Death Wobble Affected By Rake?

[MichiganDuck]

I'm not sure if this should be in Tech or the pub, but here it goes:

 

I had severe death wobble last year, forced to park jeep. Over time, replaced shocks, steering stabilizer, and trackbar, then did alignment... helped a little, but still bad. Finally got new tires this year and it solved the problem completely(worn out, probably unbalanced blizzaks replaced).

 

Last week i installed 2 inch spacers bought off ebay. Ran out of time to do rear chevy shackles, so front sat higher than rear. Well, it brought back what i would call a 'phantom wobble' while driving it (like it wanted to go full DW, but just vibrated), and in a few instances, full blown death wobble. Tonight, i installed my rear chevy shackles, bringing the stock rake back a little, but close to level, and driving it, the 'phantom shake' and odd vibrations were gone, and could not induce DW..

 

Thoughts? I doubt anybody has tested DW via rake, and it doesnt really make sense that it would change anything, but its gone now and the only thing that changed was the rear shackles/rake.

[skidoo_j]

toe and caster would be effected by rake. they can both cause shake upfront.

[MichiganDuck]

Well, now i feel dumb. Haha. Thanks Skidoo!

[MichiganDuck]

Can this be deleted? Haha. Pointless thread.

[gogmorgo]

It's got a little bit of useful info for other people. I would never have guessed myself that as little as 2 inches of rake would alter suspension geometry enough to cause wobble.

[ParadiseMJ]

The Comanche is designed stock with a slight rake...returning it to that geometry would make a difference.

[danbyrambler]

Hmmm. . . . . Think it helped me - - - Am gonna fresh my 89s rear springs shortly & anticipate 2 inch or so higher in back - - - If my Jethro Bodine style math is correct a 113 inch increase in lift would amount to 45* increase in rake/caster on my 113 wheelbase so a 2 inch increase distills to zero point 81degrees of rake/caster - - - This almost one degree of change may put me back in DW trouble but at least now I'll be ready - - - - My LCAs length is good & I added adjustable uppers - - so much for that - - Don't see how lifting the rear will change toe, but checking/changing it is no biggie - - - we'll see.

:thumbsup:

[skidoo_j]

The Toe was effected when he put 2" coil spacers on. then ad a reverse rake that would increase (closer to 0) his caster, a slight shimmy would be expected.

 

 

If you don't think rake could effect the toe, go measure your toe then put 1k of weight in the @$$ and re measure. The front will lift some due to the weight. Secondly if the rear of the truck goes down the lower arm goes forward around the pivot of the wheel. This changes the caster slightly, which in turn will also change your toe.

 

 

An alignment of both caster and toe should be performed or checked after every alteration to front or rear suspension. I learned the hard way to be sure to do the alignment with driving load. So if you plan to have a canopy the alignment needs to be done with the canopy on. and redone if you remove the canopy and plan to drive for any length of time. If for nothing other to ensure best mileage on your tires. You can check toe at home w/ a 2x4 and a tape measure and check caster with a $9 angle gauge.

[Eagle]

toe and caster would be effected by rake. they can both cause shake upfront.

 

^^^ This.

[danbyrambler]

If you don't think rake could effect the toe, go measure your toe then put 1k of weight in the @$$ and re measure. The front will lift some due to the weight. Secondly if the rear of the truck goes down the lower arm goes forward around the pivot of the wheel. This changes the caster slightly, which in turn will also change your toe.

 

 

An alignment of both caster and toe should be performed or checked after every alteration to front or rear suspension. I learned the hard way to be sure to do the alignment with driving load. So if you plan to have a canopy the alignment needs to be done with the canopy on. and redone if you remove the canopy and plan to drive for any length of time. If for nothing other to ensure best mileage on your tires. You can check toe at home w/ a 2x4 and a tape measure and check caster with a $9 angle gauge.

 

 

Only said didn't see how lifting the bed would effect caster - still having trouble with that in real world apps - bed goes up - center gravity goes forward, but it's gotta be stupid/unreal before the front springs compress to a meaningful amount - - - - - - Home alignment methods have been beacouped this site & others - - What worked for me, working alone, was using an old school folding carpenters rule-quality type with slide out tip-way more rigid than a tape-also used TM & 2 straight edges fastened to tires with identical rubber straps - Best for me was with a helper & SEs - no need for straps-no crawling around measuring - - Also, since every system's gotta have an operating range 200lb was put in DS seat/floor pan when toe was ck'd & then 'nother 200lb in PS & recheck & again after little over 100 miles wi just me adding to gvw - Did it - MJs dialed in-no dw-smooth zero to 85+ - Ready for Bonneville

:thumbsup:

[skidoo_j]

Well I'd say that if the truck was at stock height you'd probably never notice any difference. With my set up It's kinda like a house of cards. My caster is at 5.5* with driving weight now. When I had paid to have it aligned I had about 500lbs in the back of the truck with still new MT 4+1 rear springs. Well the next day i removed all 500 lbs. The springs unloaded and i had a slight wobble. Took it back in for measure and the caster had changed out of spec and another alignment was required. So i took it home and adjusted the caster myself with out the weight. and she drives great with or with out weight.