This new construction necessitates new overhaul procedures and a selective clutch plate makes a reverse clutch stack check necessary.

Forward Clutch

The forward clutch is changed from the cone type used in 1958 to a multiple disc design (Fig. 13).

The multiple-disc forward clutch has eight active faces, and its construction is similar to the reverse clutch with the exception of the return spring. The forward clutch piston bears on its clutch pressure plate.

Fig. 13 - Turboglide Forward Clutch

A new design grade retarder and forward clutch pistons permit independent piston movement. The previous waved-type return spring is replaced by a radial row of 20 coil springs acting on both pistons.

Front Gearset

Three pinions are added to the front gearset, making a total of six pinions. The reduced individual gear tooth stress afforded by doubling the number of pinions contributes to even quieter operation.

Hydraulic System

Minimum line pressure is increased from 50 to 80 psi, to provide the necessary clutch application pressure required with the new grade retarder piston and reverse clutch. The increased line pressure permits deletion of the two check valves (modulator and accumulator) which were in the ditch plate in the former modulated pressure system.

Reinforcing ribs added to the ditch plate casting permit elimination of straps formerly used to reinforce this plate. The accumulator passage plug has been removed from the main valve body.

As a result of these changes, very few valve body components are interchangeable with past models.

Oil Pan

The transmission oil pan drain plug will be removed, and draining for repair operations must be done by removing the filler tube, which is also necessary for pan removal. Early production units however, will use pans with drain plugs.

POWERGLIDE

The reverse apply pressure is now modulated in a manner similar to drive range. Since this produces lower pressures for reverse range under high engine vacuum conditions, the application of the reverse clutch is smoother.

A new reverse band adjustment procedure, similar to low band procedure, has been established. The reverse band adjusting screw should be tightened to 6-60 in. lbs. and then backed-off 2 1/2 turns. This adjustment procedure should be used on all past model Powerglide Transmissions.

The waved clutch driven plates (steel) are now reversible, so that they may be installed in either direction and still nest properly.

TRUCK

Powermatic

Numerous changes have been made in the Powermatic transmission to improve durability and performance. Many of these changes affect service operations and are fully covered in the 1959 Truck Shop Manual Supplement.

A special Powermatic transmission with modified shifting characteristics is used on school bus models. This transmission is not designed for the dump trucks or tractors. Only the clutch apply and release regulation mechanism is modified. This is done within the hydraulic system and involves the control valve body assembly, transfer plate assembly, and downshift timing valve body assembly. The high-clutch diaphragm is also modified to insure adequate oil flow through the high range and high splitter clutch passages. All school bus transmission are identified by a serial plate having a brown background.

Body and Sheet Metal

PASSENGER CAR

General Body Items

Body structure on all styles is completely new. Larger glass areas are compensated for by stiffer structure throughout.

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