MANGUSTA HANDLING
I know that most of the people restoring cars now are being very careful about originality but I felt that this story should be told again to encourage others to make some careful moves to impact the much publicized Mangusta handling problem that after many years has now been clearly identified.
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A while back I published a very detailed account about the cause of the instant change of the Mangusta rear suspension, the rear wheels going from positive to negative camber during high speed cornering. Since the car was introduced this has been somewhat of a mystery, that is the cause of this unusual and unique behavior. There has been a lot of uneducated speculation about this phenomena, everything from not enough welds in the body, tunnel and subframe structure to exaggerated weight distribution.
The cause of the problem was identified by Werner Meier, an ex General Motors chassis engineer who has a very successful Corvette restoration business. He saw strange behavior of the rear subframe when the most rearward bridge on my car was removed and he immediately called me. He knew nothing of the Mangusta handling history but what he did know was that the Mangusta bridge set-up was backwards. The attachments of the two bridges was also wrong, that is, each with one bolt on each end allowing them to act like hinges. The combined bridge structure on each side of the car takes the cornering forces translated from the upper rod attached to the hub carrier.
With one bolt on each side of the two bridges they have a hinge action that allows the upper part of the subframe behind the engine to move from right to left. In my cars case just shifting the ZF from first to reverse caused a movement of 1/2 inch as observed by Werner, when the car was standing still.
Werner designed a new bridge that is solidly mounted with welded in tubes and shoulder bolts to the frame on both sides. The transaxle is softly mounted to the new bridge to absorb power transfer vibration. This is the opposite of the original set-up. Looking at mid-engine rear structures in as many cars that I could find I discovered that all were solidly boxed in around the engine. Except the Pantera, which has a similar bridge as the Mangusta. I have been told that it also has some rear frame flex.
After installation of the new bridge the resultant impact of the change to ride and handling was amazing. The car feels much more solid, very little weight bias is felt even with a full tank of gas, it tracks straight and true under acceleration and braking.
The Mangusta with its multiple ball joints both front and rear has a very sensitive racing chassis that comes from DeTomasos early race car building experience. This being the last expression which was the P70 race car chassis developed in a collaboration with Carrol Shelby. This project was stopped when GM came out with its Big Block engine.
The question would normally be asked as to why this flaw was not found in early testing? Likely the time as well as cost pressures meant that it was overlooked. Also,
it is very likely that the flaw would only show up after many miles when the rubber bushings on the bridge would deteriorate allowing space in the system that allows changes to camber when driving.
So why am I writing this? If you have a Mangusta or are restoring one I think that you can improve or maintain good handling performance during everyday driving by making sure that the rear bridge bushings are in very good shape and tightly mounted. I would also take the the front bridge that carries the shock absorber attachments and add an additional pair of arms to it, with four points instead of two solidly bolted to the frame to triangulate the front bridge structure, this would diminish movement. This action would be completely hidden if you are worrying about your car being seen as completely original which is the trend today. This is a relatively simple fix that can result in real improvement of the chassis. Both bridges were changed on my car.
The work done on my car shows that the backbone and rear subframe are quite well conceived and executed, Structure or welds added elsewhere will do be of no added value in solving the problem if the bridges do not solidly complete the rear subframe, making it a solid box that the wheel forces input.
All the best,
DICK RUZZIN
dickruzzindesign@aol.com
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