Technical Why does my front end shake so much?!

Alignment. Check it accurately, it can make a night and day difference.

I swapped some front end parts on my previously running perfectly '32 roadster. Sheer vanity .This involved a steering re-alignment which i eyeballed / guessed and a low speed local test proved all was well. Time to go and after a couple of miles of low speed light to light and I hit the on ramp on the 405 in Orange County Ca at about 4.00pm. This ramp is quite a long one so I'd reached about 50 or so in plenty of time but the shakes were immense and i near filled my pants at the prospect of merging into the freeway traffic and not being able to maintain a reasonable speed. Long story short, i got off at the first opportunity and limped back to the shop and did the alignment 'properly' and all was well. My prognosis? Excess toe in causing the tires to jump / skip (or hop even!) once the forward force was overcoming the tires ability to slip. Repeat in rapid succession.

Correct toe is absolutely critical imo. Yours isn't checked and your problem sounds quite like what I experienced. You might have an easy fix in prospect?

Chris

 

1/4 inch toe in and 15 degrees angle on shocks. that is the old tried and true setup

 

Check king pin to axle and kingpin bushings

 

OK,I read some good info passed along by others above. Here's some things you need to do I think; Set toe near 1/4in.
* Lower your tire psi too were you just start to see the side wall near the road bend out about 3/8 to 1/2in. more then the rest of tire.{ **The front tires you picked are a bit heavy do too being a little over wide/skinnyer & liter tire would help}. ***Now about front shocks,you mounted to bone back away from axle,why this is not good,is by doing so you added to lever space from tire patch an axle center=shocks are now weeker that way{ move lower shock mount as close to axle as you can/It's OK if shocks run forword an out some at lower mount. More photos my show other things? Having shocks lean out at bottom an close to axle helps stop side to side axle movement in shackles also{shocks being straight up fails to do anything about that !!! If your front end spring is too stiff,remove next to longist leaf or more. Poor design shock mounts at rear can mess up frontend too some times.

 

My first thought when I saw the title of this thread was :"Have you thought about getting a Sports Bra!" OK, OK, I know it's wrong, but it is funny!

 

1/4" seems a bit much. I have had good results with 1/16" toe in, but all cars differ.

 

Depending on how tow taken,your right. Some take size off 1/2 way up on tire,some off a few in. off the ground,and then there is bigger an smaller tires. So ya,you right for your car the way you do it,and with all other things set as they should be,only tire life is sometimes the lost factor.

 

Why does my front end shake so much?! That's what she said.

 

If those are generic Monroe $20 shocks they suck...If nothing changes after the spring fix, tire fix, camber fix etc...try a set of Bilstein shocks. Hit them with some black paint...done.


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Shocks are gonna have to stay where they are and yes, they're $20 Monroes.

Jumping up and down on the frame horns suspension travel is pretty stiff. Below are pics today and a couple of years ago. Today I've got 10 leaves in the spring (real close to stock '38).



During construction I had about 5 leaves. General consensus at the time was, add more leaves.



Alignment. Putting a framing square 90* against the tire and concrete floor shows each tires camber looks good, although by eye it looks like the tops of the tires are canted slightly out.
Caster I measured at 11* with a HF angle meter on top of the kingpins. If I remove leaves it's gonna add to the caster angle.
Toe-in looks about right by eye. What's an easy way to somewhat accurately measure toe-in? Don't really want to take it to the local front end shop.....they probably wouldn't know what to do with it! Kingpin.....what's a kingpin?!

 

You front end guys help me on this, I noticed that the shocks are mounted to the wishbones, don't they need to be mounted to the axle? Or is this acceptable?

Larry

 

i would hope any shop with an alignment rack could at least measure toe, easy to do with a tape measure at home as well. If the spring is so stiff it doesn't deflect then nothing else is going to stop it from bouncing.

 

Get a second framing square, set each on rear ctr tread, of fronts'. Then move to front face, of same tires . Subtract the diff, between the bottom outside edge of the squares.
(If needed, get a 1" thick plank to rest squares on, if your ground surface is uneven.)

 

Jack each tire up just a little and spin it. Hold a Sharpie against the center and draw a line on each. Set the car down and roll it back six inches, then forward six inches to "set" the rod ends. Measure the distance of the line on the front and back. Might need to transfer the line to the floor with your square if there is something in the way. I'd try to set it at 1/16" inward to start with.

 

lots of good info given--remove some leaves-on 40's which are much heavier I go down to 8 from 11

 

This question needs to be answered. In one of the pics it is welded to the wishbone. Is that ok as Larry; asked?

 

Sorry, this quote...

 

Answered and covered before he even asked.
Reasons given as well.

 

all questions to the shocks can be answered by installing a panhard bar. im using homemade friction shocks which might be considered a bit of a panhard bar . the 1/4 inch toe in is on a model a axle and spring which on my car is almost impossible to flex. its steady at 135 mph hi 9s. my shocks attach to the radious rods like yours using a rod end linkage so there is no bind. standard launch is with left front about 2 inches in the air.

 

Dana did answer in his longer post earlier on here? He did mention that location in some way. The further back the shocks are, from the axle centerline, the less effective a shock is as far as "movement" of the shock piston. In other words, if the axle moves up one inch on a certain bump, the 100% vertically mounted shock placed more towards the rear of the bones, that shock will not move 1".

But, if the shock was mounted at the axle, but also "angled" like most Ford hotrods are, then that angled shock piston won't move that same one inch either. So, I'm not sure if that answers anything

BTW, I wish we could see a video of the "bouncing" to help figure this out better. With so little to go by without, I'd almost think the spring rate is way, way too stiff...causing the tires to be "forced" to act like basketballs? ................ If the spring won't budge much to absorb the road bumps, then the tires will? ( IMO). Dana did also say to drop tire pressure by "eye" to show the sidewalls bow out a bit. I think that is worth a try for diagnosis reasons alone, Then if it helps in a big way, then pull some leaves out of that spring.
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I just saw that. My apologies...

 

Little inherent roll control without angle.

 

Ditch the spring and put in a mono leaf.

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Thank you all for clearing that up for me.

 

may not be, but could the tire be out of round or have a bubble or a crooked tread?

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Something easy to do is to change air pressure in the tires. How much shock travel does it have? What is the ratio of compression to rebound of the shocks? Some shocks are made with more resistance to movement in one direction than another. You could also try some water in the tires to dampen their movement if you aren't in a cold area.

 

Last summer I went through the bouncing tire thing. ('30 tudor with a '38 or so front axle/spring) I replaced king pins, they were not that bad but replaced anyway. Tried toe-in, that did not help. Tried to grind tires back to round, no good. Bought new tires, no good. You know what fixed it? Tire pressure, I tried less pressure to stop the basketball type tire bouncing but it took more pressure. I run no less than 32 psi and I'm good to go. The OP is using different tires than mine ( 550-16 Firestone) so I cannot say if this will help, but it is a cheap easy try.

 

Thanks for all the replies! I tried 24 lbs and 32 lbs, and it bounced the same. Yesterday, I pulled 4 leaves out of the spring, so I'm down to 6 leaves. Today, I'm gonna accurately set the toe-in and play with tire pressure. Haven't checked the caster yet but I know removing leaves will raise it. I may chop up an old axe head and mount it on top of the spring as a wedge/spacer and that should (hopefully) bring my caster back to somewhat normal.

 

When shocks are angled, isn't the same true in that the tire moves much more than the shock? A shock that is perpendicular to the tire movement would seem to be the most effective at damping.

A panhard bar is intended to limit side to side movement of the axle relative to the frame. How do shocks accomplish this?

Wouldn't a straight-up shock be more effective at roll control? The axle has a greater mechanical advantage when attached to an angled shock vs one that is more perpendicular.

Maybe I'm all confused, but it seems to me that a shock would be most effective the closer to perpendicular.

 

I don't know about effective, but I've seen charts that show they act softer the more you angle them.