Suspension help - shocks locking up

I am having a moment. That, apparently, is a technical term.
(Moment = Magnitude of Force × Perpendicular distance to the pivot)
Anyone who has seen my car corner knows it handles like a POS... people following me in to fast corners have bailed because they though I was gone, and it was going to be a big one.
I always knew it wasn't good, but I never really knew how bad until I had a friend, a professional race instructor, drive the car and said straight up that the car is so bad it is scary. Admittedly he had a big one the night before, but he has driven enough variety to know good, bad and ugly.
What happens is the rear shock on my car locks up solid, the only play in the system is the tyre and the top mount (rubber at the moment - use to be a rally car and the play is good to have in that situation, too many other problems to fix it yet)

I had the struts tested and here are the results: I guess they are typical rally struts, because the force graph runs a bit concave, not convex (which is more typical of circuit) but the figures them selves are not way out of the ball park (I don't think)
Struts are quality units, 50 mm DMS double adjustables.
http://i168.photobucket.com/albums/u198/notso_swift/shock.jpg
Graph axis are Speed (m/s) and Force (Nm)

I don't get to drive my car much, but over time I have had different theories with the back:
I thought it was I had springs on that were way to hard, but I dropped them right down and the problem remained. Besides a car that previously had long travel 185 lbs springs should not be impossible to move with 320's, especially with my weight jumping on the back.
I thought that the shocks were stuffed, that they locked up on high shaft speeds (Testing ruled that out)
I thought that the shocks were stuffed, that they locked up because the adjustment mechanism had a fault. (Testing ruled that out)

I was having a discussion with a shock bloke, and running through the problem I was having and he has identified the problem is the locking of the shaft. makes perfect sense. When you release the pressure (jack the car up) and drop it again it all works normally for a while, I have had tell tails on the shaft and you can see that the "fully compressed" point is about 2" lower than the resting. Then you drive it a bit and it goes hard, generally trying to throw you of the track at the same time, the rear doesn't release until you take all pressure off it (jack it back up).

Now, what can I do about it?
Going back to the original long 185lbs springs is not an option, it unloads the front wheels as the car rolls around too much. The bearings in the shaft are fine. The car has increased camber from before, it use to be set at 0 now it is 1.5 Nothing else has changed.
I have one idea, but I want to know what others think.

havent you answered your own question, that the shocks are locking up cos of the suspension design? sounds like it from your description!
either that or something silly like the rod ends over full tilt when compressed and in roll. if u take the spring off the shock and move it i guess you would find this out!

Not at all, the fundamental design has not changed and the shocks didn't use to lock up, this is a production based car witht he same rear end as a Mazda MX5, not known for bad handling!
I can't replicate the problelm with low speed on car testing ((shock in place without spring and using a jack/lever. And High speed testing on a bench does not give any lateral loading.

does something happen in roll? does the roll bar lock up ? hard to tell statically

I pulled the ARB off, to minimise variables, wasn't significantly better or worse, I think it could be reasonable to think roll may have an effect though. Static and limitations in replicating are really what is killing me on this!

When were your shocks last revalved and checked?

i was thinking it might be the actual roll bar that is locking the suspension up?
have you run it on circuit without it?

A common fault on early Lotus Cortina Race cars was the front struts locking up due to side pressure on the bearings. Think Jim Clark and the front wheel on the inside of the corner radius waving in the air).

This was cured by re-working the bearings to form a sort of conical face and thus reduce the friction induced by side thrust.

Worth a look see perhaps.

Another fault was that the struts can bend,the works had a lot of this,especialy on the rally cars.

When were your shocks last revalved and checked?
No long ago, I thought they stuffed it up so I had it checked

THR, no ARB fitted any more see post above

Checked the true of the strut when the valving was dyno'd

SidewaysFeltham, I think we may have a winner
My latest theory is, the long springs spread the load of the lateral force ovet the length of the body, and that way from the bearing (shock tube bearing, that is) can do its work. The short spring means the force is focued in a much smaller area, further, that force is at the pivot poit (being the bearing) theis extra force is causing it to lock. It will be a little while but I am going to try long springs made in a heavy poundage.

Any comments/thoughts/suggestions?

I would probably remove the springs and then plot the suspension travel, measuring the sideways movement of the shockers.

Try all combinations: e.g. try each side independantly using a really smooth jack with long travel. Then both sides equally over the full expected travel, bump stop to bump stop.

You may well find that it's happening when the load becomes severly assymetric; for example, very fast corners as the roll induced load transfers rapidly to the outside of the radius of the corner.

What we all forget, is that no suspension system is perfect in terms of absolute straight line travel: there must always be some component of arc in travel. The whole thing is very much a compromise of best options.

Thus if the side thrust loading is excessive, then the shockers are trying, valiantly and failing to conform.

Road cars, of course, absorb this through extensible rubber mounts: i.e. compliance.

Race cars are not intended to be smooth and quiet!

I well remember a fellow competitor in Modsports with an E Type Jag. He had steel mountings and bushes made up for everything, including the front ARB.

The thing became an almost drivable bolide! Scared him rigid!

Yet another of those back to the drawing board bright ideas!

Like the other bloke, Sid summat who happened upon the bright wheeze of fitting a Morris Minor rack to his A35 racing saloon, on the grounds that it would then have more accuracy through corners.

Left the paddock at Brands, under the track through the tunnel, hit the loud pedal and headed off for Paddock.

At the first touch of the brakes, the front end dipped: and the dive induced steering effect gave him an instant 1 or 2 inches of sudden toe in!

Dramatic stuff!

Big squeals and large black marks all along the track.

:rofl: