Tow bar issue

rjcruz27 · Feb 9, 2020

So I posted previously about my tow bar. Went to tow it today and my tires were not tracking. When I turn they turn the opposite way and don’t straighten back out. Any thoughts?

72Sport · Feb 9, 2020

I had problems with too much caster. Caster helps to keep the Bronco going straight. When being towed the tow vehicle makes a turn and the Bronco goes straight. No fun towing on a road with a lot of curves. I had a brilliant idea to change the c-bushings to 7 1/2 degree from stock 2. My Bronco was stock before the change. One trip towing was a real education. It is now stock again and all is well.

rjcruz27 · Feb 9, 2020

Ok I’ll look into that

Scoop · Feb 9, 2020

72Sport said:
I had problems with too much caster. Caster helps to keep the Bronco going straight. When being towed the tow vehicle makes a turn and the Bronco goes straight. No fun towing on a road with a lot of curves. I had a brilliant idea to change the c-bushings to 7 1/2 degree from stock 2. My Bronco was stock before the change. One trip towing was a real education. It is now stock again and all is well.

Not sure this is correct. Caster makes it easier to track. I'm guessing not enough caster. It's possible that too much caster could be an issue but it's usually too little causing flat towing issues.

Nothing Special · Feb 9, 2020

Not sure how too much caster would cause the wheels to go to opposite lock. I've heard that they can tend to keep the wheels pointed straight ahead in turns, but the physics don't give any reason for them to turn the wrong way.

Negative caster however will definitely turn the wheels the wrong way.

Regardless, have your caster checked. That's the most likely culprit

(edit: Oops, posting at the same time as Scoop)

Nothing Special · Feb 9, 2020

Back in your original thread you said it had towed fine to drop it off at your mechanic. Did anything change on the Bronco between then and now that might affect this? Like was the front end aligned? Or did the mechanic install or remove the engine or something?

72Sport · Feb 9, 2020

Scoop said:
Not sure this is correct. Caster makes it easier to track. I'm guessing not enough caster. It's possible that too much caster could be an issue but it's usually too little causing flat towing issues.

Caster makes it easier go straight all the time. It makes it more difficult to turn if you can't use the steering wheel to follow the tow vehicle.

garberz · Feb 9, 2020

What are you towing it with? Several types of motorhomes have a huge amount of rear overhang. That certainly doesn’t help when turning.

Mark

72Sport · Feb 9, 2020

garberz said:
What are you towing it with? Several types of motorhomes have a huge amount of rear overhang. That certainly doesn’t help when turning.

Mark

I only had a problem when I put 7 1/2 degree c bushings. I didn't have any problems towing until I changed from stock to 71/2 degree bushings. I did nothing else. I changed bushings back to stock as soon as I got back home. The next trip towing was perfect just like it had been for the last 35 years. I could use help with RV mileage and acceleration.

72Sport · Feb 9, 2020

Nothing Special said:
Not sure how too much caster would cause the wheels to go to opposite lock. THEY DON't. I've heard that they can tend to keep the wheels pointed straight ahead in turns,THAT IS THE PROBLEM. but the physics don't give any reason for them to turn the wrong way. tHEY DON'T

Negative caster however will definitely turn the wheels the wrong way.

Regardless, have your caster checked. That's the most likely culprit

(edit: Oops, posting at the same time as Scoop)

They don't turn the wrong way. They always want to go straight.

Nothing Special · Feb 9, 2020

72Sport said:
They don't turn the wrong way. They always want to go straight.

That wasn't the problem the OP had. He said...

rjcruz27 said:
So I posted previously about my tow bar. Went to tow it today and my tires were not tracking. When I turn they turn the opposite way and don’t straighten back out. Any thoughts?

Many of you may know this, and many may not care, but for those who are interested in how caster works like this...

With caster in either direction (positive or negative) turning the steering will tend to push one front tire down and lift the other up. The one that's being pushed down needs to lift the front end of the vehicle, so the weight of the vehicle tends to want to push the tires back to neutral. That's why caster gives you a self-centering feel and more caster will accentuate that.

When flat-towing, the towed vehicle basically acts like a single axle trailer, with the rear axle of the towed vehicle acting like the trailer axle. The front axle is mostly along for the ride, getting slid from side to side. When you are driving forward and turn to the right, that slides the front axle to the right. But when you are backing up and trying to get the "trailer" to turn to the LEFT you start the turn by turning the trucks wheels to the right, which pushes the front end of the "trailer" to the right. So a forward right turn and a reverse left turn both make the towed vehicle's front axle slide to the right.

If the towed vehicle has positive caster, that means the pivot axis for the steering is tilted back, and as the axis project down it projects forward. That means that the contact point of the tire on the ground is behind the pivot axis. If the front end is slid to the right there's a force to the left against the bottom of the front tires. Since that force is behind the pivot axis it turns the steering to the right.

So whether you are in a forward turn to the right or a reverse turn to the left, either way the towed vehicle's steering turns to the right. If you are going forward this is what you want and it settles with the front tires pointing the right way for them to roll rather than slide. But if you are backing up it never settles out, so it just turns the steering to full right lock as you try to back around a left turn.

Negative caster means that the tire contact point will be in front of the pivot axis. So now sliding the front axle to the right pushes the steering to the left. So now you go to opposite lock when going forward and it settles out nicely when backing up.

No caster means that the contact point is right on the pivot axis. Now there's no compelling force trying to turn the steering in either direction. There's also no self-centering force. So the effects on the steering angle can't really be predicted. But that predicts that the tires won't stay pointed in the correct direction, at least not consistently.

Nothing Special · Feb 9, 2020

And by the way, the OP started 2 other threads with this issue. He wrapped one of them up saying...

rjcruz27 said:
Caster got it lol

rjcruz, it's a lot more straightforward if you only start one thread about any issue and stay in that thread.

blubuckaroo · Feb 9, 2020

Scoop said:
Not sure this is correct. Caster makes it easier to track. I'm guessing not enough caster. It's possible that too much caster could be an issue but it's usually too little causing flat towing issues.

If there is too much caster, the wheels can flip, or over center on a tight turn when being towed.
This adding caster thing has become an epidemic. Believe me, there are more down sides to these 7 degree "C" bushings than you realize.

rjcruz27 · Feb 9, 2020

Well that’s spectacular thank you for explaining that. What’s the best way to handle this situation?

Scoop · Feb 10, 2020

72Sport said:
Caster makes it easier go straight all the time. It makes it more difficult to turn if you can't use the steering wheel to follow the tow vehicle.

You are correct when pushing the Bronco with power to the rear wheels. However caster will make it easier to turn (track) when being pulled by a tow vehicle. Go to a grocery store and pull a shopping cart. Nothing Special's explanation is correct. Again, too much caster can cause issues too. You need to find the sweet spot.

@OP: Take to a an alignment shop and find out what your actual caster is. The bushings only tell you what the correction is at the axle, not what your actual caster is.

Madgyver · Feb 10, 2020

Whenever I flat tow an EB (with a towbar), I would strap the steering wheel down to what secure to prevent it from turning. iI wouldn't know the history of the rig so I'd strap it regardless. safety 1st.

Nothing Special · Feb 10, 2020

Madgyver said:
Whenever I flat tow an EB (with a towbar), I would strap the steering wheel down to what secure to prevent it from turning. iI wouldn't know the history of the rig so I'd strap it regardless. safety 1st.

I have done that before I got my caster worked out, but it's really hard on the front tires. So I used a couple of junk tires and changed them when I got to my destination, then changed back for the tow home.

But with good caster I've never had any problems (driving forward) so I don't tie off the steering any more.

rjcruz27 · Feb 10, 2020

How on earth would you guys strap the steering wheel down?

Nothing Special · Feb 10, 2020

I used motorcycle tie down straps, but ratchet straps or rope or whatever would be fine. I've even heard of people using the seat belts.

One way is just to tie to the rim, around a spoke and pull it straight radially to something solid. That will allow the wheel to move back and forth a little, but not enough to get you in big trouble.

Another is to come off two spokes on opposite sides of the wheel and go tangentially to something solid. This will pretty much keep the wheel pointed in one direction.

The good thing about either method is that there's no way the tires are going to opposite lock. The bad thing is that it's unlikely that they will be rolling straight most of the time, and it guarantees they'll be sliding sideways in turns. So don't expect the tires to last long.

Madgyver · Feb 10, 2020

Nothing Special said:
I used motorcycle tie down straps, but ratchet straps or rope or whatever would be fine. I've even heard of people using the seat belts.

One way is just to tie to the rim, around a spoke and pull it straight radially to something solid. That will allow the wheel to move back and forth a little, but not enough to get you in big trouble.

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