Allison 1000 output shaft seal leak is the #1 cause of TES-295 puddles under your Duramax. Catch it early before the level drops too low.
Where the seal is
- Tail housing of the transmission
- Around the output yoke / driveshaft slip
- Visible from underneath
Symptoms of leak
- Fluid drip at rear of trans
- Wet spot on driveshaft yoke
- Low fluid level (intermittent)
- Sometimes weeping vs full drip
- Burning smell from exhaust contact
Why it leaks
Age:
- Stock seal lifespan: 100k-150k miles
- Rubber hardens and shrinks
Worn output bushing:
- Bushing wears, allows shaft wobble
- Wobble destroys seal lip
- Replacing seal without bushing = repeat leak in 5k miles
Worn output shaft slip yoke:
- Yoke surface gets grooved
- Grooves destroy new seal
- Replace yoke or polish if shallow
Diagnosis
- Park truck on cardboard overnight
- Confirm leak is from tail seal (not other leak above)
- Inspect yoke surface for grooves
- Check fluid level (low?)
Replacement parts
OEM tail seal:
- AC Delco 29521961
- $15-$30 part
Output bushing:
- $30-$60 part
- Always replace with seal
Slip yoke (if worn):
- $120-$250 used
- $300-$500 new
Fluid for top-off:
- 1-2 quarts TES-295
- $20-$40
Install
- Mark driveshaft to flange for indexing
- Disconnect driveshaft (4 strap bolts)
- Pull driveshaft yoke
- Pry old seal out
- Inspect bushing (drive out and replace if worn)
- Install new bushing (driver tool)
- Install new seal (seal driver)
- Slide yoke back in (lube splines with TES-295)
- Reinstall driveshaft and strap bolts (torque to 22 ft-lb)
- Top off fluid
Time and cost
DIY:
- Seal: $15-$30
- Bushing: $30-$60
- Tools (seal driver): $30-$60 one-time
- Fluid: $20-$40
- Time: 1-2 hours
- Total: $95-$190 with tools
Shop:
- Parts: $65-$130
- Labor: $200-$400
- Total: $265-$530
If slip yoke is also worn
- Replace yoke at same time
- Add $120-$500 to parts
- Avoid repeat leak in 6 months
What not to do
- Do not just replace seal without checking bushing (leak returns)
- Do not use Dexron VI top-off (wrong fluid for Allison)
- Do not over-tighten strap bolts (warps yoke ear)
Need Allison 1000 tail seal, slip yoke, or TES-295 fluid? Shop our Allison catalog. OEM seals, slip yokes, TES-295 fluid. Free shipping over $70.
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