Thread: I think I found my problem

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I mentioned before that after driving my T for a while it developed a handling problem. It went into death wobble when I punched the gas to make a green light. I tightened up everything and redid all the alignments and it seemed much better. However, I got on the interstate a while back and when I hit it hard to merge it went into death wobble again. The car was ok at 60-65, but over that I could watch the front tires start to oscillate up and down ever so slightly and the faster I went the more they would bounce.

I pulled off my front shocks and found they were very weak. They were an Ebay purchase when I was trying to make the $ 3K figure and were used, but in good shape appearancewise. So I have now ordered new ones from Speedway that should control the front end better.

But I found the biggie today. I took my front wheels and tires to a tire shop and had the rebalanced. The balance was ok, but one rim is bent. I could watch the tire jump up and down as he spun it and a screwdriver against the spinning rim confirmed it is bent. I bought these '46 Merc wheels over 20 years ago and used two on the front of my '27 and had these two left over. Evidently the first two were ok, but one of these two was not.

So, I have decided to have the two from my '27 checked for straightness and then paint the better of the two to match my T and use it. Hopefully this will solve my handling issues. It was making it so I didn't want to drive the car on the interstates, around town was fine, but speed was a problem. I'm glad to find this was the problem though, it will be a relatively easy fix.

Don

Good catch Don, that definitely had the makings of a possible disaster!

Glad you found the problem Don! Would have been terrible to hear a disasterous story. Hopfully the other rim will do you better.

Death wobble in a 27 sounds like a nightmare, glad to hear it didn't get away from you. I had a jeep put me in a ditch after death wobble popped a tie rod apart.

It's the scariest feeling when it happens. No fun watching the front wheels jumping around out of control. The other thing is that you can never relax again because you keep wondering when it will happen the next time.

Don

Just remember to only drive your T, and to leave the wheel wobbling 27 parked.

What this sounds like to me is a natural frequency phenomena in the front end. There are many contributing factors here including suspension and frame stiffness, shock rates, geometries, and wheel/tire stiffness and damping contributions.

The wheel going round and round excites the death wobble mode in all cars; most just have the factors above either combine to totally dampen the event out (you wouldn't know it happened) or drive the frequency of occurrence well above normal operating speeds.

By changing shocks you have improved the damping and by correcting the wheel you will have greatly reduced the excitation that drives the wobble frequency. However these do not necessarily change the natural frequency or onset of the wobble, just the amplitude. For example with your corrections it is possible that you could be running OK at the death wobble onset speed and then hit a bump and set it off. Now the new shocks should hopefully dampen the vibration out quickly.

I'm not trying to scare you but I would still be a little careful until I got the feel of her for a while.

Kitz

Kitz, that is the word I was searching for.......frequency. You are right, I could see the frequency increasing with speed. I would guess every rotating mass has it, you just need to keep it controlled.

Thanks for the info.

Don

I hope your not hurting my car.....LOL
BradC

When I saw the thread title I thought you'd finally worked up the courage to post this picture of yourself...................

Glad to hear you found several problems that may alieviate this. Today I was out riding the Harley, when I had a momentary daydream(were talking split second) I refocused on the turn ahead and realized I was entering it way to fast, I grabbed the brakes and rapidly downshifted, when I let out the clutch, I got my own version of the dealth rattle, back tire skidding, bike going highside of the turn, I kicked a foot out to counterbalance, did a little jig on the road, made the turn, and came out much more focused. Down shifting , I thought I was in 4th, but was in third, was not a good idea. This bike does this to me about once every two years. The former owner warned me to watch it on the turns as the bike liked to go straight! This is very true!
Hopefully the shocks and wheels will cure your problem, and no beers with lunch will cure mine!

Bob, IT'S PURPLE!!!!

Brad, the way things were going with it, I was about ready to take that $ 300 offer.

Steve, that is one reason I stopped riding motorcyles when I was about 20, I am not coordinated enough to drive one. I owned a Benelli (sp) years ago and I came to the top of a hill to a stop sign and thought I was in low, but it was actually neutral. It started to drift back and I found low and the bike did a wheelie and dumped me and the girl riding with me flat on the pavement. I sold it right after that, but not before she dumped me.

I put a dial indicator on my wheels tonight and spun them. The bent one is out 70/1000ths and the ok one is only out 10/1000ths. No wonder it wobbled.

Don

Don did those death wobbles remind you of your knees knocking when you try to get around without your walker...........LOL
BradC

Don,
I just read this, and was wondering something. I'm always reluctant to give my opinion on some things without knowing all the facts. If this doesn't apply to your car, I'm sorry for waisting your time, but I feel compelled to try and help with a situation like this.
I had a car do this, that's assuming we all had the same death wobble, I put a pan hard bar on it and it never did it again. When you are accelerating you are transferring the weight to the rear of the car, and for some reason this would set it off. The other thing that would set mine off were a double set of rail road tracks.
What was going on in my car was the shackles would allow the front end to move back and forth, once that was stopped the problem went away.
But, our death wobbles may be different.
Ken

Don, Glad you found some potential causes. If you have not done so before I would also check alignment, especially caster, or king pin inclination. 0 or negative caster can definitely cause a wobble (think grocery cart). Positive caster keeps the wheels pointing straight. The caster can also change at different points in suspension travel.

Hope it is smooth as silk with the right wheels in place.

Pat