4L30E Transmission Master Rebuild Kit, BMW and Isuzu

If your Isuzu Trooper, Rodeo, Honda Passport or BMW 318i/328i is slipping on the 1-2 or 2-3 shift, flaring between gears once it is warm, or has fried clutch material sitting in the pan, the 4L30E inside it is ready for a full bench overhaul. This master rebuild kit puts the friction plates, steel plates, gaskets and complete seal set for that job in one box, so the unit can be torn down and put back together without waiting on a second order.

What the master kit does in a 4L30E

The 4L30E is the small GM four-speed built in Strasbourg, France, and it is unusual in one way that matters for a rebuild: the pump, the overdrive section and the main case bolt together in a straight line behind the engine, held by long through-bolts. Clutch packs inside apply 2nd, 3rd and 4th, and every one of those circuits crosses at least one of those bolted joints. A Sonnax technical specialist writing in Transmission Digest traced 2nd- and 3rd-clutch slip on a 4L30E to the thin red joint gaskets (0.012 in from the factory) creeping and tearing under driveline torque until the clutch feed oil leaked away. The aftermarket replacement gaskets are slightly thicker and more compressible, which is why a full gasket set matters as much as new frictions on this unit. This kit replaces the frictions and steels in every pack, the pump, valve body and separator plate gaskets, the case and pan gaskets, the front and rear seals, and the piston seals, O-rings and sealing rings.

Symptoms that point to an overhaul

• Slip or flare on the 1-2 or 2-3 shift that gets worse as the fluid warms up
• Torque converter slip or gear ratio codes that come back a few minutes into a drive
• Delayed or harsh engagement into Drive or Reverse after the vehicle sits
• Dark, burnt fluid with friction material on the pan magnet
• Flare into 4th under light throttle once the clutch facing is worn thin

How to confirm it before you buy

Rule out the electrical faults that mimic a worn unit first. On 1994-95 Troopers, a flashing check-trans light with code 37 and failsafe is often a loose G106 ground point on the intake plenum rather than a bad module or a burned transmission. Check fluid level and condition, then road test hot. If you have a gauge, compare line pressure in each range against the spec; pressure that falls off in one gear only points to a leaking clutch circuit. Our transmission slipping diagnosis guide walks through the order of tests, and flare versus slip helps you describe what you are feeling.

Fitment

The listing covers the 1991-1999 BMW 318i, 1996-1999 BMW 328i, 1996-2000 BMW Z3, 1997-2001 Cadillac Catera 3.0L, 1992-2002 Isuzu Trooper 3.5L, Isuzu Axiom, 1994-2002 Honda Passport 3.2L and 1996-1999 Acura SLX. Isuzu-family trucks use the low-first (2.86) gear set and BMW and Opel-based cars use the 2.40 first gear, but the clutch and seal package is what this kit replaces. Confirm the unit really is a 4L30E: many later BMW 3 Series cars used a ZF or a 5L40E instead, and a 4L60E looks nothing like it once the pan is off. If you are unsure, send us the year and VIN before ordering. Other 4L30E parts are in our rebuild kits department.

Install notes

• Use the new red joint gaskets between the pump, overdrive section and main case, and torque the long through-bolts evenly in steps so the joints clamp flat.
• Soak the new frictions in clean fluid before assembly, and air-check every clutch circuit before the valve body goes on.
• Inspect the pump bushing and gears while it is apart; a worn 4L30E pump will undo a fresh rebuild.
• On 4x4 Troopers and Rodeos, plug in the transmission speed sensor on the adapter housing before the transfer case goes back on. Transmission Digest documents rebuilt units that only had first and reverse, with no codes, because that two-wire sensor was left unplugged and is invisible once installed.
• Fit a new filter and pan gasket kit, refill with the fluid the vehicle maker specifies (BMW and Isuzu call for different fluids), and run an adaptive relearn where the controller supports it.

Will this kit fit my 2001 BMW 325i?

Probably not. Most 2001-up E46 3 Series automatics are a ZF 5HP19 or a GM 5L40E, not a 4L30E. The kit is listed for the 1991-1999 318i, 1996-1999 328i and 1996-2000 Z3. Read the tag on the side of the case or send us the VIN and we will check it.

My Trooper only has first and reverse after the rebuild and there are no codes. What did we miss?

Check the transmission speed sensor on top of the adapter housing between the transmission and transfer case. If its connector is not plugged in, the controller never sees output speed and will not upshift, and a code usually does not set because the engine rarely holds over 3,000 rpm long enough during a road test.

Does the kit include the red gaskets between the pump and the case?

The kit includes the gasket set for the pump, valve body, separator plates, case and pan. Lay the new gaskets next to the old ones before you start assembly so each joint gets the matching piece.

What else should I buy with a 4L30E master kit?

A new filter and pan gasket, fresh fluid, and any hard part you find worn during teardown. The pump, bushings and sun gear shell are the parts most often reused when they should not be.

What fluid goes in after the rebuild?

Use the fluid listed in your owner's manual. BMW, Cadillac and the Isuzu/Honda trucks did not all specify the same fluid, so do not go by what another 4L30E vehicle takes.

• Transmission Slipping Diagnosis Guide
• Shift Flare vs Slip: What Is the Difference
• Transmission Gasket and Seal Materials Guide
• Adaptive Relearn After a Valve Body or Rebuild