Okay, so it's been a long, long time since I've posted anything. But I'm looking to get some information from people smarter than me. I know there's lots of them here. My latest build, the 1928 sedan. With the usual four inch drop axle, Vega box etc etc. No different than any other Rod I've built before. The problem with this one is it really likes to wander. Anything over 50 miles an hour on the mildly twisty road and it hunts all over the place. I've done the wheel alignment three times. (Caster) The last time with the wheels off and angle iron bolted to the rotors. Running approximately 1/8" toe in. Put all new tires on (radials) steering is tight and responsive regardless of speed. But anything over 50 miles an hour and it's both hands on the wheel and white knuckles. Any ideas?
What's the caster setting? Does it have a panhard bar? If you have a panhard, does it attach to the axle on the passenger side and frame on the driver's side? Are the king pins tight? What's the king pin angle on both sides of the axle?
Sounds like the caster is zero . Do you have any way to measure the king pin inclination or caster ? is it split bones , 4 link or ? was the frame kicked up in the rear with parallel leafs or stock ? the higher your rear frame is the less caster you have , I usually shoot for 7 degrees. taller rear tires can make the situation worse . When checking caster , make sure its at ride height . I type slow ….
All good questions. Try to answer as best I can. A different road. Great idea. Not. It has split bones front and rear with a triangulated setup as well on the rear. And a panhard bar. Caster is currently at 5°. Positive. Frames stock, boxed, no kick up in the rear.
There is no track locator. I only have a maximum of about 2 in of travel at the rear so I can't see it being a problem with the panhard bar. But I've been wrong before.
Front on shot of the outer end of the axle showing the brakes and wheel. If the wheels sit out too far it can cause tramlining (the front wanting to react to and follow road imperfections).
No, it doesn't have it on the front. I've never had one on the front. Not saying I don't need one. But that should be something I'm going to look into.
Cross steer boxes need a panhard bar on the front. That’s why everyone is asking about that. Just kinda common knowledge. Please describe better what you mean by split wishbones on the rear, with triangulated setup? Are they bushed at all ends like four bars?
@chopped51 Do not add too much caster [the Hotrodders folklore myth] too much caster combined with extra scrub radius is what triggers "death wobble" in lightweight vehicles Camber and toe are "bed partners" [pos camber needs Toe-in , and neg camber needs Toe-out] or you get camber thrust. Have you checked for bump steer? Also check rear for "roll-steer" [a wheelbase variation during suspension movement] If the unstable feeling is in the steering it is usually the front end. If you feel it in your seat, it is usually the rear end.
I can't thank you guys enough for all these replies just in the last couple hours. Sometimes you need somebody looking from outside the box. This is not my first build but it's my first build with a problem like this. And I think some of you are absolutely right. I've just been lucky in the past by not having a panhard bar in the front. I'll be making one tomorrow.
Absolutely the place to start. I thought you said it had one, but after re-reading your post I see that you meant it had a rear panhard bar. One on the front will hopefully cure the problem, but if it doesn't, it will still have been a good idea.
I've noticed quite a few that put a good stabilizer on the front with good results.... I even have a model A with it done...and it works great...
I've got no panhard in the front but the Spring angle is pretty tight.caster at 10° toe 1/8".never a problem
On the front of my roadster I put a dead perch on on side and have a panhard bar in the rear. It drives like a rail and corners great. Gary
Your front end is basically "hanging" from the spring and shackles, if the shackles, perch bushings and spring bushings aren't tight and you do not have a panhard bar, you can wander all over the road. As others have suggest install a panhard bar and it will probably improve your handling. If you jack up your car and try to move the front end side to side you might be surprised at how much a "loose" front end can move, it doesn't take much.
On my roadster with 30000 miles. I set up every car I build with a lot of caster, including this coupe with 10° also.
A friend bought a 32 roadster street rod, it was a new build with under 300 miles. He drove it a bunch and after a few years it developed dangerous bump steer. It was a 4-bar and dropped axle with no panhard, and the bushings had worn enough that now he needed one. He installed a panhard and it has been fine again for several years now.
The reason I'm asking about how your panhard bar is anchored (I thought it had one on the front too), is a friend learned the hard way that it matters where it attaches to the axle. The panhard should attach to the chassis on the same side of the car as the steering box (driver's side), and attach to the axle on the opposite side (passenger's side). If it doesn't, you'll get some real bizarre bump steer characteristics. Keep that in mind when you're building your bar.
Okay, less than 24 hours and I have an update. Went out in the shop this morning. Found some 1-in tube I had left over and a couple Heim joints. Kind of overkill. But I welded a bracket at the very front of the bone on the driver's side up to the frame on the passenger side. Just got back from a drive down the twisties. Wow, wow, wow. Can't thank you guys enough for the input. I will never build another car without a panhard bar in the front. The car handles completely differently now. Very impressed. Time well spent this morning.
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