RJ Link Gearbox Repair: What Happens When There Is No Parts Catalog

Look up a part number for a catalogued gearbox and you get a price and a ship date.

Look up a part number for an RJ Link unit and you get a conversation. RJ Link builds to order, so a replacement is a new custom build with a design and production queue in front of it.

That is not a criticism of custom gearboxes. Built-to-application is why the unit fits your machine in the first place.

It does mean the normal repair playbook does not apply. The shops that can actually help you are the ones that can make the part instead of finding it.

The Part Does Not Exist Yet

Two routes lead to the same replacement gear.

On a catalogued unit, someone looks up the drawing, orders from stock, and fits it. Three steps, and the first two are administrative.

On a custom unit there is no drawing to look up. The route becomes: measure the worn part, cut a new one, fit it.

Same three steps. But the middle one is a manufacturing job instead of a purchase order, and everything about the timeline follows from that.

The measuring step is the whole difference. It is metrology, not parts sourcing, and it is why a shop with a machine floor can turn a custom gearbox around in weeks while a shop without one can only pass the lead time along to you.

What Actually Gets Measured

Reverse engineering a gear sounds like copying it. It is closer to recovering the design intent.

The part in front of you has been worn out of its original shape, and the worn geometry is exactly what you must not copy.

Six numbers do most of the work.

Measurement	Why it matters
Pitch diameter	Has to match the centre distance the housing already has. This is not negotiable
Tooth count	Fixes the ratio, and it is the one number that can be counted exactly
Pressure angle	Verified against the mating gear, never assumed from a standard
Helix angle	Governs thrust load, which decides what the bearings see
Face width	Read off an unworn edge, never off the worn flank
Backlash	Measured in the housing before anything is disassembled

The rule underneath all six is that worn surfaces lie.

Every dimension has to come off metal that has not been in contact, or off the mating component, or off the housing itself. Get that wrong and the new gear is a precise copy of a failure.

Backlash deserves the extra step of being measured before teardown. Once the unit is apart, the as-running clearance is gone and you are back to inferring it.

Cotta’s guide to managing gear clearance explains why that number governs both noise and load sharing.

Where the Weeks Go

Compare the two routes on a calendar and the gap is not subtle.

A new custom build starts with quoting and design, then waits in a production queue, then gets manufactured, then ships. The queue is usually the largest single block and it is entirely outside your control.

A rebuild skips both the design phase and the queue, because the design already exists in the unit sitting on the bench.

Ship it in, tear it down and measure, machine the parts, build and load test. The timeline is set by machining capacity, not by someone else’s order book.

Those numbers are illustrative, and any shop giving you a firm figure before teardown is guessing. The shape holds regardless, and it is why a rebuild is usually the fast answer on custom equipment even when it is not the cheap one.

What Comes Apart, and What Usually Failed

RJ Link units use helical gearing on tapered roller bearings. That is a durable arrangement and a fairly predictable one when it wears.

Helical gears pit and wear until backlash opens up and the drive runs louder under load. Helical teeth also generate thrust, so gear wear and bearing wear tend to arrive together.

Tapered roller bearings fail from load, contamination, or a lubricant that has broken down. Once preload is lost the shaft moves, the gear mesh goes off pattern, and the wear rate steps up.

Seals leak, the unit loses oil, and the overheating that follows accelerates everything above. This is the most common route from a small problem to a large one.

Two-speed transfer cases stick or drop out of gear as the shift mechanism wears.

Planetary carriers and pins wear under shock load until the carrier runs out of true. That is a different repair from replacing gears and needs to be identified early.

Output shafts and coupling splines wear from cyclic torque, or from a drive that has slipped out of alignment and has been loading the spline eccentrically.

The general failure mechanisms are worth reading alongside this. On a custom unit the cause matters more than usual, because there is no cheap spare to swap in if the same thing happens again.

The RJ Link Range

RJ Link builds across several gearbox families, most of them configured to the application. Cotta services the range.

Family	Type	Typical use
D190	Transfer case, speed reducer, or speed increaser	Mobile and stationary industrial drives
Speed reducers and increasers	Helical gearing on tapered roller bearings	High-RPM and high-torque drives
Transfer cases	Single and two speed, mobile or stationary	Vocational, mining, oil and gas equipment
Planetary gearboxes	High reduction ratio, high output torque	Track and wheel drives, high-speed inputs

Because these are custom units, the nameplate matters more than the family name. Two gearboxes carrying the same designation can differ in ratio, shaft configuration, and mounting.

The tag is the starting point for everything else. If it is unreadable, the housing and the gear count still tell the story, it just takes longer.

A shop that designs and cuts gearing for new units can recreate gearing for an old one. Precision replacement parts made to the original tolerances are what keep a custom gearbox serviceable past the point where its builder has moved on.

A Rebuild Is Also a Chance to Change Something

On a catalogued gearbox, a rebuild puts it back the way it was, because that is what the part numbers allow.

On a custom unit the parts are being made anyway, which means the specification is open in a way it usually is not.

That opens a few genuinely useful options. Bearings can be upgraded where the original selection was marginal for the duty the machine actually sees.

Seal arrangements can be improved on units that live outdoors or get pressure washed. Gear material and heat treatment can be revisited if the failure mode was surface fatigue rather than an accident.

Two cautions belong with that. Anything affecting ratio, shaft geometry, or mounting has to stay exactly as it was, or the gearbox no longer fits the machine it was built for.

And a change made because the original design was wrong is worth making. A change made because it sounds like an improvement usually is not. The failure evidence should drive it.

Where the load has genuinely outgrown the unit, the honest answer may be a different gearbox instead of a better rebuild.

Cotta’s guide to gearbox replacement for critical operations covers where that line falls. On a planetary versus parallel-shaft decision the answer depends on the space available as much as on the torque.

What to Send With a Custom Unit

Custom gearboxes reward a little extra effort at the front of the job.

• The complete nameplate, photographed rather than transcribed, including any hand-stamped numbers
• The machine it came out of, and what it drives
• Input speed and the load it actually sees, which is often not what the original spec says
• Whether it has been rebuilt before, and by whom
• Backlash and end play measured before anything is disturbed, if you have the unit in front of you
• Whether alignment has been checked at the drive, since a repeat failure usually points there

That last item catches more repeat jobs than anything found during teardown. A gearbox that fails twice the same way is usually reporting a problem outside itself.

Cotta has engineered heavy-duty gear drives in Janesville, Wisconsin for more than a century and handles repair, rebuild, and remanufacture in the same facility that builds new units.

Units are run under load before they ship. The testing standards behind that are worth asking any shop about, along with whether the quoted cost came before or after the unit was opened.

While Cotta does not repair or rebuild RJ Link gearboxes, we may have a drop-in option for a new unit, or we could quickly modify an existing Cotta design to adapt to your needs. Give us a call.