Muncie Z21 and Z25 PTO parts

What the Z21 and Z25 are

Both are clutch shift PTOs, engaged by a clutch pack rather than by sliding a gear. Each has a low profile housing, an integral solenoid, different port sizes on the activation and switch ports, and a single gasket, so there is no backlash to measure at mounting.

The Z21 is the medium duty unit, rated 265 lb ft and 50 HP at 1,000 RPM, with a rotatable output flange. The Z25 is the light duty unit, rated 125 lb ft and 24 HP at 1,000 RPM, built for direct mount gear pumps and bent axis piston pumps, with a round keyed output also offered.

Where it fits

Muncie lists both for the Ram 3500, 4500 and 5500 with the TorqueFlite HD or ZF PowerLine, and for the PACCAR TX-8. Side matters. The Z21 goes on the passenger (right) side opening only. The Z25 goes on the driver (left) side only. The Z25 installation sheet adds that a driveshaft driven device on a 4x4 Ram would need an aftermarket transfer case, and the round keyed output on the Ram Z25 is for 4x2 trucks only.

Muncie's Z21 brochure pairs it with PH and PK series gear pumps, and the Z25 with PF4 gear pumps and FX series piston pumps.

Reading a Z21 or Z25 model number

The tag reads: PTO series, input gear, speed ratio, shift, assembly arrangement, output and feature. Muncie's examples are Z21-Z11 11-DX-1-BS-BX and Z25-Z11 13-DX-3-TA-PX.

• Z21 or Z25: passenger side or driver side clutch shift.
• Z11: the input gear, for TorqueFlite HD, ZF PowerLine and PACCAR TX-8.
• 11 or 13: speed ratio, 1.13:1 on the Z21 and 1.26:1 on the Z25.
• DX or XX: 12 volt integral Ram shift, or 12 volt electric and hydraulic without activation parts. Ram trucks use DX, and XX is used only on PACCAR trucks with factory PTO wiring.
• Arrangement: 1 is right side shaft low, 3 is left side shaft low.
• Output: on the Z21, TA, BA, BS, BB, PB or II (DIN 5462), covering SAE A and SAE B 2 and 4-bolt splines. On the Z25, TA, 1X or TX round keyed, or UU for FX piston pumps.
• Feature: BX or BW (wet spline) on the Z21, PX on the Z25.

Parts that wear and what to order

• Output Shaft Assembly (Detail A): the clutch pack, with friction discs and spacer discs, plus the piston, return spring, output gear, bearings and shaft seal.
• Housing Assembly (Detail B): the housing, input shaft and gear, tapered roller bearings and the 12 volt solenoid valve.
• Cover or Output Cover Assembly (Detail D): output flanges by option, flange mounting ring, shaft seal and bearing.
• Installation kits: 48TK6780 for the Z21 and 48TK6781 for the Z25, with the gasket, studs, alignment pins, pressure switch, hoses and fittings. The Z21 kit includes the Ram wire harness 34T43408.

Questions we get about the Z21 and Z25

Can I mount a Z21 on the driver side?

No. The Z21 is passenger side only and the Z25 is driver side only on both Ram and PACCAR trucks.

How heavy a pump can the PTO carry?

Muncie says pumps over 20 lb, counting fittings and fluid, need a transmission mounted support bracket. That is stricter than its usual 40 lb limit, and it follows the transmission maker's requirement.

How do I set PTO speed on a Ram?

The PTO menu is in the vehicle information center between the gauges. The default is stationary single mode with a driver adjustable speed. The Z21 activation sheet lists the steps.

Z21 / Z25 parts breakdown

How the Muncie Z21 and Z25 PTO parts list is organised on our store. Each section opens the exploded view with every part number, the quantity used and an order button.

Muncie Z21 Series

Muncie Z25 Series

Z21 / Z25 manuals

All Z21 / Z25 books: Muncie PTO parts manuals.