Top 5 Signs Your Allison Transmission Is About to Fail

If you drive a Duramax-powered Chevy or GMC truck, your Allison transmission is the last thing you want leaving you stranded. Catching problems early saves tow fees, downtime, and lost loads. Below are the five warning signs we see most often in the shop, what causes them, and how to fix the root issue before it becomes a full rebuild.

1. Delayed or Slipping Shifts

A lazy 1-2 or 2-3 shift usually points to worn C3 and C4 clutches or a scored input shaft. Upgrading to a stronger billet input shaft plus new frictions restores crisp gear changes and keeps the power flowing.

2. Overheating Under Light Load

If temps climb even when empty, the torque-converter lock-up clutch is on its way out. Our built Allison units run cooler thanks to upgraded converters and better fluid flow.

3. Excessive Metal in the Pan

Finding silver flakes during a service means thrust washers and stock shafts are grinding themselves away. A DIY master rebuild kit gives you every hard part and gasket needed to stop the carnage before it spreads.

4. Erratic Lock-Up or TCC Codes

Intermittent lock-up or limp-mode codes often track back to weak trim valve springs. Our Mike L high-capacity springs keep converter pressure stable so the TCC stays locked when commanded.

5. Hard Downshifts or Clunk on Coast

Harsh coast-downshifts signal the C3/C5 apply pistons are leaking. The C3 oiler kit improves clutch feed oiling, extends clutch life, and smooths every gear change.

Ignore these signs and expect a tow bill plus a second rebuild within twelve months. Our Stage 1 and Stage 2 built Allisons are tested to 750 HP and 850 HP, ready for tuned or heavy-haul trucks.

FAQS

Q: Is rebuilding my Allison cheaper than buying built?
A: Up front, yes, but once you add tow fees, downtime, and the chance of a second failure, a built unit is the better value.

Q: What fails first in most Allisons?
A: C3 and C4 clutch packs, the torque-converter lock-up clutch, and the input shaft.

Q: How much power can a stock Allison handle?
A: Around 450 HP at the tire. Our Stage 1 handles 650 HP, Stage 2 handles 850 HP.

Q: Do you offer installation?
A: Yes. In-house install with hot flush and adaptive-learn reset is $1,200. Shipping both ways is available if you’re outside California.

Comment Post Comment