Big Blue's Transformation

[Gary Lewis]

No, you can't drive it w/o an engine.  But, the difference in height with/without engine might be interesting.  My guess is that the F250 suspension won't change much w/o the engine, but that the solid axle with SD springs will.

I'm thinking that might be an indicator of compliance/articulation.  No?

[ArdWrknTrk]

The fact that positive arch springs are more compliant and actually have more than an inch before bottoming is without question.

The solid D60 is nothing like the TTB D44HD.

You are comparing apples to oranges.  

[Gary Lewis]

ArdWrknTrk wrote

The fact that positive arch springs are more compliant and actually have more than an inch before bottoming is without question.

The solid D60 is nothing like the TTB D44HD.

You are comparing apples to oranges.

Ok, I take it you don't have any suggestions on what more to measure.  And, as I can see into this rabbit hole of "spring deflection" I'll cease and desist.

[salans7]

I would keep the thread as informative, and as minimal as you can. By that I mean, only include the differences between BB now, and BB after the swap is completed, and keep the rest of the discussion related to the fitment of the RSK kit. Anything else you may have an itching to measure or talk about can go in BB's transformation thread.

[ArdWrknTrk]

^^^^^ 100% agree.

This should be straight forward about the swap/retrofit.

All the banter, rabbit holes, micro analysis and what ifs should go in Big Blue's thread.

[Gary Lewis]

Yup.  So how 'bout I delete everything starting with my post of Aug 04, 2019; 6:35am?

[ArdWrknTrk]

I think the bit about inviting Erik and your hoping to get started with disassembly could stay.

Anything about motor in, motor out could go in big blues thread.

[Gary Lewis]

Ok, I've moved the discussion about more measurements to Big Blue's Build thread, meaning here.  And I duplicated the bit about inviting Erik in a post in the other thread.

Now, back to the discussion of other measurements.  My thoughts about engine-in vs engine-out measurements was a feeble attempt to address "articulation" or "travel", which I hope will be much better with the D60 straight axle than with the D44HD TTB's.  But, it was feeble 'cause I was just accounting for the travel induced by subtracting the weight of the engine, transmission, t-case, etc.  However, I can do that much better by just raising the truck on the lift.

So I'm undertaking some "before" measurements that include the actual ride-height measurements as well as the droop when on the lift.  Plus, I'll measure the distance between the springs and the bump stops in both positions, which will allow me to do some math to ascertain the max compression before hitting the bump stops.  And it seems to me like "droop" plus "compression" gives "articulation".  Right?

[ArdWrknTrk]

Yes, droop+stops= total articulation.

But the 250 has negative arc springs BECAUSE the steering and springs can't handle articulation.
The TTB pivots on the off side would rip the leaf springs sideways.
And the camber goes crazy as the axle swings

Straight up and down with the solid axle is only limited by the pitman & center link, and the panhard bar (if installed)

[Gary Lewis]

Wouldn't it be droop + stops*factor" where "factor" is the pivot/stops length divided by the pivot/tire lenght?

I'm trying to be precise so I know what to measure.  And I'm planning to measure the ride-height stop/spring distance as well as the drooped spring/stop distance to calculate the "factor" and see if it works with the droop.

Does that make sense?

[ArdWrknTrk]

None of it makes sense to me.

Carry on!  

[Gary Lewis]

Well, let me try to explain what I meant, Jim.  I spent a lot of time measuring and a bit of time drawing. This depicts the right front wheel's geometry.  It shows that it is 19" from the pivot bolt of the TTB to the bump stop, and 40.94" from the pivot to the outside of the lockout hub.

And, you can see that there is .84" of clearance between the bump stop and the spring when the truck is on the ground, and there's 22.38" between the bottom of the wheelwell opening to the center of the lockout.





And here's the situation when the truck is on the lift.  You'll see that the distance between bump stop and the spring is shown as 2.47".  That's what the drawing expects given the geometry.  But in reality the distance is 3.19".  And I can't figure out why.  

I'm beginning to think that it has to do with the way the spring is being twisted which applies force on the TTB that deflects the bushing.  What am I missing?

[Steve83]

Gary Lewis wrote

What am I missing?

I didn't read back to the beginning of this part of the discussion - only your last post.  So some of this may be redundant...

But you're missing what most people miss when they try to understand the TTB geometry.  You're trying to analyze its motion perpendicular to the truck's axis (head-on), parallel to the axle pivot bolts.  But that's not the plane it moves in.  If you look at the side view, you'll see that it must pivot on the radius arm bushing, but it doesn't move in that plane, either.

It moves on a plane perpendicular to the axis from the Left axle pivot bushing to the Right radius arm bushing; or Right APB to Left RAB.  Those lines are NOT along the truck's axis, or perpendicular to it, so viewing the suspension from the side or front will distort its motion.  It's better to view ONE axle beam & its RA from below, draw the axis line from the APB to the RAB (red in this sketch), and then calculate the motion of a point on that "A-arm" by its radius (pink) from that axis.

[ArdWrknTrk]

Where is the radius arm in a 4x4 250?

The leaf spring is what locates the outboard end of the Traction Beam.

Yes, the axle actually pulls back, because the rear of the *inverted* spring is fixed to the frame and the shackle is in front.

The big advantage of the RSK is to make it so a front suspension hit allows the axle to move rearward, absorbing the bump instead of pushing forward into it.

[ArdWrknTrk]

A) I think you mean "the top of the wheel well opening"

B) I suspect you are correct, that the twisting is distorting the pivot bushing.

And when sitting on its wheels the TTB pivot is farther away from the point where the bump stop is on the frame.

Also the tire is distorting (a little bit) with weight on it.
Throwing of your (distance of axle centerline) to fender arch measurement.

[Gary Lewis]

Steve - Jim's right, this is a leaf-sprung F250 with TTB's.  But you are also probably right that the motion isn't truly in the plane I was envisioning.

Jim - You are right as well, it is the top of the fender arch/wheelwell opening.

Anyway, I've come to the conclusion that this is a study in futility.  Apparently the motion of the leaf-sprung TTB is too complex to be analysed with my simple approach.  So all I'm going to do is to record the measurements I've taken in a, hopefully, clear manner such that I can get back to them should I want to do so in the future.

And with that, I'll move on to disassembling Big Blue.  Thanks, gentlemen.  

[Steve83]

ArdWrknTrk wrote

Where is the radius arm in a 4x4 250?

Same place as on a 150 - it's just not built the same way, but it works virtually the same.

Unless you've added a poorly-designed lift, the radius arm (or factory leaf) moves the axle straight up from normal ride height, and then rearward & inward as it goes higher.

[Gary Lewis]

Steve83 wrote

Unless you've added a poorly-designed lift, the radius arm (or factory leaf) moves the axle straight up from normal ride height, and then rearward & inward as it goes higher.

Big Blue has no lift, and I can see the leaf spring acting sort of as a radius arm, albeit with a lot of constraints.  The front of the spring is quite limited in its motion in comparison to a radius arm.  It can move up and down a bit but can't easily rotate to handle the change in angle.

And, speaking of angle, the drawing shows that the "droop" from normal ride height is 10 degrees.  So part of the spring rate is using the leaf as a torsion bar.

[Gary Lewis]

Before I get into today's activities, did I read that you can remove the A/C system w/o breaking any lines open?  How hard is that to do?

Now for today.  It is a good thing my friend Jim came over yesterday asking for help getting the Holly bush out as Big Blue is not perambulating anymore.
And here are a few pics of the work.

First, here's the engine oil cooler installation showing the routing of the lines:




And once the cooler and lines are removed here's what you see.  What problem do y'all spot?  




And, here's the engine bay:




And, here's the summary of what I did today, with the exception of the winch as it had been done previously:

[ArdWrknTrk]

I'm on a phone, but I think I see the upper hose is rubbing on the fins.