Strange 12 Bolt Install and Rear Suspension Modifications

After about 80K miles and a few runs down the drag strip I began to notice a noise from the rear of the car. It got faster and louder the faster I drove, and it got slower and quieter the slower I drove. However over the next few weeks it got progressively more noticeable. I even tried draining the differential fluid and refilling it with fresh fluid including GM Limited Slip Additive. I guess I was lucky since others have had their differential go to pieces with little warning. So it was time to replace the differential.

At this point I knew I was going to continue to take the car to the strip, so I needed a stronger differential than the stock one. I also knew that I needed to improve traction so that meant replacing the springs, shocks, torque arm, panhard bar, and lower control arms.

I decided to order a complete 12-bolt rear assembly from Strange Engineering with the heavy duty posi unit. Ordered it without ABS since I would have to remove my ABS/ASR reluctor rings from each axle and send them to be installed on the new Strange axles, plus this would require a special caliper mounting bracket to hold the ABS/ASR sensor. All this added cost, but more importantly, it would add weeks more time to receive the unit. As it was it took almost 3 months from the time I ordered until the truck delivered it. Strange Engineering was having delays getting the heavy duty posi from their supplier. I hope the process is much quicker by now.

I just pulled the fuse and ignore the lights on the dash for now. I'll do the no ABS light mod later. If you have just ABS, the reluctor ring gets welded to the ring gear and the sensor is mounted on the pumpkin. You must specify all this when you place the order.

For the suspension, I purchased Eibach Pro springs to lower the car and HAL 12-way adjustable shocks. I used Sway Bar bushings and end links from Energy Suspension. I purchased an Adjustable Torque Arm, Adjustable Lower Control Arms, Adjustable Panhard Bar, and Lower Control Arm Relocating Brackets all from Steve Spohn (www.spohn.net) You need an adjustable Panhard bar to recenter your car over the rear if you install lowering springs such as the Eibach Pro's. Also the Relocating Brackets are necessary for a lowered car and are also helpful on non-lowered cars. These let you keep the mount point for the lower control arms on the axle lower than the mount point on the frame. This improves traction and reduces wheel hop. The adjustable torque arm lets you set a negative pinion angle when racing which improves launch traction. The other advantage of Spohn's design is that the it moves the front mount point of the torque arm off the rear of the transmission and on to the G-load brace. This reduces some noise, and this is a much stronger mounting point than attaching to the transmission. It also includes a drive shaft loop.

For the most part, I followed Fred Forsythe's excellent instructions
http://members.aol.com/InjuneerZZ/Strange12.htm and http://members.aol.com/InjuneerZZ/HALEibch.htm

You can also locate these instructions from Brent Franker's F-Body Install and Fix-It Guides or Kelly Drown's Project Trans Am Database

Below are a few notes of things I did differently than what Fred describes.

1. I had the Lower Control Arm Relocating Brackets welded on after I received the rear end assembly from Strange. Then I painted the tubes Rustoleum Black Night Metalic 7250 and the pumpkin, except the end cap since it is already aluminum, Rustoleum Metalic Finish Aluminum 7715. This picture shows the rear end assembly with the Spohn Torque Arm attached, ready to be installed on the car.

2. This picture shows the installed Strange with the Spohn Torque Arm.

3. In Step 4 in the Intermission section of Fred's instructions he describes drilling a new hole for the brake hose retaining clip on the driver's side LCA bracket. The welds and extra thickness from the installation of the Lower Control Arm Relocating Brackets made reusing the bracket with the tang intact. I cut the tang off and used the existing hole in the axle assembly. This creates a sharp U turn in the brake hose but no kink. I used 1/4x1" bolt and nut and 5/16" lock washer to attach the brake hose retaining clips on both sides of the car. Later when I replaced the brake hose with Stainless braided lines, I drilled a hole In the relocating bracket and moved the bracket to reduce the bend in the line.

4. Also due to the installation of the of the Lower Control Arm Relocating Brackets you need to cut off about ¼" of the brake weight (measured from the edge of the largest diameter end of the weight. I painted the exposed metal with some of the Rustoleum Black Night Metalic 7250. The enlarged picture has an arrow pointing to the trimmed weight.

5. Another change was in Step 10 of the Install section, I removed the emergency brake retainer wire loops since I could not get them to reach the bolts in the differential cover. I zip stripped the emergency brake cables to the brake lines in a couple of places. I'll probably revisit this issue some time.

6. When reinstalling the Sway Bar, Step 14, I used Fred's trick (Arrow A) plus I included ¼" spacers (Arrow B) made from ¼ x 1 ¼" flat bar between the sway bar clamps per an excellent suggestion by Lonnie Pavtis. I also made sure that the Energy Suspension bushing brackets were mounted as far back as possible. This gave plenty of clearance and works well.

7. There are a couple of contact points to look out for. After driving the car over a few bumps my Spohn torque arm would hit the drive shaft tunnel, but a slight adjustment of the panhard bar and a couple whacks on the drive shaft tunnel and there is plenty of clearance now. The other contact point I observed was the stud on the passenger side of the differential end cap would hit what the Helms manual calls the "Rear Axle Tie Rod Bracket Brace Assembly." Probably a more descriptive name would be the upper panhard bar i.e., the brace that is above the panhard bar. I just cut a small notch out of it to eliminate the problem.

8. I was able to use a ½ x 13 tpi 3" grade 8 bolt for the shock install. I put a ½" hardened washer on the bolt then the shock, followed by another ½" hardened washer, a ½" x 13 tpi grade 8 nut, one more ½" hardened washer. This will keep the shock in the same geometry as stock. The bolt then went into the shock mount point on the axle assembly and was attached using a ½"lock washer and a ½" x 13 tpi grade 8 nut.
This picture also shows the rear springs, the HAL's, the sway bar endlinks, and the Lower Control Arms.

9. Some people have reported difficulty adjusting the panhard bar to recenter the rear of the car over the axle. The method I used was to disconnect the panhard bar at one end. Then set the car on its wheels (use ramps or blocks so that you can still get under it). The car will now be centered so adjust the panhard bar so that the mounting point hole matches the end of the panhard bar and reconnect.

Back to Modification List
Tim's Page

1.		I had the Lower Control Arm Relocating Brackets welded on after I received the rear end assembly from Strange. Then I painted the tubes Rustoleum Black Night Metalic 7250 and the pumpkin, except the end cap since it is already aluminum, Rustoleum Metalic Finish Aluminum 7715. This picture shows the rear end assembly with the Spohn Torque Arm attached, ready to be installed on the car.
2.		This picture shows the installed Strange with the Spohn Torque Arm.
3.		In Step 4 in the Intermission section of Fred's instructions he describes drilling a new hole for the brake hose retaining clip on the driver's side LCA bracket. The welds and extra thickness from the installation of the Lower Control Arm Relocating Brackets made reusing the bracket with the tang intact. I cut the tang off and used the existing hole in the axle assembly. This creates a sharp U turn in the brake hose but no kink. I used 1/4x1" bolt and nut and 5/16" lock washer to attach the brake hose retaining clips on both sides of the car. Later when I replaced the brake hose with Stainless braided lines, I drilled a hole In the relocating bracket and moved the bracket to reduce the bend in the line.
4.		Also due to the installation of the of the Lower Control Arm Relocating Brackets you need to cut off about ¼" of the brake weight (measured from the edge of the largest diameter end of the weight. I painted the exposed metal with some of the Rustoleum Black Night Metalic 7250. The enlarged picture has an arrow pointing to the trimmed weight.
5.		Another change was in Step 10 of the Install section, I removed the emergency brake retainer wire loops since I could not get them to reach the bolts in the differential cover. I zip stripped the emergency brake cables to the brake lines in a couple of places. I'll probably revisit this issue some time.
6.		When reinstalling the Sway Bar, Step 14, I used Fred's trick (Arrow A) plus I included ¼" spacers (Arrow B) made from ¼ x 1 ¼" flat bar between the sway bar clamps per an excellent suggestion by Lonnie Pavtis. I also made sure that the Energy Suspension bushing brackets were mounted as far back as possible. This gave plenty of clearance and works well.
7.		There are a couple of contact points to look out for. After driving the car over a few bumps my Spohn torque arm would hit the drive shaft tunnel, but a slight adjustment of the panhard bar and a couple whacks on the drive shaft tunnel and there is plenty of clearance now. The other contact point I observed was the stud on the passenger side of the differential end cap would hit what the Helms manual calls the "Rear Axle Tie Rod Bracket Brace Assembly." Probably a more descriptive name would be the upper panhard bar i.e., the brace that is above the panhard bar. I just cut a small notch out of it to eliminate the problem.
8.		I was able to use a ½ x 13 tpi 3" grade 8 bolt for the shock install. I put a ½" hardened washer on the bolt then the shock, followed by another ½" hardened washer, a ½" x 13 tpi grade 8 nut, one more ½" hardened washer. This will keep the shock in the same geometry as stock. The bolt then went into the shock mount point on the axle assembly and was attached using a ½"lock washer and a ½" x 13 tpi grade 8 nut. This picture also shows the rear springs, the HAL's, the sway bar endlinks, and the Lower Control Arms.
9.		Some people have reported difficulty adjusting the panhard bar to recenter the rear of the car over the axle. The method I used was to disconnect the panhard bar at one end. Then set the car on its wheels (use ramps or blocks so that you can still get under it). The car will now be centered so adjust the panhard bar so that the mounting point hole matches the end of the panhard bar and reconnect.