Expands and resizes the solid Teflon sealing rings on GM 8L90 clutch drums and shafts so the drum drops into its bore without shaving a ring.
If you are rebuilding a GM 8L90 out of a 2015-up Silverado, Sierra, Tahoe, Yukon, Escalade, Camaro or Corvette, the sealing rings are the part of the job that bites people. The 8L90 uses solid Teflon rings, not the scarf-cut rings you can hook together by hand, so every ring has to be stretched over a land to reach its groove and then shrunk back down before the shaft or drum goes into its bore. This kit is the bench tooling for that: a long tapered expander mandrel plus a set of sizing sleeves and cones, so the rings go on without a nick and come back to size before assembly.
The 8L90 is a clutch-to-clutch eight-speed with five clutches, and every one of them is applied by oil that has to cross a rotating joint. That joint is a sealing ring riding in a bore. Transmission Digest's teardown of the unit counts four sealing rings on the input shaft in front of the housing and three behind it, and two more ring grooves on the stator shaft, which is only a cover with a shaft on this design because the pump is mounted off-axis and chain driven. Each of those rings separates one clutch feed from the next. A ring that was stretched and left oversized will either refuse to let the part drop into its bore, or it shaves on the way in and leaks from day one.
A pressure leak at a ring looks a lot like a worn clutch, a sticking valve or a bad solenoid. Air-check each circuit with the unit apart: a ring that is sized and seated holds air with only a slight hiss, while a shaved or rolled ring blows straight through. Our 8L90 3-4 clutch failure guide walks through separating a leaking feed from burned frictions, and the 8L90 pump failure guide covers the no-move and low-pressure conditions that get blamed on rings when the pump is the real cause.
The kit is listed for the GM 8L90 eight-speed and is meant for the solid (non-scarf-cut) Teflon rings on its shafts and drums. The 8L90 and 8L45 share a layout, but ring diameters are not guaranteed to match across the two units or across every model-year update, so compare the sleeves against your shaft lands before you start. If you are not sure which unit you have, read the RPO code off the service parts label or send us the year and VIN. Parts for both units are on the 8L90 / 8L45 parts page.
The most common time to use this kit is during a full overhaul, so it pairs naturally with the 8L90 overhaul kit for 2015-2017. If a drum bore or ring land is damaged, replace the part rather than trusting new rings to seal it; we carry the 8L90 clutch drum for that.
| Fitment | |
| Function | |
| Kit contents | |
| Ring type | |
| Use |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
You can stretch them on, but they stay oversized and tend to shave when the drum or shaft goes into its bore. The resizer sleeve shrinks the ring back down so it slides home and seals.
A few minutes is enough for the Teflon to take a set. A slightly warm ring stretches and recovers more evenly than a cold one, so a cold shop makes the job harder.
The kit is listed for the 8L90. The 8L45 is a lighter version of the same design, but ring diameters can differ, so check the sleeves against your shaft lands before relying on it.
Transmission Digest's teardown of the 8L90 lists four sealing rings in front of the input housing and three behind it, with two more ring grooves on the stator shaft.
Use DEXRON HP, the only fluid GM approves for the 8L90. Mobil 1 Synthetic LV ATF HP is the DEXRON HP fluid GM names in its shudder service bulletin.
