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Old 08-28-2010, 08:17 AM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
Join Date: Mar 2008
Posts: 25,236
Mein Auto: 02 BMW 525i M54 auto 130K
Originally Posted by dms540i View Post
I agree it's confusing jargon
Thanks dms540i for pointing out the control arm in the realoem diagram and the fluid-filled bushing which apparently leaks at around 75K miles.

It is confusing to me. Apparently RealOem calls the "thrust arm" a "Tension Strut" when it's on the I6 but they call it a "Traction Strut" when it's on the V8. I've also seen the abbreviations CABs & FCABs, which I duly added to the E39 glossary just now so others would benefit. Then there's the matter of the apparently similar, but different "control arm" ...

So that's at least four names I need to reconcile which seem to take the place of the "A Frame" of olden days ...
- control arm
- thrust arm
- traction strut
- tension strut

Originally Posted by xraye39 View Post
Raj already has a great write up
Thanks xraye. That Beisan writeup was pretty good.

At first I thought a thrust arm was the same as a control arm but the Beisan statement "The thrust arm is longer than the control arm" says otherwise.

Confusingly, Beisan calls the "thrust arm" the "upper control arm" and the "control arm" the "lower control arm" so that adds another set of somewhat confusing terms to someone who is uninitiated. Reading on, we find the "thrust arm" on the I6 is also called the "leading control arm" making the "control arm" the "trailing control arm". Much to my chagrin, on the V8, things reverse!

So that's now six (confusing) names for the same or similar things:
- thrust arm (longer than control arm, uses hydraulic rubber bushing)
- control arm (shorter than thrust arm, uses solid rubber bushing)
- upper control arm (i.e., the curved thrust arm, longer, rises higher to the frame)
- lower control arm (i.e., the straight control arm, shorter, rises lower to the frame)
- leading control arm (i.e., the thrust arm on the I6)
- leading control arm (i.e., the control arm on the V8)
- trailing control arm (i.e., the control arm on the I6)
- trailing control arm (i.e., the thrust arm on the V8)
- traction strut (i.e., the thrust arm on the V8)
- tension strut (i.e., the thrust arm on the I6)

Originally Posted by Fudman View Post
ball joints can fail (a more common occurance on the control arm) or the bushing can fail (leak)...recommended fix is the EACTuning solid rubber bushing...much easier to buy replacement thrust arms with the HD bushing installed...
Thanks Fudman, this is useful to note that the wear to look for at around 75K miles (I have almost 100K miles on my I6) is the thrust arm bushing leak or the thrust arm ball joint ... both of which can be resolved with a new thrust arm with "HD" bushings.

BTW, I didn't know what "HD" stood for so I first went to the BMW glossary which said it was for "heavy duty"; but I think you mean "solid" when you say HD (based on your context).

Searching for "HD" I find nobody defines it but they reference it as the "solid" bushing (so what does the "HD" stand for then?).
- Looking at Meyle HD everthing from OEMBimmerParts
- new thrust arms with HD bushing or replacing your worn out fluid filled thrust arm bushings with HD bushings
- I go the Meyle Thrust Arms with HD bushings.
- Meyle HD Bushing Set - This set is solid rubber to increase longevity compared to the stock, fluid filled bushing

Overall, this is very confusing; but I'm starting to get a handle on it, thank to the three of you!

Last edited by bluebee; 08-28-2010 at 11:42 PM.
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