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Thanks Bill for your answer,
I thought exacly as you, until I removed the A-arm from the car.
Once removed, I noticed the slot in the cross member which avoid the A-arm to take its natural angular position.
So even tightenning the bolts while the car is sitting on his wheel, the front bushing can't rotate to take a center position
All that does is fix the retraining shell in place. prior to final torquing the rubber is mostly free to rotate inside the arm, after final torquing the rubber is mostly pinned in place and must stretch to allow suspension movement
Would like to revisit this topic as I'm getting ready to replace my bushings with the Elephant "Sport" (RS) bushings.
@Bill Verburg , agreed that this only gets final torque while sitting on the wheels but certainly the angle that this bushing is pressed in will have preload effects on the working range of the bushing, no? Stock control arms have this pressed in horizontally but what about RS control arms? Is the angle actually the same?
Mike @MB965 chat quite a bit and he told me that when he bought brand RS front control arms, the bushings were clocked at a ~7* offset (as measured by fancy workbench measurements), not perfectly straight horizontally like stock arms. I imagine it looks similar to your last photo above. His suspicion is that did this consciously due to the different uprights and ride height. I doubt the factory would have done this in error, with both arms having opposing angles of orientation.
I've been searching around for into on this topic (orientation of the leading control arm bushings on RS control arms) and haven't found much discussion other than this thread. Figured I'd bump this thread for posterity's sake.
I appreciate all the insight both of you provide but thought a current, public discussion on the topic might help preserve this information and help others down the road as I've been struggling to find much.
I used an air chisel with success in removing the bushings. You have to make sure that the chisel is working "exactly" on the steel cylinder of the mount as you move chisel around the perimeter of the bushing.
I can see the merits of properly clocking that forward bushing for your ride height. Don’t love the idea of guessing at 7 degrees etc. I’d set up car at final ride height then mark proper location.
Don’t love rubber bushings in that forward position anyway. Poly would be my choice. It does not have the stiction issues as it does in rear position and it does not have all the deflection of stock style bushing.
Love all the work and detail you’re putting into this.
I can see the merits of properly clocking that forward bushing for your ride height. Don’t love the idea of guessing at 7 degrees etc. I’d set up car at final ride height then mark proper location.
Don’t love rubber bushings in that forward position anyway. Poly would be my choice. It does not have the stiction issues as it does in rear position and it does not have all the deflection of stock style bushing.
Love all the work and detail you’re putting into this.
There is no discretion wrt to that bush
the notch is what it is and the shoulder goes into it, Done deal.
I'd just install it and not worry about it,
i'm going to try to get together w/ Mike next week end at LRP, see if we can maybe do a side by side comparison
I have no use for poly bushes, If you want no deflection use a mono-ball otherwise sport rubber
poly installed(boo hiss), mono-ball(yeah rah) ready to be installed, no need to worry about the notch angle w/ these
the notch is what it is and the shoulder goes into it, Done deal.
I'd just install it and not worry about it,
i'm going to try to get together w/ Mike next week end at LRP, see if we can maybe do a side by side comparison
The line of thinking here is:
- The insert is bonded into the rubber
- The rubber has some small and large holes in it, which are there for progressive flex presumably
- Based on above, there is likely a "range" of motion that is optimal for this bushing
- When you align the notch in the bushing with the notch in the subframe that the control arm bolts to, it positions the arm for preload
- The RS uprights and ride height certainly change some things, it wouldn't be surprising if the bushing was pressed in at a different angle
- Mike bought brand new RS control arms and theses bushings were pressed in with a slight offset
I'll let you two huddle up. Certainly this isn't a huge issue to bellyache about and there are tons of folks who've replaced their uprights with RS and haven't had their 993 meltdown due to front control arm bushings that are not aligned to factory RS spec (if such a spec was conscious and the guy who made Mike's control arms wasn't simply drunk on a Friday afternoon).
But this is what happens when two engineers start chatting about a topic. He already asked me, "so what are you going to do?? horizontal (0* degrees) or 7* offset like mine??".
My reply? "3.5 degree offset is the only reasonable solution of course!"
I probably won't press the bushings in for another week or two. Inclined to go 0* like everyone else and move on but curious what you two come up with.
Last edited by boomboomthump; 04-16-2022 at 10:47 AM.
- The insert is bonded into the rubber
- The rubber has some small and large holes in it, which are there for progressive flex presumably
- Based on above, there is likely a "range" of motion that is optimal for this bushing
- When you alight the notch in the bushing with the notch in the subframe that the control arm bolts to, it positions the arm for preload
- The RS uprights and ride height certainly change some things, it wouldn't be surprising if the bushing was pressed in at a different angle
- Mike bought brand new RS control arms and theses bushings were pressed in with a slight offset
I'll let you two huddle up. Certainly this isn't a huge issue to bellyache about and there are tons of folks who've replaced their uprights with RS and haven't had their 993 meltdown due to front control arm bushings that are not aligned to factory RS spec (if such a spec was conscious and the guy who made Mike's control arms wasn't simply drunk on a Friday afternoon).
But this is what happens when two engineers start chatting about a topic. He already asked me, "so what are you going to do?? horizontal (0* degrees) or 7* offset like mine??".
My reply? "3.5 degree offset is the only reasonable solution of course!"
I probably won't press the bushings in for another week or two. Inclined to go 0* like everyone else and move on but curious what you two come up with.
The control arms are left and right so it is unlikely the bushing rotation was random due to Otto's lunch beverage!
I measured the arms on a steel layout table using the bolt centers and ball joint mounting surface as datum. Used the bushing tab centerline as the angle measuring point with a 12" protractor.
Confirmed the RS arm bushings were rotated 7 degrees one side CW and one CCW.
The USA arm bushings measure 0 degrees.
So, no guessing on how much the bushing is rotated!
The factory does not sell this bushing as a separate part and there are no installation instructions for it in the service manual.
I got onto the idea of measuring the bushing clock position when I had my 1994 964 Turbo 3.6. The factory literature described how the rear trailing bushing was installed clocked to address the lowered ride height.
That 964 bushing is similarly tabbed to the chassis as the 993 front arm bushing is.
The effect of the 993 RS control bushing clocked position is at best secondary and unlikely to cause any noticeable ride difference or bushing life.
Don't forget these are factory design engineers always trying to optimize.
As a point of reference, I bet when lowered, many lowered cars did not have all control arm bushing bolts loosened/retightened with the car on the tires.
The control arms are left and right so it is unlikely the bushing rotation was random due to Otto's lunch beverage!
I measured the arms on a steel layout table using the bolt centers and ball joint mounting surface as datum. Used the bushing tab centerline as the angle measuring point with a 12" protractor.
Confirmed the RS arm bushings were rotated 7 degrees one side CW and one CCW.
The USA arm bushings measure 0 degrees.
So, no guessing on how much the bushing is rotated!
The factory does not sell this bushing as a separate part and there are no installation instructions for it in the service manual.
I got onto the idea of measuring the bushing clock position when I had my 1994 964 Turbo 3.6. The factory literature described how the rear trailing bushing was installed clocked to address the lowered ride height.
That 964 bushing is similarly tabbed to the chassis as the 993 front arm bushing is.
The effect of the 993 RS control bushing clocked position is at best secondary and unlikely to cause any noticeable ride difference or bushing life.
Don't forget these are factory design engineers always trying to optimize.
As a point of reference, I bet when lowered, many lowered cars did not have all control arm bushing bolts loosened/retightened with the car on the tires.
Great info, thank you for measuring and sharing. Clocking them makes sense.
However one decides to install these, make sure the centering nub on the bushing is in the corresponding notch in the side mount. Ignoring this will result in the nub pressing into the cast mount and possibly leading to a crack, or loss of bolt torque (leading to the bolt backing out) if it slips back into the notch.
I've always read that you cant buy Porsche replacement bushings for the control arms, it's either aftermarket or complete control arms. Is it all or only some? Not that I would have replaced with stock bushings (I went with RS "sport" type bushings from Elephant) but when I looked up the part number on the leading bushing on the front control arm, it says it's available?
the notch is what it is and the shoulder goes into it, Done deal.
I'd just install it and not worry about it,
Boomboom is talking about clocking the bushing so it sits neutral without rotational deflection at his ride height. I can understand why the factory would clock the RS bushings differently in that forward position given the big difference in ride height. No pre-loaded rotation = longer bushing life.
I won’t touch your poly comment, we’ve already agreed to disagree there. 😊
I love all the attention to detail being put into this project!
BTW, here's what my bushing looked like when I took the control arms off. Perhaps just due to age but the car had been run at RS height for quite awhile.
Very interesting! That is just were I would expect the failure to initiate, at the bond with the sleeve. Highest shear stress and lowest shear strength.
My same bushings with 88K miles at stock height had no sign of failure.
I am going to dig out my RS arms and see what the front bushing PN is. Would be interesting to see if it was available also.
12-20-2020, 03:36 PM
Certainly this isn't a huge issue to bellyache about and there are tons of folks who've replaced their uprights with RS and haven't had their 993 meltdown due to front control arm bushings that are not aligned to factory RS spec (if such a spec was conscious and the guy who made Mike's control arms wasn't simply drunk on a Friday afternoon).
