ATF Primary Pump with Plain Bearings

Special plain bearings are now used for the primary pump.

The ATF pumps supplied across our spares scheme are modified to this improved version. Secondary Pump Discontinued

The secondary pump in the automatic transmission A28/18 is discontinued. The engine can therefore no longer be started by towing or by engaging a gear while the vehicle is coasting downhill. Maximum towing speed must not exceed 50 km/h ( 31 mph), and the towing distance must not exceed 50 kilometers ( 31 miles).

When towing over greater distances, or if the vehicle has suffered accident or transmission damage, transport the vehicle with the rear axle raised or, better still, on a special car transporter or a trailer. If in doubt, always proceed according to this latter method.

Drive Pinion and Ring Gear

Following the hardening process, the tooth faces of drive pinion and ring gear are ground.

This grinding process ensures particularly low noise when the gear teeth mesh under load and during deceleration.

Machining process: Gleason

Drive Pinion Bearing Assembly

The bearing assembly of the drive pinion that is comprised of the bearing bushing (1) and two low-friction tapered roller bearings (2 and 4) has been reinforced with mounting space remaining unchanged.

The tapered rollers rotate directly on the ground running surfaces of the bearing bushing.

The inner races of the tapered roller bearings and the spacer ring (3) are preadjusted along with the bushing and are identified by a matching number.

92fl A

Modifications in the Output Shaft/Drive Pinion Nut Area

The gear for the centrifugal control drive and the snap ring (steel wire ring) used for axial location on the output shaft have been reinforced.

At the same time, the tightening torque of the drive pinion nut was increased to 450 Nm The nut must not be reused

Differential Housing with Porsche Limited Slip Differential and New Friction Discs

The Porsche limited slip differentials are fitted with new Valeo friction discs. The disc packs consist of:

8 inner discs, part no. 928.332.728.00

7 outer discs, part no. 928.332.726.05 thickness 1.5 mm part no, 928.332,726.06 thickness 1.7 mm part no. 928.332.726.07 thickness 1.9 mm part no, 928.332.726.08 thickness 2.1 mm


Adjustment instructions:

• Oil disc to be installed with transmission oil

• Line up bores of friction discs

• Stack disc pack in an alternating sequence, starting with a Valeo inner disc.

• Prepare disc pack accord ing to dimension 35.2-0.2 under a load of 50 N ( = 5 kg)


The assembled differential housing for automatic transmissions A28/18 differs from The housing for the manual transmission G28/57 only in that the oil pump drive gear is missing since the oil pump is only used on manual transmissions to cool the transmission oil.

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