Independent Rear Suspension
The rear solid axel of the original MGB is strong enough to handle the 236ft-lbs the Rover engine produces but the suspension was not up to the task. Many people just redesign the half elliptical spring system, but I wanted to do something different.
I had heard that the Jaguar rear suspension would fit in a MGB and had seen photos of the modified cars. What was not available was how they did it. I could find no reference to specs and information on the design. This is when I decided to start from scratch and design my own system using the Jaguar IRS components.
The advantages of an independent rear suspension are that each wheel can
articulate separately making the ride smother and keeping all four wheels on the
ground. The IRS system virtually eliminates “spring wind up”, or “tramping”
that is caused by to much torque to the rear wheels.
Driving over a bumpy road, a solid axle has lots of stress on the springs that
are trying to do two things. One, they are absorbing the
bumps one both sides of the axle.
If there is any uneven pavement this can become too much for the suspension and
control can be lost. Two, the leafs are having to absorb the torque that the
axle is releasing. This is a hard combination on a suspension system. The IRS
system has none of these traits. The new Jag system will provide me with better
ground clearance, can handle more torque, has better brakes, and is relatively
inexpensive.
My Jaguar rear end came out of a 1984 XJS that had 63K miles on it. I kept the Jaguar Posi-lock Differential and inboard disc braking system. I also kept the hub mounts. The parts that I redesigned were the body mounts, hubs, control arms, radius arms, drive shafts, hub locators, and spring mounts and placement. The Jaguar rear axel length was 10 inches wider than that of the MGB’s. The entire suspension needed to be designed at least 5 inches shorter on each side to fit under the MG. One very nice advantage to the Jaguar IRS system is that it has inboard brakes. This cleaned up the suspension for my redesign and made it a little easier.
After two months of working with my project I had made a few design changes. Originally I had decided to cut the axels at around 5 inches to fit under the MGB. After calculating the exact wheel track I used a measure of 4.25 inches. This would place the track the same as OE. Also I change the way I was going to cut and weld the lower arms and drive shafts. I cut the shafts at ¼ the length of the lower arm and cut the 4.25 in. out. Then I used a slip shim and used aliening rods and a magnet level to true the shaft and then welded it into place. I decided to cut the 4.25 in. out in the center of the drive shaft instead of making a press fit in the yoke. I cut the 4.25 in out and turned both of the contact points to a tip and welded the two pieces together. After welding the shafts I heated them to 1300 F and hammered the cherry hot steel to anneal it and relive any residual stress. I have also designed a bracket for the spring and damper to mount as well. The brackets were made of 1020 Steel that are .25 inches thick. The calculations made on this bracket showed that it was very strong and would not deform . The radius arms were made from a hallow steel tub with a pivot joint on the axle end and a leaf spring bushing on the other end. I used the same spring mount as OE for the radius arm to mount. The entire assembly was mounted into the body using 8 7/16 inch bolts with large washers and nylon lock nuts. There are two securing brackets connected from the bottom of the cage to the lowest part of the MG’s frame. This is seen in the photos. The alignment went without any problem. I used a measuring tape and two fixed points from the center of the hubs.
