Looking for technical reasons a dropped pitman arm is bad

[ColoJeep]

Hi all , looking for technical reasons why a dropped pitman arm is "bad"?
There seems to be differing thoughts on this, ( big surprise right ).
On strait axle chevys a dropped pitman arm is the norm. when you go over a 2" lift.
On my own Jeep it has a Rancho 2.5 " lift kit it has a dropped pitman arm as part of the kit.
I must say in 13 years and 100000 miles it has never had death wobble.
The track bar appears to be a stock type.
Just looking for a technical explanation to defend why or why not.
I am sure some of you can explain this in a solid technical way. Thanks

 

[Jerry Bransford]

A dropped PItman arm does not cause Death Wobble. What it does is screw up the steering geometry which causes Bump Steer... where the steering is forced left/right as the front axle moves up/down over bumps/dips.

That an axle is straight has nothing to do with whether a DPA is required or not, that is strictly up to the steering geometry. The TJ's steering geometry is so good that no DPA is needed for the typical suspension heights we install like up to at least 5" or so. I had a 5.5" suspension lift at one time and not even it needed a dropped Pitman arm.

Yes some steering designs need a DPA once a suspension lift is designed, like the older YJ and CJs. The '97 and newer TJ, however, does not. Installing one will screw up the geometry and cause, again, bump steer. The only way around that is to also install a dropped driver's side track bar mount. The driver's side track bar mount and the Pitman arm must match.... both must either be un-dropped or both must be dropped. Mixing dropped and undropped causes bump steer.

 

[AndyG]

It isn't " bad" , it's the wrong part for the application on any lift under 6", which is all TJ lifts.

They aren't included by good companies...they are included by uneducated manufacturers that sell a one size fits all solution for lifts.

They don't work because they create bump steer by altering the drag link/track bar relationship geometry.

Blaine and Jerry are the top dogs on steering, I'm a pup.

 

[ColoJeep]

Jerry and AndyG Thanks!
Why hasn't bump steer been a issue on my Jeep? God knows I drive on rough dirt roads as a norm.
In fact my wife's 100% stock 2004 tj has a greater tendency to bump steer, ( I always attributed this
to the "glass jaw" Mercedes, , built in India Steering sector). Thanks!
I appreciate the analysis, without the " Drama "

 

[Jerry Bransford]

With a 2.5" lift and a DPA without a corresponding dropped driver's side track bar mounting bracket your TJ has bump steer.

 

[ColoJeep]

Thanks Jerry,
Buy the way, you had a great description of bump steer in your first post.
I built and raced 1/2 1600 buggies many moons ago. steering geometry as always "fun" fighting bump steer with 9.5 " travel when locating a Wright Rack and pinion.
Did you have to drop the left side track bar mount 5.5 inches with 5.5" lift? Thanks!

 

[Jerry Bransford]

The driver's side track bar mount is dropped an amount equal to the additional drop over stock on the Pitman arm. Not that dropping them is a desirable thing to do.

 

[ColoJeep]

Thanks Jerry, It seems like you would have to build a somewhat massive mount to handle the leverage the
track bar forces to the frame at 5.5 " of lift !

Thanks for sharing your insights !

 

[AndyG]

Thanks Jerry,
Buy the way, you had a great description of bump steer in your first post.
I built and raced 1/2 1600 buggies many moons ago. steering geometry as always "fun" fighting bump steer with 9.5 " travel when locating a Wright Rack and pinion.
Did you have to drop the left side track bar mount 5.5 inches with 5.5" lift? Thanks!

There is variation with nearly every chassis and set up...I have a 3.5" lifted 03 with a dropped pitman and dropped mount and C range all terrains..it drives incredible. I also have an 06 with 2.5" of lift and stock geometry..and sadly load range E mud tires ..and it drives no where near as good. The difference is the not the pitman arms...it's the tires and quality of components on the 03. But no tires or anything else can offset what a dropped pitman arm and stock frame side track bar produces.

 

[Chris]

I think this is one of those situations where you don’t know the grass is greener on the other side until you try it.

We have guys who insist they don’t need to re-gear and that it “feels fine” until they actually do re-gear, then they smack themselves for not having done it sooner.

 

[Jerry Bransford]

I think this is one of those situations where you don’t know the grass is greener on the other side until you try it.

We have guys who insist they don’t need to re-gear and that it “feels fine” until they actually do re-gear, then they smack themselves for not having done it sooner.

Well said.

 

[ColoJeep]

Thanks everyone!
It appears that if the relationship between the track bar and the drag link are the paramount , ( as in parallel ).
If that's the case, how is lowering the drag link different than lowering the track mount the same amount as the lift installed?
If the relationship is the critical aspect, help me understand the difference .
Thanks for the drama free answers!!!!!

 

[Jerry Bransford]

You're over thinking ths, don't run a dropped Pitman arm.

 

[ColoJeep]

Ok

 

[jjvw]

As long as both ends of the drag link and the track bar are in the factory locations the steering will work correctly. They aren't quite parallel and the two links aren't the same length, so people need to stop saying they are.

 

[ColoJeep]

Thanks jjvw 1
This make technical sense.
I appreciate the response.

 

[someguysjeep]

If that's the case, how is lowering the drag link different than lowering the track mount the same amount as the lift installed?

seeing our steering gear is right up front and hung at the point of taking a hit when the bumper scrapes. i don't know why anyone would even consider dropping that pitman to DL connection.

your lift provides extra up travel now, dropping the TB at the frame end brings the TB back closer in relationship to the diff cover and could impeded the space you acquired with the lift. and needs to be done right since the leverage will increase.

the game is clearance. don't give anything back, always be going up. until you can bind it, it's not an issue. that's what cycling the axles shows.

 

[ColoJeep]

Thanks someguysjeep! That makes good sense!
I appreciate the clearer explanation, clearance is the game!
Since this is the case, I wonder why all lift kits don't include a TB frame mount drop!
Thanks again for taking the time to walk this through for me!

 

[jjvw]

The dropped stuff also reduces up travel because it gets in the way sooner.

 

[ColoJeep]

OK Thanks jjvw!