5L50E Overhaul Kit 1999-10

A Cadillac CTS, STS, SRX or XLR, or a BMW 3 Series, 5 Series, X5 or Z3, with the GM five-speed that is dripping from the pan, slipping when hot or slow to engage after a cold start is a candidate for a full reseal. This overhaul kit, listed under part number K41900JX, is the gasket and seal set for 1999-2010 5L40E and 5L50E transmissions. It is a no-pistons kit: you get the paper gaskets, rubber lip seals, O-rings, pan gasket, metal-clad seals and the sealing ring set, and you reuse the clutch pistons if they pass inspection.

What an overhaul kit does in a 5L50E

The 5L40E and the heavier 5L50E are Strasbourg-built, rear-drive five-speeds that use a Ravigneaux planetary set, several hydraulic clutches and one-way sprags to make five forward ratios, with a torque converter clutch for the upper gears. Each clutch is applied by fluid pressure on a piston, and that fluid has to travel from the valve body through the case, support and shafts into spinning drums. Sealing rings bridge those rotating joints, and lip seals and O-rings hold pressure at each piston and passage. Heat and mileage harden the rubber and wear the rings, so apply pressure leaks away before it clamps the clutch pack. The result is slipping, flare between gears and slow engagement even when the frictions themselves are not finished. A reseal restores the hydraulic side of the unit; the case and pan gaskets and metal-clad seals stop the external leaks.

Symptoms a reseal addresses

• ATF leaking at the pan, front pump seal, rear output seal or the case connector.
• Shift flare or slip that appears once the fluid reaches operating temperature.
• A long pause before Drive or Reverse engages after the car sits overnight.
• Converter lockup that slips or will not apply when the feed circuit is losing pressure.
• Keep in mind this unit is also known for valve body bore wear and solenoid faults, which cause harsh or slipping shifts that look like seal problems. Rule those out first.

How to confirm before you order

Read codes and watch live data for commanded gear, slip and temperature. Put a gauge on the line pressure tap: low pressure at idle points toward the pump or a big internal leak, while pressure that drops only in one range points at that clutch circuit. Our line pressure guide explains the test, and the transmission slipping diagnosis guide covers what else to rule out. Pull the pan as well. Dark fluid that smells burnt and a pan full of friction material mean the clutches are gone, and a reseal alone will not save the unit.

Fitment

The listing covers 5L40E and 5L50E transmissions from 1999 through 2010 (it also names the 4L40E), in select BMW and Cadillac models. Documented 5L50 applications include the 2004-2006 Cadillac XLR and SRX, the 2005-2006 STS, the 2001-2006 BMW 325xi and 330xi and the 2001-2004 X5 3.0d; the lighter 5L40E went into the CTS, STS, SRX, Solstice, Sky and BMW E46 and E39 cars. The kit photo is a representative image. Pan and case gasket style can vary by year, so read the ID tag on the left rear of the case above the pan rail before ordering, or send us your year and VIN. Every part we carry for this transmission is on the 5L50E parts page.

Install notes

• Lay the new seals out against the old ones before assembly so each one goes to the right bore.
• Soak lip seals and O-rings in clean ATF and use assembly gel on the sealing rings so they stay centered as the shafts slide in.
• Because this kit has no pistons, inspect each piston's bonded lip for cuts, hardening or swelling. A damaged piston has to be replaced, not reused.
• Air-check each clutch once assembled: you want a sharp apply and release with no hissing.
• Worn frictions mean you need the 5L50E master rebuild kit, and a scored pump should be swapped for a 5L50E pump before the unit goes back in.
• Fit a new filter and pan gasket with the 5L40E/5L50E filter and pan gasket kit, fill with the ATF your vehicle specifies and set the level hot at the check plug per the factory procedure.
• Clear the transmission adaptive values with a capable scan tool and drive through every gear so shift timing relearns.

Does this kit include pistons or clutch plates?

No. It is a no-pistons overhaul kit with gaskets, lip seals, O-rings, the pan gasket, metal-clad seals and sealing rings. Frictions, steels and pistons are separate.

Will it fit both the 5L40E and the 5L50E?

Yes. It is listed for 1999-2010 5L40E and 5L50E transmissions, which share their sealing locations. Confirm your unit from the ID tag on the case.

How do I know if my Cadillac has a 5L50E or a 5L40E?

Read the ID tag on the left rear of the case above the pan rail. Transmission Digest notes the 5L50E was used in Cadillacs only with the 4.6-liter V8.

What fluid goes back in after the rebuild?

Use the ATF your vehicle's manual specifies and check the level hot at the fill plug. BMW and Cadillac fill procedures differ, so follow the factory procedure for your car.

Will a reseal fix harsh shifts?

Only if they come from leaking circuits. Valve body bore wear and solenoid problems are common on this transmission and can cause the same complaint, so diagnose before you tear it down.

• Checking transmission line pressure
• Transmission slipping diagnosis guide
• Transmission rebuild vs replacement cost