Front T bars going soft?
 

My 72 911t has 219,000 miles on I presume are stock front torsion bars. After corner balancing and alignment, which lowered the front a little, I have a clunk when I hit a hard bump and during hard cornering at the last autox.

I took a grinder and relieved the spot where the A arm was hitting the body. I also raised the front about 1/8". I ordered a stopper that goes on top of the shock that is supposed to be progressive vs the stock rubber but it's back ordered and I haven't received it yet.

I called the shop that did the corner balance and he said it could be the torsion bars going a little soft. Never heard of that before. Anyone heard of that?

I don't want to disturb the height/corner balance and maybe this new stubber on the shock will fix it, just curious if these torsion bars ever do go soft!http://forums.pelicanparts.com/uploa...1298134766.jpg

I, for one, have never seen a factory torsion bar go "soft". I've seen them break, but not lose tension. JMHO, but you may other issues going on.

Remember, raising the car 1/8" changed the front toe setting and corner weights. :)

Once "scragged", torsion bars do not appreciably loose stiffness unless they had a large, pre-existing crack in them which has begun to propagate after cyclical loading and can eventually cause them to snap. Otherwise, steel has a "fatigue endurance limit" for small internal imperfections (cracks) where it lasts pretty much forever below a certain stress/strain, unlike Aluminum.

Bushings or bump stops on your shocks...

Would truely love to see torsion bars go elastic. Actually, I'd llike to see what you would have to do to get them to that point. Is this a "Hey, y'all, watch this!" moment?

Don,

They are elastic all of the time and obey Hooke's Law :)

They will remain elastic up to the yield point and beyond this limit any deformation will be permanent. When you unload them they will still follow the initial elastic loading/unloading line but with a small offset.

Most steels can be described as Elastic/Work Hardening-Plastic solids.

The scragging process that Max referred to above involves taking the spring to just past it yield point so that it shouldn't lose ride height even after years of service, as the suspension should hit the bump stop well before they can yield.

plastic - someone posted a graph on here at one time

if they do go plastic, either you are in an alternative metallurgical universe or have taken drugs associated with plastic fantastic lover

see post #4

Do you mean this one?

http://i197.photobucket.com/albums/a...ane/Yield2.jpg

So not to go OT, but if torsions don't go soft or essentially until they take a set, how does this compare with coils and leafs? I know leafs wearout not sure about coils... That if Im correct is why?

Yes, shocks.

Torsion bars are steel. Steel has one modulus of elasticity. Soft steel, hard steel, brittle steel, strong steel, new steel, old steel...

Only one modulus of elasticity (springiness)

For springs the important part is how far you can flex them before they reach their yield point. At that point the metal permanently deforms-> Plastic deformation (there is your plastic!) To make a good spring you need steel that will flex quite a bit with out reaching the yield point.

If your springs had reached their yield point the car would be lower but the spring rate would be the same. To change the spring rate you need to change the length or cross section of the spring. The length isn't going to change but a crack could change the cross section by a noticeable amount... for a second or two before it breaks completely...

Bad struts maybe? If they lose their dampening effect it can make the car feel "soft" as there is nothing to slow the suspensions movement.

thx for the diagram

to get back to his problem, I will bet that the rubber bushings are old, cold-flowed and/or hardened - or are made from poly-horrible material (done by a PO maybe).

Inspect them, Kent, and you will likely do what thousands of others have had to do after 20 or more years - replace them with the Elephant materials that Chuck Moreland makes. Either polybronze or new rubber. Or use the Rebel Racing ones.

I forgot to mention we put in new camber plates and replaced both front shocks,(inserts). I ordered Koni race snubbers for the top of the shocks but they haven't arrived yet.

Thanks Steve I'll have to recheck the front alignment after I finish messing around with the suspension.

Bye the way this noise (clunk) only surfaced after we did the camber plates, corner balance and 4 wheel alignment. The car was lowered in the process as well.