65 Dodge alignment specs.

rapidtrans

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I had the front end rebuilt over a year ago. I finally got around to getting the alignment done earlier this year. The alignment shop told me the SAI (steering angle inclination) is way out of spec. Equally both sides. I see no way to adjust this angle.
The car feels solid and tracks real well. After driving it more this year I notice a slight twitchiness going straight down a nice level road.
SAI is 11 deg greater, both sides, than factory spec. says it should be. (This is the angle between the centerline of the tire and centerline though the ball joints)
Other than the change to 7” rims everything should be stock replacement.
What do the FCBO suspension guys think?
 


At about 9 minutes in, they discuss steering axis inclination. They also say it's not usually checked unless the camber can't be set, which makes perfect sense to me.

I looked up the spec and assuming it's the same as a Plymouth (sorry that's the FSM I have) it should be 9 degrees. 11 degrees off that is huge! I would suspect that it's more like 11 degrees total, making it off 2 degrees.
 
Neat link! I suspect that "Steering Axis Inclination" would equate to the old "Kingpin Angle" on the king pin-design suspensions . . . straight axle and the later independent suspension front ends? I suspect this is more of a check to ensure that nothing is bent in where the suspension mounting pivot points area?

CBODY67
 
If it was off by 11 degrees, you would not be able to even drive the car. So assuming the axis is at 11 degrees on both sides, I suspect that the frame cross member may have settled some with time. This probably pulled the frame rails in and threw off the axis angle. There is not a ready fix for this other than have a frame shop realign the frame members. If it still drives ok, I would let well enough alone, especially if this is an occasional cruiser. How may miles are on the car? Usually, frame settling is found are high mileage units or units driven over a lot of rough roads.

Dave
 
I first heard of Crossmember Sag from my Chevy friends. Usually on big block Chevelles, BUT also was around on '55 Chevy small block V-8s, too. There were special offset upper control arm bushings to fix that, as I later found out. Surprise when I found similar things for Chrysler products!

What condition are the upper control arm bushings in now? Orig? Dry-rotted? And the lower control arm pivot bushings, too?

Just some thoughts,
CBODY67
 
Every other setting is dead nuts on the FSM numbers. I suspect their equipment is not, or was not, set up to measure SAI on a 55 yr old Dodge. FWIW, just using a bubble level shows the front wheels perfectly vertical as spec’d.
Car turns fine and self straightens just as it should.
The twitchiness feel is similar to a fwd vehicle slightly out of alignment. I’m fussy when it comes to front end alignments.
I would think 20 deg as apposed to the spec’d 9 deg would be visibly noticeable looking at vehicle head on.
 
I suspect their equipment is not, or was not, set up to measure SAI on a 55 yr old Dodge.
^This^
The car was probably old when the tech was born, so there's that.

I would think 20 deg as apposed to the spec’d 9 deg would be visibly noticeable looking at vehicle head on.

I don't think you could see it, but at 20 degrees, I would expect that the camber would never be able to be set right. You would see it (and feel it) if the camber was off that far.

Every other setting is dead nuts on the FSM numbers.
Then you're OK. Go have some fun with it!
 
Sometimes, "twitchiness" can be related to tires, and variable as a result. As in when changing lanes on the highway and crossing the gap between the lanes.

To me, front end alignment is pure "inches" and "angles". How much did the have to change the prior setting to achieve what they got? Just curious if the eccentric cams are pretty much in the middle of their travel?

I'm suspecting that the SAI is more of a derived number on an independent front end suspension, rather than something you can put a ruler and bubble on?

As long as everything seems to be working fine, enjoy driving it.

Just some thoughts,
CBODY67
 
The ball joints, bushings and sway bar bushings are all new. The shop that did the install I’m sure would have noticed any damage or sag. Old car specialists. They just couldn’t align my car because they could not get their equip. on the rear wheels due to the low wheel opngs.
I think I’m good to go.
Thanks guys! See ya next weekend.
 
Hey Dan,
Not that I noticed a difference when I installed it....but wondering if the billet rag joint I installed has anything to do with your "twitchiness"? The old style rubber may absorb that where the metal will not........just a thought???
 
Hey Dan,
Not that I noticed a difference when I installed it....but wondering if the billet rag joint I installed has anything to do with your "twitchiness"? The old style rubber may absorb that where the metal will not........just a thought???
Naw, you just get a little more road feel through the wheel.
 
The ball joints, bushings and sway bar bushings are all new. The shop that did the install I’m sure would have noticed any damage or sag. Old car specialists. They just couldn’t align my car because they could not get their equip. on the rear wheels due to the low wheel opngs.
I think I’m good to go.
Thanks guys! See ya next weekend.

Dan: Really looking forward to seeing you again and your car. What inflation pressures are you running? I hope its not what the door sticker sez. . .
 
Here ya go.

alignment chart.png
 
In general, the old tire pressure stickers were based on the least amount of pressure needed to support the weight, not to exceed 32psi (or more with 6-ply rated tires). As noted, they were bias-ply tires back then, too.

Given that more weight is on the front, the front tires need that 2psi more pressure to better support the additional weight on the front end vs the more lightly-loaded rear of the car. I started using that same pressure-bias on the tires of our '66 Newport, in about'68, with the OEM stock Goodyear Super Power Cushion whtewalls. Car handled better, less understeer in turns, and better steering response. Plus felt more "solid" in all turning situations! Tire wear was the same, front and rear, too.

Back in the later '60s, the old "Car Life" magazine did many great tech articles. Many specific to tires. One included a chart of tire pressures vs the weight they would individually support at such pressures. Knowing that road test data indicated that Chrysler products (as were many similar models of the time) had a weight distribution of about 55 front/45 rear, then to maintain equal proportional loading of the tires, the fronts needed to have more pressure in them than the more lightly-loaded rear tires.

Back then, it was generally accepted that the base inflation pressures were mainly for "soft ride" orientations, but speeds of 70+mph needed 4 more psi, which meant the rear tires would start at 28psi. Adding 2psi for the fronts, due to the "more weight" situation, put them at 30psi. So, theoretically, the front and rear would reach their weight-based "limit of adhesion" at the same time, resulting in more neutral handling, rather than understeer, as the tires were proportionally equally loaded by their inflation pressures.

Most OEMs, especially Ford, wanted their vehicle to understeer a bit to encourage tire squeal before the driver might "get into trouble", so they'd back off of the throttle and slow down in the corner. A valid orientation. A car with the 30/28 type of tire pressure f/r bias would still understeer at the limit, but a bit less, which also might allow them to steer-around the obstacle rather than slide into it, possibly. Other factors as "vehicle lean" and resultant camber changes of the front tires were also in the mix, too, as might be the addition of a rear sway bar. FWIW

As for the tire wear issues, the higher front pressure meant the bias-ply tires' tread didn't "buckle", with the center of the tread sharing less load, with the bulk of the load being on the outer edges of the tread, even a narrow as it was. On the rear, the tread wear was evened-out by the full tread being in contact rather than just the center of the tread, primarily. Even with the narrow treads and narrow rim widths of those earlier times.

Modern P-metric radials do have stiffer treads than the bias-ply tires, BUT not as much as the radials from the earlier '70s and later '60s, by observation. Take one of the bare tires, place it vertical to the floor, then lean on it, seeking to compress it downward. Watch to see what the inside center of the tread area does. Usually, it'll "buckle" as the sidewalls compress and flex. Just a lesser amount than a bias-ply tire might. Whereas a radial from 1975, especially a Michelin X radial, would only flex the sidewalls.

Apologies for the length, but wanted to explain how I came to my orientations on f/r tire pressures. Which concur with the earlier comments, too.

CBODY67
 

A "skosh" was somewhat related to "rch"?

I believe that chart was originally published in a Mopar magazine that was promoting the installation of urethan front suspension bushings? It MIGHT have been more from their own preferences than real-world street driving situations, I suspect. Plus what appears to me to be a lack of understanding of the camber patters of a typical Chrysler front end geometry, when compared to what GM typically did!

There is a MasterTech program on front end geometry on Chryslers, which probably goes back into the pre-torsion bar days. When a left turn is made, the outside wheel goes into negative camber by design, the inside wheel goes into positive camber, by design. As the car leans, teh wheels end up being pretty much vertical to the road surface, as their diagrams illustrate. This keeps the outside wheel's sidewall better braced against the loads it encounters, as a result. Same with the inside wheel being more vertical, too, with similar results of keeping ALL of the tread against the road surface, for best results.

In years later, with the use of larger sway bars, the amount of lean is decreased, which allows the outer wheel to already be in negative camber mode, by design, being better braced for the higher cornering loads resulting from higher speeds, wider tires, and heavier vehicles.

Caster is related to steering efforts, which is why manual-steer cars usually had lower caster settings, some a bit less than "0" degrees, as power steering cars were closer to "+1 degree". Adding caster, even to a GM front end, will increase the Chrysler-style camber affect, by observation, but in more extreme increases, it can allegedly need a steering damper (as Mercedes and others used back then) to minimize wheel shimmy.

Therefore, I consider that particular chart to be more generic than Chrysler-specific.

Adding a bit more psi in the front tires is, to me, a better way to increase handling performance in a street-driven vehicle than use-specific alignment specs. Tire pressure is much more changeable than alignment settings, UNLESS you are prepared for the tire wear issues of the negative camber situations. BTAIM

Enjoy,
CBODY67
 
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A good alignment shop can align cars without following the specs in the computer. We have K&S Wheel Alignment in town. Chuck has been aligning Indy cars for years. If you can't get your car to drive right take it to K&S.
 
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