Transmission Seal Kit: Complete Replacement Guide

Trans seals are cheap but critical. Worn seals leak fluid, allow contamination, and lose hydraulic pressure. Here's the complete seal kit guide.

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What's in a transmission seal kit

External seals:

  • Front pump seal (where torque converter shaft enters)
  • Rear output shaft seal
  • Selector shaft seal
  • Speedometer/VSS seal (if applicable)
  • Servo cover seal
  • Modulator seal (if applicable)

Internal seals (master seal kit):

  • All internal o-rings
  • All sealing rings (teflon)
  • All gaskets
  • Pump body o-rings
  • Clutch piston seals
  • Servo piston seals

What's typically NOT in a seal kit:

  • Bushings (separate kit)
  • Bands (separate)
  • Friction packs (separate)
  • Filters (separate)

When to replace seals

Mandatory at rebuild:

All seals replaced during any rebuild.

Symptom-based:

  • External leak from front of trans: front pump seal
  • External leak from rear: output shaft seal
  • External leak around selector: selector shaft seal
  • External leak from servo cover: servo cover seal
  • Internal pressure loss: internal seals (rebuild)

Mileage-based:

  • Front pump seal often fails at 100K+ miles
  • Output shaft seal at 150K+ miles
  • Other external seals as they show wear

Brand recommendations

Quality OEM-equivalent:

  • ACDelco
  • Motorcraft
  • Mopar (Cummins applications)

Quality aftermarket:

  • Transtec (industry standard for gaskets and seals)
  • Wix
  • National Seal

Premium:

  • BORG-WARNER
  • Specific manufacturer seal kits (Sonnax, etc.)

Avoid:

  • Generic eBay seal kits
  • Unmarked brands
  • Cheap "deluxe" packages

Cost summary

External seal replacement only:

  • Front pump seal: $5-15
  • Rear output shaft seal: $5-15
  • Selector seal: $3-10
  • Servo cover seal: $5-15
  • DIY: $20-60 in parts
  • Labor: varies by which seal (front pump = trans must come out)

Complete external seal set:

  • $40-80 typically

Master internal seal kit:

  • $80-200 typically
  • Done at rebuild only (trans must be torn down)

Standalone external seal jobs:

  • Front pump seal alone: trans must come out, $400-800 labor
  • Rear output seal: trans stays in, $150-300 labor
  • Selector seal: usually accessible, $80-200 labor

Need transmission seals? Shop our seal catalog. Quality seal kits for every common transmission. Free shipping over $70.

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