MK Indy Fitting Pedal Box, Brake Lines, Floor and Fuel Lines

I have finally collected my kit so, I can start the build of my MK Indy RX-5 kit car by fitting the pedal box, brake lines, floor, and the hard fixed fuel lines.

I had the massive privilege to start the build with my Dad who came down for a week to help out. Dad has been a massive influence on my thirst for engineering throughout my life. He was a toolmaker by trade, but is now retired, and can make or fix pretty much anything.

My Dad and I starting the Build

It was brilliant having him alongside me for this first week of building. Thanks for all your help Dad!

The Manual

When you place an order with MK Sportcars they send you an email with links to the MK Indy build manual. Now, as kit car manuals go, it is pretty good with quite a lot more detail than most other kit car manufacturers. However, it is still evolving and some of the latest chassis design changes have not made their way into the manual yet. At the time of writing this post, there is a big push for getting updates from builders to get the manual updated more regularly. So as part of my build, I’m trying to capture as many issues as I can to feed this back in to update the manual.

So as the MK Indy manual stands at the moment (Version 2022.1 dated May 2022) it is more of a guide on how to progress in some areas, other areas are quite detailed. You don’t need to follow the manual by the letter of the law and it may not fully reflect the chassis version you have for the moment. So bear this in mind. As a general rule though, follow the order of doing things as per the manual. There is generally a logic as to why things are done in a certain order (e.g. fitting the front suspension before the steering rack due to access).

The detail of each stage varies in depth of description. Don’t blindly follow measurements in the manual, use them as a guide but take your own measurements and judge the correct length or distance in each area.

Pedal Box

The first task in the whole MK Indy build is fitting the pedal box. A pretty straightforward task, or so I thought. I opted for the MK Indy standard billet pedal box which is a good balance between,  performance, adjustability, quality and price. It also fits straight into the chassis with, in theory, no adaption needed.

Pedal Box Preparation

There are a few things that you should do before you install the pedal box in the MK Indy chassis.

MK Indy Standard Billet Pedal Box – change these washers
  • Take off each of the pedals at the pivot and replace the washers on either side with some thinner stainless ones (circled in red above). This is to provide more thread through the nyloc washer, which can be an issue at IVA if not addressed. I don’t believe the IVA manual specifies a minimum but it is generally good engineering practice to have 1-3 threads showing past the nyloc. I have just about 1 thread with thinner washers, I may even change to thinner nuts to get another thread showing before IVA.
  • While the pivot is taken apart, grease the joint well and rebuild.
  • Adjust the pivot tightness to get a smooth operation whilst not getting too much play.
  • Install the brake bias bar with the longer part towards the accelerator pedal (see image below), not like the image above. I installed some Phosphor Bronze Washers (that my Dad turned up for me – thanks Dad!) on either side of the brake pedal (see image below) to stop some of the play. Just remember to leave a small 1-2mm gap next to the washer to allow sufficient movement of the brake bias bar.
  • Add a throttle pedal stop. This was not provided in the pedal box kit (but I think it normally is). So I used an M6 bolt as a temporary solution, and then my Dad made a much better nylon-tipped final version – thanks, Dad!
  • Dry fit the pedal box to make sure it fits and there are no interference issues with the chassis. This is when I found a problem.
Phosphor Bronze Washers for Brake Pedal Bias Bar
Custom Nylon Tipped Throttle Stop

Pedal Box Issue

When I dry fitted the pedal box I found that the accelerator pedal hit the chassis upright. No matter what I did with the adjustment it just didn’t work. It seemed that the weld that holds the accelerator pedal pivot in place had been welded on at a slight angle that they just bent back to make it work. Not ideal. A quality control issue at the supplier. So I had 2 choices, try and get a replacement and hope the quality was better. Or fettle it myself to make it work.

MK Indy Pedal Box Clashing with Chassis Issue

I decided for the latter and fettle it myself, as everything else on the pedal box was spot on. So, I took apart the accelerator pedal and bent the ‘legs’ of the throttle pivot as per below.

MK Indy Billet Pedal Box Adjustment Needed
  • I twisted the pivot so that it was straight and added a washer next to the split pin to take out some of the play.
  • I then bent the top ‘leg’ in the direction of the red arrow to clear the chassis.
  • Then bent the bottom ‘leg’ (for throttle cable) in the direction of the blue arrow, to be in line with the throttle cable hole at the back.

This fettling worked really well and when I put it back together it gave me plenty of clearance and made the pedal action feel smooth.

Pedal Box Installed

I then fitted the pedal box for the final time. The MK Indy manual states to ignore the bolts that come in the pedal box as these are 25mm and are too short to grip the nyloc. Instead, you should use the 30mm bolts provided in the bolt pack. It turns out I didn’t have these in my bolt pack. So a quick message to Neil at MK Sportscars and some are on their way. Luckily, in the meantime, the bolts needed are the same as the steering rack bolts which are 30mm dome M8s. So on they went.

Once everything was sorted, the actual installation was straightforward and as per the manual. The pedal setup will need adjusting once the brakes are installed and bled and once I have the seats and side panels on to adjust the spacing between pedals for my feet.

Billet Pedal Box Fitted

Brake Lines Front

So, the brake lines were next. This is one area in the manual that had quite a lot of detail. However it is still not quite up to date with the latest chassis in some areas. It clearly shows the root to lay the pipes and provides a good guide to the lengths of pipes you need to cut. But don’t blindly cut the length of pipe as stated in the manual and hope it works for your chassis. I used a length of house electrical cable to bend round the route for the pipe and mark. Then once I was content the length was correct I measured the cable length to give me the length to cut. In most cases, this was pretty close to the MK specified length, but further out for others.


So there are a few tools that are a must for this job.

  • Pipe bender. A basic mini pipe bender from Screwfix or similar is perfect for creating unkinked bends easily. They are only c. £15 or if you are lucky like me to know someone who has one then borrow one. Thanks, Robert for the lend, it was brilliant.
  • Pipe cutter. A basic mini pipe cutter will provide clean cuts in tight spaces. It will also allow you to even cut pipes in place.
  • Brake flaring tool. Now, this is an essential tool that you definitely can’t finish the pipes without. This makes either a male or female end to the pipe to allow it to work with the correct pipe termination. Now there are 2 main types of hand tools to do this job. I would strongly urge you to get a slightly more expensive type to make your brake pipe fitting stress-free. More detail is below.
  • A 90-degree pre-made bend of pipe. This was recommended by The Parrott Bros in their brake pipe video. If you haven’t subscribed to their channel and are not following their MK Indy build, then do, it is brilliant. Far more polished than my videos, with great banter between them both, whilst providing genuine informative content is great to watch. They recommend bending a scrap piece of brake pipe into a 90deg bend and marking where the bend starts (the zero mark on the pipe bender). You can then use this to mark when to start the bend on your actual pipe. This was a great tip and led to spot-on bends the first time. Cheers guys, I didn’t have to scrap a single pipe!

Brake Flaring Tool

So, there are 2 main types of manual hand tools you can buy. The first is available in a lot of places for around £15. Now don’t get me wrong this tool can provide a decent flare that will work. However it is not consistent and is fiddly to use to get a straight flare. You are more likely to need to redo pipes with this tool due to the inconsistency of the flare.

Basic Brake Flaring Tool

The second option is readily available on Amazon or eBay for between £25-45. This more expensive tool clamps the pipe and creates an even flare everytime. This is done with little effort and can be done in situ if you need.

Premium Brake Flaring Tool

I went the second option for around £40 from eBay which got really good reviews. I wasn’t disappointed, it was brilliant.

Chassis Changes

One thing to note is my latest MK Indy chassis (May 22) has the tabs for the front brake lines higher up on the chassis sides than the pictures in the manual. A quick check with the builders’ group came up with the reason why. With the older chassis, the steering column came extremely close to the hard brake line on the driver’s side. Raising the tab gives greater clearance. Before I riveted my brake lines to the chassis I double-checked the clearance with the steering column. I had plenty of clearance to go above the steering column.

Steering Column Clearance to Brake Line

The route I took worked out perfectly and if I had followed the manual it would have taken the hard brake line much closer to the steering column. In the image below you can see the difference between the manual and my routing. Note the position of the tab on the chassis is much higher now.

Front Right Brake Pipe Routing. Manual vs My Routing.

Other than this minor change, the front routing was pretty straightforward and follow the manual.

Brake Line Rear

The brake lines on the rear were even more straightforward than on the front. The manual was informative and accurate. The only issue I had was that my kit was supplied with a UNF 3-way t-piece instead of the M10 one. A quick trip to Halfords got me the right version for £6 to carry on with the build.

Rear Brake Lines Fitted

Brake Line Front to Back

The connecting pipe from the pedal box rear master cylinder to the 3-way t-piece was reasonably straightforward. However it did lead to some head scratching again where the manual hasn’t kept up with the chassis changes.

On the latest chassis, there are 2x separate floor panels, one underneath each seating area. In the manual it shows the old floor which is one large floor which spans both sides and provides a floor under the transmission tunnel. In the manual, the fuel pipes are then fixed to this floor under the transmission tunnel. This separates the fuel and brake lines nicely. Now without this centre flooring to fix the fuel lines to, you need to rethink the routing for both brakes and fuel lines.

I looked at various images of newer MK Indy chassis builds. It seems that they now run the fuel pipes halfway along the tunnel and take one high and one down and back up the chassis members again. This is to ensure you always have at least 250mm between each fuel line fixing. I didn’t like this approach for fuel and thought there was a neater solution, which I’ll explain later. Plus I also wanted to move the brake lines further away from the floor pan whenever I could to protect them from road debris.

Front to Rear Brake Pipe Routing

So I decided on the routing above, which follows the normal path in the manual initially. Then it comes up the diagonal chassis member up towards the top of the transmission tunnel. This nicely joins up with the standard routing round the rear of the vehicle to the t-piece at the back.

Brake Pipe Fitting Gallery

Floor Fitting

We then decided to fix the floor to the chassis before we did the fuel lines. This made it easier for us to see what fixing points we had along the tunnel. My mate Dave helped us flip the chassis over and back onto the wooden trolleys.

To note: this is where having 2x separate build trolleys helps. One for the front and one for the back. This allows you to deconflict chassis members when upside down.

I opted for MK Sportscars to predrill the holes for the floor and powder coat the floor panels. I didn’t want the hassle of having to sort the powder coating myself. The brucey bonus was the holes were already drilled. The manual here still shows the old 1 piece of floor panel as mentioned before. However, the approach is the same.

I dry-fitted the floor to make sure I knew which panel for which side. They do handily stamp a mark on each to help. I just dropped a few rivets into each corner to make sure everything lined up.

The Rivets

When I fitted the floor, the wrong rivet length was specified in the manual, they specified 16mm. This seemed way too long for the clamping distance required. I queried it with MK and got a prompt response back from Neil. He confirmed the right spec was 12.5mm and this is the only length they use in the whole build. It has now been updated in the May 22 version of the manual.

So the spec you need for the floor, and pretty much anything you rivet to the chassis is as follows.

  • Aluminium Sealed Rivets 4.8mm x 12.5mm.

As mentioned above you need to use sealed (close-end) rivets for anywhere on the build, especially where you are riveting into the main chassis. This will ensure that the rivet fully seals the hole and does not let in any water.

Open-end (standard) vs Close-end (sealed) Rivet – image origin Lituo

You need 88 rivets for the floor. So, I bought a bag of 200 for good measure from eBay to cover everything else as well. These are used everywhere and I believe the only size of rivets that MK Sportcars have in their workshop.

Fitting the floor

So after dry fitting the floor we cleaned the chassis members and the floor panel with methylated spirits. This helps to remove any grease to get better adhesion.

I then used U-POL Tiger Seal to run a 2-3mm bead of sealant around all chassis members the panel would mate with.

Tiger Seal Bead for Floor Panels

Then carefully we lowered the panel with 2x people so you can come down straight. Once lined up then put all of the rivets in their holes before you rivet any.

Rivets Placed in all holes first

Then start finishing off the rivets in a kind of star pattern, crisscrossing the floor panel as you go. Now there was a big debate on one of the build groups over manual rivet guns vs air-powered guns. We’ll tell a lie, everyone was saying just buy an air gun. I wasn’t so convinced. I have an 11-year-old son who seems to love riveting and is pretty good at it. With the manual rivet gun I have, I was convinced it would be OK.

It turned out I was right, the rivet gun I have is a breeze and there were 4 of us taking it in turns. My son did about 20 rivets in each panel. So I think everyone else on the build forum is either weak, lazy or both… 🙂

Manual Rivet Gun which is Brilliant!

Within an hour we had both panels fitted. Some white spirit cleaned up any overkill easily. But beware Tiger Seal doesn’t come off fingers and clothes very well! So wear gloves and clothes you don’t care about. The amount of tiger seal we applied was about right. It meant that there was a reasonable amount of overspill on the outside edges, which was easy to clean. On the inside edges, the tiger seal oozed out just enough to give a nice bead down the inside edge. This means it should be nice and watertight if any water gets into the foot well.

Floor Panels Fitted

Raptor Paint the Floor

Before turning the MK Indy chassis back over, I wanted to make the underneath finish even more durable. I figured that this would be the last time I would consciously turn the car upside down willingly. So, if I didn’t do it now I would end up having to do it upside down under the car later on.

On one of the user groups I saw that someone had painted their floor with raptor paint. This is in theory 10x tougher than normal paint and often used to paint pickup truck beds to make them more durable. I thought it was worth giving it a go to provide a protective coating to the underside of the vehicle.

Raptor Paint on Floor

The Raptor Paint goes on well. It has a resin in the paint. Once activated with the button on the base of the can, you have an hour to finish the painting before it starts to set. The result is brilliant, it has come out really well and fully covers the rivets providing extra protection against corrosion. A single can was enough for the entire floor. At £31 a can it’s not cheap, but well worth doing in my opinion while it is upside down.

Floor Fitting Gallery

Fuel Lines

On next to fitting the fuel lines. First a bit of info to be aware of about the differences between the Mk2 engine (MK recommended) and the Mk2.5 VVT which I have.

Mk2 NB vs Mk2.5 VVT Differences

I have the Mk2.5 VVT engine which is slightly different to the non-VVT that MK suggest you use. One of the differences is the fuel rail. The Mk2 non-VVT has a fuel feed at one end of the fuel rail and a return connection at the other end of the fuel rail. The Mk2.5 VVT version only has a single fuel feed on the fuel rail and no return. See the image below for the comparison.

Mazda MX-5 Mk2 NB vs Mk2.5 NBFL VVT Fuel Rail Differences

There are 2 ways of addressing this in the MK Indy build.

  • The first is to replace the Mk2.5 VVT Fuel Rail with an Mk2 non-VVT fuel rail. This gives you a better future upgrade path for turbo or similar. You need the fuel return when you start pushing bigger power. This stops fuel starvation on the cylinder furthest from the fuel feed.
  • The second is to add a t-piece to the feed which loops back to the return line. This is best done at the engine end. So that you have the option to change the fuel rail at a later date.

I think I will opt for option 2 for the time being as I will be running Naturally Aspirated (NA) initially. I might still change my mind when I install the engine if I find a reasonably prices Mk2 fuel rail before then.

Mazda MX-5 VVT Fuel Return T-piece – Image by Emanuel Mandat

If you are only going to be NA and never want to upgrade then you can do the return by the tank and get away with running a single feed line to the engine. The main thing for me though is to run both fuel lines the full length of the transmission tunnel. This is as per the manual so I still have the option to change it later. Running a second fuel line later once you have finished the build would be a nightmare.

Fuel Line Routing

The MK Indy manual tells you to fit the fuel lines before the flooring. It also still shows the old single-piece floor as already mentioned in the brake line section above. So, I wanted to fit the floor first so I could more easily work out where to fix the fuel lines. The manual says to fix the fuel lines to the flooring under the transmission tunnel. This is no longer there on the latest 2x floor pan version.

I looked at some photos of more recent builds using the new flooring from the forums to work out the best routing. It appears the fuel lines start from the front in the same way. They then split halfway down the transmission tunnel. With one staying high and the other going low and then coming back up again. The main reason for this is you have to maintain fuel pipe fixings at least every 250mm for IVA. So the natural routing follows the main chassis members to provide suitable fixings. Going straight across means some of the gaps are more than 250mm.

I didn’t like the idea of split routing the fuel lines. I wanted to try and keep fuel lines away from the floor of the vehicle if at all possible, to provide extra protection. So, I thought I could come up with a neater solution. I wanted to run the fuel pipes straight from front to back. To do this I needed to fabricate some additional brackets to provide sufficient fixing points.

Additional Fuel Line Brackets

So, I set about creating 2 additional brackets to fix the fuel lines. These would replicate the bracket that MK Sportscars have welded into the chassis nearer the front of the transmission tunnel for the same purpose.

I made them out of a 2mm aluminium sheet, which I cut and bent to the shape of the round tubing. Then I drilled holes for rivets in the bracket and chassis before painting the brackets. I then used a small amount of tiger seal and riveted the bracket in place. The curved shape of the bracket fixing point stopped it from twisting. This only needed a single rivet at either end to secure each bracket.

Fuel Lines Additional Fixing Point Bracket

With the 2x additional brackets in place (circled in red below) it provides less than 250mm fixing distance to meet the IVA requirement. I am very pleased with the result. I have suggested to MK Sportcars that these additional brackets could be welded on as standard. Had I thought about this before fixing the front to rear brake line I would have used these brackets for the brake line as well. This would take the brake line further away from the floor to give extra protection. Too late for me, but one for other builders to consider…

Additional Fuel Line Fixing Brackets

Fixing Fuel Lines

Now that the fixing points were sorted, I could start fitting the fuel pipes. I decided to mock up the handbrake to make sure I had sufficient clearance with the routing.

Handbrake Mock Up

I mocked up the handbrake cables with string. This was quicker than me digging out the old cable mechanism from my boxes of MX-5 bits. Plus I hadn’t bought the new cables yet. This was good enough for what I needed.

I also decided to drop in the differential temporarily to make sure I had sufficient clearance.

Temporary Install of Differential to Check Clearance

I then used some spare 10mm house radiator pipe to mock up the bends. The fuel line is an 8mm pipe so the house radiator pipe is close enough to try it out. I used the same pipe bender as I used for the brake lines which worked well.

The pipe below is what I ended up with to loop around the differential for the fuel feed.

Fuel Feed Line Shape

I then fixed each fuel line in place with cable ties initially to make sure they were bent correctly. It also allowed me to check there was sufficient clearance.

Temporary Fix Fuel Lines with Cable Ties

Once I was content, I fixed them back permanently with plastic p-clips and rivets as per the manual. One thing the manual doesn’t make clear is what they mean by a double p-clip. It is simply 2x normal p-clips using the same fixing hole as below.

Fuel Line ‘Double P-clip’ Fixing

Final Fitted Fuel Lines Routing

I am pleased with the way the fuel line routing turned out in the end. The routing was easy with minimal bending. It looks neat and keeps the fuel lines high within the transmission tunnel, to provide additional protection from under car debris. Don’t forget to take lots of photos of the fuel line fixings for the IVA pack.

Final Fitted Fuel Lines Routing

Fuel Lines Fitting Gallery

Next Job

Next up will be the fitting of the fuel pump to the tank and then fitting the fuel tank to the MK Indy chassis. Then connect up the hard fuel lines to the fuel tank using the flexible fuel hose.

Video of Progress

Summary of Build Costs and Hours

Here is a summary of the costs and person hours (total number of hours for every person that has helped) for the build so far. This should hopefully help others with the planning of their builds, by providing cost and time actually incurred for this build. A more detailed breakdown of all the costs and hours worked on the build to date can be viewed here.

Person Hours Worked This Post
Pedal Box Adjustment and Fitting and Brake Lines Install (2x People 2x Days) 32 hrs
Floor Fitting and Painting (2x People) 6 hrs
Fuel Filter, Fuel Line Brackets and Fitting of Hard Fixed Fuel Lines11 hrs
Car Build Costs This Post
Split Conduit 6.5mm x 6m - Amazon£20
Nylon P-clip 4.8mm x 100 - eBay£4
Nylon P-clip 8mm x 100 - eBay£4
Closed Aluminium Rivets 4.8mm x 12mm Pack 200 - eBay£16
U-POL Raptor 2K Protective Coating Black 400ml Aerosol = Euro Car Parts £31
FAE Brake Light Switch - Euro Car Parts£12
U-POL Tigerseal Black Pu Adhesive & Sealant - 310ML - Euro Car Parts£9
Tool Costs This Post
ASTA Brake Flaring Tool 3/16" SAE - eBay£40
10x Drill Bits 4.9mm - Amazon£15
Totals This Post To Date All Posts
Person Hours Worked 49 hrs 260 hrs 404 hrs
Car Build £96 £12,444 £13,202
Tools / Consumables £55 £369 £470
Total Cost £151 £12,813 £13,672

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