MN12 Performance Lowering Springs How-To

Installing lowering springs has become a very popular modification to our Thunderbirds and almost everyone wants to upgrade their stock Struts and Shocks at some point. If you are interested the spring and shock manufacturers for the Thunderbird/Cougar CLICK HERE. For this installation I have chosen the Eibach-ProKit springs which are of the progressive design and offer chrom silicon heat treated steel that is powder coated for a lifetime of protection. This ProKit (part#3522.140) is designed to lower the car 1.25" with a front spring rate of 286-411 lbs per inch and a rear spring rate of 514-714 lbs per inch. The freelength of the springs are 16.375" for the front and 11.625" for the rear. Eibach also offers a lower 1.50" spring but since I live in an area that has speed bumps and alot of road construction I chose the 1.25" drop. This How-To will describe the removal and installation of the stock springs, struts, and shocks. Please refer to shop manuals as reference and ALWAYS support the vehicle properly!

Rear Installation:

Raise and support rear of vehicle with jackstands and/or blocks.

Remove both rear shock absorber electronic actuator (if equipped) from the shock towers. Then remove the single nut that holds the shock in place (see picture).

Remove rear wheels from vehicle.

Remove the shock nut and bolt from the lower rear suspension arm and remove the shock assembly from the vehicle.

Using a floor jack placed under the rear suspension arm compress the spring so you can remove the sway bar end links. Next lower the jack down so it just supports the suspension arm then remove the nut and bolt that holds the rear wheel knuckle to the rear suspension arm (see picture). You may have to tap the bolt out of the rear wheel knuckle.

Lower the floor jack and rear suspension arm to release the tension from the rear spring. Once the lower suspension arm is free place your feet on it and push down so the rear spring can be removed.

With the rear shocks and springs out you are now ready to install the new shocks and springs.

The rear spring insulators (2 per spring) compress and should be replaced when the new springs are installed (see picture). Ford part# E9SZ5K617A Grease the new insulators with white lithium grease or simular to prevent suspension squeeking.

Install the new springs (spring pigtails may be in any position). Position jack under rear suspension arm and raise until the lower suspension arm is lined up with the rear wheel knuckle bores. Ensure spring seats properly. Install bolt and nut retaining rear suspension arm and bushing to rear wheel knuckle and tighten bolt to 110-148 lb-ft. Install sway bar end link and bushing. Lower the jack and check spring positioning.

Turn the shock up side down and compress then insert the shock into the rear tower. Install lower shock absorber bolt, washer and nut tighten to 83-113 lb-ft. With the upper end of the rear shock absorber protruding through the body shock tower hole, install the insulator, washer and nut assembly. 27-40 lb-ft (with ARC) 44-58 lb-ft (without ARC)

Reinstall both rear shock absorber electronic actuator (if equipped).

Front Installation:

Remove both front absorber electronic actuators (if equipped) from the strut towers. Then remove the outer three upper strut retaining nuts (see picture). DO NOT REMOVE THE CENTER NUT!

Then raise and support the front with jackstands and/or blocks. It is a good idea to leave the other wheel on until you are finished with the one side. Then reinstall the wheel and start on the other side.

Next remove the lower strut mounting bolt & nut from the front suspension lower arm. Remove the bolt that holds the bracket assembly for the brakes.

Then place a floor jack under the front lower arm and lift it to remove the tension on the sway bar end links and remove the sway bar end link from the spindle using a ball joint remover. Then remove front wheel spindle to upper front suspension arm ball joint retaining nut and bolt. With the spindle supported by the floor jack you can slowly lower the floor jack. Be sure to hold the front spindle as it is lowered. Remove the strut/spring assembly.

Do Not attempt to compress the spring with a hand held spring compressor. Take the assembly to a local shop and have them swap the springs for you. You will need a wall mounted strut/spring compressor.

To ensure the spring is installed on the new strut cartridge assembly correctly use a 90 degree straight edge and mark the top and bottom of the cartridge (see picture below) with a silver marker or paint. Use the Alignment Point on the strut cartridge as the fixed point (see picture above).

Install the new cartridge assembly back into the strut tower. Install shock absorber housing seal and three outer strut retaining nuts (hand tighten). Adjust the height of the floor jack to allow the lower strut assembly and lower control arm to align then insert the bolt and tighten nut to 125-170 lb-ft. Align the spindle to upper control arm and insert bolt and tighten nut to 50-68 lb-ft. Install the sway bar end link and tighten nut to 30-39 lb-ft. Tighten the three outer strut retaining nuts to 17-22 lb-ft. Re-attach the brake line bracket to the frame. Install wheel and start on the other side. After you are finished you will have to take the car to a alignment shop for a 4 wheel alignment. The Thunderbird alignment specs are below.

Specified Range
min -1.3o    0.3o max
min 4.8o    6.3o max
min -0.03o    0.10o max
Cross Camber
min -0.8o    0.8o max
Cross Caster
min -0.8o    0.8o max
Total Toe
min -0.05"    0.20" max
Specified Range
min -1.0o    0.0o max
min -0.03"    0.09" max
Total Toe
min -0.07"    0.19" max
MN12 Performance Inc.