Caster Mod for pre 73
 

I'm looking at having the lower a-arm shafts drilled to do the Caster Mod on my 66 C10. Here's the write-up that originally got this started but his was the 73 up bushing style.

http://67-72chevytrucks.com/vboard/s...d.php?t=501241

For us guys with the older style a-arms, what are you having them drilled at? I've read anywhere from 3/8" to 1". I just want I nice driver, nothing excessive. Mainly interstate driving in the 70mph range.

I'd like some input on how much you moved them and, if you've had it aligned, how much did you gain. Did you have any spring or shock alignment issues? I'll do the FrizzleFry shock mod so that won't be much of an issue.

Re: Caster Mod for pre 73
 

I added the extra 3/4" - http://67-72chevytrucks.com/vboard/s...=501241&page=6
Drill Hog Super Cobalt bit from eBay seller Drill Hog, on a drill press. - http://67-72chevytrucks.com/vboard/s...=501241&page=6

Re: Caster Mod for pre 73
 

I did 3/4" for the original style a-arms on my dually (which are the same as the earlier trucks).

Re: Caster Mod for pre 73
 

Do the 73+ trucks have more stock caster than those before 73?

Re: Caster Mod for pre 73
 

Not that I'm aware of.

Re: Caster Mod for pre 73
 

On my 67 I did 3/4" on the stock lowers and have CPP uppers. I ended up with 9 degs caster and with .5 camber this thing drives like a new car. LOVE IT

Re: Caster Mod for pre 73
 

I moved it 3/4" on my '66. It makes you really want power steering in parking lots :lol:

Re: Caster Mod for pre 73
 

So I'll be rebuilding my suspension this weekend and I wanted to do this...

Bought bunch of new parts including new lower control arm shafts (Moog K6147). The new shafts have only a single locating hole--not two--that is 1.25" from the shoulder. The only other person (The Rocknrod) I see who had a single hole, says his were originally at 1.75".

I don't have power steering so I'm not trying to get to 6°+ degrees of caster, just ~4°. Basically confused at what I should drill at to hit my target.E

EDIT: Found some good info after more digging: http://67-72chevytrucks.com/vboard/s...&postcount=209

Re: Caster Mod for pre 73
 

That's interesting that your original hole is in a different spot than what has been previously reported. I would compare that new shaft to the one you take out and go from there. If it's in the same spot as your old shaft, just base your new hole location on that. If the new shaft is different than your original, then maybe they drilled it in the wrong spot? With it being at 1.25 (vs 1.75) that would put the arm in the opposite direction of what you want for this caster mod, so you'd have a really poor handling truck!

Re: Caster Mod for pre 73
 

I did more digging and found this: http://67-72chevytrucks.com/vboard/s...&postcount=209

The critical measuring reference point shouldn't be the shoulder, but rather the end of the shaft. This makes sense given how the control arm and shaft are assembled with the end caps screwing on.

Measuring from the end of the shaft to the center of the existing hole I get 3", which is the same as most other posters (give or take a couple sixteenths). So now I'm debating moving the hole 1/2" or 5/8" towards the center in an attempt to get somewhere near 4° of caster. I really just want a bit more than currently, but not enough that I become Popeye in parking lots.

Re: Caster Mod for pre 73
 

Moving the hole & shifting things forward still requires shims during alignment to dial it in. I'd prob still target the max the hole can be moved w/the minimal amount of clearance related issues.

Re: Caster Mod for pre 73
 

I'm still a bit hesitant to go the full 3/4" because I'm running a manual steering box. While I want improved highway tracking, I also don't want to make parking lots too much worse. I'm trying to find a sweet spot.

It seems that most fellas that go the full 3/4" have power steering.

Re: Caster Mod for pre 73
 

That's a good consideration that I did not think about when doing mine. I went the full 3/4" and mine is manual steering as well. It was already a bit of a bear at low speed with a 15" steering wheel. I hope it's not too bad now! I have yet to drive it as I am still in the process of a motor swap.

Re: Caster Mod for pre 73
 

I went the full 3/4", still have manual steering and stock steering wheel. Sure, it can be a bit of work when turning in parking lots or tight spaces, but on the road is well worth the compromise of the parking lots. Cruising at 70 mph with one hand on the wheel and not steering between the lines really makes the driving experience much better. I ended up with 4.8* on one side and 4.6* on the other side. As mentioned above, a good shop will work with you on the shims to get closer to 4* if you would prefer that

Re: Caster Mod for pre 73
 

I just drove my '66 with the 3/4" caster mod from SC to OH and back this weekend, 1100 miles round trip. Even with the worn out stock manual steering box it tracked dead straight and required minimal effort to keep the truck in the middle of my lane, even on the rough and narrow two lane highways through Virginia. Parking isn't fun, but the tradeoff once you're rolling is worth it. I'm looking into a Borgeson power box for it once I find 250 pump brackets.

Re: Caster Mod for pre 73
 

That's great to hear a couple positive experiences with a manual box and the caster mod. I really liked the feel of my manual box when the truck was in stock form, which is why I decided to keep it when going through my LS swap. I'm looking forward to test driving this setup with the caster mod.

Re: Caster Mod for pre 73
 

If your unsure about how much caster you want there's no reason you can't put two additional index holes one at 1/2 inch and one at 3/4 inch. Space them 120 degrees from each other. That along with the upper control arm shims would give you pretty much unlimited adjustment of caster.

Re: Caster Mod for pre 73
 

That's a good idea about additional holes to adjust caster. I think I am going to test the 3/4" forward hole first and see how it feels and how much caster I have.

Re: Caster Mod for pre 73
 

I'm bringing back this thread because I have now test driven my truck and I am not entirely happy with how it steers. Just to refresh, I moved my lower arms forward 3/4" and have a manual steering box. Before the caster mod, the steering was definitely firm at low speed but manageable. Now, with the mod, low speed turning is noticeably firmer. It is quite difficult to make a right hand turn out of my driveway without going into the opposite lane. Return to center may be marginally better, but it didn't really stand out as an improvement to me. At speed, I will say that the truck does track nice and straight with virtually no needed input in the wheel to keep it that way. If I need to steer more than 45 degrees on the wheel, however, the steering starts to get really heavy and almost unresponsive. After the first drive I was already planning out a power steering swap. In the meantime, I am wondering if it's worth it to back out some of my caster either through shims or redrilling a new index hole at 1/2".

One other thing I noticed while driving is that my springs are rubbing the front edge of the cavity where they reside in the crossmember. This is due to the bottom of the spring moving forward 3/4" with the arm. Did anyone else have this problem, and if so what did you do to resolve it?

Re: Caster Mod for pre 73
 

I ended up drilling the new locating hole only 5/8" instead of the full 3/4" because of my fears noted above.

My steering at low speeds is a bit harder than it was before, but it doesn't seem drastically harder than it was. Probably worth mentioning what your tire size is since that'll affect it. I'm running 255/70R15, so decently wide rubber up front. Before and after it certainly requires some strength, especially when trying to turn the steering wheel at a complete stop.

My tracking is greatly improved; worth noting that I also rebuilt the entire front suspension at the same time, so that likely is a big reason. New ball joints, tie rods (inner and outer), bushings on the shafts...

I have no rubbing of the springs. Are you sure you have the springs seated fully on the locating features at both ends? Double check; it's easy to think they are seated correctly when they aren't quite right. Also, do you have full length springs or are you running lowering springs?

Re: Caster Mod for pre 73
 

I'm attempting this mod on a 1965 GMC Suburban 1500.
Last year I swapped power steering from a 73-87. (gearbox, pitman, idler, drag link, inner tie rods) It is extremely twitchy now that it has power. (and probably that I'm not used to a new gerar box compared to the old worn out manual box)

I had the LCA shafts milled 3/4" back from the original location.
While I have it apart, I'm swapping spindles to add disc brakes.
I'm using OEM contral arms, 2" drop coils (have been on the truck since 1987) new CPP drop spindles. I'm not planning on moving the suspension travel. RIde height should end up with the top of a 29" tire sitting exactly at the top of the wheel well opening. The leaves me about 4" travel until it rubs on the inner fender.

I am mocking it up now without the coil springs, and my lower ball joint is binding before I hit the upward travel limit beacause it's still pointing 90 degrees straight up relative to the control arm. It needs to be pointing backwards towards the upper ball joint.

The upper ball joint is aimed generally at the lower ball joint location in the caster plane, so this mod doesnt affect the upper ball joint. It is also binding close to the upward travel limit in the camber plane (it's almost 45 degress from level), but this would be doing this whether or not I moved the LCA forward. I have to solve this separately.

I can fit a digital level between my ball joints & the king pin angle (caster) is showing around 22 degrees at ride height. I have no shims on the upper arm shaft.

Even thought I'm changing spindles, I'm not convinced that this is causing the issue. The ball joints run in a straight line throught the spindle holes.

Anyone else get weird readings like this?

Mark V

:gmc2:

Re: Caster Mod for pre 73
 

Something is way off if you’re getting 22° of caster angle. Do you have the upper a-arms installed on the correct side? The rubber bumper should be on the rearward side of the arm. If they’re switched side to side the ball joints will be a lot farther back which would really add a lot of caster.

Re: Caster Mod for pre 73
 

sounds like UCAs on wrong side. I did same mod on my 67 and with CPP uppers I got 5 degs and truck drives great. Also did 4" coils and 2.5 spindles. Now on air with 2" cups in lowers. Is he sure he moved the LCAs forward?

Re: Caster Mod for pre 73
 

I did 5/8" mod and had 4" drop springs and 2.5" droup spindles. I love the way it drives but I also have a 3 turn loc-loc PS box

Re: Caster Mod for pre 73
 

Hi guys,

"cab4word" asked if I'm sure I moved the contraol arms forward. Yes, I moved them forward. But I double checked the new hole & it's .825" to the rear, NOT .750" as I planned. It is a mistake, but .075" is not enough to make this large caster error.

"theastronaut" - The arms are on the same side they have been on for the last 35 years, BUT, that doesnt mean I put them back on the right side when I repainted them for this project.

That 22 degrees I had yesterday is not accurate. I was just sticking a level on the spindle to get a rough idea. The lower ball joint boss is a lot thicker so it really affects the angle.

I made up a shim for the top ball joint boss so that the digital level sits exactly the same distance from the CENTER of the ball joint shafts. The correct caster angle is 15.5 Degrees (through the center of the ball joint shafts)

Also, the truck was not perfectly leveled yet. The rear was a lot lower than the front. As of today the truck frame is dead level sitting on 6 jackstands & a bunch of shims.

I also read a few other racing forums & checked the caster using the "turn the wheels 20 degrees both directions then do some math" method. These measurements were within .5 degree of the digital level on the ball joints. Close enough to know I'm semi accurate. Close enough to rough this in.

But 15 degrees caster is still about twice what I'm looking for.

I'm going to put the lower shaft back in the original hole & see where the caster was before I started. (why didnt I measure before I started?)