Understanding Gearbox Mounting Position Codes When Changing Manufacturers

A gearbox replacement can match the ratio, torque, shaft dimensions, and mounting footprint—and still be specified incorrectly because of one overlooked detail:

mounting position.

Industrial gearbox manufacturers use mounting-position codes to describe how a reducer will be installed relative to gravity.

Those codes can influence:

• lubricant quantity,

• oil level,

• drain location,

• fill location,

• breather position,

• bearing lubrication,

• seals,

• cooling systems and

• accessory placement.

The problem is that a code such as M1, M2, M3, M4, M5, or M6 should not automatically be assumed to represent exactly the same physical orientation across every manufacturer, product family, or gearbox style.

When changing manufacturers, the safe approach is not:

“Our old gearbox is M3, so order the new one as M3.”

The better approach is:

Identify the actual physical orientation of the existing gearbox, then use the replacement manufacturer's mounting-position diagram to select the equivalent configuration.

This guide explains how to do that.

What Is a Gearbox Mounting Position?

The mounting position describes the gearbox's orientation when installed.

A reducer can potentially operate with its:

• feet down,

• feet up,

• output shaft horizontal,

• output shaft vertical,

• input above the output,

• input below the output or

• another approved orientation.

Changing orientation changes where gravity moves the lubricant inside the housing.

That is why mounting position is not simply a mechanical-fit designation.

It can affect whether gears and bearings receive the lubrication intended by the manufacturer.

Why Gearbox Manufacturers Use Mounting Position Codes

Manufacturers use codes so buyers can specify an installation without describing the gearbox orientation in a paragraph.

For example, NORD documents six basic installation positions designated:

M1, M2, M3, M4, M5 and M6.

NORD also states that the installation position should be specified when ordering because it determines factors including oil quantity and the positions of the drain, fill, and vent.

Other manufacturers use their own mounting-position diagrams, codes, suffixes, or product-specific nomenclature.

The code is essentially shorthand.

The diagram behind the code is what matters.

The Biggest Mistake When Changing Gearbox Manufacturers

Imagine your existing gearbox documentation says:

Mounting Position: M4

You find another manufacturer's gearbox with an M4 mounting option.

It is tempting to conclude:

M4 = M4

But that assumption should be verified.

Manufacturers may define their mounting positions according to:

• gearbox family,

• housing geometry,

• shaft arrangement,

• mounting surface or

• their own documentation convention.

Even where manufacturers use the same M1–M6 naming system, verify the physical orientation shown in the applicable product manual.

Never cross-reference mounting position based on the code alone.

Compare the Picture, Not Just the Code

When changing manufacturers, obtain:

Existing Gearbox

The manufacturer's mounting-position diagram for the existing gearbox.

Proposed Replacement

The mounting-position diagram for the new gearbox.

Then compare:

• which surface is down,

• input-shaft direction,

• output-shaft direction,

• vertical/horizontal shaft orientation,

• motor position and

• mounting surface.

The correct replacement position is the one whose physical orientation matches the machine, even if its code differs from the original manufacturer's designation.

Why Mounting Position Changes Oil Quantity

Inside a gearbox, lubricant must reach the gears, bearings, and other components that depend on it.

When the housing is rotated, the internal oil level relative to those components changes.

As a result, a gearbox installed horizontally may require a different oil quantity from the same gearbox installed vertically.

NORD specifically notes that a change in installation position requires adjustment of oil quantity and can require additional measures.

This is why simply rotating a gearbox in the field without checking the manufacturer's documentation can create problems.

More Oil Is Not Automatically Better

A common misconception is:

“If we're unsure, we'll just put more oil in it.”

Too little lubricant can obviously create problems.

But excessive lubricant can also be undesirable.

Depending on gearbox design and speed, excess oil can contribute to:

• increased churning,

• additional heat,

• foaming,

• leakage,

• pressure issues and

• reduced efficiency.

Use the oil quantity specified for the actual gearbox and mounting position.

The Oil-Level Plug May Change Position

Many industrial gearboxes use a plug or sight device to establish the correct operating oil level.

When mounting position changes, the correct level-point location may also change.

For example, a housing may contain several plugged ports.

Only one may represent the proper oil-level location for a particular orientation.

Do not assume every side plug is an interchangeable level plug.

Use the manufacturer's mounting-position documentation.

The Drain Location Matters

The drain should allow lubricant to be removed effectively during maintenance.

Changing orientation can move the originally intended drain point:

• upward,

• sideways or

• into an inaccessible location.

A replacement gearbox may therefore require a different drain-port configuration.

Before ordering, check whether technicians will have practical access to:

• drain,

• fill,

• level check and

• sampling points.

A gearbox can technically fit the machine and still create a maintenance problem if those points become inaccessible.

Breather Position Is Especially Important

Gearboxes that use a breather must generally have the breather positioned appropriately for the installation.

A breather installed at what becomes the bottom of the housing is obviously not serving the same purpose as one located appropriately above the oil level.

When changing manufacturers, identify:

• where the breather should be,

• whether it ships installed,

• whether transport plugs must be changed and

• which ports apply to the selected orientation.

NORD's installation documentation explicitly connects installation position with the locations of vent, level, and drain plugs.

Mounting Position Can Affect Bearings

Certain orientations can change how bearings receive lubrication.

This can be particularly important in:

• vertical installations,

• high-speed input arrangements,

• upper bearing positions and

• specialized industrial gear units.

NORD notes that changing installation position can sometimes require measures such as encapsulated roller bearings.

That is a good reminder that mounting position can affect more than oil volume.

The gearbox should be configured for the actual orientation in which it will operate.

Horizontal vs. Vertical Gearbox Installation

One of the clearest distinctions is whether the gearbox shafts operate primarily:

horizontally

or:

vertically.

A gearbox originally built for horizontal service should not automatically be rotated into a vertical installation simply because the bolt pattern permits it.

Vertical configurations can affect:

• lubrication,

• bearing arrangements,

• seals,

• cooling,

• drywell arrangements and

• accessory locations.

Some gearbox families are explicitly available for multiple orientations, but the correct version still needs to be specified.

Mounting Surface and Mounting Position Are Not the Same Thing

This distinction is important.

Mounting Surface

The physical interface used to attach the gearbox.

Examples:

• foot mounted,

• flange mounted,

• shaft mounted.

Mounting Position

The orientation of the complete gearbox relative to gravity.

A gearbox can be:

foot mounted in one of several orientations

or:

flange mounted in one of several orientations.

NORD documentation, for example, provides M1–M6 positions for various foot- and flange-mounted configurations.

Do not confuse:

How is the gearbox attached?

with:

Which way is the gearbox oriented?

Both must be specified.

Shaft-Mounted Gearboxes Need the Same Attention

A hollow-shaft or shaft-mounted reducer may seem simpler because the driven shaft determines much of its physical position.

But mounting orientation still matters.

Check:

• hollow-shaft axis,

• input position,

• torque-arm position,

• breather location,

• oil level,

• backstop and

• lubrication requirements.

See Hollow-Shaft vs. Solid-Shaft Gearbox Replacement for the broader shaft-configuration comparison.

Bevel Gearboxes Can Make Orientation More Confusing

Right-angle and bevel-helical gearboxes can have more orientation possibilities because the input and output shafts are on different axes.

When comparing two manufacturers, identify:

• input direction,

• output direction,

• output side,

• mounting surface,

• shaft orientation and

• actual rotation.

Do not rely on a single photograph taken from one angle.

Use the manufacturer's dimensional and mounting-position diagrams.

Parallel-Shaft Gearboxes Also Need Product-Specific Verification

Even a seemingly straightforward parallel-shaft gearbox can have different mounting configurations.

NORD's MAXXDRIVE industrial gear units, for example, use six mounting positions and define them based on the specific housing and shaft arrangement. Its documentation notes that mounting surfaces and the meaning of particular positions can depend on whether the gearbox is a two-stage or three-stage parallel unit.

This is exactly why generic code matching can be risky.

Mounting Position Can Change Accessory Location

Industrial gearboxes may include:

• cooling fan,

• oil pump,

• filter,

• heater,

• temperature sensor,

• oil sight glass,

• backstop,

• breather,

• inspection cover,

• lubrication piping and

• condition-monitoring sensors.

Changing the gearbox orientation can move those components relative to the machine.

When replacing a gearbox, verify that accessories remain:

• functional,

• accessible and

• clear of surrounding structures.

Backstop Orientation Must Be Verified

If the gearbox prevents reverse rotation through a backstop, do not treat the backstop as separate from the orientation review.

Confirm:

• required output rotation,

• input rotation,

• backstop configuration and

• installation orientation.

A gearbox can mechanically fit the machine while having an incorrectly configured backstop.

That can prevent startup or create a serious drive-system problem.

Don't Determine Mounting Position From the Motor Alone

Looking at the motor can help understand the installation, but the gearbox position should be determined from the gearbox manufacturer's reference diagrams.

Two product families may place motors differently relative to the housing.

Use:

• shaft axes,

• mounting surfaces and

• manufacturer diagrams

as the primary reference.

A Practical Example

Suppose the existing reducer has:

• horizontal output shaft,

• horizontal input shaft,

• feet mounted on the floor,

• input located to the left,

• breather on top.

Its original manufacturer identifies this as:

M1

You are replacing it with another brand.

The new manufacturer's catalog has an M1 option.

Do not stop there.

Open the new mounting-position diagram.

Verify that its M1 actually shows:

• the same mounting surface down,

• the correct output orientation,

• appropriate input position and

• correct lubrication configuration.

If the matching physical orientation is called M3 by the new manufacturer, then M3 may be the proper replacement configuration even though the old gearbox was marked M1.

The machine orientation wins—not the old code.

What Information Should Be Collected From the Existing Gearbox?

Before contacting a replacement supplier, document:

• manufacturer,

• complete model,

• serial number,

• ratio,

• mounting position code if known,

• mounting arrangement,

• input orientation,

• output orientation,

• shaft positions,

• motor location,

• torque-arm location if applicable,

• breather position,

• fill location,

• oil-level location,

• drain location,

• cooling equipment,

• backstop and

• photographs from multiple sides.

If the existing dimensional drawing is available, include it.

Photograph All Six Sides When Possible

A single gearbox photograph may not reveal enough.

For a difficult replacement, photograph:

• input side,

• output side,

• front,

• rear,

• top and

• mounting/base area.

You are trying to preserve the actual installation geometry.

These photographs can make it much easier for a supplier to cross-reference a mounting position between manufacturers.

Use the Machine as the Reference

When documentation is unavailable, describe the physical orientation rather than guessing a code.

For example:

“Foot mounted. Output shaft horizontal. Motor/input on left side when viewed from driven equipment. Breather currently on top.”

That is more useful than:

“We think it is M2.”

A gearbox specialist can then compare the configuration against manufacturer diagrams.

Mounting Position and Gearbox Dimensions Work Together

Mounting position does not replace dimensional verification.

You still need to compare:

• bolt pattern,

• center height,

• output shaft,

• input connection,

• flange dimensions,

• overall envelope and

• clearances.

See Gearbox Replacement Dimensions: The Measurements That Determine Whether a Reducer Will Fit for the complete dimensional review.

A replacement must both:

fit the machine

and

operate correctly in its installed orientation.

Mounting Position and Motor Adapter Work Together

Changing gearbox brands can also change the input arrangement.

If the replacement uses a direct-mounted motor, verify:

• NEMA or IEC frame,

• motor adapter,

• pilot,

• bolt circle,

• shaft dimensions and

• overall motor position.

See NEMA vs. IEC Motor Adapters on Industrial Gearboxes.

This becomes particularly important if changing manufacturers moves the motor to a different side or changes the adapter geometry.

Mounting Position and Coupled Drives

For a separate-coupled gearbox, changing mounting position can alter the gearbox input-shaft centerline.

That can affect alignment with the existing motor.

Verify:

• input center height,

• horizontal shaft position,

• shaft-end spacing and

• coupling alignment.

What About Universal-Mount Gearboxes?

Some gearbox designs provide substantial mounting flexibility.

However, universal mounting should not automatically be interpreted as universal lubrication.

A housing may physically support several mounting surfaces while:

• oil quantity,

• plug positions,

• vent arrangement or

• accessories

still need to change for the selected installation.

Always check the applicable manufacturer's instructions.

What If the Gearbox Is Already Filled With Oil?

This is an important purchasing question.

Ask:

Is the replacement gearbox shipped with oil?

If yes:

Is it filled for the mounting position we specified?

If no:

What lubricant type and quantity are required for this exact orientation?

Do not assume the oil quantity for one mounting position applies to another.

What If You Need to Change the Mounting Position Later?

Do not simply rotate the gearbox.

Before changing the installed orientation, determine whether the manufacturer requires changes to:

• oil quantity,

• plugs,

• breather,

• bearings,

• seals,

• lubrication system,

• cooling system or

• other components.

NORD specifically warns that changing installation position without the necessary adjustments can lead to damage.

Mounting Position Is Especially Important for Obsolete Gearbox Replacement

An obsolete gearbox may use a mounting code from:

• an old catalog,

• discontinued product family or

• manufacturer that no longer supports the unit.

Do not spend too much time trying to force that historical code into a current manufacturer's catalog.

Instead reconstruct the installation.

Document:

• mounting surface,

• shaft orientation,

• motor position,

• lubricant ports,

• dimensions and

• application.

Then identify the modern gearbox configuration that recreates the required physical and functional orientation.

See How to Replace an Obsolete Gearbox When the Manufacturer No Longer Supports It for the broader replacement process.

Add Mounting Position to the Gearbox Asset Register

Your gearbox asset register should include more than a code.

Instead of:

Mounting position: M1

record:

Original manufacturer: ______
Manufacturer position code: M1
Mounting: Foot mounted
Output shaft: Horizontal
Input position: ______
Breather location: ______
Oil quantity: ______
Lubricant: ______
Drawing: Attached
Photos: Attached

That preserves the meaning behind the code.

If the plant later changes gearbox brands, the replacement can be cross-referenced much more safely.

Mounting Position Should Be Included in Standardization

If your plant is working toward gearbox standardization, include mounting orientation in the standardization effort.

Two gearboxes may share:

• manufacturer,

• series,

• size,

• ratio and

• shaft dimensions

while requiring different mounting-position configurations.

A spare gearbox strategy should account for whether a spare can be reconfigured safely between applications.

Before assuming one spare protects several machines, determine what is required to change:

• mounting position,

• oil quantity,

• breather,

• plugs,

• accessories and

• other configuration details.

Mounting Position Cross-Reference Checklist

When changing gearbox manufacturers, verify:

Existing Gearbox

• Manufacturer

• Complete model

• Serial number

• Existing mounting-position code

• Actual mounting surface

• Input orientation

• Output orientation

• Motor position

• Shaft direction

• Breather position

• Oil-level position

• Drain location

• Oil quantity

• Lubricant type

• Backstop

• Cooling system

• Installation photographs

Replacement Gearbox

• Manufacturer mounting-position diagram reviewed

• Physical orientation matched

• Mounting surface matched

• Input/output orientation verified

• Correct oil quantity specified

• Oil-level point identified

• Breather location correct

• Drain location accessible

• Fill location accessible

• Bearing configuration appropriate

• Backstop direction verified

• Cooling configuration appropriate

• Accessories clear surrounding equipment

• Dimensional drawing reviewed

What Should You Ask the Gearbox Supplier?

Rather than saying:

“Quote an M2 gearbox.”

send the existing information and ask:

“Please confirm the mounting position on your gearbox that corresponds to this physical installation.”

Include photographs and drawings.

Then ask:

“Please confirm the required oil quantity and the fill, drain, level, and breather locations for that mounting position.”

For a critical application, those questions are worth answering before the gearbox ships.

The Mounting Code Is Not the Specification

This is the central takeaway.

A mounting-position code is a manufacturer's shorthand for a physical gearbox orientation and associated configuration.

When replacing a gearbox with the same manufacturer and same product family, the existing code may be very useful.

When changing manufacturers, do not assume the shorthand transfers directly.

Instead cross-reference:

Actual machine orientation

to:

New manufacturer's mounting-position diagram

and then verify:

lubrication + plugs + bearings + accessories + rotation + physical fit.

That is how a mounting code becomes a reliable replacement specification rather than a potentially expensive assumption.

Need Help Cross-Referencing a Gearbox Mounting Position?

Industrial Gearbox Supply can help evaluate replacement options when changing gearbox manufacturers.

For the best starting point, provide:

• existing manufacturer,

• complete model number,

• serial number,

• ratio,

• mounting-position code if known,

• gearbox nameplate photograph,

• photographs from multiple sides,

• complete installation photograph,

• motor information,

• output connection and

• dimensional drawing if available.

If the original mounting code does not correspond directly to the replacement manufacturer's terminology, the physical installation can be used to identify the correct configuration.

Don't match the code. Match the orientation.

Sources

NORD DRIVESYSTEMS — Installation Positions / Nomenclature
NORD documentation identifies six installation positions, M1 through M6, and explains that mounting position affects oil quantity and the locations of the oil level, vent, and drain plugs.
https://www.nord.com/media/documents/bw/g1014_ie1_ie2_ie3_en_0621.pdf

NORD DRIVESYSTEMS — Selection Information
NORD describes mounting position as an important gearbox specification because it influences lubricant quantity and fill, drain, and vent locations.
https://www.nord.com/media/documents/bw/us_g1013_nordbloc_catalog_2719.pdf

NORD DRIVESYSTEMS — MAXXDRIVE Industrial Gear Units
Manufacturer documentation showing mounting-position arrangements for large industrial parallel-shaft gear units and the use of M1–M6 configurations.
https://www.nord.com/media/documents/bw/g1050_global_5060hz_en_2523.pdf

SEW-EURODRIVE — Industrial Gear Units
Manufacturer resources covering industrial gearbox mounting arrangements, lubrication, configurations, and application engineering.
https://www.sew-eurodrive.com/products/gear_units/industrial_gear_units/industrial_gear_units.html

Sumitomo Drive Technologies — Products
Manufacturer information covering industrial reducers, mounting configurations, lubrication, and replacement selection.
https://us.sumitomodrive.com/en-us/products

Flender — Industrial Gear Units and Applications
Manufacturer resources covering industrial gearbox configurations, vertical and horizontal applications, and application-specific mounting arrangements.
https://www.flender.com/