Lowering the Top Suspension Arms on your Classic Mustang.

 by Wal Marshall

Why?

One of the more effective modifications you can make to the front suspension of your 1964 to 1970 Mustang to improve its handling, is to relocate the top A arm mounting points on the shock towers. This modification reduces body body roll by about 8%, slightly lowers the ride height, and puts better wheel angles to the road, all of which noticeably improve cornering performance. Apart from a days work, it costs nothing in materials.

This modification was developed in the 60's by Ford suspension engineer Klaus Arning. It was originally designed to improve the effectiveness of the front suspension when mated to a special independent rear suspension. Cost killed the rear suspension improvements, but the top arm modification lived on thanks to Carroll Shelby who incorporated the modification on all 65 and 66 GT 350's. 

What's involved?

The modification is basically very simple. The upper suspension arm is mounted to the shock tower with two 1/2 inch bolts, the nuts of which can be seen from inside the engine bay. Two new mounting holes are drilled 1 inch lower down the shock tower and the arm relocated. That's it! 

To see if your Mustang has already had the arms relocated, look down the shock tower inside the engine bay. If there are a pair of unused holes, 1 inch directly above the A arm mounting nuts, the arms have already been lowered.

How do I go about doing it?

Lowering the arms involves an easy days work, and a subsequent visit to a wheel alignment shop to have the camber and toe-in reset accurately.

Other than regular sockets and spanners, the only special tools required are a coil spring compressor, a 17/32 (or 13 mm) drill bit, and a 1/2 inch chuck electric drill.

Steps involved are:

1. Jack up the front of the car and support on stands. Remove the front wheels. Unbolt the front shock absorbers (two small bolts top and bottom). Pull the shocks up out of the way or remove completely.

2. Compress the front coil spring on one side either till the spring can be removed, or its out of the way in the top of the shock tower. (See notes below on spring compressors).  

3. Support the lower suspension arm on a jack or blocks, and unbolt the upper arm mounting from inside the engine bay. (On an early 64-66 car, note the number and location of any shims for later replacement.)

4. From inside the fender/mudguard, pull the top arm off the shock tower and rotate it of the way. (Look after the brake hose....it may be necessary to tie the assembly back to stop the hose being stretched.).

5. Accurately mark the position of the new top arm mounting holes. This can be done by carefully marking on the inside of the shock tower surface itself, or by using a cardboard template bolted through the old holes. (Click the image below for the drilling dimensions. The side shown is the drivers (left hand) side, and the hard to read rear offset is 1/8inch or 3 mm) 

6. Centre punch and drill the new mounting holes, starting with say a 1/4 inch or smaller drill bit and work upwards to 17/32". ( Note: If you can't find a 17/32" drill, or it will not fit in the 1/2 inch chuck of your electric drill, use a 13 mm drill bit). As the shock towers are thick steel, make sure the drill bits are sharp.

7. Install the upper arm into the new holes, and reinstall any shims that were present.

8. Reset the camber to approximately the correct setting. Relocating the arm downwards will make the camber more positive than before, so therefore:

9. Reassemble the suspension, making sure the spring is seated correctly on the spring perch with the end of the coil behind the retaining tab.

10. Complete steps 2-9  on the other side. Note that the drilling template will need to turned over when drilling the other side.

11. With the car weight back on both front wheels, roll the car to settle the suspension. Stand back from the front of the car and look critically at the wheel angles. 

12. Test drive the car a few hundred metres and visually recheck the alignment as in step 11. Readjust as necessary.

13. Drive the car to an alignment shop and get the suspension realigned accurately. The settings used will depend on how the car is driven, but for NZ conditions, the following is suggested as a starter:

* The different left and right settings help compensate for NZ's significant road camber, the fact that we drive on the left side of the road, and the drivers body weight settling the suspension.

NOTES

1. On all cars, lowering the top arm has the effect of slightly reducing the ride height, by about 1/2 inch. This is because the suspension spring pivots on the top arm, about 1/3 of the way along.

2. On the 67-70 cars, because of the way the camber adjustment is made, the front wheels will be relocated outwards slightly, around 1/3 inch. If clearances between the tyres and the wheel arch are already marginal, some tyre rubbing may occur. "Rolling" the wheel arch lip over will usually will solve that problem.

3. While the top arm is unbolted, its is an opportune time to clean out the big dirt catching cavity at the bottom of the shock tower. This is a terrible rust trap, and a good clean out and paint/rust proofing is a good idea.

4. The suspension springs are very powerful and potentially dangerous if not handled with care. V8 springs may be rated for 600 inch/lbs, or more, so a compression of 3 inches carries a compressor load of around 1800 lb or 775 kg. There are two main types of spring compressor. The external type comes as two clamps that grip the coils from each side. By tightening the through bolts, the spring is compressed. (See photo below). If you are using this type, make sure they are heavy duty versions with at least 3 inches of adjustment, and that you get the clamps well seated and square on the spring so they do not fly off with potentially serious consequences.  

The other type is the centre pull version. One plate sits on the top of the shock tower, the other is inserted into the spring coils at the bottom. A single through bolt is used to winch the bottom plate up towards the top plate, pulling the spring up into the top of the shock tower. These can be made up with a long bolt and nut and two plates, or by copying the commercial version shown in the photos.