Front control arm rotation force with polybronze
 

Hi.
So I’m installing control arms with polybronze bushings and I’m not sure how much rotation resistance is too much. I have them pressed in in original mounts. I test installed the control arms and when I tighten the rear bolt the arm rotation stiffens up. When I tighten the front ones it stiffens up more. I would estimate it takes about 5lb force at the ball joint to rotate the arm. Is this too much? Should it be free to rotate or is some resistance ok?

Thanks

Pete

http://forums.pelicanparts.com/uploa...1516571917.jpg

Adding a photo

Have you greased them yet.

it's said an a-arm should be free enough to fall under it's own weight. ive tried again and again to find this sweet spot that I don't think really exists. in my experience with both polybronze & the hard nylon type that took sanding & interior saw curfs to grease the contact surface ive never been able to get one to "fall" under it's own weight.

if you really think about it the a-arm's actual full rotation is very, very slight, maybe 20*? I have installed both types and make sure that it's under light binding load where the a-arm is in it's natural position about level with the ground. I would also exercise them under full rotation that's available to you to see that the force required is consistent through the range of movement.

I'd suspect if you have a lick of sense, and it seems you do undertaking a suspension rebuild you'd be able to feel if the binding would influence suspension loads of our car. the rears are harder to come to grips with when checking sag rate unless you install the spring plates w/o the tbars installed.. I do this too.

I did grease them on assembly with moly based grease.
The force is pretty constant thru it’s full range of motion. I think getting them to fall under their own weight will be difficult.
Have you shaved off the integral washers on the front mount to allow shimming for adjustment? I was thinking of that or installing the front mounts upside down to gain adjustability that way. The only problem is I’d have to press out the polybronze bushings and I don’t have a press.
Pete

My experience: I had to experiment with a variety shims under one of the front brackets to get one troublesome side to have no binding. In the end, both sides glided effortlessly up and down. Both front tie down hooks had scars on them from bottoming or hitting things and I believe most 911's suffer the same. I think those impacts deform the front torsion bar holders just enough to cause trouble.

So try moving the control arm with the rear bolts tight and the front bracket(s) loose and gradually tighten the three bolts until you find which one(s) being tightened causes binding. Then start your fun with shims.

Brighton, so you shimmed the mount down? I think mine want to move “up” so I could try a thin shim at the rear crossmember bolt. Or i’ll have to turn the front mount upside down to give it room the move upwards.

Thanks

ive never had to go as far as shimming pick up points to find a rate of movement I was comfortable with. I'm not advocating one build a suspension with binding components, but really, think about it some. even with polybronze units the forces under cornering, braking, camber setting influences and sticky tires are still deforming the poly portions of the part beyond what a simple washer shim is making up for in a limp, half assembled condition..

like I said, I suggest if it's not binding where it will actually reside, parallel to the ground and a few degrees wither way I think you are fine. consider the forces of the suspension loaded and unloaded, the influence of ARBs, the torsion bars on the over all scheme of things.

targa body flex has thrown off finer running watches..

When I installed my polybronze bearings, I also installed the spherical bearings for the front anchors that were intended to eliminate the binding that might occur in the arms. After I installed the setup, the control arms fell by their own weight easily after greasing. I did not try the "fall experience" with the regular mounts in the front.

this ^

To be clear you installed Elephant's Spherical bearings? I thought they were EITHER the spherical OR Poly bronze, not both. They also have low friction control arm mounts. Is that what you mean?

Or maybe you meant you used the spherical bearings on the front control arms and poly bronze on the rear suspension.

Thanks.

No, these are spherical WASHERS that you use to mount the suspension components to the chassis. They self align:

https://www.elephantracing.com/porsche/911/bushings-bearings-for-911/low-friction-control-arm-mounts/

Thanks for the clarity.

Juanbenae, I see your point and agree. 5 lb of stiction is nothing in the grand scheme. When I take this car off the stands and put its weight on its wheels, the deflections of the chassis and A arms reacting the torsion bar loads are going to cause more/less forces on the bushings. 5 lbs is negligible.

I don't think I need the ER low friction mounts which allow some degree of adjustability. My mounts where in perfect condition and it seems the installation is not bad at all on my car. Maybe I got lucky. Now I feel like I just saved $200 that I can put towards quickchange spring plates in the rear ;)

Thanks all.

Pete

I think you can buy just the spherical washers from ER, that's what I did. You could also get them from McMaster Carr. I personally wouldn't be happy knowing that I have any misalignment or stiction going on in poly bronze bushings, knowing that a quick fix is available. YMMV

Cheers,

- Craig

Craig, I followed your R&R thread which has provided me with tons of useful tips. Thanks for putting that together. I feel like I'm talking to a celebrity!

I thought you used the elastomeric bushings up front with the low friction ER mounts? If I want to use spherical washers, I would have to get the low friction mounts. The originals are too tall to allow washers to be positioned top and bottom... unless I grind them down. After thinking about it 5 lbs of stiction is nothing when considering the loads these bushings will see in use.

Thanks,

Pete

Haha, thanks Pete. Yes, you're right, I did use ER rubber up front with the low friction ER mounts (I forgot that I did the whole thing). I figured that I would most likely switch to PolyBronze if I saw more track time, which is why I got ahead of that with the low-friction setup. I'm still happily on the ER rubber for now.

Good luck with the rest of the work!