Techical Discussions => Tech- - STEERING WHEELS AND SUSPENSION => Topic started by: Steve on May 21, 2008, 05:35:44 PM

Title: Mopar Lower Control Arm Bushings. Why they fail
Post by: Steve on May 21, 2008, 05:35:44 PM
OK  Let's talk about why lower control arm bushings fail.
From 1957 to 198?  Chrysler used the same design on most of the bodies.  The exceptions would be the K Cars and Transversal T Bar cars.  They all had the same principle.  It was a good design, it serviced them well, but they all had the same weak spot.  The lower control arm bushing.  You have to remember, the entire front end only sits on about 6 square inches of rubber, about 1/4 of an inch thick.
Here is an example of a failing bushing.  This was a Moog with about 12,000 miles on it.  I removed it from Polaraco.
It's safe to say, such a small part does a lot of work.  It absorbs the weight of the front of the car, flexes up and down, and is in constant motion. It keeps the wheels straight, especially in brakeing, and absorbs road vibrations and shocks. It is the connection point for the springs. (T Bars)  Needless to say, this simple $20.00 part is very important.
Look at a typical Torsion Bar suspension in any one of our cars.  Think about what is connected to the lower control arm..  The Frame is at one end, the Torsion Bar goes into it at that end.  There is a shaft on the other end which goes through the frame.  That is the pivot point.  On the outer end is the lower ball joint.  That is connected to the spindle where the turning and braking work is done.  The strut rod is attached to it.  The strut rod limits the back and forward swing of the arm. (Reduces leverage) And the shock absorber is attached.  The shock absorber assists in keeping the wheels on the ground.  It does exactly what it is called.  It does some cornering stability as it slows down and some limiting the travel of the control arm.
So why do lower control arm bushing fail?  There are a dozen reasons.  In our old cars, most of it is age and neglect.  But other old and neglected components can cause it too.
Strut Rod Bushings.
Picture a compass.  North, South, East and West.  Turn the compass vertical and put it at the inner end of the control arm.  The Strut Rod prevents the control arm from traveling East and West too much.  This also effects Caster alignment and could cause a pull while driving.  A Bad Strut Rod bushing, located on the front of the frame, can cause the control arm to travel too much.  This stresses the rubber in a difficult manner more than they were intended.  Between the travel up and down and the excessive sway in the control arm, it can cause the bushing to fracture.  After it tears enough times, the car begins to settle into the bushing, damaging it more.  Remember, you have about 1000 pounds on 3 square inches of 1/4" thick rubber.
Shock Bumpers or Snubber
These are important as they limit the amount travel of the suspension.  If the control arm travels too much, it can be torn internally.  Again, the same condition can start to occur.  The car starts to squash the rubber and sink in.
Shock absorbers
Shock absorbers limit the speed and some of the travel which the bushing does when it twists.  This is the North, South Motion.  Here again, a bushing traveling too fast will tear internally.  Since the up and down motion is the main motion this bushing does, most of the work is north and south.  The bushing flexes and made to flex like that.  It has too flex to allow the control arm to move up and down.  If the shock is bad, the travel distance of the control arm increases, and it moves faster.  Those two motions can tear a bushing.  The compound does not have time to react.  Bad Shocks are the Number one cause of lower bushing failure.
This is the same principle as a tow strap or cable, as an example.  Gradually pull up the tension and it pulls the weight for ever.  But snap it too many times and it will eventually fail. 
A Bad bushing will over ride a shocks ability to do it's job also.  A good mushing offers a fair amount of travel resistance and works with the shock.
So to recap the causes.
Bad Strut Rod bushings
Bad Shocks
Old Rubber
This is why many times you hear me tell someone to check the lower bushings.  They are hard to see, but visible at the right angle.  They are best checked with weight on the control arm.  If you see a piece of rubber sticking out or it bulging at the bottom, the bushing is bad.  Replace it.
Other symptoms are, excessive bouncing, even with new shocks and strut rod bushings.  Grinding with up and down motion.  Squeeking rubber sound.  Unstable driving and cornering.  Abnormal tire wear.
If you haven't done so yet, go out and check those 30 to 40 year old bushings.  I replaced the one above with a set I purchased from  I have to say, there is a world of difference in the way the car handles bumps and how the car handles across the board.  The Moog bushing failed for no apparent reason.  All the components I described above were replaced when the bushings were installed.  I think the Moog is not high quality anymore.  The ones from Justsuspensions were twice the price, but Oh what a difference.  Why do them twice?  I probably will never have to do them again now.
POLARACO2008-05-22 14:50:07
Title: Mopar Lower Control Arm Bushings. Why they fail
Post by: Steve on May 22, 2008, 10:17:23 AM
Does anyone have a better picture of the susyension other than the FSM?  I'd like to post it
Title: Mopar Lower Control Arm Bushings. Why they fail
Post by: Brian on May 22, 2008, 07:23:21 PM
Good info Steve...(

My front end kit I used in the wagon was actually bought 5 years ago from PST, so my lower control arm bushings will probably be Moog...I think I will pick up a set of the JS pieces to have on hand.

Will keep an eye on the lower control arm bushings and see how long they last.

Title: Mopar Lower Control Arm Bushings. Why they fail
Post by: Stitcherbob on May 22, 2008, 08:54:45 PM
They fail also because they should be installed loose, set the weight on the tires and then tighten the bushings.....if the rubber is tightened while the weight is off the front end, when you set it down the rubber will twist up inside the metal shell.

Title: Mopar Lower Control Arm Bushings. Why they fail
Post by: Guests on June 25, 2008, 04:36:17 AM
Moog suspension\\steering components (
I have run them on my jeep and they failed prematurely also - just the st00pid name which apparently is not what it used to be.
Title: Mopar Lower Control Arm Bushings. Why they fail
Post by: Bob Schaefer on August 05, 2013, 08:31:34 PM
I see that it appears Just Suspensions is a favorite provider of bushings, and the like. Has anyone had much interaction with Firm Feel? They have a urethane bushing kit, and lots of heavy duty replacement or upgrade parts, such as tubular upper control arms, reinforced lower control arms, and heavy duty strut rods and tie rods. I'm not in a position to do all that, but the bushings are of interest. The Just Suspensions kit is about $499, and the Firm Feel High performance kit with urethane bushings is $750. The main difference, besides the bushings, is that the FirmFeel kit has heavy duty tie rod parts, and it includes an idler arm.
Title: Mopar Lower Control Arm Bushings. Why they fail
Post by: Steve on August 05, 2013, 11:00:35 PM
Urathane has a bad history on the lowers.  It's not flexible enough.  The lowers do too much twisting.

I dunno about you, but I like to do them once and forget them for 15 years
Title: Mopar Lower Control Arm Bushings. Why they fail
Post by: dana44 on August 06, 2013, 06:55:34 AM
Once, right, and forget it.
Poly is the way to go, and comparing the two side by side, it's like taking the creme filling out of a Twinkie. Firmer, yet just as good, not quite so squishy all the way around. Tubular A arms aren't needed unless you are showing a custom or racing, inner and outer tierods, bushings, adjusters (new ones are pretty nice to have), idler arm. The adjustment tubes are your call, haven't ever seen one go bad unless a tow truck attached to it and the car was in gear.
Title: Mopar Lower Control Arm Bushings. Why they fail
Post by: dana44 on August 06, 2013, 06:56:48 AM
OH, and upper and lower balljoints. For some reason all the kits have outer, but not inner, tierod ends. Weird.
Title: Mopar Lower Control Arm Bushings. Why they fail
Post by: Snotty on August 07, 2013, 07:58:56 AM
I believe JS has both in their kits which is why theirs is more expensive that PST - but worth it as you need to replace them anyway.
Title: Mopar Lower Control Arm Bushings. Why they fail
Post by: Bob Schaefer on August 08, 2013, 02:18:14 PM
I agree about not wanting to redo them again for a long while... I'll see what I can afford when the time comes.