'75 Duster steering issue

-

340fourspeedDuster

Well-Known Member
Joined
Aug 17, 2004
Messages
336
Reaction score
99
Location
Sunspot AZ
Guys
Purchased a '75 Duster from a person that put a power steering unit in the car. The power steering and associated idler arm were from an earlier (pre 1973 small pitman arm) car. The car drove and steered fine. Many years go by and the steering box starts to leak badly. I scored a new post-1973 steering box that takes the larger pitman arm. Purchase a Moog pitman arm and install the steering box. The idler arm was in very good shape, replaced a few years back and not changed. Take the car to the alignment shop. I have fresh offset bushings in the A arms to achieve better handling specs for the radial tires. They set it up to my specs for a performance alignment.
Problem is when I drive the car and turn the wheel in either direction all the way L or R
IMG_6228.jpeg
, the wheel is very lazy to return to center. Is there possibly an issue with the length of the idler arm being different? Has anyone experienced this? Seems like the car just needs more positive caster to return to center.
 
I would put offset upper control arm bushings in it and see what you can get for better alignment specs
 
Well then. If you jack up both wheels does it turn easy right to left with the engine off.
 
Guess I should have read the post a little closer.
I know its more $$ but buy a fast ratio borgeson box and be done with it.
 
Guess I should have read the post a little closer.
I know its more $$ but buy a fast ratio borgeson box and be done with it.
Not sure I want to spend $650 for a steering box. The Boregeson is 14:1 where my factory power box is 16:1. I am thinking either add more caster, or check the length of the idler arm and the pitman arm. They should be the same length center to center, correct?
 
Well then. If you jack up both wheels does it turn easy right to left with the engine off.
Will try this. I know that when I start the car, there is NO power box turning in either direction. If there was, there would be an adjustment of the box needed to keep it centered.
 
If you jack up both front wheels and start the engine does the steering wheel move ?
 
+2° caster isn't very much, especially for power steering.

The length of the pitman arm is the same for both small and large sector boxes. The primary difference other than the diameter of the sector was the direction the ball joint on the pitman points. If you only changed the pitman, you must have had a 73+ manual steering box pitman on that small sector power box. Otherwise you would have had to change the center link as well, because you can't use a 73+ center link with a 67-72 pitman arm, the taper on the pitman arm mounting hole runs a different direction.

Pictures would help. Otherwise, I would check to make sure that the steering moves back and forth easily by itself. Jack up the front end and turn the wheels manually and see if you feel any significant resistance. If you do, you'll need to look for bad components (idler, tie rod ends, ball joints, etc). If you don't, it's probably just the low caster number.
 
+2° caster isn't very much, especially for power steering.

The length of the pitman arm is the same for both small and large sector boxes. The primary difference other than the diameter of the sector was the direction the ball joint on the pitman points. If you only changed the pitman, you must have had a 73+ manual steering box pitman on that small sector power box. Otherwise you would have had to change the center link as well, because you can't use a 73+ center link with a 67-72 pitman arm, the taper on the pitman arm mounting hole runs a different direction.

Pictures would help. Otherwise, I would check to make sure that the steering moves back and forth easily by itself. Jack up the front end and turn the wheels manually and see if you feel any significant resistance. If you do, you'll need to look for bad components (idler, tie rod ends, ball joints, etc). If you don't, it's probably just the low caster number.
Vehicle jacked up, engine off. Wheel turns fully in both directions without binding or contact with headers. Here are some pictures.
IMG_6244.jpeg
IMG_6243.jpeg
IMG_6242.jpeg
IMG_6241.jpeg
 
Vehicle jacked up, engine off. Wheel turns fully in both directions without binding or contact with headers. Here are some pictures. View attachment 1715727353View attachment 1715727354View attachment 1715727355View attachment 1715727356

Ok, so you have a 73+ centerlink. So you can put out of your head the idea it’s some kind of mismatch between the pitman and idler arm. It couldn’t be anyway, but you’re using all 73+ parts if it makes you feel any better.

If everything moves smoothly and you don’t feel any resistance in the linkage, the lazy return to center is probably just the +2* of caster. The power steering doesn’t specifically help the return to center thing, it just reduces the effort needed to turn the wheels because the steering box has a 16:1 ratio. If the box isn’t centered the power steering can force the steering to one side or the other, but it wouldn’t specifically effect the return to center. That’s basically all from the caster angle. So unless there’s resistance in the linkage or in the steering box it’s all on the caster angle.

If you’re comparing the return to center feeling to a modern car, you have to keep in mind that most modern cars run at least 3 to 4x as much caster as you have. An new SRT Challenger for example has a factory spec of like +8* to +9* caster.

With offset UCA bushings I’m a little surprised you can’t get more than +2*, typically if the offset bushings are installed to maximize caster (not per the included instructions). Most folks can get more like +3 to +4. But not always, and it does depend on ride height and other things so you may be maxed out. You could try talking to the alignment guy and see if they can get you some more positive caster, it would be worth trading some negative camber for the caster if that’s necessary. The difference between -.4* camber and -.7* won’t be a big difference on the road, but if you can get to +3* caster that would help the return to center a whole bunch.

If it’s not some kind of resistance in the box or linkage, and you can’t get more than +2* caster from your offset bushings, the only other option you have is to go to a tubular upper control arm. The non-adjustable tubular UCA’s usually allow for about +5* of caster depending on the car. Or, if the return to center is really going to bother you, you can get adjustable SPC control arms. I have those, and currently have +6.25* of caster on my Duster. It really adds to the return to center effect, and the car is nice and stable at speed. Not like the shopping cart feel you get from the low positive caster numbers these cars ran stock.
 
72blunblu, I was going by suggested alignment settings for typical performance street. Maybe this is for manual steering boxes?
Screen Shot 2021-04-23 at 2.05.24 PM.png
 
72blunblu, I was going by suggested alignment settings for typical performance street. Maybe this is for manual steering boxes?View attachment 1715727570

The SKOSH chart you posted is a good start, but you have to keep in mind how old it is at this point and where it came from. It was originally published in 2005, by Rich Ehrenberg. You can see a copy of that article here Turn of the screw: front end alignment for performance...

So, you have to keep in mind that was before the entire "pro-touring" movement and really upgrading these cars to handle well. Yeah, Rich was putting the "Green Brick" together at the time and you could get tubular UCA's from Firm Feel that had more caster built in, but they had pretty much the only game in town. The +4° of caster listed in the chart was pretty much the most you could count on getting at the time unless you made your own parts. The offset UCA bushings with factory UCA's were what most people were using, and with those +3.5° is about the most you can reliably get on most cars. And very few people were building their Mopars for handling then. I bought my Challenger in 2008 and can tell you that Firm Feel was pretty much the only source for handling parts, and the were only a handful of people on these forums that were concerned with handling.

I'll get to the point. The numbers in the skosh chart for caster are pretty conservative and a bit outdated. Even just a few years later (2011) I was running my Challenger with +5° of caster, using tubular upper and lower control arms and adjustable strut rods. And the tubular LCA's and adjustable heim jointed strut rods were a very recent addition to the market at the time.

Ultimately, it depends on what you're comparing it to. Unless there's something wrong with the steering box itself, or your steering linkage is adding too much resistance, the return to center action you'll get from +2° of caster is pretty weak. With power steering I wouldn't hesitate to dial that up to +5° even on just a street cruiser. The settings I run are more than most run on the street, but I've run everything from +3° caster all the way up to +8°, and my personal preference is around +6°. That's with a fast ratio manual steering box and 275/35/18's up front.

I don't know how much you've driven one of these cars, or how much you've driven one recently, but if you're comparing the return to center feeling of something built in this century to what you have with your '75 you'll likely need to add a significant amount of caster to put them in the same ballpark.
 
-
Back
Top