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ADJUSTABLE STRUT RODS - different designs
#1946420
11/06/15 05:11 PM
11/06/15 05:11 PM
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Joined: Jan 2010
Posts: 1,442
NW Chicago suburban area
Mopar Mitch
OP
pro stock
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OP
pro stock
Joined: Jan 2010
Posts: 1,442
NW Chicago suburban area
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There are two basic types of adjustable strut rods:
1. With heim-joint ends (example: Hotchkis, PST)
2. Without heim-joint ends (example: Firm Feel).. using poly bushings.
Advantages, dis-advantages, of each design? Both designs assist in keeping the LCA pulled forward properly, as well as to gain more positive camber.
Longevity of both designs?
Car (my Challenger) is driven minimally on the street/hwy for wknd events (cruises), but also a high concentration in pylon AX and road course HSAX/HPDE.
Would the heim-joint design eventually fail?
What type of bushings are in the heim-joint design? They appear to be flat metal plates (no bushings?).
Would the poly bushings (using Firm Feel strut rods) eventually fail (instead of using rubber bushings)? I've used the stock factory setup (non-adjustable) with rubber bushings forever and have had no problems... after ~30 years, they still look a-ok.
Winter project in-progress.
T/Anks ahead!
Last edited by Mopar Mitch; 11/06/15 05:14 PM.
Mopar Mitch
"Road racers and autocrossers go in deeper and come out harder!"... and rain never stops us from having fun with our cars... in fact, it makes us better drivers!
Check out MOPAR ACTION MAGAZINE, August 2006 issue for feature article and specs on my autocross T/A!
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Re: ADJUSTABLE STRUT RODS - different designs
[Re: Mopar Mitch]
#1946465
11/06/15 06:12 PM
11/06/15 06:12 PM
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Joined: Dec 2004
Posts: 801
central CT
cudazappa
super stock
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super stock
Joined: Dec 2004
Posts: 801
central CT
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Mitch,
You are entering the no free lunch zone.
You have potentially 3 choices going with adjustable strut rods:
1) adjustable struts w/ rubber bushings
2) adjustable struts w/ poly bushings
3) adjustable struts w/ no bushing & using a heim joint.
1) the rubber will flex and negate some of the effects of the adjustable strut. As such, you'll adjust more to compensate for the flex. Part of the reason your rubber bushings have lasted so long (besides the limited use) is the fact that they were working with the factory strut rod. Using an adjustable will introduce preload into the bushing and make it flex more than it used to. That will undoubtedly increase bushing wear, but without empirical evidence, this is still just theory in my head.
2) the poly flexes less and in my experiences poly has a shorter life compared to rubber in the same environments, but it does firm up stuff some.
3) This style actually keeps the most consistent suspension geometry as everything is a hard point with a pivot. Heim joints will actually free up the bushing bind as the LCA travels in its arc. Uncovered heim joints require inspection. They are like a ball joint. Precision fit, but a small amount of dirt can make them crap in short order. The position of the forward heim really won't get much dirt kick up like an UCA with a heim. Put a boot on it and treat it like a sealed ball joint. Just give it a good dose of dry lubricant before you put the boot on. This style of strut rod will put the tension load on the K-frame. A reinforced k-frame won't care. Non-reinforced its not much of an issue, either. HOWEVER an accident with an impact to the front wheel may incur more damage as the load path from the strike won't terminate in a bushing (that's why factory style tie rods are cheap and hollow, they are the first sacrificial part in that scenario).
My personal choice is #3. I'm just trying to keep the car pointed the right way now.
(sorry for the long post)
1971 Challenger
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Re: ADJUSTABLE STRUT RODS - different designs
[Re: Mopar Mitch]
#1946484
11/06/15 06:45 PM
11/06/15 06:45 PM
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Joined: Sep 2007
Posts: 14,889
up yours
Supercuda
About to go away
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About to go away
Joined: Sep 2007
Posts: 14,889
up yours
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Won't using the strut rod to add caster put a side load on the LCA bushing causing it to wear faster?
As said, no free lunch but I wouldn't use the strut rod to get more caster.
They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
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Re: ADJUSTABLE STRUT RODS - different designs
[Re: Mopar Mitch]
#1946486
11/06/15 06:50 PM
11/06/15 06:50 PM
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Joined: May 2005
Posts: 723
Houston Tx
Uhcoog1
super stock
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super stock
Joined: May 2005
Posts: 723
Houston Tx
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I have the Reilly Motorsports adjustable strut rods. I am pleased. The 'bushings' are aluminum with a locating ring (sandwiches K mounting point like factory).
I've got 7500 miles or so on them with a number of track days and a number of removals. No play in the heims.
I also now have delron bushings in the LCA's. Zero binding issues.
-'02 Dodge Viper Ex-World Challenge racecar
-'73 Duster, 6.1 based 392 hilborn hemi, tko600, full floater rear 9", Hellwig custom bars, viper brakes, built for road course
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Re: ADJUSTABLE STRUT RODS - different designs
[Re: Supercuda]
#1946487
11/06/15 06:51 PM
11/06/15 06:51 PM
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Joined: May 2005
Posts: 723
Houston Tx
Uhcoog1
super stock
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super stock
Joined: May 2005
Posts: 723
Houston Tx
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Won't using the strut rod to add caster put a side load on the LCA bushing causing it to wear faster?
As said, no free lunch but I wouldn't use the strut rod to get more caster.
Yes, and I believe that is part of the reason for a moog LCA bushing failure on my car. I have now swapped to Delron, and trimmed the bushing slightly to 'fix' the binding that existed.
-'02 Dodge Viper Ex-World Challenge racecar
-'73 Duster, 6.1 based 392 hilborn hemi, tko600, full floater rear 9", Hellwig custom bars, viper brakes, built for road course
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Re: ADJUSTABLE STRUT RODS - different designs
[Re: cudazappa]
#1946492
11/06/15 06:57 PM
11/06/15 06:57 PM
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Joined: Dec 2003
Posts: 22,696
Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
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Mitch,
You are entering the no free lunch zone.
You have potentially 3 choices going with adjustable strut rods:
1) adjustable struts w/ rubber bushings
2) adjustable struts w/ poly bushings
3) adjustable struts w/ no bushing & using a heim joint.
1) the rubber will flex and negate some of the effects of the adjustable strut. As such, you'll adjust more to compensate for the flex. Part of the reason your rubber bushings have lasted so long (besides the limited use) is the fact that they were working with the factory strut rod. Using an adjustable will introduce preload into the bushing and make it flex more than it used to. That will undoubtedly increase bushing wear, but without empirical evidence, this is still just theory in my head.
2) the poly flexes less and in my experiences poly has a shorter life compared to rubber in the same environments, but it does firm up stuff some.
3) This style actually keeps the most consistent suspension geometry as everything is a hard point with a pivot. Heim joints will actually free up the bushing bind as the LCA travels in its arc. Uncovered heim joints require inspection. They are like a ball joint. Precision fit, but a small amount of dirt can make them crap in short order. The position of the forward heim really won't get much dirt kick up like an UCA with a heim. Put a boot on it and treat it like a sealed ball joint. Just give it a good dose of dry lubricant before you put the boot on. This style of strut rod will put the tension load on the K-frame. A reinforced k-frame won't care. Non-reinforced its not much of an issue, either. HOWEVER an accident with an impact to the front wheel may incur more damage as the load path from the strike won't terminate in a bushing (that's why factory style tie rods are cheap and hollow, they are the first sacrificial part in that scenario).
My personal choice is #3. I'm just trying to keep the car pointed the right way now.
(sorry for the long post) You covered a lot pertinent ground, but you have not mentioned that a rigid pivot strut rod, induces a small arc in the LCA as it moves up and down. The OEM allows for this by using rubber I suspect. Almost all other LCA bushings, I suspect even the delrin bushing will allow that small motion. If that arc was resisted, you would have bind. Granted the induced arc is minor, but then those who are making this upgrade "think" they are reducing unwanted movement in the first place. I suspect the LCA might even flex in this new arc induced by a rigid strut rod mounting, since the LCA main strength is vertical by its greater height cross section. Of course those that add the lower rein forcing plate would reduce this flex, and therefore drift closer to bind, not a wanted outcome. All this means to me going full circle, not sure why bother with the upgrade if the installed rubber bushings are in good shape and tight, for anything short of Nascar use. For discussion sake, is there consensus the strut's biggest and most important loading is when under braking?
Last edited by jcc; 11/06/15 07:02 PM.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: ADJUSTABLE STRUT RODS - different designs
[Re: Mopar Mitch]
#1946509
11/06/15 07:20 PM
11/06/15 07:20 PM
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Joined: Feb 2011
Posts: 4,302
Nebraska
72Swinger
master
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master
Joined: Feb 2011
Posts: 4,302
Nebraska
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I like the "repeatable" aspect of eliminating any possible slop from the strut rod. I have RMS heim/adjustables and they work well. The nice thing about them is being able to "set" the lower control arc to move as freely as possible while also keeping the lca seated on its bushing properly. Using them to gain caster will bind up the lca bushing.
Mopar to the bone!!!
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Re: ADJUSTABLE STRUT RODS - different designs
[Re: Supercuda]
#1946706
11/07/15 12:43 AM
11/07/15 12:43 AM
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Joined: Feb 2010
Posts: 18,493
Granite Bay CA
Kern Dog
Striving for excellence
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Striving for excellence
Joined: Feb 2010
Posts: 18,493
Granite Bay CA
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Won't using the strut rod to add caster put a side load on the LCA bushing causing it to wear faster?
As said, no free lunch but I wouldn't use the strut rod to get more caster.
I have wondered the same thing. Basic bonehead logic says the LCA bushing would be distorted and fail sooner. Heim joints for the street? Smart guys like Rick Ehrenberg is against them due to rapid wear due to them being UNprotected. I don't agree with everything the guy says, but I see his point on this one.
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Re: ADJUSTABLE STRUT RODS - different designs
[Re: Kern Dog]
#1946708
11/07/15 12:50 AM
11/07/15 12:50 AM
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Joined: Jun 2007
Posts: 2,432
NorCal
RylisPro
top fuel
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top fuel
Joined: Jun 2007
Posts: 2,432
NorCal
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I will put it to the test! I daily drive my Hotchkis setup to work about 11 miles one way. I have the rubber boots on the heim joints and will see if I have any major problems in the future 
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Re: ADJUSTABLE STRUT RODS - different designs
[Re: Mopar Mitch]
#1946844
11/07/15 11:55 AM
11/07/15 11:55 AM
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Joined: Sep 2007
Posts: 14,889
up yours
Supercuda
About to go away
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About to go away
Joined: Sep 2007
Posts: 14,889
up yours
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Only benefit to a heim, as I understand it, is less compliance at the pivot point. A rubber, and to lesser extent poly, strut rod bushing will compress and relax in addition to twist as the strut rod goes thru up/down and braking/unlaoding forces. A heim doesn't compress/relax, at least it doesn't till it wears.
They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
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Re: ADJUSTABLE STRUT RODS - different designs
[Re: RylisPro]
#1946932
11/07/15 02:36 PM
11/07/15 02:36 PM
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Joined: Jan 2003
Posts: 27,453
So Cal
autoxcuda
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,453
So Cal
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This is good to know as I was wondering how long the heim joints will last on a Hotchkis setup I've got ~9,000 miles on mine. Mostly street miles. I need to replace the uppers and tie rod ends. I think the strut rods are ok. When I unloaded the suspension to check bumpsteer I did my best to look at them really close and carefully feel them while someone else tugged and pushed on them. The tie rods and uppers are obviously loose. The heims make for smooth repeatable suspension movement. We used to have to run bushings in our circle track car. They were very temperamental on binding/snagging/resistance when we digital scaled the car. If you over tightened them sometimes you wouldn't get the same static frame (ride) heights. And that completely screws up chassis setup on scale when you setting weight balances to the nearest half percent or smaller increment. The poly and rubber stut rod bushing makes the strut rod into a diving spring board.
Last edited by autoxcuda; 11/07/15 09:19 PM.
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Re: ADJUSTABLE STRUT RODS - different designs
[Re: ahy]
#1946941
11/07/15 02:41 PM
11/07/15 02:41 PM
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Joined: Nov 2003
Posts: 3,577
Long Island, NY USA
BergmanAutoCraft
master
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master
Joined: Nov 2003
Posts: 3,577
Long Island, NY USA
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That is my understanding. The LCA handles braking loads and positions the spindle... the UCA works with it to handle the alignment.
With the bushing type rod installed and T bars out and everything greased there is some resistance to up and down movement. The strut rod + bushing effectively has some very slight spring rate. I guess the Heim joint type would not. Also the "pivot point" on the bushing type would be in the middle of the bushing pack while the Heim joint pivot is behind the bushings. The Heim is effectively shorter and the LCA would have a shorter arc. Its not clear to me what the benefit of the Heim type is. I use a Teflon lined joint that usually lasts many years of the typical part time usage our cars see. For me, combined with my delrin lower control arm bushing I am looking for the most precise movement possible. True, the arc is changed from the stock arc, but its not something one would notice.
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Re: ADJUSTABLE STRUT RODS - different designs
[Re: Mopar Mitch]
#1947261
11/07/15 11:33 PM
11/07/15 11:33 PM
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Joined: Jan 2003
Posts: 1,482
Lake Orion, MI
goldduster318
pro stock
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pro stock
Joined: Jan 2003
Posts: 1,482
Lake Orion, MI
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I've had the RMS ones for about 4 years and they are fabulous. Still perfectly tight and they certainly improved the tracking of the car significantly.
'70 Duster 470hp 340/T56 Magnum/8 3/4 3.23 Sure-Grip
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Re: ADJUSTABLE STRUT RODS - different designs
[Re: TC@HP2]
#1947845
11/09/15 12:38 AM
11/09/15 12:38 AM
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Joined: Sep 2007
Posts: 14,889
up yours
Supercuda
About to go away
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About to go away
Joined: Sep 2007
Posts: 14,889
up yours
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If the centerline of the ball joint setup you mention was in line with the plane of the LCA pivot you'd remove the conflict.
They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
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