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Old 11-24-2019, 05:02 PM   #1
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thrust arm bushings

hey - anyone know why tarett lists their thrust arm bushings as different for the front and back on a 986? i thought they were interchangeable?

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Old 11-25-2019, 06:04 AM   #2
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What are you calling a thrust arm?
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Old 11-25-2019, 09:44 AM   #3
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Only the lower arm/wishbone/coffin arm are tj same front to back.
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Old 11-25-2019, 09:52 AM   #4
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we have to agree on what we are talking about. A coffin arm, a wishbone, a tuning fork, radius arm, control arm thrust arm and lower arm are confusing even before we start talking about bushings.
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Old 11-25-2019, 10:01 AM   #5
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Probably front has holes and options for adjusting castor while rear has a single hole in center. They are the same otherwise.
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Old 11-25-2019, 10:06 AM   #6
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Quote:
Originally Posted by edc View Post
Only the lower arm/wishbone/coffin arm are tj same front to back.
right. and the thrust arm bushings are part of the lower coffin arm.

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we have to agree on what we are talking about. A coffin arm, a wishbone, a tuning fork, radius arm, control arm thrust arm and lower arm are confusing even before we start talking about bushings.
there are three control arms on the boxster (front and back the same):

control arm - also called coffin arm (due to shape). porsche calls it a control arm. used to adjust camber.

toe arm - also called toe control arm. sometimes called a radius arm on other cars. porsche calls it a track rod. used to control ... toe. on the front also steers.

thrust arm - should be called caster arm as that is what it controls. sometimes called the tuning fork (due to shape). porsche calls it a control arm. sometimes called a radius arm on other cars. called a thrust arm because it attaches to the control arm via the thrust arm bushing (TAB). that is the common name for this bushing, this is what tarett and all other aftermarket manufacturers call it. and if you gotta ask ...

Last edited by The Radium King; 11-25-2019 at 10:11 AM.
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Old 11-25-2019, 10:10 AM   #7
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Probably front has holes and options for adjusting castor while rear has a single hole in center. They are the same otherwise.
ah, good catch. i'd assumed they were all adjustable, but if you re-read perhaps not. why would you not get adjustable caster option on the back - with 20mm shims on the back you could run 996 rears but would need to adjust caster to address.

https://www.tarett.com/items/986-987-981-718-products/986-987-981-718-suspension/986-987-981-718-monballs~bushings-/adjustable-thrust-arm-bushing-kit-tabka01-detail.htm
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Old 11-25-2019, 10:12 AM   #8
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right. and the thrust arm bushings are part of the lower coffin arm.



there are three control arms on the boxster (front and back the same):

control arm - also called coffin arm (due to shape). porsche calls it a control arm. used to adjust camber.

toe arm - also called toe control arm. sometimes called a radius arm on other cars. porsche calls it a track rod. used to control ... toe. on the front also steers.

thrust arm - should be called caster arm as that is what it controls. sometimes called the tuning fork (due to shape). porsche calls it a control arm. sometimes called a radius arm on other cars. called a thrust arm because it attaches to the control arm via the thrust arm bushing (TAB). that is the common name for this bushing, this is what tarett and all other aftermarket manufacturers call it. and if you gotta ask ...
Thanks, that really helps us newbs!
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Old 11-25-2019, 10:26 AM   #9
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thrust arm bushings

wow great arm..
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Old 11-25-2019, 10:27 AM   #10
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Thanks, that really helps us newbs!
no sweat; can be very confusing. more info if interested:

camber is adjustable w eccentric bolts on the inboard end of the control arm in the rear. in the front it is the top of the wheel carrier that is moved to adjust camber - the strut mount is slotted. to get more camber than factory you have to get control arms that are adjustable or strut top mounts that are adjustable or, on the front, increase the slots in the top mount. note clearance issues with moving top in vs pushing bottom out when going for more negative camber, as well as impacts on track width (pushing bottom out widens track).

toe on the front is adjustable at the steering rack. on the rear there are eccentric bolts on the inboard end of the toe arm. note that as you lower the car the outboard attachment point for the toe arm on the wheel carrier moves up and impacts toe - this is why aggressively lowered cars require aftermarket adjustable toe arms. note also the impact on bump steer as you lower the vehicle which may make you want to consider adjustable ball joints on the end of your toe arms.

caster is not adjustable on our cars. note that the thrust arms attach to the control arms and that if you have adjustable control arms and go for an aggressive camber setting then you can push the caster out of spec. as such you need either adjustable thrust arms or an adjustable bushing where the thrust arm connects to the control arm.
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Old 11-25-2019, 02:34 PM   #11
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Originally Posted by The Radium King View Post
ah, good catch. i'd assumed they were all adjustable, but if you re-read perhaps not. why would you not get adjustable caster option on the back - with 20mm shims on the back you could run 996 rears but would need to adjust caster to address.

https://www.tarett.com/items/986-987-981-718-products/986-987-981-718-suspension/986-987-981-718-monballs~bushings-/adjustable-thrust-arm-bushing-kit-tabka01-detail.htm
Yeah I would only ever get the adjustable ones for greater possible re-use down the road
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Old 12-01-2019, 10:05 AM   #12
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so, prize to steve. just heard back from ira at tarett (that guy is great; like having a personal counselor for your suspension). rear non-adjustable, front adjustable. however interchangeable.
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Old 12-01-2019, 11:10 AM   #13
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no sweat; can be very confusing. more info if interested:

camber is adjustable w eccentric bolts on the inboard end of the control arm in the rear. in the front it is the top of the wheel carrier that is moved to adjust camber - the strut mount is slotted. to get more camber than factory you have to get control arms that are adjustable or strut top mounts that are adjustable or, on the front, increase the slots in the top mount. note clearance issues with moving top in vs pushing bottom out when going for more negative camber, as well as impacts on track width (pushing bottom out widens track).

toe on the front is adjustable at the steering rack. on the rear there are eccentric bolts on the inboard end of the toe arm. note that as you lower the car the outboard attachment point for the toe arm on the wheel carrier moves up and impacts toe - this is why aggressively lowered cars require aftermarket adjustable toe arms. note also the impact on bump steer as you lower the vehicle which may make you want to consider adjustable ball joints on the end of your toe arms.

caster is not adjustable on our cars. note that the thrust arms attach to the control arms and that if you have adjustable control arms and go for an aggressive camber setting then you can push the caster out of spec. as such you need either adjustable thrust arms or an adjustable bushing where the thrust arm connects to the control arm.
Thanks, very good info. When lowering, are there any other areas to consider that might bind or cause other geometric problems (at approx. -2.5 to -3 degrees camber)? And at these cambers and "wider track", will it still be beneficial to add spacers? Or should I ask if there is a set width to effective track?

Last edited by Hasbro; 12-01-2019 at 11:23 AM.
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Old 12-01-2019, 11:11 AM   #14
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just heard back from ira at tarett (that guy is great; like having a personal counselor
+ 1
Ira is a gentleman that always answer the phone and help you with installation tips and setting suggestions based on his experiences :-)
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Old 12-01-2019, 11:30 AM   #15
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Thanks, very good info. When lowering, are there any other areas to consider that might bind or cause other geometric problems (at approx. -2.5 to -3 degrees camber)? And at these cambers and "wider track", will it still be beneficial to add spacers?
ha, loaded question. a lot of other variables come into play once you start getting outside of factory specs - wheel and tire width, wheel offset, tire sidewall height, wheel diameter, coilovers vs factory suspension. you get inner clearance issues with the struts, thrust arm, parking brake cable, sway bar drop links. ie, the struts are canted a bit; as a result, a larger diameter wheel will have better clearance than a smaller diameter wheel.

outside clearance issues are relatively obvious.

the concern with spacers is that it distances the wheel from the wheel carrier and impacts what is called scrub radius.

finally, just realise that you have four points of contact with the wheel carrier - toe arm, control arm, thrust arm and strut (length, top mount). move one and you impact the other three. this is why the go-fast parts are all adjustable.
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Old 12-01-2019, 03:58 PM   #16
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ha, loaded question. a lot of other variables come into play once you start getting outside of factory specs - wheel and tire width, wheel offset, tire sidewall height, wheel diameter, coilovers vs factory suspension. you get inner clearance issues with the struts, thrust arm, parking brake cable, sway bar drop links. ie, the struts are canted a bit; as a result, a larger diameter wheel will have better clearance than a smaller diameter wheel.

outside clearance issues are relatively obvious.

the concern with spacers is that it distances the wheel from the wheel carrier and impacts what is called scrub radius.

finally, just realise that you have four points of contact with the wheel carrier - toe arm, control arm, thrust arm and strut (length, top mount). move one and you impact the other three. this is why the go-fast parts are all adjustable.
Yeah, I guess that was a pretty broad question, but thanks for answering. Just trying to get a feel for Boxster suspensions. It's almost like starting all over.

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