worf928

I understand the settling of the suspension relative to the LCA. I do not understand what BB wrote in general terms.

Settled, unsettled, wheel on, wheel off, if the LCA cannot rotate (about the roll axis of the car) the coil spring cannot compress. There would be zero suspension travel. The geometry of the suspension results in both upper and lower control arms rotating about their "long axis" relative to the chassis to produce suspension travel.

Bill is making a point about the front bushing, mounting, and chassis interface. I simply do not understand specifically to what he refers because some part of the LCA must rotate at both chassis attachment points.

Bill Ball

Dave: That's the way it is, as Jon confirms. The front bush is elastic enough to allow the necessary A-arm movement. Also, properly torqued and properly not greased, the rear bush is all but stuck as well, otherwise it would probably wear out in no time. I think I originally heard about the front bush bonding from Marc Thomas. My front bushes are still solidly bonded and cannot be turned to a new position but spring back to the original position. I have seen one "broken" one where the front mount could be moved and would not spring back.

worf928

If the front attachment point of the LCA falls off then there's a problem. I'll stipulate to that And if you can rotate the front easily by hand then that's probably not good either. But, when driving, for there to be any suspension movement at all, both the upper and lower control arms must rotate. Otherwise the wheel hub cannot move up and down relative to the chassis. The amount the control arms must rotate is, obviously, very limited - and indeed calculable. It's probably on the order of 15° or so, but non-zero nonetheless.

Bill Ball

I think I understand the A-arm must move. It does. But that bush is bonded but flexible AFAIK. Sorry, I edited my post as you were replying. Marc Thomas could have been wrong, but my experience with the front lower A-arms seems to go along with what he told me years ago. That said, this thread corrected one of my early misreadings about the torqueing of the A-arms, and maybe it needs to correct this other notion as well.

worf928

Ok. So - to paraphrase - the LCA should rotate, but, it should be reasonably difficult to do it by hand, and once rotated it should jump back to it's "settled" position. Yes?

Hmmm... so, it follows then, that torquing the rear LCA bolts before the suspension has settled will not only make the car harder to settle for alignment, but may also lead to accelerated wear of the LCA bushings.

Bill Ball

Dave: I think your last post is right. This may be one reason why Porsche says no "renewing" of the front LCAs in the WSM. I notice Carl now offers such. I wonder what he would have to say about the front bushing.

worf928

I'm always hesitant to interpret "Germ-lish"

Are S4+ LCAs NLA now?

Mrmerlin

just a warning if you have already bolted the LCA to the car while it was on the jack stands then gotten the front end aligned then you should not loosen the LCA bolts to retorque them as the front end will then go out of alignment.

jon928se

Tell me about it.

IIRC doesn't one of the brackets have a locating lug on it - maybe it's the rear saddle to it's receiver ?

hacker-pschorr

Which is why I'm planning an upgrading to these:

http://simardracing.com/Suspension.html

depami

After further study, you should notice that the front bushing has a “full circumference” metal housing and cannot be deformed by full torque on the bolts.

Where as, the rear bushing has a two piece “clamping mount” and can be “locked” in any position. Settling the suspension with the bolts loose would let it “find home”. At that point, proper torque on the bolts will hold it in position to flex as designed.

Does this make sense or am I way off base here?

jon928se

I think you expressed that far more eloquently than the rest of us put together.

Tony

Bit of a thread resurrection ...

Reading a few posts from searches on Lower control arms...... this is good stuff.

as I look at my new controls arms, my old ones were really...reeeeeeeally bad.

leaving the rear bolts “loose” does make sense and his quote about it above explains it well.

where would we be with the info “stored” on here....??

Wisconsin Joe

Presuming you really meant 'without the info'.

I know where I'd be...

Going out into the garage and looking at a car that doesn't run.
Maybe sitting behind the wheel and crying a little every now and then.