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post #1 of 15 (permalink) Old 09-13-2009, 06:44 PM Thread Starter
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Tension-Strut Purpose/Function

O.K., exactly what is the function of the front suspension tension-strut and just how does it affect front-end alignment? I just recently replaced my ENTIRE front suspension (new UCA's, shocks, springs, LCA's, tension-strut bushings, wheel bearing/hub assemblies and inner/outer tie-rods) and my front-end doesn't "feel quite right", at least not on the highway (I'm talking around 65-75 m.p.h.). Around town, at speeds averaging, say, 35-45, my car feels very noticeably tighter and smoother-riding than it did before I replaced all those parts (my wife even says it now rides better than her 2007 Pontiac G6!), however, when I'm driving at highway speeds, it feels as though it's "wandering" ever so slightly (almost so slightly I'm not sure if I'm just imagining it) and there's a noticeable vibration in the front-end (the vibration is worse at times; at times it's almost non-existant and I can sometimes see the steering wheel shake slightly if I take my hands off of it). I just had brand-new Continental tires mounted and balanced at Sears about two weeks ago and the vibration decreased ever so slightly since then, but it's still around. I realize that the wheel balance could still be off, even though these are new tires and were just mounted and balanced, but I really don't think that is the cause of what I'm experiencing.

Could these symptoms be caused by cheap, non-Ford bushings on the tension-strut?

I recently replaced the bushings on my tension-strut with NAPA parts (at the frame side; the bushings at the LCA side are new too, but came with the TRW-made LCA's), but they suffer from the same affliction as all the other aftermarket bushings for our tension-struts - the metal sleeve that goes over the rod end that the bushings fit over is too long!!I had to cut some length off of the sleeve in order for them to work at all, but I'm not confident in their performance now. I'm going to get the Ford ones in another week or two.

Any input/advice on this annoying problem would be greatly appreciated!

Thanks,

Dennis
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post #2 of 15 (permalink) Old 09-13-2009, 06:50 PM
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the tension strut prevents torsional movement of the LCA. Its alignment usage is fairly important, it maintains or changes toe. most alignment shops just adjust via the LCA frame bolt. The aftermarket bushings are all crap, the bushings are thermoplastic and VERY susceptible to breakdown from petrochemicals.




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post #3 of 15 (permalink) Old 09-13-2009, 06:56 PM Thread Starter
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Quote:
Originally Posted by The Great Obucina View Post
the tension strut prevents torsional movement of the LCA. Its alignment usage is fairly important, it maintains or changes toe. most alignment shops just adjust via the LCA frame bolt. The aftermarket bushings are all crap, the bushings are thermoplastic and VERY susceptible to breakdown from petrochemicals.
So, could the use of non-Ford bushings on the tension-strut contribute in any way to a front-end vibration at highway speeds (65-75 m.p.h.)? Can play in the tension-strut cause vibration or make the car feel as if it's "wandering" (just ever so slightly)?

Thanks,

Dennis
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post #4 of 15 (permalink) Old 09-13-2009, 08:16 PM
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I didn't see where you said you had an alignment done; that will cause that problem.

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post #5 of 15 (permalink) Old 09-13-2009, 08:23 PM Thread Starter
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Originally Posted by Grog6 View Post
I didn't see where you said you had an alignment done; that will cause that problem.
I actually had TWO alignments done, both by Firestone - the first time when I first replaced my suspension components last month and then again last Thursday after I took the passenger-side apart to flip the coil spring over. Unbelievably, they didn't charge me for the 2nd alignment at all!

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post #6 of 15 (permalink) Old 09-13-2009, 10:35 PM
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Quote:
Originally Posted by dmw_4814 View Post
So, could the use of non-Ford bushings on the tension-strut contribute in any way to a front-end vibration at highway speeds (65-75 m.p.h.)? Can play in the tension-strut cause vibration or make the car feel as if it's "wandering" (just ever so slightly)?

Thanks,

Dennis
Yes. Lots of people have had problems using non-Ford bushings at the LCA end of the strut. Always use ONLY the oem Ford bushings there.

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post #7 of 15 (permalink) Old 09-13-2009, 11:10 PM
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The strut rod holds the lower control arm in position from front to back. The adjustment nuts on the frame side of it are used to adjust the caster of the front end. Caster is the relation of upper and lower ball joints to each other. Positive caster is when the upper ball joint is further rear than the lower ball joint. A lot of positive caster helps a car track straighter.

The 21mm bolt eccentric/nut on the lower control arm is the primary camber adjustment. Moving this eccentric will usually only throw your caster off a few tenths (if that) from your previous caster swing. Adjusting the caster (which is primarily accomplished with the strut rod nuts) will move the toe a little, but that is why the toe is adjusted last.

Will bad strut rod bushings cause your car to vibrate at highway speeds? No. I do second or third or fourth the notion that oem strut rod bushings are the only way to go however.

When you get an alignment ask for a print out, it forces the mechanic to really dial it in spot on. Ask the mechanic to throw a little extra caster in with about .5 degrees of lead (not the metal, haha). I have found that my car tracks the straightest with about 6-6.5 degrees positive caster with the before mentioned lead. Good luck.

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Last edited by coolhandzep; 09-14-2009 at 01:13 AM.
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post #8 of 15 (permalink) Old 09-14-2009, 07:08 AM
 
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which one is the strut rod, is that the one that bolts into the empty hole on the LCA with two big rubber bushings, and it has a flat spot on the rod that the book says to keep free of tools???

secondly, doesn't having a positive caster cause other problems? I mean shouldn't alignment be straight all around? would it affect handling or anything?
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post #9 of 15 (permalink) Old 09-14-2009, 08:53 AM
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Yes, that is the strut rod. Factory spec on our cars is about +5 degrees caster. If somehow you were to achieve 0 degrees caster on our cars you wouldn't be happy. Look up alignment specs for different 'modern cars' and you will see most have about +2.5 degrees caster.

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post #10 of 15 (permalink) Old 09-14-2009, 12:19 PM
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Quote:
Originally Posted by BigJohnny View Post

secondly, doesn't having a positive caster cause other problems?
At the factory spec No. At higher than recommended specs you'll have heavier steering and more feedback.

Quote:
I mean shouldn't alignment be straight all around?
No. Theres a reason theres different alignment specs from the manufacturers for different cars.

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would it affect handling or anything?
With 0* caster steering will be super light and wont have any returnability, try riding a bycicle with strait forks.

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post #11 of 15 (permalink) Old 09-14-2009, 01:07 PM
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XR-7 is right.

Btw, I run about 7 degrees of caster on my car, .5 degrees cross. After a lot of trial and error that is where I liked it best. My different setups ranged from 5 to almost 8 degrees positive in terms of caster.

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post #12 of 15 (permalink) Old 09-17-2009, 09:42 PM
 
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sorry if i missed something posted previously in this thread, but how is caster set/adjusted exactly?? is it with that strut rod??
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post #13 of 15 (permalink) Old 09-17-2009, 10:25 PM
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Yes, that is the primary adjustment. If you are setting a car up and have to adjust the camber (eccentric at frame/lca) a lot after the first caster swing, your next swing will show a little change in the caster as well. The amount of caster that changed during the camber adjustment is dependent upon the geometry of the suspension.

For all intents and purposes however caster is manipulated with the strut rod.

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post #14 of 15 (permalink) Old 09-18-2009, 09:40 PM
 
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which end adjusts it? the end that connects to the LCA or the other end that connects to the car/frame??

the service manual for LCA replacement simply states to put the nut back on and torque it....didn't mention caster adjustment at all.
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post #15 of 15 (permalink) Old 09-18-2009, 09:49 PM Thread Starter
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Quote:
Originally Posted by BigJohnny View Post
which end adjusts it? the end that connects to the LCA or the other end that connects to the car/frame??

the service manual for LCA replacement simply states to put the nut back on and torque it....didn't mention caster adjustment at all.
It's the end that goes into the subframe. There's a nut on the backside of the subframe that is used to move the rod forward or backwards; it is turned clockwise or counter-clockwise and the movement up or down the threads on the rod pull it forward/push it back.

There's really no need to disturb that nut when replacing the bushings unless it's moved all the way back on the tension-strut in order to allow the strut to move forward to aid in removing it from the car.

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