170 Manual Drive Trains and Axles Copyright by Goodheart-Willcox Co., Inc. the access cover may simply be a plain, flat plate or it may be a contoured shape with built-in shift linkage. (Refer back to Figure 8-18.) On some floor-shift models, the gearshift lever goes directly through the cover. Note that all transmis- sion covers use gaskets. Extension Housing The extension housing is made of aluminum or cast iron and provides protection for the end of the transmission output shaft. In some designs, the front of the extension housing holds the rear bearing, which supports the central portion of the output shaft. (In some designs, this bearing is held in the rear of the transmission case. In other designs, a center bearing is held in the center support and the rear bear- ing is held further back in the extension housing.) The front Case Gasket Front bearing retainer Front bearing To transmission To engine Front bearing retainer seal Lip Dust shield Hub Front bearing retainer Bearing Case Extension housing Extension bushing Transmission rear seal Splines Output shaft Bolts Figure 8-25. The extension housing keeps the output shaft aligned and seals the rear of the transmission. Common extension housing features are the extension bushing, rear seal, and housing-to-case gasket. Figure 8-23. The front bearing retainer is usually attached to the transmission case by bolts. It holds the front bearing in place. A gasket and seal prevent lubricant leaks. (Chrysler) Figure 8-24. This shows a typical front bearing retainer seal. The sealing lip prevents oil loss, and the dust shield keeps out dirt and water. (General Motors) of the extension housing is bolted directly to the rear of the transmission case. To prevent lubricant leaks, there is usually a gasket between the case and extension housing. The rear of the extension housing contains a bushing and seal. The transmission extension bushing supports and aligns the drive shaft assembly slip yoke, which, in turn, supports the transmission output shaft. The transmission rear seal prevents lubricant leaks and keeps dirt and water out of the transmission. A typical extension housing is illus- trated in Figure 8-25. The transmission mount, which supports the trans- mission and also serves as the rear engine mount, is usu- ally installed on the extension housing. The mount is an assembly essentially composed of a bracket and rubber pad or bushing. A flat surface is machined on the bottom of most extension housings. The surface is drilled to fit the transmission mount attaching bolts. In vehicles with inter- nal shift linkage, the gearshift lever usually extends into the transmission at the extension housing. A boot is used to prevent the loss of oil and the entry of dirt and water. The boot is usually held in place by a ring or bezel, which is attached to the extension housing with bolts or screws. The shift linkage extends from the extension housing into the transmission case. Accessory Parts Accessory parts may be bolted to or installed in the transmission case or extension housing. Fill and drain plugs, identification tags, shift levers, and boots are some common examples of accessory parts. Some of the accessories that are often attached to the transmission case or extension housing are shown in Figure 8-26. Speedometer assembly The extension housing usually contains the speedometer assembly. The speedometer assembly basically comprises the speedometer adapter and pinion gear, Figure 8-27. The speedometer adapter is installed with bolts or with a single bolt and clamp similar to a distributor hold-down clamp.