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

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There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.

How far off the bump stop is the car when at rest? If you run the front end too low it will beat the snot out of those bumpers.

Torsion bars are usually good until they break. I have never seen one lose tension.

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Official Cookie and Mater Tormentor.

I'll have to check the passenger side and let you know later. The ride height is set according to FSM. That being said, isn't the ride height determined as a "difference" between two measurements taken off the suspension? Could the initial height be set too low, then the ride height be relatively correct to that beginning height, but still be too low? I'll have to think about that one.

Jerry

_________________
There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.

If the torsion bar(s) are sagging (won't hold their adjustment), a right bar could be installed on the left side and possibly vice-versa too. They aren't interchangable, though they look identical except for the part number and can be installed in the wrong position. Torsion bars are prestressed during the manufacturing process according to the rotation direction they will be stressed when in service. If installed wrong they will tend to lose their preset. Eventually they might "settle down" and hold their height, or they might break too. In case this happened I would consider the torsion bar likely ruined for it's intended purpose unless it could be sent back to the factory for re-setting & heat treatment. They commonly did this sort of thing on Model T Fords for bent axles and such, and it was part of the well-established Ford service organization, but there has never been anything set up in this regard for modern Chrysler products.

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1964 Dart 225 1966 Valiant 225
1966 Dart 273 1966 Barracuda 273
1969 Dart 225
'64-170 engine '66-170 engine
(two) 198 crank/rod sets in custom-fitted wooden boxes

wooden motor scooter with hybrid-electric drive

Torsion bars don't lose their springiness. The two ways they can fail is if they sag so much you can't set the normal ride height, or if the bars snap in two. The only way to change their spring rates is to change their diameter, and if they rust enough to change their diameter, you're likely to break them outright.

My first thought was that it's sitting too low. But if you can rule that out, there's two other things I can think of. The first is a blown shock. A somewhat stranger possibility is that you've got your crossweights off. It's a problem that for some reason doesn't get mentioned much in the Mopar world, but guys with adjustable coil-overs talk about all the time, and you can get this way off if you botch a torsion bar adjustment, even if the height is correct. I'm going out on a limb here because this is theoretically possible but I haven't seen a confirmed example. It could be that you've got the suspension adjusted so that most of the weight is on the opposite side. This could make it easier for some types of bumps to compress one side more than the other, and give the bump stop a pounding on rough roads. The way racers typically check this would be with a scale under all four wheels.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

I have a 73 swinger and I got stock replacement 225/318 replacement bars. The ride got less mushy. Maybe just me?

rdr

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madam im adam

Could also be they were a different part number than what was in there, as what came with a 225 changed over the years and it's possible you may have gone from 0.830" to 0.870" torsion bars. I've seen Year One and other supply houses apparently selling 0.870" torsion bars listed as for a slant six application, even though not all slant six powered A-bodies in all the years they listed actually used that size.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Torsion bars don't change their spring rate, but during manufacture they are prestressed to just beyond the material plastic limit and released. Then, the residual shear stress at the surface of the bar with no load is 50% of the yield stress. The direction of initial stress is opposite for L vs R side bars. So, if the bar is installed on the wrong side of the car the yield stress can be exceeded during normal use resulting in greater than normal sagging.

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1964 Dart 225 1966 Valiant 225
1966 Dart 273 1966 Barracuda 273
1969 Dart 225
'64-170 engine '66-170 engine
(two) 198 crank/rod sets in custom-fitted wooden boxes

wooden motor scooter with hybrid-electric drive