1997 Mazda MX-5 Miata: Stoptech Stainless Brake Lines and Fresh Gear Juice
December 23, 2010
I took the opportunity recently to flush out Project Miata's fluids of unknown provenance and install a set of Stoptech braided stainless brake lines. For the geeky deets, hit the jump.
Gear Oil Gotchas
Be careful when choosing gear oil. It is categorized into different performance classes, known as API Categories. Mazda specifies API GL-4 for the Miata transmission. But, hey, check out this API GL-5 stuff. Bigger is better, so GL-5 must be one number better than GL-4, right? Wrong.
GL-5 oils have much higher concentrations of extreme pressure additives that make them suitable for use with the low speeds and high torque levels experienced by the ring and pinion in your differential. This sounds like the hot setup for the manual gearbox behind a highly modified engine, except that GL-5 oils lack the friction modifiers needed for the gearbox's synchros to operate correctly. Simply put, using a GL-5 oil in the Miata's gearbox will eventually turn the synchros into Captain Crunch.
Some modern manual gearboxes however can live happily with GL-5. Your owner's manual will tell you.
Redline MT-90 is GL-4 oil. It's synthetic, so it ought to tolerate higher temperatures better than non-synth stuff. Same goes for the Redline GL-5 gear oil I spurted into the diff. Both are 75W90 viscosity, same as the OEM specifications. The conventional wisdom that 'thicker is better' for performance cars really doesn't hold much weight (har har) with respect to modern oil formulations.
Stoptech Braided Stainless Brake Lines
It's true that braided stainless steel brake lines expand much less than the stock rubber ones and that this translates into better brake pedal feel. However, replacing the brake lines in Project Miata is as much about safety as it is performance. Brake lines do fail, and the older they are the more prone they are to degradation.
The car has 127k miles, and the original brake lines have lost much of their original compliance. The last thing I want is for some crusty old stock rubber brake line to spring a leak in the braking zone of turn two at Laguna Seca. Enter Stoptech stainless steel brake lines.
Stoptech's brake lines are a PTFE inner sleeve surrounded by a snug-fitting stainless steel braided sheath that resists the expansion caused high brake line pressures. Atop the braiding is a clear plastic coating that prevents the stainless braid from chewing through anything it comes in contact with (if the line rubs anything on the suspension then they're been installed incorrectly anyway).
At the ends of each line is a hefty strain relief and plated steel fittings and new copper crush washers for the banjo fittings. All robust-looking stuff. The Stoptech lines are DOT-compliant, too, each line being subjected to a 4500 psi leak test before being packaged up. The only thing that's missing from the Stoptech lines is an orientation tab on the fitting at the caliper end (the stock ones have this), so you just have to take some care to ensure you've aligned the fitting properly before and after torquing the banjo bolt. No big deal at all.
During threshold braking, Miata brakes have a tendency to be difficult unlock once you've locked one up (exacerbated by too much front brake bias, particularly in the early cars sans ABS). This is due to compliance elsewhere in the system -- flexy calipers are the likely culprit. The stainless lines won't cure it, but they will reduce a bit of that hysteresis in addition to the peace of mind they provide.
Jason Kavanagh, Engineering Editor