Project e21 320i Car

Update: Subframe Rebuild

The rear sub frame assembly has three mounting points. At each end of the subframe assembly is a large square rubber mount that attaches it to the uni-body via a 14mm bolt. The differential mounts to the center of the subframe and has a large rubber mount at the rear that also attaches it to the uni-body assembly. These three mounting points offer secure attachment; yet offer additional dampening to reduce road and chassis noise into the driver compartment. We will be removing the entire subframe including differential and brakes. Remember since our goal it to have a like new reliable 1979 320i we will be cleaning and painting all fasteners and components. This will give us a better look at all components that could be worn and needing further attention.

Additional items that will be unbolted and steps to release the subframe from the body are:

• Exhaust Resonator and muffler.
• Rear driveshaft U-joint assembly from the differential. Use a large screw driver to lock up the driveshaft while using a wrench to loosen the nuts.
• From inside the passenger compartment remove the rubber hand brake boot and release the hand brake cables. Do this by unlocking the two 6mm jam nuts from each other and then remove both nuts from each cable. This will allow the cables to slip out of the body tubes when you release the assembly.
• Loosen and remove the lower shock points. This will require a 17mm wrench.
• Disconnect the brake lines that connect the brake flex lines at the body. Cap the lines to reduce drainage using one of the small bleeder caps from the rear wheel cylinder or front caliper.
• Place a floor jack under the differential to support the assembly, and proceed to remove the 3 mounting point bolts. These include the 2 subframe end bolts and the single differential cover mount bolt. Once the assembly is loose and has dropped you can lower the floor jack and pull the assembly out from under the vehicle.

When removing the rear subframe and rebuilding it - we will do the following which will be detailed in future articles.

• Differential front pinion shaft bearing seal replacement.
• C/V joint rebuilding, and boot installation.
• Installation of K-Mac adjustable trailing are bushings.
• Rear subframe mounts replacement.
• Painting the subframe and trailing arms.
• Replacing rear shocks and springs.
• Rear drum brake rebuilding.
• Install stainless brake lines.