Steering woes: Skinny tires vs. Fat tires?

[JWMcCrary]

"Drop pitman arm
Track bar riser and 3-way adj track bar and track bar drop bracket (welded)"

I still say the above combination could have something to do with it

 

[welndmn]

95% of all people who complain their bronco wonders of hunts down the road is due to a caster issue.
Have a shop measure it.

 

[strokers]

95% of all people who complain their bronco wonders of hunts down the road is due to a caster issue.
Have a shop measure it.

x not sure how many.

 

[Casey835]

I had the same problem, wandering over the road. It was like the steering wheel would free wheel, there was no resistance when steering. I checked and rechecked measurements on front rear suspension components. Adjusted tire pressure, blah, blah, blah. In the end nothing corrected it but a simple cut and turn of the knuckles. It was simple, easy, and didn't cost anything except a set of stock c bushings only because that was where I wanted to take it. Now I have return to center steering, stability on the road, I can drive faster than 45 mph, there's actual resistance in my steering wheel, and most importantly, I can now drive the bronco I dumped all that money into! If I hadn't cleaned it and painted it, it could have been done in one weekend. I even mocked everything up with the stock bushings BC I didn't want any surprises when done.

 

[Gweiner]

Thanks guys. I ordered a set of radius arm drop brackets today from one of the vendors on here and am ring to try to increase castor. I trust the shop (They have worked on tons of broncos) and they just did not feel comfortable cutting the knuckles. Thought that might compromise them and may fail/slip.

Thanks again for all this great advice - without you guys I probably would have given up and sold the SOB!

I'll provide an update after I get the brackets on and check the castor again.

 

[jbass]

The rim clears 77 big drum brakes in the rear and GM disc brake conversion on a 74 D44. It is a close fit in the rear, I may have to roll the inner portion of the fender, the ultimate test will be with the tire on.
I could not find a rim with more back spacing, 4.5" would have been my choice.

(I have a 2.5" suspension with a 1" body lift)

Gah... that has me nervous... I was told that 33x10.50's would work fine under a 2.5 SL and 1" BL.

 

[broncnaz]

Gah... that has me nervous... I was told that 33x10.50's would work fine under a 2.5 SL and 1" BL.

They will be fine I've ran 33x10.50's with only a 2.5in lift and only got slight tire rub on the rear inner wheel well lip. You can easily bend it over for more clearance but with a 1in bodylift you should be fine.

 

[WheelHorse]

Thanks guys. I ordered a set of radius arm drop brackets today from one of the vendors on here and am ring to try to increase castor. I trust the shop (They have worked on tons of broncos) and they just did not feel comfortable cutting the knuckles. Thought that might compromise them and may fail/slip.

Thanks again for all this great advice - without you guys I probably would have given up and sold the SOB!

I'll provide an update after I get the brackets on and check the castor again.

Please provide a before and after caster reading. Currently you're at what degrees and she's all over the road and then to measure the difference with the RADB.

 

[DuctTape]

I did some calcs last night using guesswork on radius arm length. If a radius arm is thirty inches long then every inch of drop theoretically should increase caster by 2 degrees.

Circum of circle =2pir, or roughly 2*3*30 =180. Move an inch along that circle circum and you have moved 1/180 * 360 degrees. If I get the chance I will go measure radius arm length to refine the radius part of the calc. It isn't perfect trig but this method worked well enough when I was estimating degree rotation for perches on my rear axle so I figure it us a simple method that can be used in this application as well.

Point being when you put drop brackets on you could use this to order appropriate c bushings as I think most vendor drop brackets are 4". The interesting thing about the 4" drop brackets with a 3.5" lift is that the center of both circles (axle and radius arm mount) drop about the same, so depending where you started (and ignoring pinion angle) stock c bushings combined with 4" drop should give you 0.5 degree more caster than stock (subject to the 30" radius being right meas).

I think what I am going to do is mock up some temp drop brackets, put them on, then check pinion and caster before welding new drop brackets on.

 

[DirtDonk]

Ours are listed in that 4" drop category (for standard non-adjustable type) and are expected to result in a 4° correction. So your calcs are sounding pretty kosher.

Would like to hear what the current caster reading is too Gweiner. It's always beneficial to know where you are, where you started and where you end up, with these things. And even though proper caster is a top priority to strive for, many of us have very good handling Broncos with sub-normal caster readings. So it's obviously not the only thing at work.
But since you've been dealing with other things already, maybe it is the only thing left.

Good luck. Can't wait to hear the results.

Paul

 

[DirtDonk]

...They spent the last few days looking at it and made some minor adjustments including...centering the ps box, adjusting the ps box (it's a new Delphi unit, they loosened slightly to find the center)...

Most of what they did sounds beneficial, but can you explain this "loosening" in a little more detail? What exactly did they loosen, and why did they need to in order to find center? Were you there, or are you just relating what they said?
Reason I ask is that you don't need to loosen anything to find center. In fact, you don't really want to re-adjust the preload screw (if that's what they meant) on a brand new box unless you're prepared and equipped to reset the preload to factory-new specifications.
So I was wondering about it.

...Track bar riser and 3-way adj track bar and track bar drop bracket (welded)...

Here too, I think someone asked about that before, but I don't remember seeing an answer. I'll go back and re-read, but if you have both a riser and a drop on a '74, your angles are likely way out of whack and this could easily cause the bumpsteer and wandering you describe.
All the more reason to see some full-frontal pics of your linkage.

Tires are new 33x10.5 BFG KM2's on stock 15x5.5 wheels. My mechanic is suggesting tires are too skinny/tall and recommends a wider tire but I am looking to go back to uncut and want to keep the tires under the wheel well and avoid flares (going back to LUBR).

Are you sure he didn't mean wider wheel? A 10.50" wide tire is wider than stock, so I can't see the tire (by itself) being the main issue. But, as was also mentioned here, the combination of tire and wheel can give you some things to fiddle with. I don't think the combo is an insurmountable problem personally, but it needs to be factored in at least.
What air pressures have you experimented with? Have you lowered it into the high-teens yet? Just as an experiment? You're certainly not running it at the listed pressures on the side hopefully. That's probably in the 45 to 55 psi range on that tire, correct?

Like I said, I'll re-read to see if I missed any replies, but if not, these are things you need to address before even adding the drop brackets. If these other areas aren't fully experimented with, simply adding more caster is not the cure. It might help of course, but it's not the whole equation/picture/enchilada.

Paul

 

[DirtDonk]

I forgot to ask about the steering box. Is it a 3-turn or 4-turn box?
Either one is good, but obviously a 3-turn is going to make everything more sensitive and twitchy sometimes.
And with power steering, more caster is typically a good thing, so I'm not wanting to sound like I'm totally against the added drop brackets. Just that the other stuff is still important.

Your '74 was likely similar to most of that vintage, which had less than desirable caster for power steering. That was just about the time you started seeing more caster built in, but no consistently. We don't see consistently more caster from the factory until about '76 or so.

Crossing fingers that it helps noticeably, but I know a bunch of us are on the edges of our seats waiting for pics of the steering linkage.

Thanks. And good luck.

Paul

 

[savage]

Gweiner,I have the James Duffy adjustable drop bracket's and love them for their adjustability. Plus they are great looking bracket's.