1968 AMX Front Trunnion Elimination

My contention is and remains, the lower control arm is a weak spot in the Existing AMC front suspension as to it's operation and reliability.
What ever else one does to them is pretty much personal opinion. Mine is, urethane bushings aggravate the inherent weakness of the design.
Stiffness is not an attribute, it is a preference. And stifness does not solve design problem.
Arguing it is a positive attribute is a lost cause, it is an opinion.
And not mine.
However in either case AMC designed the lower control arm to flex in order for it to do it's job more or less and my experience in working on them the mechanical failure rate is high as a function of time and miles.
Trying to eliminate flexing aggravates binding.
I've done my home work and research to verify that.
For what ever that is worth. '
This comment excerpted from an article on the Chris Alston designed Pinto or Mustang II suspension in terms of improving on the original design by including a free standing lower control arm to eliminate the strut rod and pivot point, and inherent problem in that suspension which needed to be solved also as it is similar if not identical in operation to the AMC control arm indicates the same piece of information needed to be taken care of.

By redesigning the lower control arm into an A-arm design and incorporating a new rear mounting point that rotated on the same axis as the forward pivot, Alston eliminated the inherent binding experienced with stock-type components caused by the two off-axis pivots.

I have made my decision how to deal with the situation as I see it. And A stack of damaged lower control arms is a significant factor in making it.

The information is there for others to see and use as they see fit.
But again
using urethane because it makes things stiffer, is not a solution. In fact in certain instances, it is part of the problem.

There is apparently currently available only one option to replace the existing AMC suspension with a modern equivalent and with the associated benefits. Admittedly a tad pricey but it is one more than none.  And is probably worth every dime spent on it if you want it.
And if that works for some people the option is there.
It is not a Rambler mentality decision to use or not use it as was narrowly pointed out. It is one of evaluating need vs expense and then making an educated decision. The more knowledge that is available the better the decisions can be. Doing something for cheap rarely gives the best solution. Neither does arbitrary throwing money at things.
After all the U.S. did not get billions of dollars in debt by making financially smart decisions.

tyrodtom wrote:   A lot of 4 cyl.  circle track cars have a similiar design lower strut rod,  some behind the lower arm, some ahead.   When rules allow it,  some replace the sleeve bushing with a heim rod ends.   They let the suspension go thru much more range of motion without binding.    I done this myself to a few cars,  and looked at my 66 American's strut rod and think I might try that on it.

I've looked into replacing my trunions too, I'm going to use a knuckle from something non-trunion and make an upper arm, I think Howe sells a kit if you would prefer a kit, but I plan to just use tubing, heims, and some plate...

There is NO WAY I would pay that kind of $$$ either, esp. when you can make it yourself...

You only have to change the spring towers to use the upper arm and spring from a 70+ car in a 68-69. The Hornet/Gremlin spring tower will work in the 68-69 Javelin AMX with a little tweaking. This is a lot of work though, lots of spot welds to drill out. I'd rebuild the upper trunnions (or get rebuilt ones). Costs less in the long run, and can be installed in a day if you have the spring tools. Car will handle great with the urethane trunnions too.

The only thing you gain is the ability to dial in more positive caster by changing. As John says, you can only get 3 degrees in the trunnion suspension before it starts to bind -- he's saying the ball joint suspension does the same, I believe. I have 3 degrees in mine now and it wants to wander a bit, as John also mentioned. This is on a 112" wheelbase Classic wagon though, not a short wheelbase AMX or Gremlin. I'm going to have it set at 0 degrees when I have it aligned next and see if anything changes.

I agree with John on the flexing of the lower arm, trunnion or ball joint suspension. It was designed to flex. If the inner bushing on the lower arm is urethane it is more resistant to twist and the arm itself must twist more and the suspension movement is hampered. I don't use urethane strut rod bushings. In my car I can feel a pot hole jar in the floor when I did. Half as much with rubber. I'm not sure the urethane bushing stresses the arm a lot more, because the whole suspension doesn't move as much. The harder urethane will bind more, restricting movement slightly. Modern smooth roads, radial tires, and good gas shocks mean the suspension doesn't HAVE to move as freely as it did in the 60s with rougher roads, harder tires, and stiffer shocks. So as Dan says, it's about full circle and doesn't matter as much. Rubber will ride a bit smoother, and good new rubber will handle just about as good as poly. Poly holds up longer though -- 10 year old rubber won't handle as good as 10 year old poly. Don't use NOS rubber, use new! NOS is still old and may be dry rotted -- won't hold up long. Should be okay for a seldom driven show car, but the NOS strut bushings I tried about 10 years ago disintegrated after a few months of driving.  I have rubber suspension bushings with urethane sway bar bushings.

For performance I've recommended "half-n-half" strut bushings -- urethane in front, rubber in back. Urethane isn't as soft and flexible as rubber, and the strut bushings restrict up and down movement a bit. The hard bushing in the front prevents caster changes on acceleration, the rubber in back allows a bit more and faster movement. Not so concerned about caster changes backing up!


Edited by farna - Jan/12/2013 at 1:42pm

I've never had any complaints with my trunion suspension, but all I ever hear is CONTROL FREAK. So just how expensive is it for a 69 AMX?

Edited by 0069X - Jan/22/2013 at 8:45pm