What This Seal Does
The rear main seal closes the gap where the crankshaft exits the block at the flywheel end. On the ISX-series that means a PTFE lip riding directly on the crank sealing surface, holding back crankcase oil under the pressure and heat the platform makes at highway load. It is the last barrier between the oil pan and the clutch or flex plate.
PTFE seals do not get installed like an old rubber lip seal. They ship dry with a plastic installation sleeve that centers the seal and protects the lip. Do not oil or grease the lip, do not remove the sleeve before the seal is on the crank, and do not spin the crank before it is seated. Skipping any of those steps is the usual cause of a repeat leak.
Failure shows up as oil weeping from the bottom of the bellhousing, oil film on the flywheel or clutch disc, and clutch chatter or slip that gets worse under load. On automated manuals you may see it as fluid on the input shaft. A hard leak here means the transmission is coming back out, so plan the labor once.
Why These Numbers Cross
Cummins revised this seal through the ISX production run. 3680095, 4101422 and 4926527 are earlier and superseding Cummins numbers for the same rear crank sealing position on the ISX / QSX / X15 block, with 4962603 as the current headline reference. The bore diameter, shaft ride surface and wear-sleeve arrangement are common across the family, which is why one part covers the range.
136131 is the PAI catalog number for the same application. Aftermarket suppliers index the Cummins part into their own numbering, so a shop that orders through PAI will have that number on the invoice while the box on the shelf traces back to the same seal position. All of those numbers are listed here for identification only.
Supersessions matter on this part. If your old seal carries one of the earlier Cummins numbers, that does not automatically mean the current design drops in the same way — some revisions changed installation depth or the sleeve. Check your engine serial number against the service data before you order, and read the number stamped or printed on the seal you pulled out.
Before You Order
Pull the engine serial number off the dataplate, not the truck VIN plate alone, and confirm the ISX, ISX12, ISX15, QSX15 or X15 build. These engines went into Cascadia, Columbia, Coronado, Kenworth, Peterbilt, ProStar, LT, Western Star and Volvo chassis, so the truck badge tells you very little about which rear seal revision the block takes. Cross-reference is a starting point; fit is confirmed by serial number or by the number on the old seal.
While the transmission is out, inspect the crankshaft sealing surface for a groove worn by the old lip, and check the flywheel housing bore for scoring or corrosion. A grooved crank will chew a new PTFE lip in short order. Also check crankcase breather function — a plugged breather raises case pressure and pushes oil past a good seal, and it will do the same to the new one.
4962603 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to 4962603. Use them to identify the part — then confirm the exact fit by VIN or the number stamped on your old unit before you order. An interchange is a starting point, not a fitment guarantee.
| Brand / Line | Cross-Reference Numbers |
|---|---|
| Cummins | 3680095, 4101422, 4926527 |
| PAI | 136131 |
Frequently asked questions
Is 4962603 the same seal as 4926527?
They cover the same rear crankshaft sealing position on the Cummins ISX / QSX / X15 platform, and 4962603 is the current reference number. Cummins revised this seal during the production run, so earlier numbers can carry different installation details. Verify against your engine serial number before ordering.
Can I install this rear main seal without pulling the transmission?
No. The seal sits behind the flywheel at the rear of the block, so the transmission, clutch or flex plate and flywheel all have to come off to reach it. Since the driveline is already apart, inspect the crank sealing surface and the flywheel housing bore at the same time.
Do I lubricate the lip on a PTFE rear crank seal?
No. Install it dry. PTFE lips are shipped on a plastic sleeve that centers the seal and protects the lip during installation — leave the sleeve in place until the seal is on the crank, and do not rotate the crankshaft until the seal is fully seated. Oil or grease on the lip is a common cause of a comeback leak.
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