Hello, I have a straight axle on a 47 Plymouth gasser. I have no idea who made it but it appears to be an old original cast unit. It steers very hard. I checked the caster and found that it has a ton of Positive caster. I made temporary shims to tilt the axle and have almost zero caster now and it steers great. Do I want pos or neg caster and what degree of caster am I looking for? Also where can I get axle shims? These shims will need to be at least 3/8 thick and taper to 0... Thanks, RH
Should be positive around 5 to 7 degrees to track straight and not end up with death wobble. Yes, it won't steer like a Cadillac. If it's a real gasser it only needs to go straight anyway.
5-7 degrees is the range most recommended, but that's not always the case for every car. I've found the shorter the wheelbase the car has, the more angle they need. This may make steering slightly harder, but a short wheelbase car needs more to keep them going straight and not be squirrely going down the road or track at higher speeds. The 6 degrees I have on my 115" wheelbase of my '39 Chev works great, but so does the 11 degrees I have on my Austin gasser with 89" wheelbase. With zero degrees you may develop death wobble, but toe in is more likely to cause this situation. Make sure your in the 5-7 degree range, but also check toe in to adjust it in the 1/8"-1/4" range. Another thing to check with stiff steering is kingpins. Raise the car's front wheels off the ground, and try to turn the wheels by hand, not with the steering wheel. If you can't sit beside one front wheel and grab the tie to turn it left and right, then the kingpins or bushings may be dry and need grease, or just bad and need a new kingpin kit installed.
Wide tires , low tire pressure , excessive wheel offset , condition & type of steering box , steering ratio , size of steering wheel , little positive caster all contribute to hard steering . Crawling out of your modern car with power assist everything makes " older " manual steering vehicles " seem" hard to steer , just like the folks who think 3000 rpm @ 70 mph ,the engine is "screaming" going down the road .
Thanks guys , to answer a few questions. Yes, it is a real gasser but I want to drive it on the street so I would like it to steer decent. Yes, I have checked all the obvious components king pins , tires etc etc and they are all good. I did do a search on axle shims and the specs give the largest shim at 8 degree, but exactly how thick is this? There are no other specs that I can find. Im needing a 3/8 thick shim get it any where close......RH
@krylon32 , when I search for castor shims, I see a lot that will work with parallel leaf springs (approximately 3" wide and 5" long slope), but I don't find any that will fit in the early Ford front crossmember, for the buggy spring. https://www.ebay.com/itm/203519124816 Do you cut them down?
You do have parallel springs, correct? How wide are the springs? Check Ebay, there's a ton of spring wedge shims in various widths and degrees on there including 8 degree.
@Roadhog56 , do you have pictures of what your front suspension looks like? It's hard to suggest what you need without pictures or a better description. Only thing you've told us is that it's a "real gasser".
Ok, Here is what I have. The builder installed the springs with solid mounts in the rear and shackles in the front. The spring mounts in the front are higher than the rear which gives the car a lot of positive caster. Also he moved the axle forward on the spring to center it in the weel well. The plate under the spring is actually a hard plastic material with a hole drilled behind the rear U bolt for the spring center bolt, it doesn't look like there is any taper to it at all. With this set up I could barely steer the car and it would "bind" about halfway through the steering travel. When I jacked it up I could easily turn the steering stop to stop. SO, I Loosened the u bolts and inserted a 5/16 spacer between the spring and the plate, right behind the front u-bolt to reduce the pos caster. It worked great. I was able to turn the steering, on the ground, stop to stop and I tested it in the parking lot turning in hard circles rt and Lt. Thanks for all the help, RH
It is good to have the front spring eye higher than the rear, lets the spring absorb bumps better. Either make wedge to suit with offset spring bolt hole or make the shackles a little longer?
I made 1 degree shims some time ago for an old Scout. Night & day! breathtakingly stupit of IH not to do that until the last year of production!
I bought 5 degree shims from a 4x4 place as they seem to always have plenty. Too wide for my 2" springs, but being aluminum I cut the excess off easily in my bandsaw. They are about 5" long, and thickest end is about 3/8" thick. When installing them you should first clamp the spring pack, and then remove the centering pin and put washers or bushing under it so it extends through the shim or it wont locate properly. You really do not want to go less than 5 degrees positive in your attempt to make your car steer easier, or you'll end up with the car wandering all over the road as you're driving.
If there is excessive positive caster, the front tires will want to fall over lol. From level, I rolled mine back 7⁰
Thanks for all the help. The shims are working great and I am taking it out on the highway today to see how it handles. I have just been "guestimating" the caster angle, Is there any way to get an actual caster measurement without a front end machine?
Be sure the spring locating pin goes through the shim and into the axle as 1971BB427 noted a few posts up. U-bolts alone are not enough to hold the axle in place. Trailer shops, or spring shops will have extra long center pins, allen headed bolts also work.
A cheap angle finder and a level floor will get you close enough to get a good idea of where you are at.
Yes they will. But doesn't usually happen unless you start getting up to rail type casters that typically run 23-30 degrees. I notice my 10 degrees on my Austin will tend to want to "drag" the front tires when turning the wheels sharply when backing up. They never turn that far when driving, and never feel the drag going forwards. But I can be going 80 mph forward and let go of the wheel and she tracks straight.
Back to the caster shim. First you have to actually figure out what caster it has when it is/was hard to steer. Then you need to figure out what you want the caster to be and then figure out what degree of shim you need to be able to make the change. Going by guess and by golly does't do a lot of good unless you can figure out what the taper of what you use to change it to where you want it is as far as degrees. That may just take setting that piece on a flat level bench or table top and setting your angle finder on top of it to read the number of degrees it changed the original setting.
In the stock position the best I can measure is 10 degrees. So I need 5 degree shim to get this in the range of 5 to 7 . Damn! I didn't know there was a level option on my phone! I ordered and received a pair of 5-degree shims that I am installing today. Thanks, RH
When you said that the plate under the spring is "a hard plastic material" it sent up a red flag for me. If it is truly plastic and not powder coated metal it could hardly be in a worse place. I'd replace those with metal pads and have the local machine shop cut the desired degree of caster correction into them.
Why the dislike of plastic , the proper product used as directed is as good or better than metal in many cases
The Jalopy Journal
