Front Spindle

A custom Morgan-style spindle was designed and fabricated during the 1970-71 Conversion to a Race Car, and an improved version was created during the 1999-2003 Major Upgrade. Both used the AMC bolt-on stub axle, hub and brake disc. The following describes the later one, including a sketch and two photos.

The SKETCH shows the custom left front spindle, consisting of a weldment, a caliper bracket and an AMC stub axle. The weldment has Top and Bottom Pieces that were cut out of 5 x 5 x 3/8 in. steel angle and a length of 1 ½ in. OD x 1/8 in. wall steel tubing. The area of the Top Piece where the tube intersects is where the Steering Damper would be in contact and is denoted as the Spring Perch. The Steering Arm is part of the Bottom Piece.

Spindle Sketch

Fabrication began with the Top and Bottom Pieces being welded together at their top and sides, and then the hole bored for the tube. The hole was bored so the tube tilts outward, producing a built-in camber of negative 1 ½ degrees. The Spring Perch was relieved with a 1 ½ degree cut so it would remain at 90 degrees with the tube. The tube was welded in, and the area between the tube and Top and Bottom Pieces was boxed-in with gussets of 3/16 in. steel plate. A fitting to attach the Morgan shock-mounting stud was cut from 1 in. steel rod, drilled and tapped for Whitworth threads, and welded to the tube and Bottom Piece. When welding was completed a surface cut was taken on the face to insure a flat surface for bolting the caliper bracket and stub axle. The caliper bracket was made from 3/8 in. steel plate.
The photo below shows the assembled left front spindle as viewed from the front. It shows the Top and Bottom Pieces, the tube, the boxed-in area, the caliper bracket and the stub axle. The Morgan shock-mounting stud is shown as is a Zerk grease fitting. It is assembled with 7/16 in. AN bolts of proper grip length, hardened washers, locknuts and red Loctite. The welds are evident, as is the relief cut on the Spring Perch.

DSC02749.JPG

 

The photo below compares the  custom spindle and one from a 1958 Plus 4.

DSC02741

It is clear the custom spindle is larger and heavier, weighing 12 lbs. The Plus 4 spindle with a  caliper bracket (not shown) weighs 8 lb.

The tube OD for the custom spindle is 1 ½ in., and is 1 3/8 in. for the Plus 4 spindle, requiring different bushings, which are:
1 5/16 in. OD, 1 in. ID, 2 in. long.
They are available from many sources, one being:
C.E. Gobiel Co., 715 Raymond Ave., St. Paul, MN 55114, PN BB-1621-32.

The axle portion of the custom spindle is farther outward from the tube than on the Morgan spindle. As discussed in the Conversion to a Race Car in the Chronology of Modifications section, the use of wide tires required the wheel to be placed farther outward from the king pin which places a higher bending load on the spindle. The custom spindle locates the stub axle farther away from the tube, while a stock spindle would require wheels with a large negative offset. The custom spindle reduces the bending load on the axle portion, is easier on the wheel bearings and does not require special wheels. The higher bending loads are resisted by the sturdy weldment rather than the axle portion.

The Vertical Distance between the Spring Perch and the axle centerline is greater for the custom spindle. This was done for two reasons. The obvious one was to lower the front end, since the axle is raised with respect to the spring. The other reason was to experiment with the use of a three-piece thrust bearing in place of the Morgan steering damper. This had been discussed in Morgan circles as a way to reduce steering effort. The stock damper is a thin bronze plate with a hole that fits over the tube and is placed between the spring perch and the bottom of the coil spring. The bronze plate is bolted to a thin spring steel arm which limits its rotation. The thrust bearing was thicker than the bronze plate, so the spring perch was lowered to accommodate the difference.

However, a shimmy occurred at certain speeds at the end of a race weekend. I reasoned that as front tire wear changed a bit during the weekend, a slight out of balance condition could result. The friction of the stock steering damper was enough to absorb any vibration from the slight imbalance, but without that friction, a shimmy could occur. The thrust bearings were removed, the stock dampers reinstalled (with new bronze plates), and aluminum spacers were placed at the top of the springs to make up for the thicker thrust washers. The shimmy no longer appeared.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s