LCA Suspension Modifications and Adjustments
Written By CrazyAl
Edited and illustrated by Octavio Diaz



What is an LCA?

The Lower Control Arm (LCA) is used to connect the vehicle's differential or axle housing to the car's body.  It's function is to translate the forward moving force of the differential to the vehicle's body thus pushing it forward. The OEM Lower Control Arm is made of stamped steel and under hard acceleration; bushing deflection combined with control arm flex creates erratic handling and inconsistent rear end stability.  The effect is sometimes referred to as wheel hop.  By replacing the stock lower control arms with a stronger aftermarket device will eliminate this wheel hop and depending on the pinion angle, even increase traction.  We'll talk more about that later.

Choosing an LCA

If you have not lowered your car or do not plan to lower car, a fixed length LCA is an acceptable option.  There are two basic choices a billet type or the tubular type.  The billet type is made from a single piece of billet aluminum that is milled into shape.  They are typically a bit more expensive then tubular LCAs.  They are considered to be more attractive but realistically, the LCAs are difficult to see so it makes little sense to spend the extra money on these.



   


In the stock configuration, the lower control arm is parallel to the ground.  If you've lowered your car, the front of the LCA is now lower then the rear since the vehicles body is lower but the differential's has not been modified.  As a consequence as the forward motion of the differential increases, the rear of the LCA pushes the differential up resulting in a loss of traction; again, we'll talk more about this later.

To correct  this, and adjustable control arm is desirable.  By adjusting the length of the LCA, the pinion angle can be corrected.  Adjustable LCAs are available with a variety of different bushing ends.

So what happens if you buy a fixed length LCA and later decide to drop your car?  Not to worry, you don't need to change your LCAs; instead you can adjust the pinion angle by replacing the upper control arm (UCA) with an adjustable one.  Ideally it is desirable to make the adjustments on the LCAs instead of the UCAs because the LCAs are easier to access and thus much easier to adjust.

Choosing LCA Bushing types

The less poly and the more steel you have, the stiffer and louder the suspension will be:

Poly/poly:  Better than stock, but still fairly soft.  Very small road noise increase compared to stock.

Poly/spherical combo:  A lot stiffer than stock.  Also maintains better articulation due to the spherical bearing.  A slight-to-moderate road noise increase vs. stock.  Most people are OK with this though some people that expect a Cadillac-like quiet ride may not like it.

Spherical/Spherical:  Extremely stiff, excellent articulation, and very loud.  Not acceptable to most people on a street car.  Typically used for race use only; not a daily driver.


1)    Lower Control Arms with poly/poly bushings
2)    Lower Control Arms, non-adjustable, with polyurethane bushing and spherical bearing combination 
3)    Adjustable Lower "Street" Control Arms with poly bushing/spherical rod-end combination
4)    Adjustable Lower "Race" Control with Spherical rod ends





Adjusting LCAs for OEM 2 piece DR. Shaft


 OK, here is the pinion angle setting procedure for an OEM 2-pc driveshaft.  (This is NOT correct for a solid 1-pc aftermarket driveshaft)

First, lift up the car so that you can work under it.  Be sure you use safe lifting procedures.  You must have the rear suspension loaded--in other words, you need to have the tires on ramps or the rear axle tube on stands so the weight of the car is compressing the rear suspension.

It is best if the car is as level as you can get it, so if possible lift up the front to the same height as the rear.  You're not going to be working on the front end, so it doesn't matter if the front suspension is loaded or not.

You are now ready to take measurements.  I attached a rough sketch that shows where you are doing the measuring.

Now, use the angle gage to measure the angle of the driveshaft right next to the rear end.  It doesn't really matter what this number is, just measure it and write it down.  Take the measurement at the place labeled "1" on the sketch.

Move the angle gage over and measure the angle of the pinion itself.  The actual pinion shaft is inside the rear end housing, so you have to take the measurement on the pinion drive flange.  This is the place marked "2" on the sketch.  Make sure you are holding the gage firmly on the wider part of the flange.  Don't allow the gage to lean across the little step machined on it.  (See the note on the sketch)    Write this number down too.

You are interested in the difference between these two numbers.  So, take the angle of the driveshaft and subtract the angle of the pinion from it.

The correct measurement will be about 3 to 1.5 degrees difference, with the pinion being closer to horizontal than the driveshaft is.  In other words, 0 degrees would have the measurements the same:  The driveshaft and the pinion would be perfectly in line.  You want the pinion to be angled down lower by about 3 to 1.5 degrees.  (Technically, this is called a negative angle, as in "-3 degree pinion angle", but wether or not the actual measurement is negative depends on how your angle gage is calibrated, so that is not always reliable)

If your measurement is not correct, then you need to adjust it.  To do that, loosen the locknuts on your LCAs and then turn the center adjusters.  Lengthening the LCAs will bring the nose of the pinion down, which will give you a larger angle difference.  Be sure you have both LCAs set the same.  You can either count turns and repeat the same change on both sides, or you can use a tape measure to measure the LCA lengths and keep them the same that way.

Once you've adjusted them a bit,  check the angle again.  Repeat adjusting and checking until the angle is where you want it.  Once you've got it set, put a few drops of loctite on the adjusting nuts and tighten them down.  Lower the car and go for a test drive.


How do you know what the proper angle is?  Well, some of this is trial and error.  You might have to reset it if things aren't to your liking.  However, the general rule is that the more aftermarket parts you have in your rear suspension, the less the angle difference needs to be.  3.0-2.5 degrees is about right for a street car with relatively minor suspension mods.  If you have a lot of aftermarket parts in the rear end (combo type UCA and LCAs+ more) then you could try 2.0 degrees instead.  A full race setup might be 1.5 or even 1.0 degrees, though this would be an extreme situation:  no rubber or poly anywhere in the rear suspension, reinforced frame, etc.

What is the theory behind this?  Well, when you accelerate hard the whole axle assembly rotates a bit.  Newton said every action has an equal and opposite reaction.  Well, when the engine turns the wheels, a reaction torque is applied to the axle.  On a race car with a SOLID suspension nothing much happens, but on a street car the rubber/poly bushings flex a bit and the axle housing rotates a little.  You are setting it up so that when you get on the gas hard, and the axle twists a bit, THEN the driveshaft and the pinion are in perfect alignment.





Adjusting LCAs for aftermarket 1 piece DR. Shaft

 
Ok, here is the pinion angle procedure for a ONE PIECE DRIVESHAFT.  This procedure is not correct for the OEM 2-pc shaft.  This works for lowered cars or for stock-height cars, but this is for 1-pc shafts only.

Jack up both the front and the rear of the car so you can get under both the transmission area of the car and the rear-end area.  The rear suspension must be loaded.  This means the rear tires must be sitting on ramps, or the rear axle tube must be supported by a lift or jackstands.  The front end can be lifted however you like.

It is good if you can get the car level, but it is not required.

Get under the car and remove your 1-pc driveshaft.   (or if you are installing the driveshaft for the first time, you can do this after you've got the OEM one out, and before you put the new one in).

Get your angle finder and measure the angle of the transmission output flange.  Write this number down.  Refer to the sketch for taking this measurement.

Move over to the rear end of the car and measure the angle of the pinion flange.  Write this number down.  Note that this can be tricky if you have a "triangle" shaped angle gage.  If you flip the triangle over, you are now measuring angles from a different reference point--don't do that, it will mess up your results.  Use a carpenter's square as shown in my sketch, so the angle gage is held in the same orientation as it was for the trans flange.  If you have a "square" type of gage then just use the side of the square opposite the one you used for the trans flange.

Now adjust the LCAs so that the two angles are the same.  Keep adjusting and checking until the angle at the pinion (#2) matches what you recorded for the transmission flange.

At this point the two flanges are parallel.  If you are running a full racing suspension then you're done here, skip to putting the driveshaft back in.

On a typical car with minor mods,  you now need to add a little negative angle.  Adjust the LCAs so that they lengthen (if you are using an adjustable UCA, then shorten it instead), making the nose rear end housing dip down a little bit.  Go about 2 degrees beyond the trans flange measurement.  Again, this is called a negative angle but depending on how your angle gage is marked, it might not actually be a negative number by your measurements.  The same thing I wrote above applies here.  If you have a fully aftermarket rear end, you could run about 1 to 1.5 degrees.  If you are running a common street setup with one set of control arms only, then 2 degrees or so is more appropriate.

Once your angle is set where you want it, loctite your jam nuts and torque them down.  Re-install your driveshaft, and go for a test drive.




Choosing LCA Bushing types


 

The less poly and the more steel you have, the stiffer and louder the suspension will be:


Poly/poly:  Better than stock, but still fairly soft.  Very small road noise increase compared to stock.

Poly/spherical combo:  A lot stiffer than stock.  Also maintains better articulation due to the spherical bearing.  A slight-to-moderate road noise increase vs. stock.  Most people are OK with this though some people that expect a Cadillac-like quiet ride may not like it.

Spherical/Spherical:  Extremely stiff, excellent articulation, and very loud.  Not acceptable to most people on a street car.  Typically used for race use only; not a daily driver.



A quick comment about suspension parts and noise:


If you hear a "clunking", "banging" or "rattling" sound then something is either broken or installed wrong.  NO suspension parts, even the full-on race parts with nothing other than rod-ends will do this when properly installed.  These kinds of sounds mean that something is dreadfully amiss--either a part has failed or there is a loose bolt or some other installation error.

What you WILL hear from suspension parts is an increase in road noise.  Road noise isn't clunking or banging.  Road noise is a constant, steady, "static" or "hiss" type of sound.  You know the sound that any car makes when you drive over gravel on the road?  THAT is the kind of sound that stiffer suspension parts will make.  It shouldn't be as loud as driving over a gravel road, but that is a good example of the type of sound involved.

In this case, there is a DIRECT correlation between the firmness of the suspension and the degree of sound that is made.  The firmer (better) the suspension parts are, the louder they are.  This is because stiffness of the suspension parts is what allows road noise to be transmitted.  The firmer the parts are, the more noise is conducted into the body of the car.  Parts like LCAs do not make road noise.  They do, however, allow it to be transmitted from the rear axle into the body of the car.

 If Car A is quieter than Car B, and there are no failed parts or improper installs on either car, then Car B will have a stiffer suspension.

I hesitate to use the word "Better" suspension because this depends on what your goals are.  On a daily driver, a stiffer suspension isn't always "better" because it may be too loud for comfort.  However, firmer (louder) parts are better from a performance point of view.

That being said, BMR--like many other brands--make different grades of parts for different applications.

The poly-poly control arms are a little stiffer than stock, and consequently they are only a little louder than stock.  Most people wouldn't even notice the increased road noise.

The poly-heim combo parts are stiffer still, and they are also a little louder.  I recommend these because most people won't find the extra noise objectionable--and at the same time they are a lot stiffer than OEM, and the heim joints offer much better pivoting than poly bushings.  These parts are great because while they are only slightly louder than the above type, they offer much better performance.

The double-heim type (rod ends on both ends) are of course the stiffest possible,  they have the best pivoting, but they are also very loud because there is no damping material at all in them.  These would be used whenever the extra noise is not a problem.

LCA Relocation Brackets

There's been a lot of questions lately about LCA relocation brackets, so instead of answering the same question ten times I thought I'd explain everything carefully and then leave it here for all to read, and so I can link back to it when it comes up in the future.  So here goes:

LCA Angle.  There has been a lot of discussion about how adjustable LCAs let you change your pinion angle.  But what about LCA relocation brackets? What do they do? LCA brackets attach to your rear axle, at the rearmost end of the LCA.  They have multiple different bolt holes that you can choose between, allowing you to choose what the angle of your LCAs is.

The LCA angle is important because of what the LCAs do.  The main job of the LCA is to transfer the force from your rear axle to the body of the car.  They are literally what pushes your car forward when you accelerate. (The UCA contributes too, but to a lesser extent).  The LCAs have a pivot at each end.  This means that they cannot apply a torque or "twisting" force.  They can only apply force in a straight line, along their length.  You could not, for example, use an LCA as a wrench.  But you could push against something with it.

When an 05+ Mustang rolls out the door at Ford's plant, the car is configured so the LCAs are basically parallel with the ground.  They are horizontal.  Thus, when the axle starts to push forward, the LCAs push along their length--horizontal--and they push the car straight forward.  Makes sense, right?

So what happens if you change this angle?  The most common case of this is if the car is lowered.  When you lower the car you lower the car's body.  But, the rear axle stays put.  This has the effect of lowering the front of the LCA.  Instead of being horizontal, the LCAs are now lower in the front and higher in the rear.  When you accelerate, the LCAs push in a straight line, just as they always do.  But now the straight line is angled downwards at the body connection of the LCA.  This means that MOST of the force from the wheels is still pointing forward, but a portion of it is actively pushing the body of the car down towards the ground.  Newton taught us that every action has an equal an opposite reaction.  And it's this reaction that's bad.  The reaction to the body being pressed down, is that the rear axle is being pressed UP.  This force actively lifts the tires off the pavement....as if you had a big helium balloon tied to your axle.  The harder you accelerate, the more your axle gets lifted up...and that costs you traction.  A car that is lowered without LCA relocation brackets has LESS traction under acceleration than a stock-height car because of this!  The angled LCA also causes a rougher ride.

How can we fix that?  LCA relocation brackets let you change the position of the rearmost end of the LCA.  By switching them to a lower mounting position, we can restore the OEM horizontal configuration on a lowered car.  That means you can have your car lowered, but without suffering the ill effects I just described.

But we can also change things to our advantage.  If we lower the rear end of the LCA even more, so now it's lower in the rear than at the front,  we get a similar situation to what I described above...but backwards.  Now, the force from the rear axle is pushing up on the body.  The reaction force pushes DOWN on the axle, planting it to the pavement.  In this case the harder you accelerate, the more the tires are pressed onto the road...providing more traction.  This is excellent for drag racing, and this kind of adjustment is key on all successful drag race vehicles.  This is why all serious drag race cars run a multi-link rear suspension or ladder bars (if the rules allow it), because it enables better traction at launch.

Thus, using LCA relocation brackets lets you correct your LCA angle if you lower the car.  They also give you the option of running an even more aggressive setting (lowered or not) which will enhance your traction at launch.


Note that running the LCA at an angle (any angle, good or bad) will result in slightly ride harshness on rough roads.