Hot Rods Death Wobble/Hop almost cured...but not quite

Ok, so I have looked over about every thread I could find on death wobble and wheel hop and I got most of the wobble/hop gone but I can't seem to get rid of the last bit. Here is what I have done so far plus some pics/info of my setup, if anyone has any other things I can try please let me know. The shake almost always start at about 50-55mph.

Split Wishbones (from speedway motors)
Went from Bias tires to Radials - All (4) tires are Coker Classic 235/R15
Driveshaft balanced / new slip yoke and tail shaft bushing (yoke was .20 out of round)
Camber is set at about 7*
New kingpins and spindles
Added 3 leafs to the front spring (this helped get rid of a lot of hop)
Not sure on where toe-in is at (hard to measure on my setup) but the more I gave it the less wobble

 

First thing, get a real alignment. If dw persists, make sure all bolts are TIGHT. Same with all joints, tight and solid, no slop. I haven't had to deal with dw on a hot rod, but seem to see it often on lifted Jeeps/trucks and these are the first things we look at to fix the problem.
Do you have a panhard/track bar? You may find you need one...

 

I had a hot rod that wandered a little at 3.5 degrees of caster so I cut the bones and kick the caster up to 7 degrees. cured the wandering but then when you would hit a bump at around 30 -40 mph it would induce a violent death wobble, Cut the bones and took the caster back down to 5 degrees and it seemed to work well. I put a VW steering stabilizer on just for good measure after that.

 

Suicide front suspensions are know for bouncy rides but it looks like you have the shocks mounted pretty far back on your bones. HRP

 

Try a steering Damper from So-Cal or VW.

 

Is cross steering rod on same plane as the tie rod? Looks to be sloping down from steering arm to spindle. That could be a possible bump steer or initiation source for the death wobble?? Get someone to measure toe in and set it at about an 1/8" in at front. Not relevant , but the T fitting for your brake lines looks like it is hanging loose. Others know more than I, but I have had the death wobble in A's before, and it is scary. Make sure all your rod end are new or very good.

 

Wheels are true?
Front wheel/tires balanced w/dynamic method?
Rims fit the hub and center-up when tightened?
Tires need to be shaved/made round?

 

......................This is a good place to start. You might be amazed at just how out-of-round a lot of brand new tires are.

 

Try ALL of the above ^^^^^^^^^^^^^^Check them off your list as you go.

 

had same problem until all tires were trued and balanced end of problem.

 

First try to get the actual specs that you are set at now. You may find that your caster is to little. 5 positive should do it with toe set at about 1/8"

 

1. shocks are upside down,turn them over. 2. Move shocks closer to axle. 3.Get alignment done.

 

Toe in.

 

New king pins and spindles. Were the bushings line-honed, as in do you have vertical free-play?
Are the wheel bearings adjusted to have minimal free-play?

 

I set my toe by just using a tape on the front and backs of the tires -- same point on front and back -- 1/8" in. Came out fine and took out a death wobble. Close enough for a nice ride.

 

measure the wheelbase on each side of the car and see if they are the same

 

Lets look at this issue as having contributors.
Get the geometry/alignment set up and confirmed.
Front end; king pin bushings, tie rod ends, steering and wheel bearings set.
Then you only need rims and tires that are round, balanced, and mounted correctly.
I doubt you'd need a damper on the tie-rod.
I think that wheel offset could cause this effect, given the right conditions.

 

Shocks are upside down.. Yes it does matter if shocks are oil filled.. I see someone else mentioned this, sorry...

 

Thanks for all the replies, I took the car for a spin and watched the front closely and it is definitely a bounce instead of a wobble. Gonna start with geometry and work my way through the suggestions. Will update once I have some new results, thanks!

 

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The "shocks are upside down" comment is valid. As others said, Unless they are gas charged with isolation from the oil they will suck air upside down and have a "dead spot" with no resistance.
Kind of like what is shown at 7:10 here, although for slightly different reasons.



Inverting the shox is where I'd start.

 

Yep, this is your biggest problem. The shocks are way too far away from the axle to control the bounce. They need to be moved forward or you will never get any control over the problem. In their current position they are basically useless and doing nothing, just like having no shocks at all.

Don

 

THIS, and have you confirmed the tires are round? You can balance an egg.....but it still won't roll smoothly.

I had this on my first Model A. It ended up being a warped rear housing. In being such a short wheel base I always thought it was front end related.

 

Start with flipping the shocks.

 

OK I flipped the shocks and no difference, I made up some new mounts at work so going to move shocks up this weekend and see if that works. Having them back where they are at now makes sense as to not holding the front end down. Results to come...

 

This may sound stupid , but I had the same problem when I put my T on the road..... I had a REAR tire out of round ,this caused a frt.end hop , after going thru 5 different rear tires ,the tire guy & me found 2 rear tire that were round enough to cure the "hop" that was occuring between 45-55 mph
dave

 

If it is a bounce instead of a wobble I would be looking more at a balance or out of round issue.

 

You could try leaf clamps on the front spring. The friction of the leafs provide some amount of damping.

 

The reason I suggested moving the shocks is this: If you imagine the shocks located directly over the axle, that is where they would have maximum control over the movements of the axle. As you move them further back they lose some of that control. (for example, if they were all the way back on the wishbone they would have zero control)

I had the same issue with my 23, because of the suicide front end the shocks had to be back somewhat, and I did sometimes experience the tires starting to progressively bounce more and more as I went over uneven road surfaces. I could actually watch the tire on the drivers side start bouncing like a basket ball and I would have to slow down for a second to stop it.

Don

 

thanks for the input Don's Hot Rods, I think there lies my biggest issue. I can watch the driver side bounce going down the road if I slow down it backs off. Thanks!

 

Also. Get rid of those short shocks. They way you have them mounted you have no travel at all even if they were right side up. Move your mounting point on the inside of your split wish bone if you have to have them on it. It will give you a little more travel. Put spring clamps on as well like mentioned earlier. Without them your spring will be hopping all over the place. My 2 cents for what it's worth.