137-3722 final drive for Caterpillar 320B midi excavator
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Product Overview
The CAT 320B is a 1990s classic — the B‑series that put Caterpillar's 20‑ton platform on job sites all over the world, and many of them are still digging today. Under each track frame sits the travel motor with reduction, covered by references 137‑3722, 234‑4630, 1373722 and 2344630, that takes high‑pressure oil from the main pump and trades speed for the low‑speed torque pulling the machine across muddy cut slopes and rough haul roads.
On a 320B this age, the drive rarely gives a dramatic warning. It wears down in quiet stages: the two tracks stop quite matching, the machine drifts on level ground, the track shell warms after a trundle, and a note builds through the floor. Most crews nurse it until a track hesitates on a grade — but by then the piston block and valve plate have already been shedding swarf into the oil. This aftermarket unit reproduces the original motor‑and‑reducer pairing as one sealed, bench‑run assembly, so the worn drive lifts out whole and the new one bolts straight in.
Core Advantages
1. Keeps a legacy 20‑ton workhorse earning
Original 320B drives grow scarcer as the fleet ages. This aftermarket unit gives owners a path to keep a still‑useful machine on the job rather than writing it off over a dead track.
2. Simple, tough gearing that wears slowly
The B‑series drive has none of the complexity of later Cats — just hardened planetary teeth meshing cleanly. No electronics to fail, just gears that last when kept sealed.
3. Even pull between the two tracks
A lapped piston block and valve plate hold pressure internally, so neither track lags. The machine tracks straight across a yard without the operator fighting a sideways tug.
4. Sealed for mud and dust of old‑site work
B‑series machines work through long days in clay, dust and standing water. Fresh shaft and housing seals keep that grit out of the lube — the protection that decides whether the drive reaches its next overhaul.
5. A direct, no‑nonsense fit
Flange, studs and ports reproduce the original, so removal and refitting follow the old CAT manual. No adapters, no fabrication, no guessing.
Manufacturing & Quality Control
Components are machined to the original B‑series drawing, heat‑treated where wear bites, and assembled in a clean area. Each finished drive runs on a hydraulic stand while torque, leakage and noise are checked; units outside tolerance are reworked before packing. The internals are fogged with preservation oil, ports are plugged, and the unit is crated on dunnage for freight.
Frequently Asked Questions
Q1: Which reference suits my 320B?
A: Read the tag on your existing drive against the four numbers and send the machine serial number. B‑series build variants can differ, so we confirm the correct unit before dispatch.
Q2: Is this interchangeable with the 320C or 320D?
A: The B, C and D series use related but not always identical drives. Mounting and output spline can differ between generations. Send the serial number and we will tell you honestly whether it crosses over.
Q3: Can a home workshop fit this?
A: The swap needs a track‑frame lift and basic hydraulic tools. If you already service undercarriages, it is a straightforward day job; otherwise use a mobile fitter.
Q4: What should I do with the old drive?
A: It is yours to keep. Many workshops send failed motors to a local rebuilder for cores; if you want, we can advise on what parts inside are usually salvageable.
Q5: What is the warranty position?
A: Materials and build defects are covered. Damage from dirty oil, debris in the motor, track obstruction, overload or incorrect fitting is excluded. Photograph any arrival damage before uncrating.