Automatic Transmission Power Take Off (PTO) Gasket (PartTerminologyID 2324): Where Transmission Model and PTO Opening Profile Determine Whether the Unit Seals
Written by Arthur Simitian | PartsAdvisory
PartTerminologyID 2324, Automatic Transmission Power Take Off (PTO) Gasket, is a gasket that seals the power take off unit to the automatic transmission housing at the PTO mounting opening. That definition correctly identifies the sealing interface. It does not specify the transmission model designation, the PTO opening profile and bolt pattern, the gasket material, the ATF compatibility of the material, the gasket thickness, whether the PTO opening is on the driver side or passenger side of the transmission, whether the opening is a standard SAE PTO opening or a proprietary transmission-specific opening, what the bolt hole count and bolt circle are, or whether the gasket seals against ATF from the main transmission circuit or against a separate PTO cavity fluid. A listing under PartTerminologyID 2324 that provides vehicle year, make, and model without the transmission model designation, the PTO opening profile, and the sealing surface specification cannot be evaluated by any technician who has the PTO on the bench and needs to confirm the replacement gasket matches the mounting face.
For sellers, the automatic transmission PTO gasket is a component at the intersection of two specialized markets that rarely overlap: the automatic transmission service market and the power take off equipment market. A buyer ordering this gasket is typically a commercial vehicle technician, a fleet maintenance specialist, or a vocational equipment installer who is servicing a truck-mounted PTO on a vehicle with an automatic transmission. That buyer is not a passenger car do-it-yourself buyer browsing by vehicle model. They know the transmission designation, they know the PTO model, and they need a listing that confirms the gasket fits the specific transmission-to-PTO interface without ambiguity.
The most common automatic transmissions equipped with PTO openings are heavy-duty units including the Allison 1000, 2000, and 3000 series, the Ford 5R110W TorqShift, the GM 6L90, and several ZF automatic transmissions used in medium-duty commercial vehicles. Each of those transmissions has a PTO opening with a specific bolt pattern and profile, and the gasket for each is unique to that transmission's opening geometry. A listing that does not specify the transmission model and the PTO opening profile cannot be verified against any of those applications.
For sellers, the listing under this PartTerminologyID is only useful if it specifies the transmission model, the PTO opening side, the SAE or proprietary opening class, the bolt hole count and pattern, the gasket material and ATF compatibility, and the sealing method. Without those six attributes, the listing serves only buyers who are replacing an identical original gasket and are matching by measurement alone.
What the Automatic Transmission PTO Gasket Does
Sealing the PTO mounting interface against ATF leakage
The PTO unit mounts to the side of the automatic transmission housing through a machined opening that provides access to a drive gear inside the transmission. When the PTO is engaged, the drive gear inside the transmission meshes with the PTO's input gear and transfers torque out through the PTO unit. The PTO mounting opening is sealed by a flat gasket compressed between the PTO housing mounting face and the transmission housing machined face.
The gasket must seal against the ATF pressure at the PTO opening. On most automatic transmissions with PTO openings, the PTO opening is in the transmission's main fluid circuit and is continuously bathed in ATF at operating line pressure. The gasket is therefore a pressure-loaded static seal rather than a simple static face seal at atmospheric pressure. The gasket material must maintain its sealing contact under the thermal cycling, the vibration, and the ATF pressure that the PTO opening experiences throughout the transmission's operating range.
A failed PTO gasket produces an ATF leak at the side of the transmission at the PTO mounting face. On a truck in commercial service, a PTO gasket leak is not a driveway inconvenience: it is a fluid loss that can deplete the transmission fluid level rapidly if the PTO is operated at high duty cycles, leading to transmission damage from fluid starvation. A leak that develops under PTO operation and seals when the PTO is disengaged, because the drive gear disengages and the internal pressure at the opening drops, is characteristic of a PTO gasket that has lost sealing contact under the higher-pressure engaged condition.
The SAE PTO opening standard and proprietary openings
The Society of Automotive Engineers defines standard PTO opening profiles for transmission-mounted PTOs. The most common SAE PTO openings are the SAE two-bolt, six-bolt, and eight-bolt patterns. Each SAE pattern has a defined bolt circle, bolt hole size, drive opening diameter, and face geometry. A gasket designed for one SAE pattern will not fit a different SAE pattern even if the bolt counts are the same, because the bolt circles and the central opening diameters differ between patterns.
Some automatic transmissions use proprietary PTO openings that do not conform to any SAE standard. The Allison 1000 series PTO opening is a proprietary six-bolt pattern specific to Allison transmissions. The bolt circle and the central opening profile of the Allison opening do not match any SAE standard pattern. A gasket described only as a six-bolt PTO gasket cannot be verified against an Allison 1000 opening without stating that it is specifically the Allison 1000 proprietary pattern.
The listing must specify whether the PTO opening is an SAE standard pattern and which SAE class applies, or whether it is a proprietary opening and which transmission model the proprietary pattern is specific to.
The PTO opening side: driver side versus passenger side
Many automatic transmissions with PTO capability have PTO openings on both the driver side and the passenger side of the transmission housing. The two openings may have the same bolt pattern, but they are at different positions on the housing and may face different directions. A PTO unit installed on the driver-side opening is oriented differently from a PTO unit on the passenger-side opening, which affects the PTO's output shaft direction and the plumbing connections to the driven equipment.
The gaskets for driver-side and passenger-side openings on the same transmission are typically the same part because the opening profiles are identical. However, if the two openings have different profiles on a specific transmission model, the listing must specify which opening side it covers. Even when the gaskets are identical between sides, the listing should state which side is covered to confirm that the buyer is ordering for the correct opening.
ATF pressure at the PTO opening and gasket material requirements
The ATF pressure at the PTO opening varies by transmission model and by the transmission's operating range. In drive ranges at line pressure, the pressure at the PTO opening can exceed 150 psi on some Allison and ZF transmissions. The gasket material must maintain sealing contact at this pressure without extruding out of the joint or compressing beyond its elastic recovery range.
Compressed fiber gaskets, also called paper or cellulose gaskets, are the most common material for PTO gasket applications in automatic transmissions. The fiber material compresses uniformly under the bolt torque to fill any minor surface irregularities in the mating faces and maintains sealing contact under the thermal cycling and pressure cycling of normal operation. The fiber formulation must be compatible with the ATF chemistry: older mineral-oil ATF compatible gaskets may swell, soften, or degrade in modern full-synthetic Allison TES 295, Dexron-VI, or ZF Lifeguard 6 formulations.
Molded rubber gaskets with a steel carrier are used on some proprietary PTO openings where the face geometry requires a formed seal rather than a flat cut gasket. The molded rubber profile matches a specific housing geometry and cannot substitute for a flat fiber gasket or vice versa.
PTFE-coated metal gaskets are used on high-pressure PTO openings where the ATF line pressure exceeds the capacity of a compressed fiber gasket. These gaskets are thinner than fiber gaskets and require precise bolt torque to achieve the correct compression without crushing the PTFE coating.
The Specifications That Determine Correct Gasket Fitment
Transmission model designation
The transmission model is the primary fitment attribute. For the Allison 1000, specify the generation (first-generation, second-generation) because the PTO opening profile changed between generations. For the Allison 2000 and 3000 series, specify the series number and the output shaft configuration if the PTO opening profile varies by configuration. For the Ford 5R110W, specify the model year range because the PTO opening profile changed during production. For ZF transmissions, specify the complete ZF designation including the variant suffix.
PTO opening class: SAE or proprietary
Specify SAE two-bolt, SAE six-bolt, SAE eight-bolt, or the proprietary designation with the transmission model. Include the SAE class number if applicable: SAE Class I, II, or III PTO openings differ in torque rating and bolt pattern even within the same bolt count.
Bolt hole count, bolt circle diameter, and central opening diameter
All three must be stated. The bolt hole count and the bolt circle diameter together define the pattern. The central opening diameter confirms that the PTO drive gear engagement bore is correctly sized for the PTO input gear tooth envelope. A gasket with the correct bolt pattern but the wrong central opening diameter will either block part of the drive gear or leave an unsealed gap around the gear.
Gasket material and ATF compatibility
State the material and the ATF formulations the material is compatible with. Include the Allison TES specification, the Dexron specification, and the ZF Lifeguard specification as relevant to the transmission application.
Gasket thickness
The gasket thickness determines the compressed joint height and the engagement depth of the PTO drive gear with the transmission internal gear. A gasket that is thicker than the original specification increases the center distance between the PTO input gear and the transmission drive gear, which reduces the tooth contact depth and may produce noise or accelerated gear wear. A gasket that is thinner reduces the center distance and may prevent the PTO housing from fully seating against the transmission face.
Why This Part Generates Returns
Buyers order the wrong automatic transmission PTO gasket because:
the transmission model is not specified and the buyer's transmission uses a proprietary opening that differs from the SAE standard pattern
the SAE opening class is not stated and the buyer receives a Class I gasket for a Class II opening with a different bolt circle
the generation or production year of the transmission is not stated and the PTO opening profile changed mid-production on the specific transmission model
the gasket material is incompatible with the synthetic ATF formulation specified by the transmission manufacturer and degrades under pressure cycling
the central opening diameter is not stated and the gasket blocks part of the drive gear tooth profile, reducing torque capacity at the PTO drive interface
the gasket thickness is not stated and the replacement is thicker than OE, increasing the center distance between the PTO and transmission gears and producing engagement noise
Status in New Databases
PIES/PCdb: PartTerminologyID 2324, Automatic Transmission Power Take Off (PTO) Gasket
PIES 8.0 / PCdb 2.0: No change
Top Return Scenarios
Scenario 1: "SAE six-bolt gasket received, Allison 1000 uses proprietary six-bolt, bolt circle does not match"
The buyer's Allison 1000 transmission uses a proprietary six-bolt PTO opening. The listing specified a six-bolt PTO gasket without stating whether it was the Allison proprietary pattern or an SAE standard. The buyer received an SAE six-bolt gasket. The bolt circles are different between the SAE pattern and the Allison proprietary pattern. The bolts do not align.
Prevention language: "PTO opening type: [Allison 1000 proprietary six-bolt / SAE six-bolt Class II / other]. Verify your transmission uses this specific opening pattern before ordering. The Allison 1000 proprietary PTO opening is not interchangeable with any SAE standard six-bolt pattern. A gasket labeled only as six-bolt PTO gasket may be either pattern. Confirm the transmission model and opening type."
Scenario 2: "Gasket thickness 0.5mm thicker than OE, PTO engagement noise after installation"
The replacement gasket is 0.5mm thicker than the original. The increased thickness increases the center distance between the PTO input gear and the transmission drive gear by 0.5mm. At this center distance, the tooth contact ratio drops below the designed value and the gear mesh produces a rattle under PTO engagement load.
Prevention language: "Gasket thickness: [X.X]mm. Verify this matches your original gasket thickness. A PTO gasket that is thicker than the OE specification increases the center distance between the PTO input gear and the transmission drive gear. An increased center distance reduces tooth contact depth and may produce gear noise under PTO load."
Scenario 3: "Fiber gasket incompatible with Allison TES 295 synthetic, extruded at line pressure within 10,000 miles"
The replacement gasket is a standard fiber formulation rated for Dexron-III. The Allison 1000 operates on Allison TES 295 approved full-synthetic ATF. The TES 295 synthetic softened the fiber binder in the gasket material, causing it to extrude at line pressure within 10,000 miles of operation.
Prevention language: "Gasket material: [Allison TES 295 compatible fiber / Dexron-VI compatible fiber / standard fiber Dexron-III only]. Verify the gasket material is rated for your transmission's ATF specification. Allison transmissions require TES 295 approved fluid and compatible gasket materials. Standard fiber gaskets rated for Dexron-III will extrude under line pressure when exposed to TES 295 full-synthetic formulations."
Scenario 4: "Central opening too small, drive gear teeth clipped by gasket, torque capacity reduced"
The replacement gasket's central opening diameter is 4mm smaller than the original. The gasket material overlaps the outer tooth tips of the transmission drive gear. The PTO cannot be fully engaged because the gasket material resists the gear mesh. Forcing engagement shreds the gasket material into the ATF circuit.
Prevention language: "Central opening diameter: [X.X]mm. Verify this diameter clears the full tooth circle of the transmission's PTO drive gear before installing. A central opening that is smaller than the drive gear tooth circle will block engagement and will shred gasket material into the ATF circuit when engagement is forced."
Scenario 5: "First-generation Allison 1000 gasket received, vehicle has second-generation with updated opening profile"
The Allison 1000 PTO opening profile was updated between the first and second generation of the transmission. The listing specified the Allison 1000 without noting the generation. The buyer received the first-generation gasket. The second-generation opening has an additional alignment pin bore that the first-generation gasket does not have, which prevents the gasket from seating flush.
Prevention language: "Transmission generation: [Allison 1000 first generation / Allison 1000 second generation]. The Allison 1000 PTO opening profile changed between generations. Verify your transmission's production date and generation before ordering. The second-generation opening includes an alignment pin bore that requires the correct generation gasket."
What to Include in the Listing
Core essentials
PartTerminologyID: 2324
component: Automatic Transmission PTO Gasket
transmission manufacturer and model designation (mandatory)
transmission generation or production date range when opening profile changed (mandatory)
PTO opening type: SAE standard class or proprietary designation (mandatory)
PTO opening side: driver side, passenger side, or both (mandatory)
bolt hole count (mandatory)
bolt circle diameter in inches or mm (mandatory)
central opening diameter in mm (mandatory)
gasket material (mandatory)
ATF compatibility specification: Allison TES, Dexron, ZF Lifeguard, or other (mandatory)
gasket thickness in mm (mandatory)
quantity: 1
Fitment essentials
year/make/model/submodel for commercial vehicle applications
transmission model designation (primary fitment attribute)
transmission generation or production date range
PTO model designation when the gasket is specific to a PTO model as well as the transmission opening
Dimensional essentials
bolt circle diameter in mm
bolt hole count and bolt hole diameter
central opening diameter in mm
gasket outer profile dimensions in mm
gasket thickness uncompressed in mm
alignment pin bore location if present
Image essentials
gasket in isolation showing bolt holes, central opening, and full profile
both sides of the gasket if different surface treatments are applied to each face
transmission housing PTO opening shown with bolt pattern and central opening visible
PTO unit mounting face shown for context
gasket thickness callout on edge view
Catalog Checklist for ACES/PIES Teams
PartTerminologyID = 2324
require transmission model designation (mandatory)
require transmission generation or production date range (mandatory)
require PTO opening type: SAE class or proprietary (mandatory)
require bolt hole count and bolt circle diameter (mandatory)
require central opening diameter (mandatory)
require gasket material with ATF compatibility specification (mandatory)
require gasket thickness (mandatory)
do not apply to manual transmissions: PartTerminologyID 2324 is specific to automatic transmissions; manual transmission PTO gaskets are a separate PartTerminologyID
differentiate from PTO gasket set (PartTerminologyID varies): a PTO gasket set may include the transmission mounting gasket plus the PTO housing cover gasket and internal gaskets; PartTerminologyID 2324 covers only the transmission-to-PTO mounting gasket
differentiate from transmission pan gasket (PartTerminologyID varies): the pan gasket seals the bottom oil pan; the PTO gasket seals the side-mounted PTO opening; both are transmission gaskets but at different locations with different profiles
differentiate from automatic transmission differential carrier gasket (PartTerminologyID 2312) and differential cover gasket (PartTerminologyID 2316): those gaskets are at the differential end of a transaxle; this gasket is at the PTO opening on the side of a longitudinal automatic transmission in a commercial vehicle application
flag SAE versus proprietary opening as mandatory: a gasket labeled only by bolt count without specifying SAE class or transmission-specific proprietary pattern cannot be verified for fitment
flag ATF compatibility as mandatory: TES 295 synthetic incompatibility with standard fiber gasket materials produces extrusion at line pressure in commercial duty cycles
flag central opening diameter as mandatory: a gasket that partially blocks the drive gear tooth circle shreds under forced engagement and contaminates the ATF circuit
FAQ (Buyer Language)
How do I identify the SAE PTO opening class on my transmission?
The SAE PTO opening class is typically stamped on the transmission housing near the PTO opening or is listed in the transmission service manual under PTO provisions. If neither is available, measure the bolt circle diameter of the PTO opening bolts and cross-reference to the SAE PTO standard: SAE Class I has a bolt circle of approximately 4.50 inches, Class II approximately 6.50 inches, and Class III approximately 7.25 inches. The Allison 1000 proprietary six-bolt opening has a bolt circle that differs from all three SAE classes. If the bolt circle does not match any SAE class, the opening is proprietary and the transmission model is the required identification.
Why does PTO gasket thickness matter for gear engagement?
The PTO gasket is sandwiched between the PTO housing mounting face and the transmission housing face. The gasket thickness sets the gap between the two faces, which in turn sets the center distance between the PTO's input gear and the transmission's internal drive gear. The center distance is engineered to produce the correct tooth contact ratio between the two gears at the designed backlash. A thicker gasket moves the PTO body away from the transmission, increasing the center distance and reducing the tooth contact depth. A thinner gasket moves the PTO body closer to the transmission, reducing the center distance below the designed backlash and potentially causing the gear teeth to bind. Always match the original gasket thickness.
My PTO gasket leaks only when the PTO is engaged. Is that a gasket issue or a PTO issue?
A leak that appears only under PTO engagement and stops when the PTO is disengaged is consistent with a gasket that has lost sealing contact under the higher ATF line pressure that appears at the PTO opening when the drive gear is engaged. The ATF line pressure at the PTO opening increases when the transmission is in a drive range and the PTO is engaged because the opening is in the main fluid circuit. A gasket that seals at idle line pressure but not at drive range line pressure is typically a gasket that has partially extruded from the joint or that has compressed beyond its elastic recovery range. Replace the gasket with a material rated for the full line pressure specification of the transmission.
Can I reuse the original PTO gasket if the PTO was removed for inspection only?
Compressed fiber gaskets that have been in service should not be reused after removal. The compressed fiber cannot recover to its original thickness, which means the reinstalled gasket will produce a thinner joint than the designed specification and may not achieve the required sealing contact pressure at the specified bolt torque. A new gasket of the correct material and thickness should be installed whenever the PTO is removed from the transmission, regardless of the reason for removal.
The PTO mounting bolts are metric but my transmission is domestic. Is that correct?
Some domestic automatic transmissions use metric fasteners at the PTO opening even though the vehicle is domestically produced, because the transmission design was sourced from or influenced by a European transmission manufacturer. The Allison 1000 and several GM six-speed automatic transmissions use metric fasteners at the PTO opening. Verify the bolt thread specification before sourcing replacement bolts or applying torque specifications. Applying inch-pound torque specifications to metric bolts of the same nominal head size will either under-torque or over-torque the joint depending on the pitch difference.
Cross-Sell Logic
PTO Gasket Set (PartTerminologyID varies: if the PTO internal cover gaskets and housing gaskets require replacement at the same service event as the mounting gasket, a complete PTO gasket set covering all positions is more efficient than ordering the mounting gasket alone)
Automatic Transmission Fluid (the ATF is inspected and topped up whenever the PTO is removed; if the fluid is contaminated or degraded, the full fluid service is performed at the same event)
PTO Input Shaft Seal (the PTO input shaft seal at the transmission mounting face is adjacent to the mounting gasket and is replaced if it shows any weeping at the same service event)
PTO Mounting Bolt Set (if the mounting bolts are corroded, stretched, or have damaged threads, replacement bolts of the correct thread specification and torque rating are sourced before reinstallation)
Transmission Filter (if the PTO gasket failure allowed ATF to leak externally or allowed external contamination to enter the PTO opening, the ATF filter is replaced at the same service event)
Frame as "the PTO gasket seals the opening where the PTO takes power from the transmission. The ATF lubricates the drive gear the PTO engages through that opening. The PTO input shaft seal seals the shaft that exits the PTO through the same interface. The mounting bolts clamp the gasket that seals everything."
Final Take for PartTerminologyID 2324
Automatic Transmission PTO Gasket (PartTerminologyID 2324) is a commercial vehicle component where the buyer population is technically specific, the application population is narrow, and the consequences of a wrong gasket are felt in a commercial duty cycle where a leaking PTO interface can deplete the transmission fluid level under sustained operation. The two return drivers that dominate this PartTerminologyID are the SAE-versus-proprietary opening confusion and the ATF chemistry incompatibility of the gasket material, and both are prevented by two attributes that most listings omit.
The SAE-versus-proprietary opening distinction prevents the buyer from receiving a generic six-bolt or eight-bolt gasket that looks correct but has a bolt circle or central opening that does not match the specific transmission's machined face. The ATF compatibility specification prevents the buyer from installing a standard fiber gasket in a TES 295 or Dexron-VI application where the gasket material will extrude at line pressure and contaminate the ATF circuit with fiber debris.
State the transmission model and generation. State the SAE class or proprietary opening designation. State the bolt circle diameter and central opening diameter. State the gasket material and ATF compatibility. State the gasket thickness. That is the same listing strategy as every other PartTerminologyID in this series: the generic PartTerminologyID requires specific attributes at every level to become a listing buyers can act on without guessing. For PartTerminologyID 2324, the commercial technician ordering this gasket already knows their transmission model and their PTO model, and a listing that does not match that specificity wastes the expertise they brought to the search.