Scary death wobble - caused by bump steer?

[Timmy390]

They look especially steep in those pics because that was before the engine/trans went in. They've calmed down a bit. I'll measure the angle this weekend.

I see you've added an adjustable drag link - would that be a worth while upgrade for us?

It will allow you to center the steering.......

Tim

 

[triracer67]

Double check trac bar bushings, and rebalance front tires. I've fought this issue on broncos and jeeps, this solved the problem.

 

[75MIKE]

I might swap the front tires to the back and try it. I lost a belt on a front tire once that gave the same symptoms.

 

[Rustytruck]

Get under the truck and have your wife bump the steering wheel back and forth slowly dont run the engine or actually try to turn the tire. Just bump to bump. Start at the steering coupler an work to the steering knuckles and both ends of the track bare. Replace anthing loose.

 

[NATEandALLI]

Thanks for the additional suggestions gents. Going to look everything over very closely this weekend. I'm thinking a dropped track bar mount and dropped pitman arm are in order to help level out the track bar and drag link which should help reduce bump steer.

The other thing to go along with this would be caster adjustment. Did some looking around online and it seems the general recommended caster adjustment for D44's in Jeeps, trucks and other things is 4°-6°. Anyone want to weigh in on a good caster value?

 

[bronconut73]

Yikes 2wd eb.

I love all eb's though. Kinda like dogs. I love all dogs, even those little yappin' ankle biters, lol.

I will say this, "That 2wd axle is cleaner than my kitchen counter".
Nice work.

 

[englewoodcowboy]

I am digging what you did here. I like how you did it in the fact it would not be difficult at all to return it to 4wd so pretty cool approach although some have gotten their knickers in a twist. Anyway, I see several issues, first we need to know what your alignment specs are as it sits to really help you dial it in. While your track and drag link angles are in line, they are a bit steep for my likings for a rig that will be running modern highways speeds. You have a couple options, swap to tie rod over and weld on a track bar riser or bolt on a track bar drop bracket and a drop pitman arm. This will help with the bump steer. As for death wobble, you need to dial in your tire pressure, we are finding most love about 28psi but with less weight up front you may have to drop to 26. This is something you need to play with 1 pound at a time, it effects these short wheel bases very quickly. When you welded your axle up, how did you ensure you set you caster equally between the two? You do not want a cross caster of more than 1° that will also lead to wobble characteristics. You will also want to dial in your camber, I like to run about 0.25° + camber on both sides, just enough to make it hug the crown of the road but not enough to make it wear on the shoulders of the tires. If you have questions, feel free to PM me. I deal with this stuff every day now.

 

[NATEandALLI]

Hi EWC - alignment results are here: https://drive.google.com/file/d/1UtqJ-dZCVLB8wFKsK1QKSEjLNIAbsFkC/view

Camber is .6° on both sides so "in spec" as far is the book goes but I personally would like to run less - like the .25° you mentioned. Someone was making adjustable camber shims for D30/D44 but I guess they're not available any more. Camber shims came off the Chevy Blazer that the D44 disc brakes came from but not knowing a base camber value, we didn't put them on this D30. Besides using old OEM shims, how else would I adjust the camber?

We made a jig to hold the axle while it was welded. I'm sure it moved some during welding but cross caster is in spec.

I think our K bar S lift kit uses 4° caster bushings and I'm thinking about going to 7° bushing would should bring caster up in to the 4°-5° range. Seem reasonable?

 

[Timmy390]

I don't know my specs but the 2.5 SL I have came with 4 degree C bushing. It didn't drive well so I put on 7 degree (because that's what most people seemed to be running with 2.5 SL) and it drove much better.

Did this years ago....

Tim

 

[Digger556]

Your caster is low and your toe is way out.

Add 2-3° of caster and set toe to 0.25° total and drive the truck again.

 

[Apogee]

Your caster is low and your toe is way out.

Add 2-3° of caster and set toe to 0.25° total and drive the truck again.

X2...if I'm doing my math correctly, 1 degree of toe per side is equivalent to about 9/32" [.287" per degree) on a true 33" tire, so that means you have something close to 9/16" of toe now? Wow! The .25° total toe Digger556 noted above (.125° per side) would give you a toe-in of about .07", however I think you could easily double that and still be okay.

 

[Rustytruck]

Changing to 7 degree bushings should bring you in spec for a power steering Bronco. Especially since you have no worries about front pinion angle.

 

[NATEandALLI]

Yes, the toe is way off. Couldn't be adjusted because the adjuster was frozen which has since been replaced. We didn't set the toe initially - that's just how the D30 came.

 

[englewoodcowboy]

Your caster is way low. Stock specs are based on a high speed of 55 mph and manual steering. We try to get caster at a min of 4° or more the more you get the better the road manners will be. That is where I would start first. Do your tires rub the radius arms?

 

[NATEandALLI]

Okay, I'm a contributor now. Did a quickie "build" thread that you can check out here: http://classicbroncos.com/forums/showthread.php?p=3159392#post3159392

 

[TOOLMAN]

I would agree with the track bar riser or drop bracket, maybe a drop pitman arm. Also, it looks like your track bar is installed backwards. Most I've seen have the adjustment at the top. Not sure if that matters a bunch.

 

[Justafordguy]

I'm thinking track bar drop, drop pitman, 7 degree bushings, and set the toe and it will be a whole new ride.

 

[NATEandALLI]

Got a chance to work on the Bronco some this past weekend between rain storms. The frozen toe adjuster was replaced and toe was set to 1/8" in. I had someone rock the steering wheel back and forth and went down the line to look for anything loose. The only thing I noticed was the new toe adjuster was allowing quite a bit of flex between the two tie rods because the adjuster clamps hadn't been tightened down yet. I torqued them down and the flex went away. When we test drove it last time and encountered the wobble, the adjuster was frozen but the clamps were loose - I'm guessing this may have contributed to the problem. %)

I measured the angle of the track bar and drag link. Checked axle for base reference - it was 0°. Track bar was 15° and drag link was 14°. Pics attached plus overall pic of the front end with the Bronco sitting at normal ride height.

I went through and torqued and cotter pinned everything. Before that, I centered the axle in the chassis - it's within an 1/8" so close enough for me. While I had the track bar off, I decided to measure the amount of slop in the upper mount bolt hole. I had the bolt in place and used a dial caliper and pushed the bolt full left and then pulled full right and total slop measured out to be 0.020" - that's twenty thousandths of an inch. I think that's just normal hole clearance for the bolt so we're good there.

Drove back over the same bumpy sections of road and didn't encounter any wobble. There is what I would describe as a very minute "shimmy" but honestly, those K bar S springs are so damn stiff, the whole Bronco pretty much just shimmies when you hit a bump.

I'm still going to put 7° caster bushings in to bring the caster up some more. Also going to get an adjustable drag link so we can properly center the steering box.

Oh, last important detail. We checked for bump steering by bouncing the front of the Bronco up and down and watched the steering wheel. Surprisingly enough, there was ZERO movement in the steering wheel. I saw a video from someone else who was having wobble problem showing there bump steer and it was massive so that's what I was expecting to see but there was none so I was surprised and happy to see that.

 

[Timmy390]

The angles in that pic look much better.....

Tim

 

[crab]

I just saw this thread after replying to your build post
Looks like you are getting there. It probably doesn’t equate to much, but I hate seeing the pivot point of the draglink on top. Personally I think they are much happier on the face where they can pivot freely as the suspension travels up and down. I’ve always done this with good success right or wrong.
Also, there is a sweet spot with the DL and TB angles and It appears you are just out of that spot. You really can’t recreate real world driving by bouncing the body up and down since a lot more geometry happens when you hit a bump or pot hole. I’m sure it’s tollerable but I would still drop the pitman and raise/drop the TB. Good luck!