ACT AT78 Clutch Alignment Tool for Honda/Acura

ACT AT78 Clutch Alignment Tool

Keep the ACT clutch parts you've already got and replace the missing alignment tool with AT78. We'd buy it separately when the tool has disappeared between jobs, when yours is damaged, or when you're ordering a matching disc and pressure plate individually. Check your complete kit first: ACT includes AT78 in the AR1-HDSS for the 2002-2006 RSX, so you may already have one.

Choose it by the pilot as well as the splines

We'd start with your ACT clutch number and the pilot diameter. AT78 has 24 splines on a 1 1/32-inch hub section, with a 0.830-inch pilot at the tip. That smooth end seats behind the disc; the splines locate its hub while you secure the pressure plate. You'll pull the tool out once the disc is clamped. Getting it through the disc is only the first part of the fit check.

AT61 is the easy one to confuse with it. You've still got 24 splines and the same hub diameter, but the pilot measures 0.787 inch. ACT calls for AT61 with the HC12 kits for the Civic Type R and Integra Type S. For an Integra A-Spec 1.5T with an HC10 kit, choose AT78. We'd keep the kit number with the car's details rather than ordering an unspecified Integra tool. The molded 78 beside the pull ring also helps when you've got several loose tools to sort.

Black plastic, used during assembly

You're buying a black plastic tool for the assembly stage. It comes out before you refit the gearbox, so engine torque doesn't pass through it once the car's running. Before reusing an old AT78, we'd look over the tip and splines. Damage there is a reason to get another tool, even if you've still got all the clutch parts. Keep the good one with your clutch paperwork afterward, ready for the next time you service that assembly.

Honda and Acura manual fitment

Use the engine and manual application shown here; automatic and CVT versions aren't included. Say you've fitted a K20A2 drivetrain to a Civic and you're using a matching ACT AR1 clutch with its required flywheel. We'd choose the tool from that clutch and pilot setup, rather than order from the Civic's original engine listing. Check the assembly on the car before applying a chassis-based fitment table to a swap.

Sort out the rest of the assembly too

On a Base RSX with an ACT AR1 clutch, you'll need an RSX Type-S flywheel or ACT 600295/600125, even with the five-speed. Don't let a matching tool number make that flywheel decision for you. AT78 is right for the clutch, but it doesn't make the original Base flywheel right for the new assembly.

Keep the supplied ACT flywheel with the specified AR2 kits for a 2009-2014 TSX or 2013-2015 ILX. The HC10 single-mass conversions require their included ACT flywheel too. If you're assembling the order from individual parts, account for those requirements before you start the job.

For your original B-series 1994-1997 DOHC VTEC Del Sol with an ACT AI4 clutch, order AT88. Its pilot measures 0.590 inch; its 24-spline, 1 1/32-inch hub section matches AT78. K-swapped that Del Sol? Choose from the clutch you've fitted, rather than keeping the old B-series tool just because its splines still fit through a disc.

Street and race discs: the same tool, different driving

ACT includes AT78 with both the AR1-HDSS and AR1-HDR4, although the discs have quite different jobs. The HDSS uses a sprung organic street disc and carries a 255 lb-ft crank torque rating for the kit. The HDR4 uses a rigid four-pad ceramic race disc; its kit rating is 330 lb-ft at the crank. Those ratings belong to the clutch kits, not AT78.

Our advice for your daily RSX is to stay with the organic street disc if it covers your engine's torque. You don't need to accept a rigid race disc's behavior just because it offers more capacity. ACT recommends the HDR4 for race use only and describes harsher engagement and more gear rattle. We'd take those compromises for a race build that needs them, rather than choosing the bigger number for a commuter. Either specified AR1 setup uses AT78.

For the ACT T1RR-H04 twin-disc clutch

If you're servicing an existing T1RR-H04 7.25-inch Honda K-series twin-disc assembly, ACT's dedicated instructions also list AT78. You're aligning two hubs in this job. The lower SI184010B disc, floater and upper SI184010T disc go in the kit's specified order, with the hubs kept aligned while you secure the assembly. Use the twin-disc procedure; sharing the tool number doesn't make it the same job as a single-disc installation.

You don't have to start over with a whole twin-disc clutch just to replace a missing tool. ACT lists the T1RR-H04 components separately, including AT78. Check that you've got that kit before making the match; a different K-series twin-disc assembly needs its own tool check.

Refitting the gearbox

Center and clamp the disc or discs using the instructions for your clutch, then take AT78 out. Support the gearbox for the refit. If you've still got a gap at the bellhousing, leave it supported while you check where it's hanging up. We'd go back to the disc alignment, input-shaft engagement and case dowels before tightening anything. ACT's general instructions say not to use the bellhousing bolts to pull the transmission into place. You need the dowels to locate the case as well as the tool to center the discs, and you'll still need the bearings and hardware specified for your assembly.