I am working on replacing all the original hard lines on my 87 S4 Turbo II. Its a Wisconsin car, so it has some of the natural weight reduction. I was wondering what all the hard lines were. I know brake, fuel, fuel return and _____? Does anyone know the diameters of these? All I know is they use a M10 x 1.0 double flare end.

 

The fourth hard line connects the gas tank to charcoal canister/EVAP system. It collects gasoline fumes while the car is off and burns them instead of releasing the vapor into the atmosphere.

In terms of US/Imperial equivalent sizes, the fuel lines should be 5/16" and the brake should be 3/16" (or 8mm and 4.75mm, if you can find metric tubing). I don't know the size of the charcoal canister line offhand, but I'd guess it is also 3/16. Take a pair of calipers and compare it to the brake line to check.

 

Thank you, Ill buy a caliper and verify tomorrow, Ill let you know.

 

The brake hard line that runs from front to rear is still available from Mazda. The p/n is FB01-45-360C (https://www.tascaparts.com/oem-parts...ear-fb0145360c). It's a 5mm steel tube with 10mm x 1.00 fittings. If you decide to buy it from a Mazda dealer, than buy it locally as shipping costs will be prohibitive due to its volume. The fuel vapor return line (p/n FB01-45-711B) is NLA from Mazda. I bought the last one available in North America last spring. It's also a 5mm steel tube. The high (supply) and low (return) pressure hard fuel lines are NLA from Mazda. These two steel lines are 8mm diameter, which is nearly identical to 5/16" (8mm = 0.315" and 5/16" = 0.313"). I bought a 25' coil of 5/16" steel tubing from Summit Racing for about $30.

 

Do you happen to know if the fitting for the 5/16"/8mm is also 10mm x 1.00?

 

The two 8mm steel fuel lines that run along the left frame rail from the fuel tank to the engine have no fittings. They just have a bead on each end where the rubber hoses slides over. The high pressure line runs from the tank to the fuel filter and the low pressure line runs from the tank to near the fuel filter. There are tools available for making beads in the lines but many of them (such this one: https://www.aircraftspruce.com/catal...s/ezbeader.php) are not suitable for steel line due to its hardness. The tools that do work on steel line are expensive (https://www.grahamtool.com/smalltubebeadingtool.aspx). There are a few shops out there that will custom fab your fuel/brake lines, but they will need your originals. Shipping these lines are expensive due to the volume of the shipping box needed. There's one company in MI (https://www.inlinetube.com/) and there's another company in upstate NY near Buffalo (https://classictube.com/). This company in IN might be able to custom fab lines too (https://www.calltruckservice.com/cus...nd-brake-lines).

My low pressure fuel line has a small crack near the rear of car and sometimes drips some fuel. I haven't tackled this job yet on my '90 GXL but hope to get to it soon.

 

For fabricating my own brake lines and fuel hard lines running under the car, I prefer using the nickel-copper alloy (Cunifer trade name) over steel. Lots of advantages in using it as compared to steel lines - they are much more flexible & easier to bend and easier to get good flares made. But the best improvement over steel is they never rust or corrode, so do it once and done. Here's my go-to vendor for these lines: Fedhill brake line - Where to buy brake line, fuel line, brake line flaring tools, brake line nuts and brake line fittings

 

>>> I prefer using the nickel-copper alloy (Cunifer trade name) over steel.

That's a good point. I don't know what type of material the coil of 5/16" steel tube that I bought from Summit Racing is. I called Summit Racing about this, but they weren't of much help. I might buy a coil from Fedhill if I decide to make the line myself.

 

FWIW, I got the pre-flared brake line I needed from the local automotive store (steel) and bent it by hand, and it worked fine. I even bought the bending tool, it was just clumsier than doing it manually so I stopped using it.

However, if I had to do the flaring myself I definitely would've gone for the NiCop line. Plus the anti-corrosion properties are great (even though the pre-flared steel line was coated).