722.5 Sun Shell

A sun shell is a small part that stops a big car. When its splines strip or its welds crack, a Mercedes with the 722.5 five-speed automatic can suddenly lose one or more gears, or lose drive altogether. This new sun shell is listed for the 722.5, the W5A 030 transmission Mercedes-Benz offered from 1990 to 1996 on the W124 E-Class, the W140 S-Class and C140 coupe, the R129 SL and the first W210 E-Class. If your car is in that group and the teardown found a chewed-up shell, this is the replacement.

What the sun shell does in a 722.5

In a planetary gearset the sun gear sits in the middle, and to make a ratio the transmission has to either hold that sun still or drive it. The sun shell is the bell-shaped piece that does that job: it splines to the sun gear at its center and reaches out around the neighboring gearset to a drum or brake that can grab it. In the 722.5 the main case uses a compound Ravigneaux front gearset and a simple rear gearset, and the overdrive housing adds a fourth gearset whose sun is held by the S brake for fifth and locked by the S clutch for the lower gears. Every time a brake clamps a sun member, the full reaction torque of that gear passes through a shell and its splines. Shift flare and slipping make the load worse, because each harsh, overlapping shift hammers the splines.

Symptoms of a failed sun shell

• Sudden loss of certain gears while others still work, for example no second or no reverse
• No drive at all after a loud bang, with the engine revving freely
• Grinding or a ratcheting noise under load
• Bright steel particles and sharp chips on the pan magnet
• Visible damage at teardown: rounded inner splines, a cracked weld between the hub and the shell, or a shell that has spun on its sun gear

How to confirm it before you buy

A lost gear on a 722.5 can also come from a burnt clutch or brake pack, a stuck valve, or a failure in the overdrive section's electrical control, so do not condemn the shell from the driver's seat. Check the fluid: burnt fluid and lining material point at a slipping pack, while bright steel points at a mechanical break. The shell is confirmed when you have the transmission apart and can see the splines or the hub weld. Also note why it failed. The 722.3, 722.4 and 722.5 are known for a harsh 1-2 upshift and soft or flaring 2-3 and 3-4 shifts; flare and tie-up put shock loads through the shell, so correct the hydraulics at the same time. Our 722.6 common problems guide explains how worn valve body bores cause flare in Mercedes automatics, which helps when deciding what else to fix.

Fitment

This shell is listed for the 722.5 and does not name a year. Because Mercedes built the 722.3, 722.4 and 722.5 alongside each other for the same models, read the code on the transmission case and confirm it is 722.5 or W5A 030 before ordering. The 722.5 also has more than one sun member, so lay the new shell next to the one you removed and compare the spline count, the hub diameter and the depth before you assemble anything. If in doubt, send us your year, model and VIN. If your E-Class turns out to be a 1996 or later car with the fully electronic 722.6, our E-Class 722.6 problems guide and the 722.6 sun shell are the right starting points instead. The matching 722.5 planetary is available if the gearset was damaged along with the shell, and the full 722 range is on the 722 transmission parts page.

Install notes

• Inspect the mating sun gear splines and the drum or brake hub the shell engages. A worn partner will destroy a new shell quickly.
• Replace the thrust washers and bearings on either side of the shell and check end play during assembly.
• A broken shell spreads steel through the unit, so replace every friction it contaminated, clean the valve body and flush the cooler.
• Fill with the fluid and quantity Mercedes lists for your transmission code, then check the level hot.
• Fix any harsh-shift or flare complaint before the car goes back in service so the new shell is not overloaded.

What does a sun shell do?

It connects a sun gear in the planetary gear train to the brake or drum that holds or drives it. When it fails, the gears that depend on that sun are lost.

Which Mercedes models have the 722.5?

The W5A 030 five-speed was an extra-cost option from 1990 to 1996 on the W124 E-Class, early W210 E-Class, W140 S-Class, C140 coupe and R129 SL. Confirm the code on your transmission case.

Is this sun shell new?

Yes, it is listed as new.

How do I know I need the sun shell and not a clutch pack?

A failed clutch pack leaves burnt fluid and lining material. A broken sun shell usually leaves bright steel debris and shows stripped splines or a cracked hub weld once the unit is apart.

Will this fit a 722.4 or 722.6?

It is listed for the 722.5 only. The 722.4 and 722.5 share a basic layout but are not guaranteed to share this shell, and the 722.6 is a different design. Compare the spline count and dimensions with your old part.

What should I replace with it?

Thrust washers and bearings next to the shell, any contaminated frictions, the filter and fluid. Check the mating sun gear and drum splines too.

• 722.6 Common Problems and Fixes
• 722.6 Mercedes E Class Common Problems and Fixes
• 722.6 Mercedes E Class Shift Problems: Diagnosis and Fix