'72 K5 - Greg's @MightAsWellK5 Build

[Greg72]

A few more....

Here's a good photo that illustrates why it's such a PITA to clamp a loose Saginaw box to the side of the frame...

The 3 mounting pads are about 3/4" lower than the large lower cap area. It took quite a while to pull accurate center hole dimensions off this box to make an accurate template, but eventually there was a paper template to lay up to the frame...

Finally, the intermediate plate was rendered with a bunch of pre-made 1/4" tabs and some scrap metal. This created a nice flat mounting surface and made attaching to the frame a LOT easier.

The three mounting holes just barely squeak inside the frame dimensions, but it did allow the box to be mounted lower than last time so radiator clearance should be pretty good.

The only problem with working so late into the evening is that sometimes the "math" gets a little fuzzy..... For some reason this plate was tack-welded about 3" too far back (toward the firewall).

OOOPS!!

Guess that gives me something fun to (re)do tonight!

-G

 

[Greg72]

2013.07.24 -UPDATE! - DUDE, WHERE'S MY ACKERMAN???


ARGGHHHH!!!!!

Last night was supposed to be an easy night.

There was a simple plan to accurately measure the total swing of the steering box, the total swing of the front knuckles and do a little math to confirm all of my steering ratios..... Then reset the steering box location to a more accurate spot.

Things got ugly in a hurry.

After dropping some plumblines and figuring out an exact "straight ahead" position for the the wheels, the tie rod was adjusted to insure zero-toe. The values were drawn on cardboard directly below each knuckle to track the progress....

Then the wheels were cranked hard right.....And things went all to hell. I'd known for a while that the factory Unimog 404 steering stops weren't touching equally on both the left and right sides during hard turns. Since the calculations were all checked (and double checked) when the Ackermann was set up, the assumption was that Mercedes hadn't actually used a true Ackerman steering setup originally.... No biggie, the simple solution was to carefully grind the steering stop on the side that hit first so that eventually both the left and right side stops would make contact at EXACTLY the same moment.

With an Ackerman setup the inside wheel is supposed to turn more sharply than the outside wheel, and should be quite noticeable at full-lock steering. The outside wheel is supposed to have a maximum turning angle of around 30* while the inside wheel should be at around 40*.... At least that's what is SUPPOSED to happen!

After making all of the necessary adjustments to the steering stops and getting FULL steering in both directions, the maximum angle went to ~35*..... ON BOTH SIDES SIMULTANEOUSLY!

Basically, it looks like the truck now has what is called "parallel steering", not Ackerman steering. This sounds like a steering setup that is not going to do very well on the street. Things like U-turns are going to take a LOT of room to accomplish. At this point, my only guess is that the original assumptions used to calculate the Ackermann (tie rod position) on the front axle must have been wrong.... The solution may end up being pushing the mounting points on each steering arm a bit further to the outside (like maybe 1" per side? ). This should produce the desired effect of getting that inside tire to turn more sharply than the outer tire....

I need to check the Unimog 404 manual again, but the spec for maximum turning should be something like 30* steering angle for the outside tire, and 40* steering angle for the inside tire.

EDIT:

From the UniMog 404 Manual directly...





This may require some graph paper (or expert advice) before I decide to start chopping up my fabricated steering arms to try a new tierod mounting scheme.


-G

 

[Greg72]

I think I found it.....

Here is a revised calculation for Ackerman:



The first time these numbers were run, the Ackerman was calculated for both the "upper" kingpin and "lower" kingpin... knowing that they would have different values since the spacing laterally (y-axis) is different. (Upper Kingpins are 45.5" apart, and lowers are 49.5" apart) That seemingly small difference DOES have an effect on the Ackerman value that is achieved. Unfortunately, when the steering arms were actually built....this was forgotten, and the values for the "Upper Kingpin" were used even though the tie rod was being built substantially lower than that (z-axis).

What appears to be true now is that the calculation MUST be run for the "effective" kingpin spacing at whatever height the steering arms are built for. In this case, the steering arms were built just about 1/2 way between the upper and lower kingpins so the value for the kingpins spacing at that location needs to be calculated.

If the upper kingpin height is used, the tierod length ends up being 47.33"
If the lower kingpin height is used, the tierod length ends up being 51.36" (4" different !!)

In this case, it looks like what really needs to happen is that the steering arms need to each be re-drilled (or rebuilt) with the holes pushed 1" further out on each side so that a new tierod length of 49.34" can be used (effectively 2" longer than what was originally built). This will probably make all the difference in the wheel angles and should get some Ackerman into this front suspension after all.....


-G

 

[Z71paramedic]

I don't have a clue what you're talking about, but it sounds like you've got it figured out... I'll just keep throwing compliments your way!

 

[Deuling]

I don't have a clue what you're talking about, but it sounds like you've got it figured out... I'll just keep throwing compliments your way!

X2!

I'm like


I have never even considered such a thing. But now that I think about it. At full lock my tires are pointing at slightly different angles..

 

[Greg72]

I don't have a clue what you're talking about, but it sounds like you've got it figured out... I'll just keep throwing compliments your way!

Cliff Notes:

If the inside tire doesn't turn more sharply than the outside tire under full-steering lock, you will make really lousy U-Turns on the street.

Solution: Increase Ackerman with some Excel spreadsheet calcs.... re-do a bunch of stuff that was previously built (and was really nice) and try again, remembering that BlazerBash 2018 is now less than 1888 days away!


-G

 

[Deuling]

So where the tie rod mounts is what dictates this.

Are the kingpins/ball joints on vehicles then not sharing a vertical axis like I always imagined?

 

[Greg72]

So where the tie rod mounts is what dictates this.

Are the kingpins/ball joints on vehicles then not sharing a vertical axis like I always imagined?

The answer to that question will certainly make your head hurt.

Vertically the upper kingpins (or ball joints) are closer together than the lowers. This establishes what is called SAI (Steering Axis Inclination) which is a whole 'nuther discussion. The tire doesn't only turn more sharply on the inside of the turn, but they also "lay over" vertically as a result of SAI. Crank your wheel hard to one side and take a look at the tires....you'll see what I mean.

Fortunately for most everyone on CK5, the engineers that designed and build this stuff worried about all these details to make sure it all works properly. Unfortunately, with a hybrid Ford and Mercedes front axle combo....I'm in a situation where all of these details need to be worked-through on my own.

-G

 

[Deuling]

That makes sense though. Wouldn't work if everything was all lined up vertically.

Just something I've never noticed or really thought of.


I'm glad it's come up though (even though it sucks for you) . When we get to building our dune truggy it will most likely be fabbed knuckles and components and I never would have considered it.

 

[Greg72]

For a dedicated "off road only" type vehicle it is much less important whether you do Ackerman or Parallel-type steering.... you can read that debate on Pirate4x4 for literally HOURS when the time comes to pick which way you want to go.


-G

 

[Deuling]

For a dedicated "off road only" type vehicle it is much less important whether you do Ackerman or Parallel-type steering.... you can read that debate on Pirate4x4 for literally HOURS when the time comes to pick which way you want to go.


-G

Well yeah true. But if you want to be able to street it on a normal basis. It'd be nice.

 

[Z71paramedic]

Well yeah true. But if you want to be able to street it on a normal basis. It'd be nice.

I knew what you were talking about, I just never thought about it, and I am not what you would call a mathematician

 

[westn11]

Z71Paramedic with the post of the year so far! Hahahaha

"I don't have a clue what you're talking about, but it sounds like you've got it figured out... I'll just keep throwing compliments your way! "

 

[Greg72]

Here in this thread we call those "Prouds"!!!

-G

 

[TheBeast_88K5]

Oh my gawd... aAckerman Angle.... Steering/Supspension Theory, all over again!!!

 

[ktmoutfront]

Most people, even in the auto industry, don't understand front end geometry. I did a SAS for a guy. He call a couple of weeks later wanting to know why the steering was all screwed up. Basic custom cross over with hydro assist.

He'd him drive the truck to me. Everything was good. Then he jumps in and turns the wheels to hard lock. Gets out and starts bitching about how the tires are not posited the same amount. I about fell over laughing. Try explaining Ackerman angle to a know it all idiot.

Evidently he had been out wheeling and somebody noticed the screwed up wheels when he was at hard lock going over something. So I printed some stuff off and told him to read it. Ended up at their club meeting 2 weeks later educating them all. Went out into the parking lot, had them all turn hard lock right, and look at their trucks. Never heard anything again.

 

[Greg72]

4 more hours logged in the shop last night and Ackerman is falling into place....

The first step was removing the tierod and draglink so that the wheels could turn independently. Then the target values of 30* (outside tire) and 40* (inside tire) were drawn on the floor below each wheel...

Unfortunately, to get to those values some material had to ba added to the steering stops (to reduce the angle back to 30*) and the opposite side of the steering stop needed to be carefully clearanced to get up to 40*. Ultimately, that involved removing about 1/8" of material from the steering stop.... The factory had it pretty close, but not EXACT. Now it's exact.

Attic View:



If you look carefully, you can see that both sides are cranked hard-right. The passenger side is turning a lot shaper than the drivers side.

So... Next step is to pull a few measurements for a tierod at those new "full lock" steering positions to confirm that my worksheet is accurate. Getting the numbers wrong once was bad enough.

-G

 

[blazinzuk]

If you want an even more in depth discussion of ackerman angle, then go to any posting board where they are doing solo 1 or time attack type racing.

Those guys get mad I mean really mad about stuff. But some interesting reads for sure.

I think its less important the bigger the sidewall you run as I have seen sidewalls on 40"+ flex more on a turn at street pressure than I ever thought they might

I oddly enough have driven a unimog though at low speeds and man can they turn tight. I mean they were designed to haul produce to town after they plowed the field that said produce was grown in. So turning at low speeds was pretty important.

I say forget it all and just do front digs everywhere

 

[Greg72]

2013.07.28 - UPDATE! - STEERING ARMS IN THE SCRAP PILE...

It's awfully hard to admit defeat and throw away hours of work, but sometimes that is what's necessary to make forward progress. The steering arms that were such a proud accomplishment about a week ago, are already sitting in the scrap heap:



Here's why....

As the Ackerman stuff played itself out over the last few days, it became clear that the tie rod mounting locations on the steering arms were going to need to extend out at least another 1" per side. That meant that the brackets would have to be heavily re-worked to allow the heims to clear the angled side plates that were blocking that area, and a substantial amount of reinforcement would need to be scabbed onto the arms to put the strength back into them. Not to mention, the draglink hole would also need to be relocated so that a single large bolt could pass all the way through both heims on the passenger side knuckle. It was becoming clear that the amount of effort would be large, and the end-result would probably end up looking like a cobbled-together piece of crap.

Adding to the misery yesterday was a second in the "Dude Where's My...." series. This time it was related to my caster. During the fender experimentation phase a few weeks back, the axle was pushed back substantially (a few inches) but the upper link mount / link length was never set correctly.... It was one of those things that I meant to do, but lost track of it in the heat of battle.... and when you look at the same parts day-after-day sometimes you don't even notice the problems after a while no matter how careful you try to be. (Looking back at my photos from the last couple of weeks in this thread it seems obvious now. The pinion vs. driveshaft angles were a total mess)

So, the caster was basically sitting at 0* yesterday and unfortunately all of my link mounts and careful clearancing was built with the axle in that position. Fortunately, it was not a major oversight... the axle was rotated to my preferred caster value of 8* positive (the front driveline as at 9* BTW) and then shortened the upper link so that it still landed in the same spot that I'd already created clearance for. The 3-Link calculator confirmed that the change to that link length has no adverse effects.... unfortunately, it meant that the monting brackets for the upper link had to be re-built (for about the 5th time! ) and thanks to Colby for jinxing me, I was just about to run out of 1/4" flat plate.

Anyway, back to the "new" steering arm design. Ultimately, it looks like it will be a lot more simple on this second revision. Without the need for an inwardly-angled plate, the main part of the arm can be built with a long section of beefy 3/8" flat plate.



With the forward part of the plate leveled to the ground, you can easily see the 8* of caster (and the way the portal backing plate is rotated) in the front axle.

Here's a slightly different 3/4-view of that same plate installed on the passenger side:



By the end of the night, both sides were cut and matched perfectly to each other with all the necessary holes drilled and bolted into position.



From this point, it should be easy to square-up the knuckles to each other and then tack weld a lower plate on each side (horizontal to the ground) which will serve as the landing pad for the tie rod heims... a few simple tests should allow me to set me tierod length and confirm that both wheels are hitting their steering stops simultaneously (inside wheel at 40* and outside wheel at 30*) and that will validate that the tierod is finally correctly positioned and at the proper length.



-G

 

[Deuling]

Man that really stinks Greg. But I'm sure the second set will come together quicker and easier.

But it is a shame to see those other arms in the scrap pile.

They were so pretty