My caster mod (with pictures)

[crakarjax]

Originally Posted by picklito

Crakarjax,
In this photo of your drilled hole, how far is the center of the hole from the end of the shaft? It looks FAR! In light of the recent discussion about all the different hole locations we're finding... did you end up farther than 2"?

Good catch on my math, not sure why I was using the formula for area! But I was just trying to illustrate how it might be calculated and is simplified, idk the actual spindle distance or anything.

If I recall, the center of that hole is at 2.25"

[BMERDOC]

Uhm yeah, just goes to show how bad I am with Geometry. Picklito, are you sure about those numbers? Using my truck as an example again, my LF has 2.7 degrees of positive caster. According to your numbers just moving the index .5" would make my caster 9.05. That couldn't be right. Or am I reading it wrong and total caster would be about 6.35?

[picklito]

No, you're right that you'd have 2.7 + 6.35 degrees of caster. You're also right that nobody is getting that much caster increase. The math is right, the numbers are right, but the model it's based on is poor and doesn't really represent what actually happens in the truck...

We're assuming the lower ball joint is moving around the circumference of 9" circle. It actually moves straight forward. And we'd need to use the center-to-center distance between ball joint pivots. If that's (just guessing) 12" rather than 9", then the circumference is 37.68" rather than 28.26" and moving the control arm forward by .5" produces 4.77 degrees of additional caster rather than 6.35. Then add in the (small but real) cosine error and you'd get slightly less. So,

2.7 + 4.77 = 7.47 degrees of caster in your case before removing the cosine error. That's probably closer?

[picklito]

SCOTI,
You mentioned previously that you didn't have to trim a whole bunch. Do you remember where you put the hole from the end?

[SCOTI]

Originally Posted by picklito

SCOTI,
You mentioned previously that you didn't have to trim a whole bunch. Do you remember where you put the hole from the end?

http://67-72chevytrucks.com/vboard/s...d.php?t=487363

2". See post #273 & 274 in the above thread for dimensions w/pics.....

[picklito]

Originally Posted by SCOTI

http://67-72chevytrucks.com/vboard/s...d.php?t=487363

2". See post #273 & 274 in the above thread for dimensions w/pics.....

Doh! I had just read that the other day. Thanks.

[solidaxel]

Waiting to see if I order them !

[crakarjax]

So, I trimmed my arms with 2.25" to center holes and didn't have to take all that much off. I did not trim my crossmember at all. (see pics)

I have a question that is sort of unrelated to this caster mod though (sorry to be off topic) -- if you look at the pics of my lower arm with the bumpstop on (pic 3) vs removed (4th pic), it looks like there's no way the shock could be mounted at that much droop because the shaft would need to go through the crossmember. Am I right? Obviously this is affected by moving the control arm forward...

I removed the stop because I read that was necessary when bagging to get max drop. I'm planning to bag with plates and I can't see ever dropping that much just due to the thickness of whatever bag I use. How much clearance between the lower arm and the crossmember can I expect when aired out with that kind of setup?

[picklito]

What Johnny said.

I haven't done my front end rebuild yet, still collecting parts. But knowing how they go together I think he makes a very important point. That, and the variance we've seen on the cross shafts that we're pulling out of these trucks. We just have to be careful verifying our starting point and how we put it back together if we want a good caster mod.

[crakarjax]

You're right that it's possible to have the shaft off-center, but it's not that hard to ensure that each bushing is threaded an equal number of revolutions per side to keep it centered.

[Domer]

Sorry for the long delay, been out to sea. Here are my stock measurements, and then my new ones.

[highanglehell]

http://www.lateral-g.net/forums/showthread.php4?t=42467

Reading this we should be trying to get 9+ caster on our trucks

[chevyrestoguy]

Wow, 9+ is a bunch of caster. In my opinion, 7+ (max) is the sweet spot. We don't run huge tires on the front, we are limited to the old technology of our suspensions, and we aren't road racing. High caster numbers are not always a good thing. You start getting issues of increased steering effort at low speeds, and an irregular contact patch in corners when the suspension is under compression or extension.

[solidaxel]

With that much castor I wonder what it is like to back down the alley !!!

[BMERDOC]

Yeah, 9 degrees is a bit excessive. 6-7ish should be enough with upwards of 8 being max for a street truck. There is such a thing as too much of a good thing.

[Theboatandcarman]

Enjoying this thread. Doing alignments at my shop, European cars always have the most caster and have the best highway feel in my opinion! I'll have to do this with my truck to get a target of 6 degrees

[The Rocknrod]

I have my entire chassis apart for powder-coating. Finding this thread now is great. I'm going to work on this mod this morning.
With any luck I'll bugger it up enough to have to buy a whole new front end.
Edit:
I only had one locating hole 1-3/4" from one end not two. So I drilled another (opposite side) at 2-1/2". Removed the front lower A-Arm bracket and am heading to the store to get the allen bolt for the locating pin now. Looks like maybe I will have to trim about 1/4" off the rear side of the A-Arm to make it work though.
I removed the rivet on the front a-arm bracket only as there is no pin on the rear of mine. No doubler plates either. and it has 7/16" u-bolts. Will have to upgrade. The rivet hole is 7/16" so I'm good there.
Must be the older a-arm set-up is different, mine is a 64. Good thing I'm doing this, someone put this unit together and one a-arm shaft didn't have the locating pin in the hole and mushroomed the pin head some. It was about halfway in and out of the hole originally.
Update:
Have to go get Cobalt Drill Bit today. I have a smaller cobalt and it worked (I have a drill press). But not a 11/16".

[crakarjax]

I have a bunch of 5/8" masonry bits that can be used to drill these holes, I bought a lot of ten or something ... if anyone needs them I'll ship them out at cost + shipping ($7 I would guess)

[The Rocknrod]

Originally Posted by crakarjax

I have a bunch of 5/8" masonry bits that can be used to drill these holes, I bought a lot of ten or something ... if anyone needs them I'll ship them out at cost + shipping ($7 I would guess)

I'll buy a couple of those from you if you don't mind. I PM'd you also.

[BMERDOC]

I just remembered a thread that was up a while back. Bumpsteer will happen in a stock situation but be aggravated once the Caster Mod has been performed. This is a great way to help alleviate the situation.

http://67-72chevytrucks.com/vboard/s...d.php?t=620584

[The Rocknrod]

Originally Posted by BMERDOC

I just remembered a thread that was up a while back. Bumpsteer will happen in a stock situation but be aggravated once the Caster Mod has been performed. This is a great way to help alleviate the situation.

http://67-72chevytrucks.com/vboard/s...d.php?t=620584

Good info.

[The Rocknrod]

I bought a drill bit from these guys last Sunday - still not here...
http://www.ebay.com/itm/Drill-Hog-11...item27fd254772
But I was able to drill a pilot hole with a cobalt bit on my drill press using a 650 rpm setting and using dry lube. The slower speed really made a difference in the cut.
Mocking up the lower as-arm it looks like I will be doing the slight trim of my a-arm exactly like crakarjax did in his pics shown on page 5 of this thread.

[BMERDOC]

Just got mine back from the machine shop. I plan on doing some experimenting in my alignment thread soooo... Hopefully mine will be driveable again by Halloween so I can post the results.

[The Rocknrod]

Cool beans.
I drilled mine with the Super Cobalt bit I purchased. Put it together on the cross member and trimmed the a-arms as needed (not much). My current status is "on-hold". Been out of work - Put down, kicked around . . .

[SCOTI]

I originally drilled my lowers for this mod but ultimately switched to Porterbuilt lower arms for additional clearance w/the front bags. I drilled them to move the shaft .750" forward so the PB arms added .250" to that (1" forward lowers & factory uppers). I finally got my turn on my buddys machine & I'm pretty happy w/the results:

Left Right
-0.7 Camber -0.6
6.4° Caster 6.9°
.12° Toe .12°

Rear thrust angle was -0.12°

Not bad for a dually.