McLeod Racing RST HD Twin w/ Steel Flywheel - 05-17 Ford Mustang 4.6/5.0L 8 Bolt - 1-1/8 x...

Running a 2005-2017 Mustang with a 4.6L or 5.0L V8 and a 1-1/8 x 26 spline gearbox behind it? The McLeod 6435807MD is the RST HD twin disc on a steel flywheel, drilled for the 8-bolt crank and carrying a 164 tooth ring gear. It is the kit for S197 and early S550 owners whose clutch slips with a blower, turbo or built engine, and who still want a car they can drive to work.

What the RST HD twin does in an 8-bolt Mustang

Instead of one large disc, the RST HD uses two discs separated by a floater, so the pressure plate is squeezing four friction faces. That gives the holding power of a heavy single without the heavy pedal. On each disc McLeod puts full-face organic material on one side and segmented ceramic on the other, a mix that engages smoothly in traffic and still bites hard at the top of a gear. McLeod rates the RST HD at up to 950 horsepower and places it above its street RST and below the RXT.

The steel flywheel adds inertia that helps a heavy Mustang get rolling without slipping the clutch, and it handles repeated drag launches well. The kit ships at roughly 44.7 lb.

When a Mustang owner needs this kit

• Slip at high rpm in third or fourth after adding a supercharger or turbo
• Stock clutch glazing and chattering on takeoff after a few track days
• Gearbox swap to a stronger six-speed with a 1-1/8 x 26 input, where the factory clutch disc no longer fits the shaft
• Burnt friction smell and a hot bellhousing after repeated launches
• Release point moving higher in the pedal as the old disc wears

How to check before you buy

A high gear, low rpm, full throttle pull is the quickest test: if engine speed rises faster than road speed, the clutch is slipping. Rule out a soft pedal, low fluid or an air pocket in the slave line first, since any of those can hold the bearing against the fingers. Read our slipping diagnosis guide for the full check, and see the manual transmission repair cost breakdown for what a clutch job costs in labor.

Fitment

McLeod lists this kit for 2005-2017 Ford Mustang 4.6L and 5.0L engines with the 8-bolt crank, a 164 tooth ring gear and a 1-1/8 x 26 spline. That spline is the detail to check. Ford fitted the 2005-2010 Mustang GT with the Tremec TR-3650 five-speed and switched the 2011-up GT to the Getrag/Ford MT82 six-speed, and neither of those is the gearbox this disc is splined for. The 26 spline version is meant for cars that have been swapped to an aftermarket gearbox with a 1-1/8 x 26 input. If your 2011-2017 GT or Boss 302 still has the factory MT82, buy the 1 x 23 spline RST HD for the 11-17 Mustang GT instead. Measure or look up your input shaft, count the crank bolts, and send us the year, VIN and transmission model if there is any doubt. More clutch and flywheel parts are in our hard parts section.

Install notes

• Swapped gearboxes often need a different release bearing height. Set the bearing for this twin rather than reusing the stock bearing blindly.
• Replace the pilot bearing; the Lisle pilot bushing remover pulls the old one cleanly.
• Slide each disc onto the input shaft by hand first. A disc that drags on the splines will cause a clutch that will not release.
• Fit flywheel dowel pins where required and use McLeod's adapter ring bolts with no washers added.
• Torque the pressure plate nuts in two passes, 25 ft-lb and then 35 ft-lb, working across the pattern. No thread locker.
• Balance changes go on the flywheel only, never on the adapter ring. Break the clutch in with about 1,200 gentle street engagements.

Will this fit my stock 2011-2017 Mustang GT with the MT82?

No. This disc is splined 1-1/8 x 26. A factory MT82 car needs the 1 x 23 spline RST HD, part 6435825MD.

Does it fit a 2005-2010 Mustang GT?

The 8-bolt crank and 164 tooth ring gear are covered for 2005-2017 4.6L and 5.0L engines, but the stock TR-3650 is not a 1-1/8 x 26 input. It fits these cars when they run a gearbox with that input spline. Send us your VIN and transmission to confirm.

How much power is it rated for?

McLeod rates the RST HD twin at up to 950 horsepower.

Why a steel flywheel?

Steel adds rotating mass, which makes launches and low speed driving easier in a heavy car and tolerates heat from repeated passes.

What should I replace with it?

The pilot bearing, a release bearing set up for the twin, and the clutch fluid. Inspect the rear main seal while the flywheel is off.

• Transmission Slipping Diagnosis Guide
• Automatic vs Manual Transmission Repair Cost