I would like to get my car to be a bit more stable at Highway speeds. It does not have the tendency to "Self-center" the steering as most cars do. My car is a '38 Chrysler that has power rack & pinion steering with original spindles (with discs added) and original control arms. I've also moved the upper shock mount from the upper control arm to a bracket attached to the frame. I've dialed back the pressure on the power steering pump, so I don't think it is over-***isted, it just doesn't have that sweet spot to bring it back to straight ahead driving. Here is a diagram of the O.E. setup: My thinking is that the front end was designed for a caster angle of 1.5 degrees (per the original manual) which made sense back then, but is not appropriate at 65mph on a modern highway. I've maxed the existing adjustments out and got about 2.5 degrees, but the stock parts aren't made to go any farther. Does anyone have a suggestion how to get more caster without doing surgery on the frame? As it is now:
Would machining the shock side at the top of No 35 + adding the same amount in the way of a shim to the opposite of 35 side work ?
It appears in your picture that you have it adjusted all the way forward at the top? That's negative caster. You should be wanting positive caster. It should be adjusted all the way BACK at the top for positive caster. Ref: http://en.wikipedia.org/wiki/Caster_angle
I would be looking at the top wishbone mounting ( no 23 in your first pic ) at the ch***is and moving the mounts back a touch kingpin inclination on most original 30's , 40's cars trucks etc were nearly vertical , so for modern steering and comfortable speed ......you need more caster cheers Steve in Oz
Yes, it looks like negative camber in the photo, but that pic was before I adjusted (maxed it out). As measured by the alignment shop 2.5 degrees positive was all I got. I tried shimming under the front of the upper control arm, and under (atop, really) the rear of the lower arm, but was unable to make a measurable difference- maybe because the mounting surface of the control arms still remained flat against the mounting surface of the frame. I was thinking something like the wedge-shaped shims you use when hanging a door- though made of suitable hard metal- might work. I looked at rear-end pinion angle adjustment shims, but they were too short. What else might work? While I'm at it, I could use suggestions on how best to measure camber angle at home with an angle finder, a level, and other basic tools. TIA
Then why does the caption say "as it is now:"? You can't expect us to help you if you give us TOTALLY WRONG INFORMATION about the current situation!
All I can say is this. I've driven early Mopars at highway speeds for many years and never had the problems you're talking about. The root of the problem, in my opinion, is spelled "RACK and PINION" or "R&P INSTALLATION".
I've driven my '50 Plymouth with stock steering at freeway speeds too. Its OK- not great. This car came to me without a usable steering box & column, and I wanted my wife to be able to drive it easily so I put in the power R&P. I like it fine except for this one issue. Anyone else have any other suggestions?
You can lower the back which will tilt the upright b ak, gaining caster. You can try bending either the upright or the upper arm. I'd take it to an old school or heavy truck alignment guy for that.
Slot the hole under #23, a little at a time, and pivot the upper control arm toward the back of the car, on the horizontal plane, until the desired caster is achieved. It should not take a huge amount. I start everything non-stock at 7 degrees and work from there, based on road feel.
Hey there 4 woody, glanced at your post about your steering and I do not see that increasing the caster will solve your return issue. Jacking with the caster severely with an IFS of this type creates some other issues in caster/camber/toe gain or loss as the suspension operates and may create other problems with tire wear etc. With out a good picture and description of what exactly parts you swapped to I'm voting that the poor return feel issue is with the power rack and pinion that you choose and cannot be cured by just increasing the caster.. You should be looking into the pressure specs of the steering rack on the return side. Your alignment specs should not differ much from the ones indicated by the year of manufacture of your car and can be found in any early pre 55 Motors manual.
Yes, what **** says is entirely true, but I am still concerned that he's only got 2.5 degrees of caster. It seems slim to me.
2.5 degrees of caster should be more than enough for the steering to center. How did the steering return before the modification ? Whats the toe set at ? Out of spec toe can cause a similar feel.
I couldn't say how it was before since it didn't have functional steering when I got it at all. The sheet from the alignment shop says: Caster 2.4 deg Camber 0.7 deg Toe .08 deg SAI 5.5 deg (What is this?) Included Angle 6.2 degree Lateral offset .6 degree Cross camber 1.1degree Cross caster -1.2 degree Total Toe .16 degree
I used the Fatman R&P kit. It calls for a TRW rack #15774 as used on '87-'92 Cavalier, Grand Am, etc. The power steering pump is mid-70's GM canned ham type with the pressure backed off using the Borgeson pressure reduction shims. There is no pressure on the return side. My '38 Chrysler manual calls for: Camber: +1/4 (that's one fourth) degree with a permissible range of -1/4 to +1/2 degree Caster: 1.5 degrees Toe: 1/16" permissible range of 0 to 1/8" TIA
I agree the problem sounds like its with the rack not necessarily with the alignment. My next question would be . Where are you taking it to be aligned?
Those numbers seem about right for the size of car. All I can think of is that the power steering isn't set up right. Either there's too much ***ist, or too much friction in the column (? or something) which would signal the ***ist to fight the self-centering, or both. How about disconnecting the power ***ist and seeing what it feels like?
Looking over the responses I'm still unsure of what you expect or desire the car to handle and feel like. There are a number of factors that are still unknown that are needed to help find the correct answer. Such as. What type of tires are you using ? Radials or Bias plys. What are the complete alignment readings for both sides ? Do you have a couple of good pics of the steering rack as its installed in the ch***is ? Is the rack positioned correctly to the outer steering arms and suspension ***emblies? Does the rack operate smoothly ? No binds or drags ?
Went to a buddy's shop with a real lift and put the car up to look things over with a fresh set of eyes. There is a slight but visible bend in the "Steering Knuckle Support" (part #35 in the original diagram). The spindle still moves freely, but I can't get more than 1.25 degrees caster on the driver's side. I'm thinking this is at least part of my issue. It is a forged piece, so I'll look into straightening it. If that isn't possible then its off to WalMart for a '38 Chrysler knuckle support.
Not a real fan of straightening steering components. Only do this as a last resort and if so make sure your magnaflux the part before using it again.
Thanks for the suggestion- I thought straightening forged was OK, but now that you mention it I'm not sure why I thought that. I'm pretty sure I can find another somewhere without too much problem.
4Woody, What you are looking for is an extra 1.25 degrees of caster on the drivers side. Right? Measure the distance between the upper and lower joints and then do what the alignment guy from a 1950s shop would do. Calculate the amount that the upper arm has to move back to get 2.5 deg caster, remove the spindle support and shock from the arm, break out the "blue wrench" and heat it up and bend it back. Sounds crude but that is how they did it. Do not quench and make sure that there is no breeze which can cause the arm to cool to rapidly. Rex
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