Steering Linkage / Bumpsteer

[Jeff76]

76 Bronco recently added 2.5 inch lift (new JBG springs/shocks all around) and new 'T' linkage / adj track bar from TBP. The new linkage required a change to a '75 pitman arm, which is a solid used stock OEM model. New stock rubber bushings. Toe In set in spec at 5/32" In. After explaining to the alignment shop that, while they cannot change the caster, I needed the reading, they did not take the reading, so I will have to take it back to get that another day.

I have purchased parts for new ball joints and hub bearings, but have not pulled / replaced them yet.

The driving result is a really tight fun to drive truck, up to around 45-50 mph, where it gets a little tricky. It was very tricky until I adjusted the tire pressure down from the POs 35psi to a more reasonable 28 PSI all around. Now it tracks pretty straight, slowly 'returns to center', about a 1" 'float' in the stock steering wheel at speed, but I always remember that even when driving new EBs back in the '70s with stock height suspensions and linkages. It exhibits some symptoms of bumpsteer at slow speed, but gets more dramatic at speed, to the point I'm not satisfied that my wife or 15year old could take it out on the road. The truck does have the mega 1" spacers on the front hubs (the kind with their own wheel studs)because of the Ford Truck wheel back spacing.

My plan is to:
1) rework the hubs / ball joints (not optimistic this will have an effect - very little movement in them now, but they are still unknown from the 2 previous owners of the truck, and may be the 36 year old original parts)
2) Try to find a way to make the adjustable track bar and the drag link more parallel.

I originally stuck with an OEM style pitman arm, because as you can see from the pictures, the pittman and the top track bar mount are very close to the same height. But that still leaves the linkages a bit skew. I am thinking that a slight drop of the pittman on the order of 2" would make the track and drag links close to parallel, but most of the drop pitmans I can find are 4" drop, and I think one from BC Broncos is either 3" or 3.5". I am concerned that too much drop in the pitmann will just cause bump steer in the opposite direction.

Looking for thoughts, ideas, opinions, and they are greatly appreciated!

Jeff

 

[TBS-POPS]

Drill a new set of holes in the frame bracket for the trace bar and raise it up to get the trac-bar and drag link more on the same plane. from the looks in the pic, you have plenty of room to move it up without worrying about binding it on the frame.

Get your castor #'s and find out where your at. curing bump steer is one thing. curing the flighty feeling is another.

 

[Jeff76]

Drill a new set of holes in the frame bracket for the trace bar and raise it up to get the trac-bar and drag link more on the same plane. from the looks in the pic, you have plenty of room to move it up without worrying about binding it on the frame.

Get your castor #'s and find out where your at. curing bump steer is one thing. curing the flighty feeling is another.

Clever suggestion. I just took a look, and there is definately room to do that. I guess I would have to take a look at all the clearances at full compression, but initially that appears OK. I would also have to check to see if the adjustable track bar has enough extension.

The thing you mentioned about the bump steer vs the flighty feeling is on point. My intuition tells me that ideally I would have both the drag link and track bar parallel, but also as horizontal as possible to improve the road manners.

Drilling the hole higher on the track bar fram mount would make the track bar more vertical, though also more parallel to the drag link.

I wonder how a more vertical track bar would affect the handling, if at all? Is it more important to make these guys parallel than to make them more horizontal?

I also agree on getting those caster numbers, and need to do that as soon as possible. Thanks!

 

[asinor]

The more horizontal they are, the less side to side movement there will be throughout the suspension travel. As the track bar moves through its range of motion, it will influence the side to side positioning of the entire front axle. The drag link will cause the wheels to turn as it moves through its range of motion, which is the bump steer you are getting.

For the parallel question, I believe it has to do with the track bar moving the front a different amount than the drag link can compensate for or vice-versa, which exaggerates the bump steer.

 

[Lmfp]

Ah your drag link has the same bend as mine... Did it come like that?

 

[Jeff76]

Ah your drag link has the same bend as mine... Did it come like that?

Its the 'T' conversion kit for the '76-77 from Tom's Bronco Parts. Brand new. Eliminates the inverted 'Y' linkage that was stock on these models as they were not very adjustable.

Basically a standard 'T' with adjustability that fits the 76/77 knuckles. Had to change the Pitman for a pre-76 arm to fit the drag link.

 

[.94 OR]

Is a dropped pitman arm out of the question? That might bring the drag link and track bar into alignment and keep both bars more parallel with terra firma.

 

[Jeff76]

Is a dropped pitman arm out of the question? That might bring the drag link and track bar into alignment and keep both bars more parallel with terra firma.

That's what I'm thinking as well. Probably only need a 2" drop though, and all the ones I've found are 4" drop.

 

[asinor]

You might check this:
http://www.explorerforum.com/forums/showthread.php?t=251387

All the ones I have seen sure look a lot like the middle one rather than the right one.

 

[Jeff76]

You might check this:
http://www.explorerforum.com/forums/showthread.php?t=251387

All the ones I have seen sure look a lot like the middle one rather than the right one.

Thanks for the heads up. I will call some of the vendors of the 4" drop pitmans for EBs and see what the actual drop measurements are!

 

[Jeff76]

Caster Reading

OK, finnaly got it to the shop to get the caster readings. Looks like negative caster. And looking at my front drive pinion, the yoke looks to be pointing slightly up.

So, caster is currently -1.7* left, -1.6* right. This is a '76 with PS and the quick turn steering box.

What do you guys think? I am going to table the drop pitman idea for now, and change bushings, ball joints, and inspect / rebuild the hubs first. Then see how it drives before changing pitman.

Does that sound like a correct plan?

Should I plan on 6.25* bushings? If my math is correct, that would leave me with +4.55* left and +4.65* right caster.

Would that be too much caster considering the PS and quick turn box on this vehicle?

 

[Greg_B]

Mine drove worse with the drop pitman arm... I took it off after the first drive... it was scary.

If it didnt have that bend in the drag link it looks like it would be very close.

What "C" bushings do you have? You may have posted that but I didnt see it...

I run about 22psi in my 35s... Much more than that and it wanders around...

Drive great like it is though. I did flip my linkage to the top of the knuckles so that eliminated the need for the drop pitman arm.

Greg

 

[Jeff76]

Mine drove worse with the drop pitman arm... I took it off after the first drive... it was scary.

If it didnt have that bend in the drag link it looks like it would be very close.

What "C" bushings do you have? You may have posted that but I didnt see it...

I run about 22psi in my 35s... Much more than that and it wanders around...

Drive great like it is though. I did flip my linkage to the top of the knuckles so that eliminated the need for the drop pitman arm.

Greg

The current C bushings were installed by the previous owner, so I don't know for sure, but they are Rubber, not poly. I'm guessing they are 0* (particularly because of the caster readings and orientation of the yoke with the 2.5" lift springs), but I guess they could be 2*.

Tires are 31", and they have 28psi. Truck darted severely at 35psi. I think it would wallow at less than the 28. Really doesn't handle too bad now, but I'm trying to make it a pleasure to drive (because I plan to drive the wheels off it) and that's going to take a bit more effort I think. Right now I'm thinking if I can get this caster back to positive, the bump steer, while the condition will still exist, may become a non issue.

The question is what bushing to order? 4*, or 6.25* ?

 

[m_m70]

I have fought this for years and over time finally got it.
In 2001 I put in the 2 1/2" lift and had wandering issues.
Went with the drop pitman and drop trac bar. That helped a little.
Went with an adjustable trac bar to center the axle and that helped some more.
Installed new quick ratio steering box (3.1 turn to turn) and that took some getting used to But really didn't change much
Then added adjustable drag link to get the steering box centered and that helped
some
At the timeI did the lift the vendors suggested 2 degree bushings so we went with that.
After getting tired of that skittish feel I changed to 4 degree and that helped as
well but did not completely cure it. Just yesterday I pulled everything back out
and installed 7 degree bushings.
Well I just got back from a 40 mile trip on winding roads and freeway with speeds up to 75 and the truck handles great. Honestly I felt like I was driving someone elses rig. All Broncos are different and have different needs. It only took me 11 years to get mine where I am totally satisfied with it;D.
I would go with the 7 degree bushings (I am asuming you have power steering) and see how it goes. They're relitively cheap and once you have done it a few times not that difficult to swap out.

 

[Jeff76]

I have fought this for years and over time finally got it.
In 2001 I put in the 2 1/2" lift and had wandering issues.
Went with the drop pitman and drop trac bar. That helped a little.
Went with an adjustable trac bar to center the axle and that helped some more.
Installed new quick ratio steering box (3.1 turn to turn) and that took some getting used to But really didn't change much
Then added adjustable drag link to get the steering box centered and that helped
some
At the timeI did the lift the vendors suggested 2 degree bushings so we went with that.
After getting tired of that skittish feel I changed to 4 degree and that helped as
well but did not completely cure it. Just yesterday I pulled everything back out
and installed 7 degree bushings.
Well I just got back from a 40 mile trip on winding roads and freeway with speeds up to 75 and the truck handles great. Honestly I felt like I was driving someone elses rig. All Broncos are different and have different needs. It only took me 11 years to get mine where I am totally satisfied with it;D.
I would go with the 7 degree bushings (I am asuming you have power steering) and see how it goes. They're relitively cheap and once you have done it a few times not that difficult to swap out.

11 years! Are you trying to cheer me up or piss me off !?! ; )

Seriously, I think I am pretty close. Your vote, 7* then.

What does everyone else vote? I would like several inputs, and I will take the concensus. I already pulled that axle once, and really don't want to do it two more times to get it right...

 

[m_m70]

No no no, not trying to piss anyone off. My truck was not a daily driver and with every different thing I changed made it better over the years. I think we all have voice in the back of our head that says "I can make it better" and mine speaks as time and money become available . Good luck and keep us posted!

 

[surfer-b]

Put the 7* in, you want get too much caster, also it prob will have less caster than what the math calculations would show, at least everyone that I have done turns out that way. Try that but you will prob have to get the drag link and trac bar more parallel and horizontal. DO a TRO and a riser and the problem will be fixed, I would stay away from the drop pit arm if all possible some have good luck with them, I dont like them.

 

[Jeff76]

Guys,

Not trying to resurrect a dead thread, but I wanted to update my experience.

Yesterday, I removed the old (new condition though) rubber 'C' bushings that the PO had installed. They were 2* bushings, but the fronts were installed upside down, and the rears were installed correctly. With the old bushings, my measured caster was (-1.7 left/-1.6 right). I installed 7* bushings from Energy Suspension. My guess is that change gives me something closer to +5* caster on both sides. I'll have it checked and verified later.

Long story short, I think this was the missing element to my handling improvements. The linkage Geometry is close, the tire pressure (28psi) made a huge difference, and the new shocks/springs helped, but the caster was obviously holding it back from reaching its optimium drivability potential. This Bronco now handles a go cart with its top off, PS, small lift and 31" tires. Just got to get that cage installed before I get too crazy on the test drives.

Initial impression is that the problem with the bump steer seems to have gone away. Most likely its still exists (due to the slight skew issue with the track bar and drag link), but the positive caster masks it almost completely. Since I just made the change, I've only taken a couple of short test drives, and have not had it on the freeway yet. But I have had it up to about 50mph, and hit my 'test track' which has some bumps and 'G outs' that would initially cause the erratic behavior, and it sticks in a solid straight line. I'll drive it some more and pass on any additional feedback.

Thanks for all the comments and help. You guys are great!

 

[Justafordguy]

With a 2.5" lift you need the 7 degree C bushings if you have power steering. This will make a huge difference in the stability at speed and the return to center. I run 8 degrees + with my 2.5" lift and it drives great up to 75 with one finger on the wheel.

 

[Rustytruck]

When you changed the C-bushings it not only effected the castor but since the steering linkage is in front of the pivot point of the c bushings it also rotated your front steering linkage up making it closer to your track bar angle helping with your bump steer issue. Have fun and relax now.