Technical Why does my front end shake so much?!

Just got the roadster up and running again and whenever I hit some bumps in the road, the front wheels start bouncing up and down rather severely. If the road smooths out, the bouncing smooths out. I haven't had it over 50 mph and I'm kinda afraid to do so! I'm pretty sure it's not the famous 'death wobble'.
'38 Ford axle/spring/split bones, new kingpins, '56 Ford truck brakes, stock Chev steel wheels (not bent), new tires and recently balanced. In the air, wheels and tires spin smooth with no noticeable distortion. Haven't aligned it yet, but the toe-in seems real close, camber looks about right and I have a bit more caster than I'd like, 11 degrees. I'm thinking maybe the front end is too light? Not much too it and I'm only running a turbo 4 cyl. Anyone have any insight??

 

Don't hit bumps...
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Maybe its just the distortion of the picture but......you sure about the camber?!
As far as "being-too-light" in the front end.......Think it weighs less than maybe a top fuel flopper?!! I'd get the alignment before doing any thing else.
6sally6

 

Air pressure?

 

How much air pressure in the front tires? My 26 coupe weighs 2000lb and drives best with26 lbs. of air in the front tires. Also you don't think you have death wobble I would still consider a panhard dampner. Hope everything works out...……...

 

With light cars like your roadster you will need to run less tire pressure. In my 27, I run 18-20 lbs on the front. If I run more, it’s like driving with basketballs up front.
r


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Lots of front end men on here!
Wheels bouncing up and down on a car as light as yours is indicative of being 'oversprung'. The '38 spring leaves are the 2" variety, compared to the typical 1-2/4" wide leaves on '28-'34, usually seen on fronts of street roadsters/coupes.
The number of leaves on a 2,000 lb. car might be as few as 5, (usually 5 or 6) BUT they are 1-3/4" wide leaves, so 5 leaves of 2" width would number 4, to start. (fairly long leaves, as I'm seeing on yours)
My son's '27 'Nose Job' had a monoleaf he tried out...we went to Billetproof (90 miles away) and his roadster dribbled like a basketball.
He changed to a lightweight Posie's and it rides like a dream...Potholes can be felt, but bounce ('rebound' in the trade) is gone.
Alignment? Whaaat??? Toe-in? LOL
BTW, 11 degrees positive caster is excessive, but not 'deadly'...
Tune the spring. Just a matter of 4 nuts and a centerbolt! I guarantee it...

 

I double checked and have not seen the word(s) "shocks" or "shock absorbers" mentioned by the original poster or replies...............

 

It is just the picture. I need to align this thing pronto, but I have to drive 20 miles tomorrow morning to have the windshield fabbed. It'll have to wait 'til I get back.

I ran 24 lbs then bumped it up to 35 lbs...………...same difference.

Originally, I had 4-5 leaves on it but the general consensus here on the HAMB was 'add more leaves'. So I did. Now it's back to about a stock '38 spring. I'll have to go count the leaves. That may be something.

 

I thought the same thing. I then noticed them just behind the headlights. You don't see them at first, but they look to be there.

 

Yup I was questioning if and or what it had for shocks as well.

Upon closer inspection it does have shocks....are they any good?


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Good shocks?

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I would set the toe in at 1/16 .

 

They're not high end (there's nothing high end on this car), just generic but they're new and they work.

 

Shocks are WAY too vertical.

 

I rather have to agree with that but at least he does have real shocks on it rather than some cute substitute. From the looks of things he may be stuck with them at that angle or lack there of though. That bothers me the more I look at it as they angle out rather than in.
We are going on the assumption that the shocks are new and in good shape. if they are used off a donor rig with some fresh paint they may be worn out.
Is everything in the front end tight and in good shape? No stuck on worn parts just because the budget was tight? Cutting corners because money is tight is usually the cause of an issue like this.

 

I read somewhere on here that the bump induced tire bounce was a side to side oscillation pivoting around the spring perch. The suggestion in that thread was the shocks should have more angle to address it. Since this don't happen to all similar front ends, it seems there should be more to it, maybe something in how the spring works and reacts.
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Whhhhoooooeeee. Glad you said that, as that was the first thing that struck me when I saw the shock pics. I feel smarter already knowing we are on the the same wave length .

 

Being vertical the shock will move more than if at an angle, with the same amount of suspension travel. I don't see how that would be an issue with drivability. To reduce side to side movement a panard bar would be more useful.

 

As well as the angle as Gimpy said, what are the shocks off? How is the valving? Are they meant for something heavier? Remember the shocks purpose is to control spring oscillations, if they can’t do that than it will be bouncy.


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@BJR Pretty sure he is asking about vertical movement, not side to side. When one tire hits a bump, the other reacts and they start to bounce back and forth. Totally different action than death wobble or bump steer.

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There's a whole lot of iron realestate in motion between the moving tire and the shock mount. There's a bunch of leverage ratios in action there.
You can calculate or actually measure the distance the shock will move (work dampen) for a given distance of tire movement.
My guess is the tire moves much more than the shock - results of that would be like not having shocks

 

I always set my axles with a 7° caster. HRP

 

From just reading the title I was going to say maybe your tits were to big and to quit trying to run with them but I see after reading farther on that you are talking about the roadster.

I agree I would like to see more angle on the shocks. how about a little better picture straight on down lower in front that shows under your track nose full length side to side?

 

"My guess is the tire moves much more than the shock - results of that would be like not having shocks "

That makes sense.

 

How's it feel when you push on it at rest? Got travel? Too stiff?

 

That’s exactly what I was saying....shocks are supposed to control or dampen that up and down “bounce”

The spring could also be to stiff or as mentioned above wrong amount of travel in the spring and/or shocks

the other thing to remember about shock angle is the wheel does not move straight up and down, it moves in an arc.


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Some leverage ratio in the shocks
Probably have room for rocker set up

 

I disagree with the shocks being to straight up. It works just fine for me.

 

With a stock '38 spring and half or less the weight, shocks won't matter if there is no travel.