Panhard Bar Attachment to Axle

MGB Rear Suspension Setup

(originally published in British V8 Newsletter, Volume XI Issue 1, January 2003)

by: Kurt Schley

Many years ago, when I was originally converting my chrome bumper '74 MGB to V8, I was quite aware that the car would often be pushed hard in turns and would probably be seeing some occasional track time. Therefore the rear suspension set-up had to meet several criteria, including: 1) Very limited side-to-side movement, 2) No differential wind-up under hard acceleration, 3) Not be so stiff as to induce tire hop on rough roads, 4) Allow for a wide tire, and 5) Be cheap to build. A smooth, comfortable ride on the road was not a priority.

Fabricating and setting up the rear suspension was performed in stages, each to address one of the points above.

First was to limit the lateral movement. In hard cornering, the rear of car's body will tend to shift toward the outside of the turn and away from the centerline of the rear end. This motion upsets the handling as well as decreases the space between the outside tire sidewall and the inner fender lip. The two traditional methods of counteracting the lateral movement are either a Watts linkage or a Panhard rod. I did not have the equipment (or expertise) to properly design a Watts linkage, so decided to go with a Panhard rod set-up.

Panhard Bar Attachment to Body

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A Panhard rod is basically a solid link or bar with is anchored to the underside of the body near one tire and attaches to the rear end near the opposite tire. As the body wants to move over the rear end in a turn, the Panhard rod in essence locks the two together and lateral movement is prevented. At each end of the Panhard rod is a swivel joint so that vertical movement of the body and rear end is not impaired. Two of the critical factors in the design of a Panhard rod system are:

1) To make the rod as long as possible. The rod end attached to the rear end will actually travel in an arc, in relation to the body anchored rod end, as the body moves vertically on the suspension. This in turn will allow or induce a small amount of lateral movement between the rear end and the body. The longer the rod, the larger the arc and the smaller the induced lateral movement. Most of the Panhard rod kits I looked at attached the rod to the rear end with a clamp or bracket inboard of the spring mounting pad. I found that by fabricating a bracket which bolted to the back of the axle flange, and immediately behind the brake backing plate, a much longer rod could be utilized.

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The body mounted bracket bolts to the bottom and side of the trunk floor, just above the spring bracket on the rear end. This is the outermost practical mounting point to the body and results in the longest Panhard rod possible. The mounting bracket dimensions and construction were described in detail in Vol.V Issue 2 of the Newsletter as are the traction bar mounts discussed below.

2) The Panhard rod should be level horizontally and parallel with the rear end when the car is loaded with fuel and a driver. Remember to include these loads when making measurements for the Panhard rod construction.

Traction Bar Attachment to Axle

To prevent axle wind-up in an effective, yet economical manner, conventional traction bars and their brackets were measured up and fabricated. The forward bracket utilizes the front spring mount with additional bolting to the car's floor ahead of the spring mount. The rear bracket was built from 1/4" steel plate sections welded to the stock MGB shock mounting plate. The traction bars themselves were NOS Cal-Custom swap meet finds, items originally for an early Mustang. I merely had to shorten them to fit. Some degree of traction bar tuning can be made by varying the material in the bushings. A softer rubber will provide some give during a hard launch and soften the shock of the hook-up when the tires get traction.

Traction Bar Attachment to Body

Urethane bushings are harder and do not transfer as much motion, giving a faster transfer of restraint on the rotating rear end and a quicker launch. The racer boys sometimes use solid metal bushings to minimize axle wrap up; however this is very tough on the traction bar hardware as well as the rear end itself.

To keep the ride supple enough to prevent the tires from losing contact with road on bumpy roads, I rebuilt the stock '74 rear springs and they have worked very well over the last several years. A slightly stiffer ride can be obtained by using MGB/GT springs.

For shock absorbers I used a set of Delco air shocks originally intended for a Corvette. These shocks give me a degree of tuning ability and also are very convenient when the "B" is heavily loaded for a road trip. I can raise or lower the body about 2-1/4". The bottom of the shock installed quite nicely on a bolt run through the stock lower MG shock mount. The top of the shocks were secured to the body using a set of old Moss Motoring tube shock conversion mounts. However, the top mounting plates are very simple and could be easily fabricated. Unfortunately, the shocks I used have been discontinued. A measurement and some time at the parts store catalogs should locate something useable. The air fitting to pressurize the air shocks in mounted inside the trunk.

Shock Absorber

I initially installed 195 series tires on Datsun 240Z wheels and these fit nicely. However, they did not afford as much traction as I wanted and 215 series tires seemed as if they would fit. Mounted on Prime aftermarket wheels, they did squeeze under the fenders, but with insufficient clearance for hard corners. The Panhard rod minimized the lateral movement of the wheels; however the tire sidewalls actually deflected enough that I did get some tire rub on the lip of the fenders. I tried to fold the lips up and back to get them out of the way, but the double ply of sheet metal was way too stiff and I started to actually bend the fender out of shape. The recourse was to cut the lip away in about the center of the spot welds which hold the two plies together. I used a 3" abrasive disc on an air grinder. It took a steady hand and some patience, but a smooth cut was finally made on both sides, giving about 3/8" additional clearance per side. The raw cut edges were dressed with a power sander, painted and sealed. I have had no more tire rub even when doing a 360 spin on the race track. (Though that was the least of my worries at that particular moment!)

As the traction bars, Panhard rod system and shock mountings were either fabricated or swap meet buys, the cost of the rear end suspension was minimal, probably under $50.00. Add $35.00 for the shocks (a purchase at the Hershey swap meet) and the whole set up came in at under $100.00 and this over a period of a year, thus keeping it under the radar screen of "upper management" who kept a close eye on any fraud or shortages in the family.

Disclaimer: This page was researched and written by Kurt Schley. Views expressed are those of the author, and are provided without warrantee or guarantee. Apply at your own risk.

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