Adjustable Strut Rods

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Raul

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I'm in the process of rebuilding my lower control arms and have heard of upgrading the strut rods for better steering reaponse/cornering. I'm wondering what differences there are between the hotchkiss ,and the PST adjustable rods and how they compare to stock. And also the reason for adjustment and the spec as to where and how much to adjust. What would the setting be? Is it just adjustment for Caster or does it also affect Camber? And how is Caster adjusted otherwise without the adjustable struts?
 
I've used them on a few cars and was able to achieve 7* of castor but I don't like the twisting bind they put on the LCA bushing when trying to increase adjustments. Much better to use adjustable UCA's for that. The UCA is where the factory adjustments for castor and camber are made. Having adjustable UCA's allows you to increase those settings without undue stress on components.
 
Most of the adjustable strut rods on the market are basically the same, a pillow block that takes the place of the bushing followed by a heim joint. Some of them have a fastener that screws in from the backside of the LCA, some of them use a screw in stud on the end of the tube so there’s just a nut on the back of the LCA. The latter makes it harder to install the strut rod initially but easier to adjust. Firm Feel makes a set that’s adjustable but still used a bushing at the front. I like the QA1 strut rods personally, but they’re really all pretty similar. Making sure they have flats on the tube to adjust them makes them easier to adjust.

As far as why you need them, it’s all in the stock design. The factory strut rods are a “one size fits most” operation. The factory tolerances on these cars are fairly loose, even at the suspension components. The factory got around that using pretty thick rubber bushings, so the soft bushing takes up any difference. The problem with that is if the strut rod isn’t exactly the right length you get binding in the suspension at the LCA, which you don’t want. The strut rods also allow for movement in multiple planes. So, the soft bushing is bad in fore/aft direction, because it allows a lot of movement of the LCA in that direction which causes caster changes. But, it has to be soft in the up/down direction otherwise the binding is exacerbated. Which is why I don’t like poly strut rod bushings- they reduce caster changes but increase vertical binding.

The adjustment shouldn’t be used to add caster. The whole idea is that you make the strut rod the right length for your car so that there’s no binding in your suspension within the range of travel. That improves the suspension reaction and reduces caster changes. You may see some increase in positive caster when they’re adjusted correctly, but that shouldn’t be the end goal.
 
I agree with that. They are great for getting the LCA where it should be. That I'll use them for. I'm liking the turn buckle style over the Heim joint style myself. Keeps the rod more in the factory location.
 
I agree with that. They are great for getting the LCA where it should be. That I'll use them for. I'm liking the turn buckle style over the Heim joint style myself. Keeps the rod more in the factory location.

Yeah but you keep the bushing, so you keep the caster changes. I see people making a big deal about the heim being further back, so the strut rod is shorter and so the arc it traces is smaller. Which would pull the LCA more at the extremes of suspension travel. But that ignores where the pivot point of the strut rod really is, it’s not at the front end of the strut rod, it’s between the original bushings. So the heims aren’t even an inch further back.

When I adjust the strut rods on my cars I cycle the suspension completely through its range of travel and adjust the length so there’s no binding. I haven’t had an issue setting them up so they don’t bind at all, which means that length change isn’t translating to a big enough change to cause any problems. The stock strut rod and bushing set up has had more bind on all of my cars.
 
Thank you for all your replies, though I do not understand everything stated so please bear with my questions. First, when replacing the bushings, it seems better to replace them with the hard rubber bushings rather than the poly ones due to the allowance of movement in multiple planes as opposed to the poly bushings. Polys may last longer but the original rubber most likely will perform better.....
Second, the adjustable strut rods are more to prevent binding on the lower control arms throughout its motion during use. How does one even know whether the suspension is binding or not? What does that mean to cycle the suspension through its complete range of travel and adjust so that there's no binding? Where is the binding checked at? Third, to be sure I'm understanding right, this strut rod adjustment is not used at all for Caster specification adjustments? Only for assurance of release/dissipation of binding? Would a front end alignment tech know what to look for in regards to set it so there's no binding??
 
Thank you for all your replies, though I do not understand everything stated so please bear with my questions. First, when replacing the bushings, it seems better to replace them with the hard rubber bushings rather than the poly ones due to the allowance of movement in multiple planes as opposed to the poly bushings. Polys may last longer but the original rubber most likely will perform better.....
Second, the adjustable strut rods are more to prevent binding on the lower control arms throughout its motion during use. How does one even know whether the suspension is binding or not? What does that mean to cycle the suspension through its complete range of travel and adjust so that there's no binding? Where is the binding checked at? Third, to be sure I'm understanding right, this strut rod adjustment is not used at all for Caster specification adjustments? Only for assurance of release/dissipation of binding? Would a front end alignment tech know what to look for in regards to set it so there's no binding??

If I was going to use bushings at the strut rod I would use the rubber ones, yes. The poly ones aren't always the right width, and they would tend to cause more binding rather than less.

To check for binding, what I do is put the car up on jackstands and remove the wheels. Then I remove the torsion bar adjusters and the plate that holds the adjuster in the LCA. Then remove the shock. With all of that done, you should be able to lift and drop the control arms and spindle, moving the suspension through its entire range of travel between the bump stops. All you should be working against is the weight of the suspension parts when you lift them. What you typically find when you do this is that the suspension does not move freely from bump stop to bump stop, there are generally areas of added resistance that occur at the extremes of travel right before you hit the bump stops. That's binding. If you remove the strut rod and check this again you should be able to move the suspension freely with very little added resistance anywhere.

Setting the adjustable strut rods so there's no binding follows the same procedure. If you measure the original strut rod from the back side of the K frame to the LCA, and then set the adjustable strut rod so it's the same length from the back of the K to the LCA you should be roughly in the ball park. Then with the adjustable strut rod installed you can look at the LCA and see if it's perpendicular to the frame rail. If it's not, adjust the strut rod so the LCA is perpendicular to the frame rail and check for binding. If the LCA is perpendicular to the frame rail there shouldn't be much or any binding. Then normally what I do from there is shorten the adjustable strut rod until is starts to bind, then back it off again until it moves freely. If you start to shorten it and find it immediately binds worse, you may need to lengthen it. The first time you do this it may take awhile to find the "sweet spot" where there's no binding.

With rubber LCA bushings there will always be more resistance as you get to the extremes of travel, because of how the rubber LCA bushings work. Nothing spins, so, the entire range of travel of the LCA is based on the rubber LCA bushing flexing. That's why you tighten the LCA pivot nuts at ride height with OE style rubber LCA bushings, because you want them to be neutral at ride height. That way compression is flexing the bushing in one direction and extension flexes it in the opposite direction, which minimizes the amount of flex in one direction. Over flex the rubber bushings and they tear.

With poly or Delrin LCA bushings the bushing spins on the LCA pivot pin, so there's no real resistance for moving the LCA up and down. It also makes it easier to set the length on the adjustable strut rods, you shorten them until the LCA is pulled against the poly or Delrin bushing, then check for binding, and usually shorten the strut rod another turn or two. With the adjustable strut rods and poly or Delrin bushings at the LCA there's very little resistance in moving the spindle and control arms up and down.

And no, I would not expect any alignment tech that I've met lately to have any idea how to do this. You'd need a race shop that also does alignments. The alignment techs at wheel and tire shops are generally at the limits of their capability just turning caster/camber bolts or adding shims to put the suspension "in the green" on the computer screen. Most of them know very little about actual suspension design or function, and aftermarket adjustable parts are not something they typically deal with. Many of them won't even do the alignment if you have aftermarket parts installed that they didn't install at that shop, and usually they will only set the alignment to the factory specs, which on these cars was for bias ply tires and is completely wrong for radials. Which is why I bought my own alignment tools and do my alignments myself.
 
YOU WRITE: if you have aftermarket parts installed that they didn't install at that shop, and usually they will only set the alignment to the factory specs, which on these cars was for bias ply tires and is completely wrong for radials. Which is why I bought my own alignment tools and do my alignments myself.

So my question is, what kinds of adjustments do you make for alignment angles for radial vs. bias ply tires? Less camber, more caster? (that'd be my guess) -- how much more or less?

And thanks for such an informative post!
 
So my question is, what kinds of adjustments do you make for alignment angles for radial vs. bias ply tires? Less camber, more caster? (that'd be my guess) -- how much more or less?

And thanks for such an informative post!

The factory specs were for bias ply's, and called for +.25° to +.75° for camber, and 0 to -1° of caster. So, positive camber and negative caster, which is basically the opposite of what you want with radials.

For radial tire alignments the SKOSH chart is a good resource.
alignment-specifications-jpg-221767-jpg.jpg


I think the SKOSH chart is a little conservative on the amount of positive caster it calls for, personally I'd add +2° to its caster recommendations across the board. But it is an older chart and the parts needed to get more caster than it calls for weren't widely used at the time it was published. If you have stock UCA's with stock bushings it's unlikely you'll get to even +2° of caster. If you have stock UCA's and offset bushings then you might get to +3.5° caster. To add that much more than that you'd need tubular UCA's, which have additional caster built in to most of the designs. +5° is usually pretty easy to get with tubular UCA's. Positive caster also tends to make the steering a little heavier, the steering wants to resist change and the re-centering effect is magnified. Which is good, but if you have manual steering you may not want to just add a ton of positive caster as it will increase steering effort. Going past +5° caster on a manual steering car makes the steering effort noticeable heavier.
 
The factory specs were for bias ply's, and called for +.25° to +.75° for camber, and 0 to -1° of caster. So, positive camber and negative caster, which is basically the opposite of what you want with radials.

For radial tire alignments the SKOSH chart is a good resource.
View attachment 1715536535

I think the SKOSH chart is a little conservative on the amount of positive caster it calls for, personally I'd add +2° to its caster recommendations across the board. But it is an older chart and the parts needed to get more caster than it calls for weren't widely used at the time it was published. If you have stock UCA's with stock bushings it's unlikely you'll get to even +2° of caster. If you have stock UCA's and offset bushings then you might get to +3.5° caster. To add that much more than that you'd need tubular UCA's, which have additional caster built in to most of the designs. +5° is usually pretty easy to get with tubular UCA's. Positive caster also tends to make the steering a little heavier, the steering wants to resist change and the re-centering effect is magnified. Which is good, but if you have manual steering you may not want to just add a ton of positive caster as it will increase steering effort. Going past +5° caster on a manual steering car makes the steering effort noticeable heavier.

I have a question. If you were going to run bias ply tires today, would the above settings still be correct or are there updated numbers for that? I would think (I could be wrong again) that even bias ply ties have gotten better since the 1970’s.

What do you think?
 
I have a question. If you were going to run bias ply tires today, would the above settings still be correct or are there updated numbers for that? I would think (I could be wrong again) that even bias ply ties have gotten better since the 1970’s.

What do you think?

Honestly, I've never looked into it.

I would agree that even modern bias ply's are probably constructed differently than the original tires these cars ran. Radial tires have changed a bunch just in the last 10-15 years, and the new modern radials can take a more aggressive alignment than the older ones could. So it's totally possible that you could do better than the factory alignment specs with a modern construction bias ply tire.

But I haven't looked into running bias ply's on anything recently. I know Coker has some replica's out there for those looking for the original look, but I don't know enough about their construction to say much. Some of the drag race tires are bias ply's too, but I would think that if you were that serious about the 1/4 mile you'd be running drag race alignment specs too, which are closer to bias ply specs anyway. Mostly close to 0 for everything to keep the rolling resistance down.
 
even Coker, who has bought up as many of the old tire molds as they could find, only has one actual bias ply on there site. the others are "bias ply look radials".
 
even Coker, who has bought up as many of the old tire molds as they could find, only has one actual bias ply on there site. the others are "bias ply look radials".


I’m running cheater slicks and I’m pretty sure they are bias ply. I have radials on the front now and I’d rather use a front runner that isn’t a radial if I can.

I know the cheater slicks are M&H but I’m not sure which ones I have.
 
Ok, the website had gotten better.

What I have is M&H 12.5/28-15 bias ply cheater slicks. What I want up front is a 4.5/27-15 front runner. The web site says that’s bias ply too.

How much better this stuff is now than it was 40 or more years ago is hard to say but I’d think it would be at least somewhat better.
 
Ok, the website had gotten better.

What I have is M&H 12.5/28-15 bias ply cheater slicks. What I want up front is a 4.5/27-15 front runner. The web site says that’s bias ply too.

How much better this stuff is now than it was 40 or more years ago is hard to say but I’d think it would be at least somewhat better.

They probably are better than they were back then. But with that narrow of a tire up front I don't think it'll make a lick of difference. You don't need to run much positive caster with a bias ply as some of that "self centering" response comes from the tire construction itself, radials want/need more positive caster. Part of the reasoning behind the factory alignment specs was also the factory designing in understeer and tailoring the alignment to the "little old lady" that didn't want any steering effort. That whole 70's no feedback steering and floaty ride quality was as much a part of the design consideration as the bias ply construction was, the slightly negative caster was part of making manual steering cars feel like the super over boosted power steering cars.

So, as I said earlier, if you're running bias ply's because you've got cheater slicks for drag racing, you might as well align it for drag racing. Running 0° camber won't hurt anything if you have bias-ply tires up front, and those front runners are so skinny negative camber wouldn't dramatically improve cornering anyway. All it would do is add more rolling resistance which you don't want on a drag car. I wouldn't run negative caster regardless, but with bias-ply's you don't need much positive caster either so if you ran a degree or so positive it would be fine.
 
I’m running cheater slicks and I’m pretty sure they are bias ply. I have radials on the front now and I’d rather use a front runner that isn’t a radial if I can.
good point, because we sort of end up assuming Raul's original post was about a street car he's just driving around, but none of us acctualy asked what his intentions were.
so, hey Raul, what are your plans for the car?
:popcorn:
 
Mine's just an all around street car with occasional time trials down the drag strip once or twice per year. I have to wonder what the new Stroker motor will do
 
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