Reply to "dickruzzindesign@aol.com"

Dick,

I agree with your thoughts on the rear bridge. The stronger you can make this area better. This flexing in the rear fame is only effecting camber however. Camber change through chassis flex is not desirable of course but the real problem on the back of the Mangusta is toe change as the rear suspension goes into bump. I spent a long time making laser jigs specifically for the Mangusta.

I also spent time studying the GT40 rear suspension and found the Mangusta to be identical in design except for one very important part - the top link on the Goose only has a Rose joint on the inside. On the outside (upright end) it has a "T" bar with bushings. This T bar means the top arm cant move side to side thus making it impossible to incline the rear upright in order to adjust the rear toe change under bump. It's hard to get your head round this until you have the spring and shock off the car, mount the laser jigs on the rear wheel and then wind it through it's travel so that you can see the toe change.

All Mangusta's I have worked on with the standard rear set up go from 1.0 degree tow in to 0.0 degree toe at full bump. In other words it toes out by 1.0 degree from ride height to full bump, very dangerous! I believe this is the main reason the Goose got such bad press in it's day. All they had to do was look at a GT40 like I did. If you read any chassis engineering book they all say to avoid rear toe out like the plague.
Having rear toe out is dangerous enough, but the Mangusta is even worse - it can bump into tow out in the middle of a corner!

Fortunately, this is very easy to fix with one simple modification. I remove the top arm and cut the "T" bar off and replace it with another Rose joint. This then makes the rear suspension the same as a GT40 - infinitely adjustable.

Then you can lean the rear upright back (effectively increasing the castor) until it bumps neutral or slightly into tow-in (a totally safe condition). Make sure you have enough Rose joint left in the rod of the top trailing arm. The rule of the thumb here is if it's and 18mm Rose joint you need a minimum of 18mm thread in the rod.

I did all this on Jonathan Roots car and spend hours and hours. I think it's way beyond the scope of the average alignment shop even if they have got 30K worth of Hunter equipment. Any owner would be better off doing it themselves at home because the alignment shop will get pissed off with it and not get it right.
Warning, aligning the rear of a Mangusta or GT40 takes a very long time!

Here is the principal I used to set the bump steer front and rear on the Mangusta
https://www.youtube.com/watch?v=LO07qmJ9zkk

In the above video I dont think the measurement from the wheel to the mirror is relevant.

There is another way of reducing (not fixing) this rear bump steer problem, by using much stiffer rear springs. This method helps by simply reducing rear suspension travel but also rips the top shock mounts out of the chassis on the early cars that have a two bolt crossmember rather than the later 4 bolt crossmember.

Johnny