M body- is it a handling nightmare

[Aspen500]

The basic design and operation of a Mopar PS gear requires a certain amount of free play when the input shaft moves in and out to "push" on the reaction springs so it's impossible to ever have zero free play in the wheel. You can see this by turning the input shaft, it'll move back and forth a little bit.

 

[Bruceynz]

I see, I always saw them do that and never knew why, thanks for that, good info to know.

 

[compubert]

Wow, my car has NO upper a-arm bushings, tie rod ends are wrapped in heavy copper wire, to take some of the play out and the steering box has 540k miles on it and it STILL isnt scary at 60 or even 70... of course my ball joints are in good shape still, is the geometry that different on Cordobas?

 

[kkritsilas]

Front Ends are ideantical on F, M, or J bodies, to the extent that parts interchange pretty well across the board. There may be some tuning changes (harder rubber bushing on some of the "special models" (F body Road Runner, Cordoba LS, or first year Mirada CMX) or sway bar diameter differences (along with bushings to fit), but essentially, all the same. I don't really know if there is a torsion bar difference between the /6 and the V8, though.

Wandering/scary at speed is usually a combination of worn ball joints, worn tie rods, possibly worn wheel bearings, and disintegrated bushings, assuming that nothing is bent or broken. With all of that, it usually means wheel alignment isn't within a country mile of being correct.

 

[Bruceynz]

Hi Kkritsila,

The ball joints are all good, I replaced the idler arm as it was shot, steering gear has play in it (pretty normal for these boxes) I have had 5 Chrysler now and they were all shot with less than 100,000miles on them. They had play in them before they turned. The rubbers are worn, I can see it but all are still there, you know how they start looking cracked?? At 30mph the car is fine at 60mph on uneven surface roads the car is all over place, not what I would call very good at all. Here is the alignment specs.

 

[Jack Meoff]

Something must be worn out if it's that shaky at 60.
My Fifth seems to do just fine. :blob1:

 

[kkritsilas]

BruceNz:

The part that really stands out is the SAI (don't know what that actually is, but it is way off) as is the included angle. The only other point to make is that these are all static adjustments, so going down the road, the worn bushings can create a problem that you won't see on an alignment rack. As well, is the car wandering all the time, or is it in turns, under braking? Is there just some slop in the steering on center or is it there in all positions? How is the pitman arm and the tie rods (I assume they are OK because the alignment shop would have picked up on anything that was amiss)? Not wanting to rain on anybody's parade, but has the frame sustained any damage? Also, take note of the comments above regarding the worn upper control arm bushings allowing caster to wander all over the place, which sounds like something that may be creating the unstability at speed on your car.

I am making the assumption that wheel bearings are OK, brake rotors are not severely warped, the wheels are properly torqued down, and that the tires are in good shape.

 

[Bruceynz]

Hi kk,

I suspect it is just worn/rotten rubbers, the car has done 73,000miles but the rubbers have done 33 years, I haven't given up yet, the ball joints are all good, the steering box has play in it. So I have ordered but will be a while before I get them, FF up control arms with the extra caster, new bottom arm bushes, torsion bar bushes. FF have said the arms will allow for up to 5 degrees caster. The bushes are urethane type (that hardish plastic stuff) Also the solid aluminium body amounts along with a steering gear I have had rebuilt here with bearings fitted and heavy feel to it. I am hoping once all this is done the car will drive much better, its going to take time, so will keep you posted on progress.

SAI also known as kingpin inclination, its where you draw are line through the top and bottom ball joints and where it hits on the road is the angle, it changes when you change your wheels to different widths, no one can really tell me what it does, but its something that is designed into the car, some one else may know more, have we got a wheel alignment tech in the forum?

See You
Bruce

 

[kkritsilas]

Is this kingpin inclination measured from the side of the car (seems related to the caster in that case) or from the front (which would affect the amont the wheels push in or out at the top. similar to camber)? Mot that I know this, just have a general idea, but that it seems to be the measurement that is off by the greatest amount, and could be the best clue as towards figuring out where thee problem may be. The other measurements seem to be either within the factory range, but this one doesn't.

If there is a front end guy here, he can probably offer more insight into the SAI being off by so much.

Kostas

Would SAI Be steering arm nclination (our cras, like most American cars, stopped using kingpins in the mid 1950s to early 1960s; they were replaced by ball joints).

 

[Bruceynz]

What I know about it is this - Chrysler set up where they want the tire to sit on the road, there is a line they draw through the top and bottom ball joints, they work out where the tire should sit, when you change the offset or back space of the wheel shifting it in or out then you may not have the SAI correct with what Chrysler designed. I dunno how critical it is because Chrysler had different width wheels on cars of the same type of car. My car has after market wheels on it. I went from 205 x 75 x 15 to 215 x 60 x 17, I tried to keep the back space the same but I did notice that the wheels sit out further than the old wheels, I put this down to using knock on wheels and the 1/4" thick adapter used to bolt on to the hub pushes the wheel out by that much (Something I didn't count on) maybe this is what my SAI is out but I am hoping there is some expert in this field out there on the forum who can tell me how critical SAI on a car as you are aware people have been fitting after market wheels to cars for as long as they have been making cars so not sure how much SAI is a problem unless you put really wide wheels on. Oh yeah king pins have been gone for years but still the same principal.

 

[kkritsilas]

Bruce:

I con't really know how critical the SAI is, just like you don't. I was only wondering if the SAI being off is a clue as to what may be wrong. I guess we would have to wait for a real front end gy, or a suspension guy to eductate us both.

Have you tired to put the factory sized wheels back on? Just an idea so see if the larger wheels have an effect or not with the variations in whidth and offset you wrote about. I am of course assuming (start up the Benny HIll skit on "ASSUME") that you have the original wheels and tires, but this may help establish a baseline for you to work from. If you go back to the original wheels and tires, see if anything improves; if not, then it isn't the wheels/tires. If there is a significant change, then you may need to look at the wheels/adapaters.

Wrong wheel offsets can have some pretty dramatic effects on steering, and even more importantly on the loads on the suspension pieces.

Kostas

 

[Bruceynz]

I have the rims and no tires, but I did drive it with the factory wheels/tires on it and it was the same as it is now, the plot thickens, come on experts help us out on SAI

 

[Bruceynz]

Should we start a new thread on SAI, Caster, Camber, toe and its effects we need educating

 

[kkritsilas]

I did a little bit of research while waiting for a raal expert to show up. Ran into this:

http://www.anewtoronto.com/wheel alignment.html

They say (direct quote from the web site):

"Like caster, it provides directional stability and also reduces steering effort by reducing the scrub radius.

If the Steering Axis Inclination (SAI) is different from side to side, it will cause a pull at very slow speeds. SAI is a nonadjustable angle, it is used with camber and the included angle to diagnose bent spindles, struts and mislocated crossmembers.

The most likely cause for Steering Axis Inclination (SAI) being out of specification is bent parts, which has to be replaced to correct the condition. On older vehicles and trucks with king pins instead of ball joints, Steering Axis Inclination (SAI) is referred to as (KPI) King Pin Inclination. "

You can read the rest yourself, but the whole question seems to come down to this: "Why is your SAI off by so much?" If it were in the 10-12 range, I might not have questioned it so much. It is triple the factory maximym. This may be a reason for the instability at speed you are seeing, the SAI measurements from your alignment shop are correct, and as per the above web site, SAI has a defininte effect on stability.

I am going to ask a stupid question here, bur it is possible that the upper control arms have been swapped left to right? Or the lower control arms? Reason I am asking is that a 25 deg. SAI sounds very, very off.

Kostas
"

 

[Bruceynz]

Yes I see, wonder how the machine can measure it, it must be able to, wonder if my wider wheels are effecting it, hmmmmm if the wheel alignment machine knew the factory width from wheel to wheel and I fitted wider wheels then it then measured it then it could work out the SAI, eg if it knew it should be 8 degrees if the wheels were 60 inches from edge to edge and with the new wheels it was 64 inches it could work out the new SAI???

 

[Bruceynz]

Ok I did some research - It would seem that you have positive and negative scrub radius, this page explains it well http://www.clubprotege.com/forum/showthread.php?47204-Effect-of-Wheel-Offset-Change-on-Scrub-Radius

Now I would say the spec for my car is 8 degrees, the wheels are pushed out, this has made and effective increased to the SAI to 25 degrees?? This would mean I had a positive scrub radius, see below from above article. The SAI is fixed so I really have no idea how it could change, the alignment machine doesn't measure the angle so it must have programmed in what it should be and with the wider wheels looks like 25 degrees is all I can think of.

"A positive scrub radius will increase steering effort, torque steer and kickback on bumps to a considerable degree. At the same time, a blowout or a failure of one front brake could yank the wheel hard enough to pull it out of your hands. The advantage is that there is much greater road feel and feedback so that you can feel when the front tires start to break loose in a corner. Consequently, this is often the set-up of choice on race cars."


So it looks like making the SAI angle greater could increase "....torque steer and kickback on bumps to a considerable degree"

This is very interesting and educational, who can explain how an alignment machine works out SAI? Does it work it out on the scrub radius when you turn the wheels left/right, in the alignment business I think they call it the swing.

 

[Bruceynz]

Hmmmm from Allpar - if I am not allowed to post this please let me know but I found this. This is a good description of what I am feeling when I drive it "squirrely"

The K frame member was not built properly from the beginning. The wrong tensile steel was used, and it was not sufficient in thickness. Over time, repeated abuse was causing the K frame to bend, which pulled the front shock absorber towers inwards. Then there was no way to be able to adjust the camber enough.
The K frame held the support brackets that extended upwards to the shock absorber towers along with the upper A frame suspension control arms, and the tops of the shock towers. When the K frame bent, the towers would go inward, causing the suspension camber to go negative or “dip in at the top.” The inside of the tires would then wear and scrub off quickly. You could not find any means to make enough adjustment to cure the negative condition using the regular fixes as we had. That meant of course that the handling got squirrely, the brakes would pull side to side, whichever side felt like it was in control first, and tire mileage was just plain nonexistent.

http://www.allpar.com/mopar/suspensions/transverse-torsion-bars.html

 

[Jack Meoff]

That's an interesting article. I knew that the original K frames had an issue on the first gen F's. They would go south just with civilian driving. I believe they did make them stronger but possibly not strong enough to be constantly beaten on.

The police were pretty hard on those cars. As far as the civilian drivers they seemed to hold up after the initial fix but if they get beaten on they bend.

Maybe it's possible that your car was beat on?

 

[Bruceynz]

Who would know what my car has seen it in its past, quite like this one maybe I should buy it http://inlandempire.craigslist.org/cto/4979387574.html

 

[Jack Meoff]

I haven't done any Dukes Of Hazzard moves in my Fifth but I will say it's a tough little beast.