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Exocet Update 5: Brake & Fuel Line Initial Routing

  • Jan 10, 2024
  • 10 min read

12/28/23 Build Update: Fabrication and Guesstimation


With the powertrain removed from the donor car, our focus turned to preparing the Exocet frame where we need brake and fuel lines routed front to back. The existing brake and fuel lines on the donor car are not formed to contour around the tube frame chassis - we need to make new ones from scratch.


There is no YouTube tutorial on how to do this (specifically for our car). We looked up many tutorials on cutting, flaring, and bending lines but we needed to determine the exact routing ourselves so it was safe, robust, and would clear other components.


The first step for doing this was mounting the brake booster, master cylinder, clutch master cylinder, drive pedals, and gas tank to the chassis. With these items in place, we roughed in line positions using coat hangars bent by hand. This allowed us to try different routings, determine possible interferences, and estimate the length of line needed.


The first issue we ran into was the clutch hard line to the clutch master cylinder. We wanted to use the OEM hardline but it interfered with part of the frame (a lot of clearances are tighter on the Exocet it seems). This was an easy fix - Exomotive sells a braided clutch line with banjo fitting to clear the frame. When installing this line, I had an idea about addressing an issue on the rear brakes, more on that later.


The second issue we ran into was routing lines to the rear of the car. The fuel and brake lines were routed along the bottom of the donor car, protected by unibody frame components. Underside routing isn't possible on the Exocet, the floor is completely flat and low to the ground. Any lines running along the underside are the lowest point of the car and at risk of being damaged by the road - not an acceptable risk for brake and fuel lines. The transmission tunnel is much narrower on the Exocet than the donor car and is fabricated from sheet metal - mounting lines to the tunnel itself poses risk of interference with the powertrain and will have the ends of rivets protruding into the passenger cell.


A 1-1/4" square metal frame tube runs from the front to back of the transmission tunnel at the bottom of the car. Two 5/16" fuel lines won't fit alongside a 3/16" brake line along this frame member. The lines must be spaced to avoid having them pass over rivets holding the P-clips that suspend the neighboring lines, close proximity to a rivet head may cause them to wear as they vibrate during driving.


Our solution was to fabricate 12 gage aluminum brackets and fasten them to the passenger side frame tubing using M6 rivet nuts and bolts. Both 5/16" fuel lines and the 3/16" brake line can be riveted to these brackets. Alternative solutions seen online were to rivet either the brake or fuel lines to the PPF, we did not want to do this as it creates a massive headache if you need to service the transmission. The PPF is also attached to the frame through the differential bushings and engine mounts, we would need to add loops to the lines to allow for relative movement between the chassis and powertrain. We also did not want to run lines along the driver side of the frame as the exhaust runs on this side, posing a heat hazard, and the PPF would not protect the lines from the driveline if it broke (I have never seen this happen on a Miata so it is not a great concern).

On an NA Miata, there is a send and return fuel line so we have to run two front to back. At the rear, the fuel lines run underneath the tank and twist over the tank edge on the passenger side. Rubber fuel line would attach the feed and return to the hard lines. We placed the rear tank cover on the chassis to get an idea of clearances. We also had to be conscious that the rear subframe sits below the tank and the lines would have to pass between the subframe and tank.


The third issue we ran into was the rear brake connection. On the standard Miata, a single brake line runs from the brake bias valve at the master cylinder to the rear of the car, it attaches to a distribution block at the passenger side rear suspension which splits it between the rear wheels. On the Exocet chassis, this distribution block sits against the rear bulkhead creating a headache for line routing. I worked with Kevin Patrick at Exomotive to have a custom braided brake line with a banjo fitting created that would attach to our hardline. Because we don't know exactly where the brake line would need to terminate, we left an excess length of line to cut and flare later once we had mated the powertrain and frame. This idea will be tested at a later time when we mate the powertrain and frame.


The fourth issue we ran into was the engine bay fuel line termination point. Ideally, the fuel lines would be supported at their ends so they aren't vibrating and moving excessively during operation. Unfortunately, all of the frame forward of the firewall is round tubing on the Exocet and you cannot install rivet nuts to hold brackets on round tube. We looked into using a split clamp typically used on ATVs and UTVs with roll cages to mount lights etc. but the front subframe position would not allow access to the fastener on this split clamp. Without a computer CAD model of the Exocet and subframes, we could not confidently come up with a solution so we decided to leave excess fuel line length and address this after we mated the frame and powertrain.


We used coat hangers, bent by hand, to estimate needed line lengths and routing. For the 3/16" brake line and 5/16" fuel line, we used copper-nickel line as it could be easily formed by hand (for smaller bends) and easily bent using standard tube bending tools.


I started an Excel spreadsheet to track fastener use, applied torque, tools required, and whether Loctite is applied. As part of this tracking sheet, I calculated the necessary length of thread to ensure proper fastener installation. The goal of this sheet is to create detailed work instructions for all fastened joints that are unique to our Exocet for future maintenance purposes. I will detail this in its own blog post at some point.


Time Prepping Donor: 11.5 hours (06/11/2023-08/28/2023)

Total Teardown Hours: 45.75 hours (08/29/2023-11/04/2023)

Total Exocet Build Hours: 31.5 hours (11/07/2023-12/28/2023)

Total Hours on Project: 88.75 hours


Exocet Build Journal:

11/07/2023 - Peter

 - 3:30PM Start

 - Using simple green mix, spray and wipe down passenger side of subframe and anti-roll bar

 - Removed A/C bracket from engine

- 5PM End

 - 1.5 Hours of Labor


11/11/2023 - Peter, Paul

 - 1:15PM Start

 - Unpack Exomotive boxes

 - Labeled brackets, bags of items

 - Test mounted clutch pedal and master cylinder

 - Test mounted brake master cylinder / booster & driver pedals

 - Attached brake booster vacuum tube

 - 2PM End

 - 0.75 Hours of Labor


11/12/2023 - Peter

 - 3PM Start

 - Cleaned front subframe with simple green mix

 - 3:45PM End

 - 0.75 Hours of Labor


11/14/2023 - Peter, Paul

 - 5PM Start

 - Removed high pressure fuel hose from donor car at hard line to tank connection

 - Measured fuel lines --> 5/16" confirmed

 - Discussed how to address rear subframe braces

 - Mounted gas tank, undid drain plug and refitted with copper washer

 - Using coat hangers to bend and fit, mocked up fuel lines and rear brake line in chassis

 - Mocked up brake line for rear subframe, discussed how to connect to the master cylinder

 - Discussed how to run lines

 - Do not run on driver side of trans tunnel - exhaust runs here

 - Do not attach to the PPF - increased service difficultly

 - Do not rivet directly to the trans tunnel - ends of rivets will stick into passenger cell

 - 7:15PM End

 - 2.25 Hours of Labor


11/18/2023 - Peter, Paul

 - 10:15AM Start

 - Talked through brake / fuel line routing

 - Unbolted rear brake distribution block on rear subframe, discussed brake routing

 - Discussed fuel line routing to the tuel tank

 - Choose aluminum 12 gage sheet metal for the trans tunnel brackets used to mount lines

 - Using hangers, mocked up fuel lines at rear

 - Using cardboard, mocked up trans tunnel brackets

 - 11:30AM End

 - 1.25 Hours of Labor


11/26/2023 - Paul

 - 10:55AM Start

 - Tested Exomotive braided clutch line banjo on rear distribution block

 - Banjo and fitting appear to match correctly, bolt works as well

 - Removed stock clutch line

 - Installed Exomotive braided clutch line

 - Adjusted pedal and added clutch pedal spacer; no torque on any items

 - 11:25AM End

 - 0.5 Hours of Labor


12/03/2023 - Peter, Samuel, Paul

 - 11AM Start

 - Put chassis on 2-post lift, ratchet strapped to lift arms

 - Tested rivet nut tool and drill bit sizes necessary for rivet nuts, rivets, fasteners

 - Mocked up bracket, test fitted by hand in transmission tunnel, discussed options

 - 2:45PM-4:45PM - Lunch Break

 - Fabricated aluminum brackets, test fitted in transmission tunnel

 - Mocked driveline using cardboard to check clearances inside transmission tunnel

 - First bracket iteration: concern for clearance to the PPF, excessive material use

 - Second bracket iteration: concern for clearance to the PPF, doubling P-clips works

 - Third bracket iteration: doubled 5/16" P-clips, spaced 3/16" P-clip too close to 5/16"

 - Fourth bracket iteration: chosen design, low profile, compact, good clearance

 - Fabricated three additional brackets, test fitted in transmission tunnel

 - Discussed line mounting:

 - Three brackets along transmission tunnel, placed along tightest spots

 - Rivet P-clips to the 1"x 1" square frame tubing at the ends of the transmission tunnel

 - 7:30PM End

 - 6.5 Hours of Labor


12/17/2023 - Peter, Paul, Samuel

 - 10AM Start

 - Setup "paint booth" using cardboard boxes

 - Applied primer to transmission tunnel brackets

 - Mocked up fuel line bracket for mount near termination at tank in the rear

 - Fabricated fuel line bracket (2 iterations)

 - Mocked up lines with coat hangers

 - Hanger is ~33" long

 - ~133.25" needed for each fuel line (~22.2ft total needed)

 - ~125" needed for brake line (~10.4ft needed)

 - Discussed mounting options for fuel line termination in engine bay

 - Use 1.75" tube frame clamp mounts

 - 1PM Break for Lunch

 - 2:15PM Start

 - Applied grabber blue paint on transmission tunnel brackets

 - Drilled 1st holes in frame: 3/8" for M6 Rivet Nuts (x3)

 - Covered surface with painters tape, used punch - no chipping of powder coat

 - Applied rust preventative black paint to drilled holes before rivet nut install

 - Attached transmission tunnel brackets (no torque or Loctite)

 - Cut, straightened length of 3/16" brake line

 - Discussed line routing options, created PowerPoint diagram of engine bay line routing

 - Taped firewall frame, marked mounting locations

 - Drilled 5/16" holes in firewall, installed M5 Rivet Nuts (x5)

 - Applied rust preventative black paint to drilled holes before rivet nut install

 - Discussed line routing for fuel lines in engine bay

 - Fabricated fuel line mount for engine bay

 - Drilled 3/8" hole in frame member in engine bay, installed M6 Rivet Nut for fuel line mount

 - Applied primer to front and rear fuel line mounting brackets

 - Notes:

 - Use 5/16" bit for M5 Rivet Nut Install (not 1/4")

 - Use 3/8" bit for M6 Rivet Nut Install

 - Open 3/16" P-Clips with 7/32" Drill Bit for M5 fastener to pass through

 - Leave painters tape on frame for hole drilling (prevent chipping) and painting (masking)

 - 7:15PM End

 - 8 Hours of Working, Brainstorming


12/26/2023 - Peter, Paul

 - 9AM Start

 - Applied primer to brackets

 - Installed x1 Lizard Go Clamp using 4mm Allen Key

 - Checked for clearances between the clamp and suspension

 - Concluded that clamp would not be accessible with the subframe installed

 - Removed clamp, leave fuel lines free at end and reevaluate after powertrain install

 - Applied 1st coat of paint to brackets

 - Bent rear brake line running through transmission tunnel

 - Marked P-Clip locations for brake line

 - Drilled marked locations for M5 rivet nuts

 - Used stepped drilling 5/32" --> 1/4" --> 5/16"

 - Installed M5 rivet nuts

 - Adjusted brake line by hand, added rivets and P-Clip locations as needed

 - Finished roughing in rear brake line --> no flaring, no torque on fasteners, no rivets

 - 12:30PM Lunch Break

 - 2:45PM Start

 - Drilled and installed M5 rivet nut at rear brake line termination

 - Extra length left to mate with union after powertrain install

 - Straightened 5/16" fuel line, cut 133" in length

 - Removed fuel tank

 - Installed rear fuel line bracket using M12 bolt and nut

 - Used x2 19mm sockets to install prevailing torque nut

 - Bent 1st fuel line

 - Marked locations for, drilled and installed M5 rivet nuts at front and rear

 - Roughed in 1st fuel line --> no flaring, no torque on fasteners, no rivets

 - Using leftover length of 5/16" line (167"), roughed in 2nd line - cut as needed for clearance

 - Riveted all lines into place

 - Installed M5 fasteners for all P-clips

 - Checked clearances, adjusted lines by hand as needed

 - No torque or Loctite applied to any fasteners

 - Unequal length M5 fasteners used; need stack-ups, reorganization before final install

 - All lines left with extra length, no flaring, in case that adjustment is necessary

 - 6:45PM End

 - 7.5 Hours of Labor


12/28/2023 - Paul

 - 6PM Start

 - Started fastener thread engagement calculation Excel spreadsheet

 - Checked existing fastener usage

 - Based on thread engagement calculation, swapped some fasteners for correct lengths

 - 8:30PM End

 - 2.5 Hours of Labor


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