of some description is needed to mount the actuator to the rear chassis cross-member.  Since I made the decision to go with the Hollins kit, AK has actually started using them in their factory builds and has started selling an electronic handbrake kit including a mounting bracket.  However, I felt the price they were asking for the bracket alone was a bit steep and as I enjoy spending valuable time that I haven't got, making unnecessary bits for this build, I decided to make my own...

Fortunately, I got a bit of a headstart via Steve Sutton's build blog which referenced a solution by another builder Michael de Kok, who had included the details of the bracket he had fabricated for his own Cobra electronic handbrake install.  So, giving credit where it is due, I have borrowed the same design.

I completely forgot to take any photos of the fabrication process, so thankfully you can all just see the final bracket before and after powder coating!

Final bracket before coating (don't be too harsh on my welding)...

...and after powder coating

I fitted the handbrake actuator to the bracket using a long M6 bolt with a couple of spacers that I machined from some offcut of steel bar.

The actuator is installed into the bracket.

I then drilled and tapped some holes in the rear cross-member and fixed the bracket/actuator to the cross-member with some M8x1.25 bolts and spring washers.

The handbrake actuator & bracket are fixed to the rear cross-member.

I also needed to replace the operating lever from the item that AK supplied.  I fabricated a new lever from a 5mm thick steel plate with a small section of steel channel welded on the end.  The channel end needed to be reworked with some light grinder action to prevent the lever from fouling on the chassis at full throw.

New handbrake operating lever

I trial-assembled all the bits and wired up the control board temporarily to test out the operation.  Thankfully it all seemed to work OK with the actuator shutting down at extension once the load from the handbrake cables started coming on; the control box is preset from Hollins at 50kN load.

The final assembly involved powder-coating the operating lever, making up a couple of nylon spacer washers and bolting it all back together with copious amounts of copper grease.

Final handbrake assembly

Body Preparation - Part 2 - Pedal to the Metal

AK recommends fitting the pedal box to the body before installing the body on the chassis.  Most builder's blogs also suggest that installing the brake servo and master cylinder is a much easier job if done with the body off the car.  So that was my next job!

I obtained my brake servo unit, from a Rover 200, via that renowned internet auction site.  When I was looking for this, there seemed to be none available in the UK and I ended up having mine shipped from Lithuania!

My unit arrived looking in not too bad a condition.  Importantly it also came with the grommet and the spigot for attaching the engine vacuum line.  I gave it a quick scuff-up with a scotchbrite pad, masked up the bolt threads and bellows and applied a couple of coats of primer, followed by some matt black spray paint.

The servo unit was given some gentle abrasion...

...followed by a couple of coats of primer...

...and some black spray paint

Looking almost as good as new!

The master cylinder from a Rover 25 or Rover 200 is also needed.  However, as I had opted for the big brake upgrade kit I needed to also upgrade the master cylinder.  

This got a bit confusing for a while as I really struggled to find the right part.  AK suggested that the required bore of the master cylinder was 22.7mm as opposed to the standard Rover 25/200 component, which has a 22.2mm bore. This meant that I needed to search for a master cylinder from a Rover 220 Turbo model, which according to Jon at AK is easily identifiable as the brake pipe outlets on the master cylinder point to the outside of the car as opposed to pointing toward the engine bay.

I completely failed to find any Rover master cylinders with a bore of anything other than 22.2mm and the majority seemed to have the outlets facing the engine.  In the end, I bought a brand new unit from TRW, which had the outlets on the correct side, but still had a bore of 22.2mm; so fingers crossed it works!

New master cylinder unit - bore 22.2mm

The master cylinder was bolted to the servo unit using some M8 Nyloc bolts, remembering to install the rubber O-ring between the master cylinder and the servo.

Servo and master cylinder

In hindsight, it might have been easier to install the servo into the engine bay and then bolt the master cylinder on.  There is not a lot of space between the pedal box firewall and the inner wheel arch.  It required a lot of careful jiggling around, taking care not to scratch the stainless steel engine bay cladding before I managed to get the servo and master cylinder in place.

In place - and it's not coming out again!

I'm running a 'Drive by Wire' (DBW) throttle set-up so I needed to drop the GM DBW throttle pedal (which includes the position sensor and electrical connector) off with AK so they could modify their normal pedal box and install the new pedal.

Modified Pedal Box with DWB Throttle Pedal

I had hoped that I could use the studs from the brake servo to 'hang' the pedal box off while installing it to make life a bit easier.  Unfortunately, the weight of the box and its centre of gravity conspired against me.  So installation of the pedal box is definitely a two-person job.

The pedal box is secured to the firewall with M8 bolts.  I bought some stainless steel Allen-head bolts, which as they will be visible in the engine bay, I treated to a bit of an extra polish to match the shiny engine bay cladding.

Shiny!

With me standing in the engine bay, trying to hold the pedal box against the firewall with my fingers through the hole for the clutch master cylinder and holding an Allen key into each of the bolts, and with my son lying in the driver's footwell with a socket and extension bar, we did manage to get the pedal box installed into place and secure the brake servo in place.  It is impossible to get a socket onto the upper bolts, so we had to resort to a spanner for those.  

While my son was trapped in the footwell I also took the opportunity to install the clutch master cylinder.  I bought a Girling unit with a 0.75" bore from Car Builder Solutions.  Again this was installed using 2No. shiny 8mm Allen-head bolts. 

Another "easy" job completed...

...and as seen from the inside!

And with that done, I am one step closer to getting the body on!