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Track bar and DPA Geometry...

3K views 29 replies 11 participants last post by  Triple88a 
#1 ·
Gentlemen, I just installed a Fabtech 4" suspension lift and I have been learning a lot about the subject title. I read about TJ's not needing a DPA with up to 6" of lift. If this is the case, then why manufacturers such as Fabtech include one with their kits? My kit had me drill another hole 3/4 of an inch towards the driver's side and relocate the track bar. Ssome kits come with a relocation bracket...to me, drilling a hole and relocating it looks cheesy. I'm thinking about buying a heavy duty adjustable track bar and mounting it in the original location hole. I have not experinced the so called "bump steer", but I do experience severe steering wheel vibrations at speeds of over 40mph on uneven roads. My jeep is a 2006 SE with 33X12.5 on 15" rims. I'm stationed in Okinawa so I have "limited" off-road tech support. Your help is greatly appreciated.:confused:
 
#2 ·
The general idea is to keep the track bar and drag link parallel. If you relocate or drop the track bar, you generally use a DPA in conjunction to keep the two parallel to minimize bump steer. However if you use an adjustable track bar, generally a DPA is not used. I've got 4" lift, no DPA and a JKS adjustable track bar and the bump steer is fine. Anything above 6" lift often uses a DPA because the angle of the TRE on the drag link becomes too geat.
 
#3 ·
However at full articulation a lift of 4" will bind up at the stock pitman arm because it is outside of its range of movement. For 4" lifts I suggest a stock XJ pitman arm. It is right in between your stocker and the pitman arm they include.

You will read a lot on this board about this idea of not using a dpa with anything under 6". It's bad advice. Give Fabtech, or any other company that has engineered a suspension a call, and they will explain it.
 
#4 ·
I'll side with those saying a DPA is not recommended for standard height lifts without a dropped upper trackbar mount also being installed. Fabtech would NOT be a company I'd call for advice on any Jeep lift, they're barely a second-tier player in the Jeep marketplace. And having worked for the parent company that owned ProComp, admittedly a crappy lift maker for Jeeps, I met a couple of their engineers at their Chula Vista that knew next to nothing about when TJs needed DPAs and when they did not. They just assumed it was similar to Ford, Chevy, Dodge, etc. since they had to be jack-of-all brands. Few really understand the changes made to Jeep steering with the TJ.
 
#5 ·
My kit had me drill another hole 3/4 of an inch towards the driver's side and relocate the track bar. Ssome kits come with a relocation bracket...to me, drilling a hole and relocating it looks cheesy.
Just to echo Jerry's statement on this subject. I really wouldn't trust any lift manufacturer that would just tell you to drill a new hole in your trac-bar bracket and move it over to center the axle. I would bet that probably half of all lifted jeeps that develop death wobble have a stock trac bar that has been relocated and the hole that was drilled is wallowing out or cracking the bracket.
 
#8 ·
Gentlemen, thank you all for the vast and controversial advice. My vibrations were due mostly to unbalanced tires. I have BFG Mud Terrains and the placed that installed them told me they did not need balancing because they were "too big." Anyhow, the tires were so badly balanced that it took 225 grams of weights for the worst one and 85 grams for the best one. I still have the OEM track bar (drilled over 3/4" towards the driver side) and the DPA provided with the lift kit. Not for long though. I have decided to go with a heavy duty adjustable track bar and put it back in its original location. I have also purchased a better steering dampner and a skyjacker heavy duty steering tie rod. Last question, and I think I'll get mixed replies again, should I used the stock DPA when I install the new adjustable track bar in its original location? Or should I use the OEM DPA? Is there anyway to test steering geometry other than on the road? Thanks again for all the suggestions and help.:)
 
#11 ·
Last question, and I think I'll get mixed replies again, should I used the stock DPA when I install the new adjustable track bar in its original location? Or should I use the OEM DPA? Is there anyway to test steering geometry other than on the road? Thanks again for all the suggestions and help.:)
Rather than listening to all of us I would suggest you call one of the numerous companies that employ engineers who design suspensions rather than listening to a bunch of backyard mechanics giving advice based on their limited experience and knowledge on what they believe to be true. Unless you believe they are all in on the dpa conspiracy.

Anyway, call around and make up your own mind, and don't listen to any of us.
 
#9 ·
If you are not installing a drop trac bar bracket on the frame side then you do not need a drop pitman arm. The stock pitman arm will be perfectly fine for you.
 
#15 ·
I really think that everyone can benefit from Jerry's knowledge. IMO, he has more jeep knowledge and experience than anyone else. Also, he is very gracious with sharing his knowledge and never talks down to anyone. He shows respect to everyone and he has all of my respect.

Take a look around the forum at some of Jerry's posts. You will learn.
 
#23 ·
Quote:
Originally Posted by Jerry Bransford
I NEVER made a flat statement that installing a DPA always causes bumpsteer and you know it. WTF is your issue with trying to twist what someone has repeatedly said into something they did NOT say?



Quote:
Originally Posted by Jerry Bransford
Ditto all that 100%. Even more, installing the DPA on your rig set up as it is would just cause bumpsteer.


The second quote answers your first quote.
 
#25 ·
Jerry did not say installing a DPA causes bumpsteer. he stated that installing one " on your rig set up as it is" would. He is correct. If you don't add a TB drop bracket as well, a DPA will cause bumpsteer.

If you take two parallel lines drop one end of one line 1" you must also drop the same end of the other line 1" to keep them parallel. You guys keep talking about geometry but don't understand that?

If the DL and TB are not parallel, the cycling of the suspension causes the axle/steering to shift hence bumpsteer.
 
#27 ·
I think there seems to be a communication problem here. No one is saying that DPA's are crap. I stated that "anything above 6" usually uses a DPA." Some manufacturers do at anything above 4". Most do not at 4" or below. The OP is at 4". Is a DPA necessary in his instance? I don't feel it is. Can he use one? Absolutely. As long as he does a drop TB bracket as well. I think DPA's are great. They are just not necessary in many instances and often do more harm then good if you don't take into consideration the changes that have been made by lowering the drag link and accounting for it by dropping the TB as well.

I don't think you're views on a DPA are necessarily wrong, I was arguing because you keep misinterpreting/misrepresenting what people have been saying.
 
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