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