Builds The Truck of Theseus (1 Viewer)

[littlevulture]

Finished relocating the diff stud holes, dunno what happened but the old holes I welded up got HARD when they cooled. I burned up 2 brand new high quality drills, 2 endmills that were maybe at half their life, and one chinesium tap. Everything fits now though albeit it's a little tight slipping it over the studs.

Unrelated but does anyone know if leaf springs are supposed to be parallel or be slightly angled in on one side? I can't find any OEM dimensions to study online. My front axle had the perch holes on exactly 74cm centers. My old Trail Gear front hanger is at 73.5cm and the truck drove great with that hanger and axle combination. My gut says keep them parallel and that's just within acceptable tolerance.

 

[aztoyman]

Really nice work on a cool project. IDK about the difference in the spring centers but I trust Toyota's tolerance more than TG's.

I wondered if you were playing with the lathe because that's the kind of stuff I did when I first got mine. Gotta learn somehow.

 

[Lucille]

Id say they are supposed to be parallel to each other front/middle/back. Bushings wear out faster if things arent square. Unless you compensate with a mount that is off to take this into account.

 

[littlevulture]

My dad came out over the weekend to hang out in the shop with me for a couple days. Started with some suspension and steering mockup. I don't have any pictures but I really wanted to use a RHD IFS box I have on the inside of the frame rail instead of the typical box mounted to the outside of the frame. I was pretty sure it was gonna fit from some rough measurements I took but unfortunately it ended up trying to coexist with the radiator. I got caught in a research rabbithole regarding leaf spring suspension design, spring hanger placement, and shackle length so we moved onto something else the next day.

 

[littlevulture]

Didn't make much overall progress on the truck over the next 2 days but we did make keyed steering arm blanks for the low crossover steering I want to do. These ended up getting machined to a dimensional accuracy that is almost completely unnecessary but it was fun learning more about the machine to get that kind of accuracy. The one place the accuracy does matter is the fitment between "key" on the knuckle and the keyway on the arm and we got it nearly perfect.

Raw materials and some of my collection of steering parts. I got the highsteer arms years ago for free, I have no idea what brand they are but they donated trunnion pins for the new arms and will be my rough template for locating the holes for the rod ends.

First knuckle on the mill after adding a flat to the knuckle to make the key. I opted to make this symmetrical with the face on the back of the knuckle where the wiper seal goes, the key ended up being 55mm wide.

Before and after comparison.

Knuckle stud holes drilled and a hole was bored for the reclaimed highsteer trunnion pins (not pictured). The knuckle studs are on 30mm by 55mm centers if anyone needs that number.

Keyway added, I made a slip fit trunnion pin blank out of aluminum so I could fit everything up without pressing the steel ones into the arms then tested the fit. Getting the setup and dimensions for fitting this up took the better part of 4 hours but most of that can be attributed to learning. The keyway is 0.250 inches deep, 55mm wide, and about 140mm long (the length of the keyway doesn't matter so long as it clears the rest of the knuckle casting).

Trunnion pin blank installed.

Installed studs into the knuckle and test fit it to the newly keyed arm.

Finished blanks.

 

[littlevulture]

Some measurements, I'm planning on using a spring under setup up front which means I can drop the steering arms down lower...which is the whole reason for this side project. The top of my arms are about 1 inch lower than the top of the highsteer arms.

I'm planning on running the tie rod to the bottom of my new arms instead of the top which should place the tie rod right about inline with the top of the axle housing. This should lower the whole steering assembly by about 2 inches compared to a normal highsteer setup so I can in theory I can be about 2 inches lower than a comparable truck with the same amount up travel. Obviously this will be at the expense of ground clearance under the axle since the springs will be down there.

 

[aztoyman]

NICE work! The steering arms look like my TG arms. I think the TG have a 7/8 pin and the Marlin ones have 1" pins. Assuming my memory is still intact that is.

 

[littlevulture]

These ones had a 3/4" pin that uses the factory 17mm trunnion bearings, they do look very similar to a TG set. I do have another random RHD set I got from somewhere with a 1" pin setup for some early trunnion bearing eliminators...they're very odd parts and look to be machined from solid 3" billet. I think the 3/4" will be fine for what I'm planning on doing for now.

After spending all this time making my steering blanks I really don't wanna mess up the placement of the holes for the rod ends. I started reading about Ackerman angles for the tie rod and using the most simplified model I could find (picture below) I came up with about 12º for a 112" wheelbase and stock SFA width housing. Unfortunately this isn't possible with the location of the steering arms and wheels/tires so I'll likely just put the drag link rod end holes as close to the tire side of the arms as possible. I really don't think this matters too much for a truck like this, if it's close to the factory angle or the common aftermarket angles I think it'll be fine.

 

[littlevulture]

The location of the hole for the drag link rod end seems more critical to me and I'm not sure the aftermarket crossover steering arms get it right. I'm pretty sure the pivot of the ball joint needs to be inline with the knuckle rotation axis for the steering to feel the same in both directions. I looked at pictures of some OEM setups that have a crossover style drag link that goes direct to the knuckle (Ford and Ram trucks, Jeep WJ/JK/JL, FJ80) and they do seem to put the ball joint pivot through the kingpin/trunnion axis.

My reference high steer arms have the drag link hole roughly centered on the trunnion pin. When the height of the highsteer arm, rod end, and 10º angle of the knuckle steering axis are accounted for I think it would locate the straight ahead position of the rod end pivot asymmetrically in the arc that the steering arm moves through while turning. I'm not 100% convinced this is the case or if it matters in the real world but I started on some CAD tonight to help think though the geometry. Hopefully this isn't complete jibberish...there's a non-zero chance this is a solution in search of a problem.

High steer drag link hole centered on trunnion axis.

I'm assuming the rod end pivot is in the center of the casting, so approx 10mm up from the base of the housing, using this and dimensions from the knuckle I made a CAD model.

From the side it's easier to see the axial alignment I'm trying to target. If these axes aren't aligned I'm pretty sure that the same amount of drag link input would result in different amounts of knuckle rotation depending if the steering is going left or right. I'm trying to target the green circle, I'm pretty sure the highsteer arms put the rod end pivot somewhere near the red circle.

This is looking down the trunnion axis that the knuckle rotates on (also the mounting face for the steering arms), which is 10º off from being perpendicular with the ground. The arc shows the sweep of the arm as steering happens, the steering arm is mostly transparent in the picture to show the rod end better. Again, I'm targeting the green circle for the location of my rod end pivot; the red circle is where I think the rod end pivot sits at when everything is straight ahead with the highsteer arm. I'm pretty sure I can see that the motion the of the arm would not be the same when steering left vs right if the rod end doesn't start with the pivot centered on the arc.

 

[aztoyman]

This stuff is way over my head but you got my attention. How does the geometry compare to the stock steering arms? How much of a difference left to right are you talking?

 

[littlevulture]

This stuff is way over my head

Way over my head too...I spent my whole evening modeling up a pair of knuckles in CAD to compare and took a bunch of virtual measurements, turns out I was onto something but it probably doesn't matter in the real world.

I modeled a passenger side knuckle here and assumed the knuckle steers 40 degrees to both the left and right of center. 40 degrees to the passenger side occurs at 118.1mm of drag link deflection from its neutral position, when steering to the driver side 40 degrees happens when the drag link is displaced 122.5mm...so both directions are within 3mm of each other. Placing the pivot point of the rod end for the drag link inline with the trunnion axis does eliminate this and make the steering perfectly symmetrical but I'd argue that difference doesn't actually matter in the real world. I'm doubtful it would even be measurable at the steering wheel.

With all that being said I'll put the rod end for my drag link in the optimal position, I have the measurements now from my CAD model so I might as well put it in the "right" spot.