Newsletter › Archive › Issue 1
ChassisDex #1: STI hubs on a GD, the 15x8 +25 question, and two oil-leak fixes
Issue one. ChassisDex answers "will it fit?" and "what breaks?" for the GD WRX/STI and the NA/NB Miata, and every answer links to its sources. Here's what's new this week.
New and updated: Subaru WRX / STI (GD, 2002-07)
- 5x114.3 hub conversion (2005-07 STI hubs). Fits with work. This is the proper way to run 5x114.3 wheels on a 5x100 GD instead of adapters: STI knuckles and hub units up front with matching struts, STI hubs and bearings in the rear. Safety-critical, so it's rated "reported," not confirmed. read the entry
- VA WRX wheels on a GD. No-fit without adapters or a hub conversion (5x114.3 vs 5x100). read the entry
- GR WRX wheels on a GD. Reported fit, with a source conflict flagged on the page. read the entry
- Known issue: EJ25 head gasket leaks (2006-07 WRX, 2004-07 STI). Symptoms, what to rule out first, and what a proper repair includes. Sources are mixed, so it's a low-confidence entry to check, not a verdict. read the entry
New and updated: Mazda Miata (NA 1990-97, NB 1999-05)
- 15x8 +25 wheels on an NA. Confirmed fit, with work. read the NA entry
- 15x8 +25 wheels on an NB. Reported fit. read the NB entry
- NC Miata wheels on an NA or NB. Confirmed no-fit. read the NA entry and read the NB entry
- Known issue: NA oil leaks from the CAS O-ring and valve cover gasket. Cheap DIY fixes, plus the heater hose to check while you're there. read the NA entry
Every part page also got richer this week: key specs, a short answer per generation, and related parts.
One tip per car
GD WRX/STI: test before you tear down a 2.5L. If you suspect a head gasket, ask the shop for a combustion dye test, which checks the coolant for exhaust gas with the engine idling. If the heads do come off, budget the extra time and cost to have a machine shop mill them flat for the new gaskets. And if you're turning up the boost, know that detonation is a common way turbo EJ25 gaskets die. Source: Underhood Service, "Subaru EJ25 Head Gasket Problems" (underhoodservice.com).
NA Miata: mark the CAS before you pull it. When you replace the cam angle sensor O-ring, mark the sensor's position first so your ignition timing stays where it was. It's held by one 12mm bolt, and oil from a leaking CAS can drip onto the heater hose below it and rot it, so inspect that hose too. Source: Miata.Repair, "NA Miata Cam Angle Sensor (CAS) O-Ring Replacement" (miata.repair).
Reader corrections
None yet. If something on ChassisDex is wrong, write to hello@chassisdex.com with a source. We credit fixes by handle.
—Steve, ChassisDex
ChassisDex is an independent reference. Always verify fitment and torque specs before you wrench.
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