Death wobble; magic speed formula 35-40 MPH

[jvazquez53]

Why the death wobble occurs almost always between 35-40 MPH?

 

[ntsqd]

Every part has a resonant frequency and every system of parts has has one too. Just happens that this speed range produces the right frequency to make things shake. If the geometry of one part changed it could move the speed up or down. I think the D60 DW's happen at a slightly higher road speed, say in the 45-55 range somewhere.

 

[alaska60]

Death Wobble................. We have all been there and the question still remains...... why 35 - 40???
honestly,.... I'm glad its not at 65-70!!!

 

[ntsqd]

Death Wobble................. We have all been there and the question still remains...... why 35 - 40???

Short answer: Because.

honestly,.... I'm glad its not at 65-70!!!

Amen!

 

[jvazquez53]

Every part has a resonant frequency and every system of parts has has one too. Just happens that this speed range produces the right frequency to make things shake. If the geometry of one part changed it could move the speed up or down. I think the D60 DW's happen at a slightly higher road speed, say in the 45-55 range somewhere.

Strange, but never happens at 55-60. Always at 35-40.

 

[All Four]

i have it too, as of last week. the DW make me fear going through the 30-35 range up or down.

 

[Overlord]

I have it too. Mine happens between 40-50, but my speedometer is reads slow (3-5 mph slow).

 

[weak-link]

Every part has a resonant frequency and every system of parts has has one too. Just happens that this speed range produces the right frequency to make things shake. If the geometry of one part changed it could move the speed up or down. I think the D60 DW's happen at a slightly higher road speed, say in the 45-55 range somewhere.

Funny, I've had three different one ton trucks, all 4wd, all of them had death shake(no PM). two Fords and one Dodge. a reg cab, ex cab and a crew cab. all 93-98'

They all had death shake from 35-45.

maybe because they all had diesel engines?

and both my 40(1-2*) and my 60(10* of caster) will get death shake @ 35-45 if I have a bad bushing or loose bolt.


weird

 

[ntsqd]

Or I could be remembering wrong. Didn't apply directly to me, so I didn't internalize it.

My best guess is that the speed finally results in enough energy to excite the system. If everything is *right* then nothing happens, but if even one thing is wrong then DW comes to town. I put *'s around "right" because I've read of complete rebuilt front suspensions that did it. Dunno. Part of me thinks that there isn't enough damping in the steering system. Anyone ever heard of, seen, or read of DW's with a ram assist?

 

[jvazquez53]

Strange, but never happens at 55-60. Always at 35-40.

My 60 is engine is gas and I more or less learned to control the death wobble, when I feel it coming, I either slow down or hit the gas to go faster.

 

[weak-link]

Anyone ever heard of, seen, or read of DW's with a ram assist?

yes




And I have seen engineers of new vehicles(4wd, solid axle) have problems with death shake.

 

[ntsqd]

yes

Interesting. I'd have thot that a ram would just about kill off the possibility.

And I have seen engineers of new vehicles(4wd, solid axle) have problems with death shake.

So have I. Which tells me that it's not something well sorted out by the OE's that we in the hobby have missed.

If forced to point a finger I'd want to see what the incidence of DW's was with the larger OD aftermarket tie rods.
I wonder what excessive toe-in does for DW incidents?
I'm sure that smarter guys than me have studied it. Sure would like to know their conclusions.

 

[jvazquez53]

It just happened today (DW). I noticed that a combination of factors started it. I was doing aprox. 35 MPH, and changing lanes. I tried to gas up to get rid of it, but it kept doing it, so I had to basically stop (scary!!). Next week I'm replacing all the spring bushings and I'll see if the problem is solved.