MUSING ON THE MORGAN REAR END
by Lorne Goldman

Morgan trads can exhibit some unpleasant characteristics as torque increases (200 lbft+). Of course, one can adjust and drive around them, and most will do that automatically and unconsciously. However, I believe that one should resist that tendency. After all, this is a car you bought to have fun, so why allow yourself to make your  playground smaller unnecessarily?

The first phenomenon examined is called axle tramp.  This is a form of wheel hop that occurs on cars with live axles, caused by the axle repeatedly rotating slightly with the wheels and then violently springing back from the leave springs returning to their proper form before the torque deforms them again. It looks like this.

The Morgan rear is suspended at the wheels using long elliptical leaf springs at each side attached between two points fore and aft on the car's chassis, with the axle in their middle. In the normal course, these springs should allow the car to pleasantly interface with the road by absorbing impacts and moving the weight of the car up and down. However, when there is sufficiently high torque, a jack rabbit start will force the leaves to curl on themselves or "windup". When this happens, the axle tries to lift the fronts of the springs, and more noticeably, drop their rear ends. The axle twists the normally straight springs into an S-shape, and the rear wheels start to hop up and down. This diminishes their traction and causes them to bounce and chatter violently. Additionally, the normally straight drive shaft from the front is forced to angle up to meet the now angled differential's input shaft, and power train performance is seriously affected. With some Morgans, the movement of the axle is so extreme, that it causes the propshaft to impact the tunnel or worse. (See Roadster Anti-Tramp Issue)

It can be cured with anti-tramp (aka traction) bars. But one must take care not to throw out the baby with the bath water in choosing them. Morgans have so little suspension travel that it is sad to limit it with add-ons.

Normally, these bars are hefty rigid items or tubes of tempered steel with pivoted holding brackets on both ends. The front ends of the bars connect to the front spring mounts on the vehicle frame. The rear brackets bolt to the bottom of the drive axle at the axle u-bolt saddle plate. These bars will keep the axle from twisting backwards while it forces the drive wheels to turn forwards, completely eliminating leaf spring windup, and keeping the rear drive wheels forced down to the pavement for superior traction.

However, most bars will prejudice your rear suspension. They have adjustable metal brackets at both ends and these are adjusted to eliminate play. In doing so, they also limit some of the up and down movement your leaf springs need to do their job. Peter Mulberry has an excellent solution which many use (and the Factory has tried to copy) which solves this issue. Instead of an adjustable bracket at the rear, Peter has designed a fitting that is contained within a rubber "doughnut". This eliminates tramp while still allowing full suspension movement. See the picture to the left to see the differences between the two types.

Installation is not complicated...only long. The seats must be removed to properly access the front leaf spring eyelet and add the forward anti-tramp fitting. The leaf springs must be unbolted at the axle and Mulberry's special plate (with stronger, longer u-bolts and a threaded hole for the anti-tramp bar) exchanged. I have found that the rubber doughnuts wear after about 25,000 miles but it is not difficult to remove the rear section of the bars and have the old doughnuts pressed out and new pressed in. As the hardness of the doughnut is a key, I strongly suggest that these be replaced from Mulberry. Their cost is negligible.