GM Rear-End Rigidity

From 1964-67, GM offered a rear suspension-bracket package (#9777613) for their A-body muscle cars. This kit was specifically designed for cars equipped with the four-speed transmission option, but it will normally fit any of these model years with manual or automatic trans. The rear suspension consists of upper and lower control arms attached to the axle and utilizing coil springs. These brackets were designed to add extra rigidity and improve the load distribution in the frame rear crossmember and lower control-arm area. Obviously the design wizards at GM realized that some of these cars would experience hard acceleration on a regular basis, so these brackets (Part No. 3869875 for the left side and 3869876 for the right side) were made available over the counter for non-four-speed cars. The parts are relatively easy to install, and doing the job on a lift makes it much easier. Normal hand tools are required, and the upgrade shouldn't take more than a couple of hours.

Lower Mounts
The bracket's lower mounting point utilizes the same bolt that attaches the front of the lower control arm to the frame. Begin by removing the lower control-arm nut and lock washer from the forward connection at the frame, leaving the bolt in position. The same must be done at the top connection point, but the bolt will be removed. Don't install the bracket until both areas are prepared, as it will be in the way of the top access point and must be installed at both points at the same time. These reproduction brackets from a restoration supplier fit perfectly. They are heavy-gauge steel and come with installation instructions.

Upper Mounts
The upper control arm is attached with a bolt to its mounting point. The bolt must be completely removed to install the bracket. To do this, support the rear end on a floor jack (or on a transmission jack if using a lift). This will take the pressure off the bolt and allow you to remove it. In this case, we used a punch and hammer to drive the bolt completely out. The punch followed the bolt, holding the arm in place. The exhaust system and other rear suspension parts make access somewhat difficult.

Brake Clearance
This is the lower attachment point on the control arm. The bracket angles up and over the muffler, requiring some contortions to re-insert the top bolt, washer and nut. Once the bracket is positioned but not tightened, check the brake-line routing through this area. Make sure that the brackets won't contact the brake lines. If necessary, re-route the brake lines before installing the brackets to avoid premature wear or crimping problems in the lines. In this case, the brake lines were completely clear of the area, so we proceeded with the install.

Tied Up
The attaching point at the upper control arm is hard to see. The bracket was positioned and the original bolt, washer and nut reinstalled. Cleaning the bolt threads on a wire wheel will remove any rust and makes the install a little easier. Once the bracket is secured at both ends, you can tighten the bolts. In effect, these brackets tie the upper and lower control arms together, tightening up the rear suspension considerably. Installing a rear swaybar will be the crowning touch for those occasional times when you feel the need for speed.