Muncie GB Series gear box parts

What the GB Series is

The GB Series is a family of gear boxes. The front mount boxes are crankshaft drive units that offer more speed ratio choices than a standard PTO, with forward and reverse options and shift choices that include Lectra-Shift. Each is built around a TG, RL, RG or clutch shift gear section.

The GB1 is a different kind of box. It is an add-on gear box that bolts to the output of a PTO with an SAE "B" (GB1B) or SAE "BB" (GB1P) mounting, and the install sheet mentions the RS6S-P89M series PTO. The GBFR is a gear box for the FR Series PTO; the PTO is not included and is ordered separately.

Where it fits

The design number tells you which PTO series the box is built around, and the ratings below are intermittent duty at 1,000 rpm.

The GB60 is the clutch shift design, so it is engaged and released with the engine at idle. The GB10, GB30 and GB40 must be engaged and released with the engine off.

Reading a GB model number

The order is PTO type, design number, gear type, speed ratio, shift type, assembly arrangement, output shaft, special feature. Muncie's example is GB10-U68 06-A 1 K X: a GB10 with the U68 gear, ratio 06, manual air shift, input and output on the same side, an SAE "B" pump flange and no special feature.

• Gear type: U60 (6 pitch, 20 degree spur) or U68 (6 pitch or 6/8 pitch spur).
• Shift: X none, A manual air, C cable, E electric air 12 volt, F electric air 24 volt, L lever, S Lectra-Shift (GB10 only).
• Arrangement: 1 input and output same, 2 input and output opposite.
• Output: B 1 1/4 inch round keyed (all); K, S and L are SAE "B" pump flanges, F, M, Q and R are SAE "A" pump flanges, and G and N are special flanges, each limited to the designs the brochure names.

The GB1 reads differently: GB1B-2 05 125A is the add-on gear box with SAE "B" 7/8 inch 13T input (P is SAE "BB" 1.0 inch 15T), a 2 gear design, output ratio 05 (0.50:1) and a 1 1/4 inch keyed output shaft.

Parts that wear and what to order

• Bearings, shaft seal and O-ring. The GB1 list has needle roller bearings, thrust races, an output seal and a Viton O-ring.
• Gaskets: the GB1 and GBFR books each list a housing or cover gasket.
• Breather assembly 44T35868 and fill plug 25M50014 on the front mount box.
• Stud kit: 20MK6623B for the GB10 and GB60, 20MK6625B for the GB30 and GB40 (which also needs 25M60200), tightened to 35 ft lb.
• Lube kit 43TK5020 for the GB1, and the FR66 "D" activation kit 43TK5280 listed in the GBFR book.

Questions we get about the GB Series

Is a GB1 the same as a GB10?

No. The GB10 is a front mount box built around the TG. The GB1 is an add-on that bolts to a PTO's SAE "B" or "BB" output.

Does the GB1 need extra lube lines?

Muncie's install sheet says no additional lines are needed and the box is filled with transmission fluid after installation. The newer GB1 parts book also lists lube kit 43TK5020, so check which applies to your unit.

GB manuals

All GB books: Muncie PTO parts manuals.

Need a complete rebuilt unit?

Our sister site rebuiltmunciepto.com covers rebuilt GB units. This site is the parts and model reference side.