Is this a symptom of worn out torsion bars?

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'74 Sport

'74 Sport

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My son Aaron has been driving the Dart Sport we rebuilt for less than two years. While we were installing all new suspension components under his Duster this weekend, we took a look under the Dart for a reference on something and noticed the rubber bump block under the driver's side lower control arm is split and falling apart. The frame is almost sitting on the torsion bar adjuster (has actually scraped some paint off).

We used a new bump block when we built the car, and already had to replace it once about a year ago. This is the second new one in less than two years, but only on the left side. Is this indicative of worn out torsion bars not providing enough spring action to maintain lift under a load, such as bumps and dips. The street we live on has a concrete valley gutter at the intersection. When turning left into our street, the car will naturally dip down with more force on the left side. It's not like Aaron does a power slide into our street, he tends to take the dip fairly cautiously.

What else, other than low quality parts, would contribute to the frequently failing bump blocks. Would larger torsion bars prevent this from occurring?

Thanks for any insight,
Jerry
 
Torsion bars, like any spring, will not "wear out" or get "soft". Most likely your splitting of lower bump stops are a symptom of too soft a bar, too low a ride height setting, crappy bumpers from China, or some combination of the three. If you are using anything less than the .870 (HD V-8) bars on the street, your bars are probably just too soft. .890 bars and a front sway bar, along with some good shocks, will add quite a bit of control to the motion of your front suspension, keeping it from bottoming too hard.
 
Well, let's see...
Original stock torsion bars for the slant six power train, ride height as specified in service manual, not sure about origin of new bump stops, and 2-yr old Monroe Monroe-matic shocks.

Other than adding sway bars when able, everything should be equal to or better than stock setup. That's why I questioned the possibility of torsion bars losing a bit of their "spring" as they age, I have heard of a few snapping due to fatigue. And I do know that leaf springs are susceptible to sagging over time and can be re-arched.

Might just go for some heavier duty V8 bars and see what that does.

Jerry
 
Have the bars been removed before ? If so are they reinstalled properly ?
I'm not sure but I think you can wind up the correct ride hieght and still not have the correct preload on the bar if the end hex is a tick off.
 
If you are running base slant six bars with a V-8, thats your problem. Even with a six, they are way too soft.

Any spring will eventually fail and break, but the rate will remain constant up to the point of failure (actually it will increase dramatically at the time of failure). A leaf spring will sag or take a "set", but the rate will not change appreciably. The spring has simply become bent over time. The same spring can be re-arched, or bent back to it's original camber, and it will be the same as new. In some cases the camber can be increased beyond the original amount, but external suspension geometry constraints will limit this. Shackle angle in particular.

Think of a torsion bar as a coil spring that has been uncoiled. It too will take a "set" in time and will become permanently twisted. This is why the thoughtful engineers at Chrysler put an adjusting screw at one end. Even so, they don not lose their "spring" over time. If you have added a V-8, you are asking the spring to carry more weight than it was originally designed for. With that added burden, the spring will deflect more on each bump and you'll be whacking the bump stops harder and more often. If Mopar had felt the slant six torsion bars were adequate with a V-8, they wouldn't have specified larger, stiffer bars for V-8 cars. Like most cars of the period, the front suspensions of our A-Bodies were really softly sprung, and benefit from much firmer spring rates. The "cloud soft" ride went out of favor because it caused mushy handling and frankly was unsafe.
 
Guess I didn't make it clear initially. My bad. The original slant six is still in the car, as well as the original slant six bars. The question, I guess, now becomes how do I ensure that the torsion bars are installed properly?

I know the rear of the bar will seat into a fixed socket in the cross-member. To seat the front of the bar properly in the pivot shaft's hex socket, how should the adjuster be positioned (threaded in or out), and should the lower control arm be hanging freely (with upper bump block removed)? In other words, how do you know you aren't "off a tick" to begin the ride height adjustment?

Jerry
 
I agree with C130 Chief. My 68 Barracuda had a \6 but also had the heavy duty suspension so the bars were base v8 .850 diameter. They were all together to soft a rate and would bottom over most any bump even with the ride height cranked up, can't imagine what it would have been like with base \6 bars.

In preperation for a future v8 swap I put in .890 big block bars when I did the disk brake swap. These bars were perfect for the slant six, eliminated the bottoming, firmed up the ride to be equivalent to modern car ride and made the car handle dramtically better.

Now with the 360 installed the ride is still firm and the car does not bottom out but the handling degraded some. I installed a 1 1/8" sway bar that cured the increased body roll in corners.
 
Jerry, I am going to throw something else out there. First of all, you said dart sport, which I am assuming is a 73 or up model a body?

On my 75 duster, I had a similar problem. When i hit a hard bump, or pothole, the car would actually "jump", for lack of a better word, slightly towards the curb. My car has a 340, but I believe that other than the mounts, the K members attach at the same place in the suspension regardless of engines.

Now you said the left side, so I am not sure if that is passenger or drivers side, but the weak part of these K members is on the passenger side. The problem I have found on more than one of these later style "tower" mount K members is that, the passenger side lower control arm bolts through the K member right through the torsion bar mount. This is a weak point on the K members. The metal is thin here, and the lower control bar attaching bolt will actually "waller" out the through hole in the K member, which introduces slop, which leads to excess travel and unwanted reactions. It has happened on more than one later style a body k member that I have seen, and it has always been on the passenger side

The reason, I believe, that it is always this side is because the passenger wheel is always on the outside of the road, which naturally has more potholes and bumps, as well as curbs and other things to hit. The solution I found to this, if it is the problem, is I have welded two large washers on either side of this hole in the K member to strengthen it, and have yet to have a problem with the new one.

Just as a quick check, when you put your car up on a jackstand, and take the tire off so you can see, when you grab the rotor/drum on that side, can you wiggle it up and down slightly? I could on mine. If so, I would highly recommend checking that bolt hole out. This is my .02 cents, but good luck, and if you need any help just ask.

Will
 
moparmade43 said:
Jerry, I am going to throw something else out there. First of all, you said dart sport, which I am assuming is a 73 or up model a body?
Click to expand...

Correct, it's a 74 Sport, and the disk brake suspension came from a 76 Duster.

Now you said the left side, so I am not sure if that is passenger or drivers side...
Click to expand...

Left side is driver's side as you sit behind the steering wheel, right side is passenger.

I would highly recommend checking that bolt hole out.
Click to expand...

I will, as soon as I can.

Thanks for the reply,
Jerry
 
I am learning myself...
Did you remove the torsion bars before? If so, are you sure they were replaced correctly, right and left sides?
C
 
Bars were removed when suspension was upgraded to disc brakes. They were installed on correct sides of car.

Jerry
 
How far in are your adjusting bolts on the lower control arms? I would jack the car up so both wheels are off the ground and then back off both torsion bar tension adjusters and then keep cranking them up equally on each side. It sounds to me that you don't have enough tension on the left side or perhaps you do have the bars reversed since the left and right side bars are different. Put the weight back on the car and then keep cranking up the tension on the bars until you get good stiffness. If your suspension is bottoming that badly, you should be able to reproduce the problem by vigorously bouncing the front corner. How are the shocks? Is the left one wet and oily? Perhaps the left one has collapased?
 
I'll be investigating this mystery later this week -- off work for the holiday
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I'll post the results of my study.

Jerry
 
memeroy sux so someone correct me if I'm wrong . I think all factory manuals state that you'll meed to remove the upper arm bushing thru bolts or atleast remove the cone shaped bumper under the upper arm to get the lower arm down far enough to properly insert the torsion bars.
If you do pull them back out, roll them on a flat floor or table. Some bow is expected given their age. Over 3/8 inch bow is cause for replacement.
Again factory manuals are worth their weight in gold.
 
i wouls check the rear t bar socket also. probably not but it may be broken
 
Just for your information, a Slant Six weighs the same as the 3.31" stroke LA motors and the 360 is only 25# more. From BigBlockDart.com:
331/354 Hemi with alum. intake and water pump ------504
392 Hemi with alum. intake and water pump ----------564
Slant 6 ---------------------------------------------525
273-340 --------------------------------------------525
360-------------------------------------------------550
361-400 --------------------------------------------620
413-440 --------------------------------------------670
426 Street Hemi ------------------------------------765
 
Use this method to make sure ride height is the same on the passenger side and driver side.

Measure from the ball joint to the floor, measure from the torsion bar anchor housing to the floor, subtract first measurement from second, the value should be 2" +or- 1/8". The height should not vary more than 1/8" side to side. Adjust by cranking on the torsion bar adjusters (up or down). Just make sure you have a LOOOOONG breaker bar as the adjustment bolts are a pain to turn.

A little over kill but make sure the seats are adjusted fully back wards and the tank is topped off good.
 
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