3.19 Pedal Box  (Quote from the GD Manual and my starting point)

The pedal box bolts to the footwell bulkhead at the desired height for foot size, sandwiching the bulkhead between it and the master cylinders. A typical height position is with the top edge of the pedal box casting level with the engine bay ledge underside. Position over to the outside, but leave enough space in order to remove the throttle pedal. For a trial run you can self-tap the pedal box in place prior to cutting the holes and fitting the cylinders.The tandem master cylinder is pressure outlets are identified as ‘P’, connect to the rear circuit, and connect ‘S’ to the front circuit. Use Kunifer pipe to make up the short links to the bulkhead hoses or use GD ready made items EBR01A. In the case of the adjustable pedal box these are substituted for EBR06A flexible type.

Correct pedal adjustment is when the brake pushrod is adjusted so that there is 2mm of free play between the rear of pedal edge and casting, do not assemble with excess free play as you run the risk of the pushrod dropping out of the master cylinder. Ensure the pushrod retained with the locknut tight. The clutch cylinder may need spacing off the bulkhead to achieve similar adjustment and pedal height. The throttle pedal ratio can be set to suit throttle rate, fitting the cable at the top of the pedal pull will give minimum (approx. 5”) pedal movement and quick throttle action, lower down will give longer movement and more progressive throttle action. The cable outer should fix through the bulkhead in line with the pedal fixing.

Pedal box and hydraulic cylinders pre-planning: Lots of thinking and measuring was the first order of play for this because a.) This is a very important piece of the build not to get wrong; and b.) I had to decide on 'distances.' They being:

  1. Pedal Box Placement: How high off the floor do I want the pedals to be?
  2. Clutch Pedal Positioning: How much room do I need between the clutch and the left-hand side of the body?
  3. Pedal Bending: How far apart do I need the pedals to be? Do I need to bend any?
  4. Accelerator Positioning: How much room do I need between the accelerator and the right-hand side of the body?
  5. To Space, or not to space, that is the Question: Do I need to put spacers on the cylinder side of the bulkhead? And if so what how thick do they need to be?
  6. Hydraulic Plunger Shortening: Do I need to shorten the hydraulic plungers? And if so by how much?

Preparation: I decided to cut out the footwell extension corner first to allow me to get my hands to both the front and the back of the pedal box at the same time. Easy access to both sides of the bulkhead is key for a one-person pedal-fitting operation... Note: I've documented the fitting of the footwell extension in a different article.

And, what is now common practice for me before doing anything is, I review the GD guidance, read other peoples' blog's, and fiddle with and measure everything a hundred times to "get-my-eye-in"... I also make sure I have Andy's phone number close at hand... Just in case.

So Here Goes...

1. Pedal Box Placement: The first thing I needed to establish was a set of references to work towards. So I measured the pedal configurations and seat heights on my other household cars to see what I'm used to.

Footroom & Distance Comparison Chart:

                                Volvo    Polo   Cobra (after my adjustments)

                                (cm)      (cm)    (cm)

Clutch to Brake            13         10       11     (Pedal centre to pedal centre)

Brake to Accelerator     11.5      12        9.5   (Pedal centre to pedal centre)

Pedal Height of Floor    14         14      14       (bottom of pedal to floor minus 1 cm (for carpet))

Seat Height                 28         24       xx     (Haven't got any seats yet so don't know)


The biggest difference was the vast amount of space to the left and right of the pedals in the family cars, there's acres of room..... In the Cobra, these areas being comfortably snug.

I used the GD recommended position as my starting point i.e. the engine bay underside ledge, but I went down 1 cm for my vertical position. This position, with allowing 1 cm for the carpet, was in keeping with what I'm used to.

Made my now customary cardboard template and taped it to the bulkhead. Then I drilled one 8 mm hole to accommodate the bottom centre fixing hole of the rear brake cylinder. I used this lower centre hole because it is best placed to straighten things up vertically and horizontally. Then, with the box firmly, but temporarily fixed in place, I tried out the position of the pedals.

After some tap-dancing on and around the pedals, the final positional adjustment was made and the other five 8 mm and the three big cylinder holes were drilled and cut out.

2. Clutch Pedal Positioning: With the footwell extension in place I sat on my simulated seat (an old squashed duvet and a piece of wood,) and once again tap-danced on -and around the pedals. From this, I determined I had the room to move the clutch pedal over to the left a bit. Better done now than later. It seems prudent to have as much room to each side of the brake pedal as possible. Can't be doing with the risk of unintentionally twitching a wrong pedal, or hitting two at the same time. With a 350 bhp V8 gurgling a couple of feet away, and with 4 pot, 330 mm AP racing brakes on each corner just waiting to do the biz', things could happen quite quickly.

3. Pedal Bending: Moving the clutch pedal a tad to the left by bending it was less traumatic than I was expecting. I did, however, have to be careful as the arm was quite a complicated shape, and care was needed not to distort anything near to, or above the top-most curve.

I used my 4-inch vice and three spanners as fulcrums to bend the pedal arm. I didn't want the drama of hammers or blowtorches or the tried and tested multiple-mole-grip-and-brute-force technique, I just calculatedly clamped everything up and gave a couple of gentle turns until the desired bend was achieved. Had to do two bends; one to move the arm laterally and the other to re-square it up.

Moving the clutch pedal ~1.5 cm to the left should be enough. However, I do think there is room for the footwell extension to be a bit wider as I believe there is space there... I'll have a chat to Andy about this.


4. Accelerator Positioning: I've read a blog or two where reference has been made to cutting into the right-hand inner body skin to provide more right-foot room. Undecided at this stage as to what to do. I do have just enough room without this surgery, but it is an option I will be contemplating during the cold winter nights. Currently, I have ~6 cm from the centre of the pedal to the right-hand body wall (5 cm when the carpet goes in.)

Note: Reading cobranut's blog. I've decided to manufacture a similar, mechanical accelerator stop. As I won't be "flying-by-wire" (as the Chevy LS drivers do,) I need to ensure I don't put unnecessary pressure on the mechanical parts of my ECU fuel linkage. I know correct adjustment of the cable should not allow this to happen, but I like this additional measure to guarantee it not happening. (Design TBD.)

Not concerned with the accelerator travel at this stage as I have nothing to attach it to.

5. To Space, or not to space, that is the Question: Did a mock up on the bench of the clutch and brake cylinders fitted to the pedal box, and I simulated the 6 mm bulkhead using washers. Now I can see -and understand- why I need to space for, and/or trim the plungers. From my measurements, I estimated I needed to space 1 cm for the brake cylinders and a tad more for the clutch.

Making the Spacers: A couple of options here, and I went with the 1 cm thick aluminium bar option. This because I like the fact of having substantial plate metal on both sides of the bulkhead clamping everything together. I believe this will create a more rigid assembly. i.e. Sandwiching the GRP between very strong, very flat metal plates obviously provides a more solid foundation. Or to put it another way, having the cylinders butt directly onto lumpy GRP with just a couple of bolts and a stack of washers might be less rigid.

Did some [very manual] metalworking on the 1 cm aluminium bar and produced three spacers. One each for the brake cylinders and one for the clutch. No easy way to make these, just lots of drilling and hand filing.

No easy way to do this

(that's if you don't have a CNC machine in the garage)


I also have a bar of 5 mm aluminium that I have decided to use in addition to the 1 cm spacer for the clutch cylinder. As the clutch plunger is longer than the brake ones, it protrudes further forward. So it was back to the drill and vice bench and an hour or so later I had made the 5 mm spacer. Believe me, a 5 mm thick aluminium bar is a lot easier to work than a 1 cm one. Put both spacers on the clutch cylinder, bolted them up and I'm happy with this. Everything now looks more in proportion.

Just some hole drilling and separating and job done

6. Hydraulic Plunger Shortening: Couldn't mess this up so lots of measuring done here. And in reality it was [eventually] quite straightforward. The main thing to ensure here was, they needed to be not skew-whiff with respect to the balance bar. ... Nearly messed up  big-time here though, as I didn't have the balance bar level when I first measured... A very very close shave.

Initial Spacing Measuring

Putting It All Together On the Bench: Test fitted everything on the bench, and I accurately measured how much I needed to trim off the pushrods to create the necessary 2mm gap at the front of the pedal box. I also, on the advice of Andy, rounded the inside edges of the clutch fork. This because the inside square-edged lip could 'catch' on the back of the pedal thus causing undue pressure on the internals of the cylinder..... General Comment: 'Catching,' if any, could be dependent on how much spacing and plunger shortening you do, so for your configuration, it might not be an issue.)

Brake Cylinders Balance-Bar: Lining the balance bar was supposed to be quite straightforward. Some lining up, a good greasing and job done... Not quite!!! Lining up is one thing, but securing and setting up are, to me, critical mechanical functions that I need to fully understand. Get the set-up wrong and you fail the IVA test. Get the securing wrong and a similar IVA fail will just as ceremonially be presented to you... Not good!

        Alignment: Measured the distance between the cylinders (61 mm) and attached the pistons to the clevis's ensuring they were equidistant to the balance-bar pivot point (30.5 mm each from dead centre.) What I understand as being essential is, both pistons must sit 90o to the balance bar. Couldn't understand this for some time as it didn't make sense. But, as I've discovered, as the front and rear brake cylinders are of different [tube diameter] sizes (0.7 and 0.75,) the internal pressure differential takes care of business; so the balance-bar 'initially' needs to be set up centrally i.e. pivoting directly in-line behind the pedal. Then, only a slight tweaking adjustment should be needed to the centre pivot point to accurately set the necessary brake-bias differential. This will be done when my car goes back to GD for its pre-IVA check... I'll leave it to Andy to sort out.

         Securing: According to the latest "Car Builder Solutions" magazine (issue 30, page 7.) And I quote: "IVA compliance requires that, after the brake-bias has been set to an appropriate and acceptable ratio, the adjustment be rendered immovable, We understand that drilling and pinning is no longer acceptable and that the locking nut must now be welded to the threaded shaft." It goes on to say "check with your local testing station for the latest rules."

            I must say I find welding on the balance bar is a bit drastic and extreme. I can see the locking pin and sleeve being a more practical solution (as per their diagram.) But, they [CBS] being a very credible source of parts and information, I need to find out more. (No way am I putting any heat near anything.)

A Couple of Concerns: (Don't forget, I'm still test fitting on the bench)

  1. The brake pedal, when fully depressed, touched the back of the pedal box. Initially not happy with this, but apparently it's because there is no fluid in the cylinders i.e. it's an open and unpressurised circuit so there is no resistance against the forward motion of the pedal. I am assured, however, when everything is charged up, sealed up and bled, the depression distance will only be a couple of inches. So, in reality, this is not an issue.
  2. Clutch spacer: When I depressed the pedal, the concertina part of the rubber gaiter was touching and squashing slightly against the outer edge of the hole. Rubber chaffing against metal is not good, so I increased the diameter of this hole by about 3 mm.
  3. The clutch pedal, when fully depressed, made contact with the inside edge of the clevis. This is not an issue because the pedal will never go this far back [when in situ'] as the bulk head will stop this amount of forward movement.

The cylinder, when spaced, catching on the hole.

Brake Switch: To fix the brake switch bracket to the pedal box I drilled and tapped for M5 bolts. That's the size of the holes on the bracket so that's what I'll used. Practised my tapping skills on a scrap piece of aluminium and I realised that for an M5 screw I needed to drill a 4 mm hole and then tap it with an M5 tap... There's probably some 'drill-size/tap-size' reference table somewhere on the internet, but it's easier to do a test piece and get it right in practice.

In Situ' Test Assembly: With the components dismantled (for the umpteenth time) I mounted the pedal box (with pedals fitted) in the footwell and attempted to bolt the cylinders in place. However, I came across a small but significant issue.

As I previously mentioned, I used M8s as my 'holding-in-place' bolts for all the cylinders (all the fixing holes on the pedal box are M8 size.) However, the clutch cylinder bolt holes are M10 size. So, in my humble opinion, if a hole in an important piece of kit is of a particular size, it must be that size for a reason. I know there is 'practically' no difference between an M8 and M10 in this case, but I will feel happier using the correct size bolt as defined by the cylinder, rather than the generic pedal box.

Disassembled everything [yet again] and drilled out the two holes to M10. Test fitted everything again  and now the clutch cylinder rubber gaiter was rubbing on the M10 hex bolt head... Not good. So I replaced the Hex' headed bolts with socket heads... Now it's good.

Mounted the three cylinders and screwed their respective plungers into their respective clevis's and adjusting for the required 2 mm gap from the back of the trailing edge of the front of the pedal box. Quite fiddly this, but using an inspection lamp and mirror I got there in the end. I also made sure no rubber was making contact with anything. And I checked to see if the clutch fork was 'catching' (which it wasn't.) I also remembered to grease up the bias bar... Tightened everything up and tested the pedals' functionality to my my satisfaction, and I am happy..... What a kerfuffle!