BMW Type 188 Differential Bearing and Seal Rebuild Kit

A BMW rear end that howls on the highway, whines when you lift off the throttle, or leaves a ring of gear oil around the output flanges is almost always telling you the Type 188 differential needs bearings and seals. This kit rebuilds the medium-case 188 found under E30 and non-M E36 3 Series cars, E28 and E34 5 Series, E23 and E32 7 Series and the Z1 and Z3 roadsters. One box carries both pinion bearings, both carrier bearings, every case seal, a new crush sleeve and the pinion nut lock plate, so the diff only has to come apart once.

What the bearings and seals do in a Type 188

The 188 is named for its ring gear diameter in millimeters. The pinion rides on two tapered roller bearings that have to be preloaded against each other so the pinion cannot walk forward and back under drive and coast load. The carrier, which holds the ring gear and the spider gears, sits on two more tapered bearings held by bolt-on side caps. Those caps are what make this an early "mm" style case, built up to 1999. When a pinion bearing wears, the pinion moves out of its set position, the gear contact pattern shifts, and the whine you hear is the ring and pinion running on the wrong part of the tooth. The seals keep the gear oil in: one at the pinion flange, one at each output flange behind a lock ring, and O-rings on the side caps.

Symptoms this kit fixes

• Whine or howl that rises with road speed, often loudest on decel or at steady cruise
• A constant drone that does not change when you weave the car gently left and right (a wheel bearing usually changes pitch when loaded)
• Gear oil weeping from the pinion seal at the driveshaft flange
• Oil wetting the inner CV joints or output flanges from failed side seals
• Clunk or extra driveline slack after a pinion bearing has been noisy for a long time

How to confirm before you buy

Do the weave test first: on a quiet, safe road, sway the car gently side to side. If the noise changes with load, look at the rear wheel bearings before the diff. If it stays the same, the diff bearings are the likely source. With the car up, grab the pinion flange and check for in-and-out play; any movement you can feel means the pinion bearings are done. Drain the oil and look for fine metal on the drain plug. Catch it early - a pinion bearing left in too long can ruin the ring and pinion, and then the job gets far more expensive.

Fitment

Built for the Type 188 rear differential with bolt-on side caps in the E30, non-M E36, E28, E34, E23, E32, Z1 and Z3. BMW fitted three case sizes in this era - 168, 188 and 210 - and which one a car got depends on engine and model, so some four-cylinder cars carry the smaller 168 and higher-output and larger models carry the 210. Confirm your case before ordering: measure the ring gear, check the casting, or send us the year and VIN and we will look it up. If your case turns out to be the larger unit, see our Type 210 bearing and seal kit. More overhaul parts are in our rebuild kits collection.

What is in the box

• Two tapered pinion bearings (HM89410 and HM89449 series)
• Two tapered carrier bearings (LM503349 cone, LM503310 cup)
• Front pinion oil seal, two side carrier seals with lock rings, two cover O-rings
• New pinion crush sleeve and pinion nut securing plate

Ring and pinion, setup shims and gear oil are not included.

Install notes

• Before the pinion nut comes off, mark its position on the pinion and measure the rotating torque so you have a baseline.
• Press off the old cones, drive out the cups and seat the new cups fully in the case. Never reuse the crush sleeve.
• Set pinion bearing preload by rotating torque, tightening the nut in small steps. An inch-pound torque wrench reads the low turning torque accurately. Overshoot the preload and you have to start over with another sleeve.
• Shim the carrier for preload and backlash, then check backlash at several points around the ring gear with a dial indicator and magnetic base. Confirm the contact pattern with marking compound.
• Fit the side seals and lock rings last; a BMW seal installer set keeps them square in the bore.
• Refill with the gear oil BMW specifies for your car - limited-slip units need the correct LSD-rated oil.

How do I know my BMW has the Type 188 and not the 168 or 210?

The number is the ring gear diameter in millimeters. Which case a car got depends on engine and model, so do not go by chassis alone. Measure the ring gear or check the casting, or send us the year and VIN and we will confirm before it ships.

Does this kit include the shims to set backlash?

No. It includes bearings, seals, O-rings, the crush sleeve and the pinion nut lock plate. Carrier and pinion shims, the ring and pinion and gear oil are separate.

Can I reuse my old crush sleeve?

No. The crush sleeve deforms when pinion preload is set and cannot be crushed again accurately. Use the new one in the kit, and replace it again if you overshoot the preload.

Will new bearings stop the whine if my ring and pinion is damaged?

Only if the gears are still good. Bearings fix noise caused by bearing wear, but if a worn bearing has run long enough to mark the gear teeth, the gears will keep whining. Inspect the tooth faces and the contact pattern during teardown.

Does this kit work on the later E46 or E90 rear differential?

It is not listed for them. This kit is for the early bolt-on side-cap 188 case built up to 1999. Later cars use different differential versions, so send the year and VIN before ordering for anything outside the listed chassis.