My caster mod (with pictures)

[BMERDOC]

Originally Posted by 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 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.

Pretty good results but can I ask... .75" from what? There seems to be some discussion about the stock indexing location. Mine was at 1 7/32" so I just did holes at 2" and 2.25". Then again mine is non-bushed 67-72. I get a feeling that as much trucks hit the alignment rack we'll see varying results as the original index holes are not in the same spot all the time.

[SCOTI]

Originally Posted by BMERDOC

Pretty good results but can I ask... .75" from what? There seems to be some discussion about the stock indexing location. Mine was at 1 7/32" so I just did holes at 2" and 2.25". Then again mine is non-bushed 67-72. I get a feeling that as much trucks hit the alignment rack we'll see varying results as the original index holes are not in the same spot all the time.

I would have to measure the shafts again to give an accurate answer. They were new Moog shafts & I just drilled new holes .750" from where they were (this was before it came to light about the variations found).

That being said, the aligned set-up is the currently available Porterbuilt 1" forward lower a-arms so the lower BJ's are 1" forward of the OE location.

[chevyrestoguy]

Excellent caster numbers, Scoti!!

[BMERDOC]

Originally Posted by SCOTI

That being said, the aligned set-up is the currently available Porterbuilt 1" forward lower a-arms so the lower BJ's are 1" forward of the OE location.

I'm trying to gauge this before I hit the rack . Did you happen to print out your before and after sheet? Given input from guys who have done the mod it would seem that for every 1/4" the index is moved its worth about 1° of Caster. If your alignment was about 2.5 and 3.0 without shims before the alignment that would solidify my thinking. Not taking anything away from Rob because his track record is proven but I think we need to get away from the .75" measurement and start measuring from the end of the shaft. Anyone who has pre-mod (non-shimmed) specs could redrill their shafts to have equal caster once it hits the rack.

[BMERDOC]

It would seem that this has turned into a lot of research but I think the answers will be worth it. Any guy on a budget will be able to modify the stock stuff and make vast improvements on how his/her truck performs.
FWIW, my progress is slow but I work and research (watching everyone here) to figure this out. 1/4" of movement for 1° of caster is fuzzy numbers at this point but lets step that up one notch. If 1/4" is worth 1° on the bottom why not machine the uppers 1/8th" to have the extra .5" movement to equalize caster on both sides? Again, all research and little to no development at this point but I'm thinking. You would only end up shimming to equalize camber at that point. Then again you could machine the uppers down to equalize camber. Certainly, there is a time when all that machine work adds up and it may be worth it to pay the money for tubulars but then you are still at the mercy of the guy manning the alignment rack.

[picklito]

Originally Posted by BMERDOC

If 1/4" is worth 1° on the bottom why not machine the uppers 1/8th" to have the extra .5" movement to equalize caster on both sides?

Not sure I'm following this. 1/8" (where?) equals .5"(where?).

Uppers back is a good idea, too. Before I found these threads I was only thinking of lowers forward cuz I also wanted to move the wheel forward in the well, mainly for cosmetics. Obviously, uppers back would negate a little of this, but I'd take 6 degrees over a perfectly centered wheel!

[BMERDOC]

Originally Posted by picklito

Not sure I'm following this. 1/8" (where?) equals .5"(where?).

Uppers back is a good idea, too. Before I found these threads I was only thinking of lowers forward cuz I also wanted to move the wheel forward in the well, mainly for cosmetics. Obviously, uppers back would negate a little of this, but I'd take 6 degrees over a perfectly centered wheel!

I probably shouldn't include myself in the conversations while I'm half asleep on the couch. Now I need to go back and re-read everything I wrote.

I have been thinking about elongating the upper cross shaft locating holes for finer adjustments, leaving the shims only for camber adjustments (1/8" of motion would equal .5 degrees of movement). I need to go back and look over your math and Scoti's alignment numbers.

[69gmcc10]

Originally Posted by BMERDOC

I have been thinking about elongating the upper cross shaft locating holes for finer adjustments, leaving the shims only for camber adjustments (1/8" of motion would equal .5 degrees of movement). I need to go back and look over your math and Scoti's alignment numbers.

I spoke with an old hot rodder/racer about this the other day about this and he said the uppers see so much force under breaking that it would probably shift. My uncle was a front end mechanic for chevy for 30 years. I told him what I was doing and the upper arm shaft idea and he suggested to fine tune the uppers he would unbolt the shaft from the studs and twist it. He said he used to do it all the time and each turn on the shaft is just under 1/4" forward or backwards off the top of his head.

[BMERDOC]

Originally Posted by 69gmcc10

I spoke with an old hot rodder/racer about this the other day about this and he said the uppers see so much force under breaking that it would probably shift. My uncle was a front end mechanic for chevy for 30 years. I told him what I was doing and the upper arm shaft idea and he suggested to fine tune the uppers he would unbolt the shaft from the studs and twist it. He said he used to do it all the time and each turn on the shaft is just under 1/4" forward or backwards off the top of his head.

Was he referring to twisting the upper shaft in the end caps? It would kinda make sense. While installing them you want the caps to go on equally and tighten them down from there. The only problem with this is that you wouldn't want to have the the shaft improperly engaged in one cap (front in this case). I will agree that it is worth a closer look. Im not so sure the shafts would shift if properly torqued but his idea is free and machining isn't. The front suspension on my truck is disassembled at the moment and I was just about to order new u-bolts to reassemble it so it I do think its a good time to investigate the possibilities. Its been a while since I've even thought about this whole thing.

[BMERDOC]

Thanks Scoti!! You have provided me with a wealth of info. Given your before and after numbers along with the shims installed I have almost too much info to process. Now if this was my only job. From now on thats how I want everyone to report their results! Ha! I know your truck is a dually but its not far from getting us where we need to be. Soon enough we'll be talking about relocating tie rods and sectioning crossmembers and the lower crossshaft thing will be a non-issue because we'll have that part sorted. Between the math and the real world results its almost a done deal. If you can get your stock index numbers that would be great, if not then its no big deal. I have a feeling 67-72 guys will end up at different numbers than the 73-87 guys. Itd be great to get this down to 1/8" but frame and crossmember differences will be the end result. Someone will end up with a graph (probably not me) that charts this whole thing out and everyone will have the recipe to get their truck done right.

[69gmcc10]

I have become quite fond of this thread as of late, probably because I am at this point in my build and I wanted to say thank you all for being a part of this growth and development to improve our vehicles.

I know there is some discrepancy in the OE and aftermarket lower shaft index holes and I Just wanted to share what I removed from my truck last night. As far as I can tell from the amount of play on the ball joints and the shaft bearings coupled with speaking to the brother and mechanic of the long term owner of the truck my lower shafts on my 72 are original. The hole is indexed 1 1/2" back from where the shaft decreases in diameter to accept the arm (photo may be deceiving). I will post numbers on what my moog replacement shafts come indexed to and then have them re-indexed with 2 or 3 longer indexed hole locations for adjustment at a machine shop.

[picklito]

Originally Posted by 69gmcc10

I have become quite fond of this thread as of late, probably because I am at this point in my build and I wanted to say thank you all for being a part of this growth and development to improve our vehicles.

You, too! Thanks! Good pic.

[jnickell41]

The pictures below are of my recently delivered CPP lower shafts. As you can see the indexing holes are already at 2" from where the shaft drops in diameter.

These will be going on an '87 2wd, should I bother getting holes drilled at 2.25"?

[Johnny_Lamebridge]

Originally Posted by jnickell41

As you can see the indexing holes are already at 2" from where the shaft drops in diameter.

Just my opinion... but I don't think you can compare the steel bushing and rubber bushing type shafts with one another. Who's to say that the shoulder you're measuring from is the same on both types of shafts?

I think all of these measurements would be best taken from the centre of the LCA shaft. That way, we could accurately compare any type of LCA shaft. Like this...

[crakarjax]

Originally Posted by Johnny_Lamebridge

Just my opinion... but I don't think you can compare the steel bushing and rubber bushing type shafts with one another. Who's to say that the shoulder you're measuring from is the same on both types of shafts?

I think all of these measurements would be best taken from the centre of the LCA shaft. That way, we could accurately compare any type of LCA shaft. Like this...

Very good point, iff the shoulders are indeed different. Anyone have two types of shafts that they can compare?

[Domer]

What is the distance from hole to hole center? The factory ones are around 8.xx inches. Where as the pins are 9"

[jnickell41]

I'll check when I get home. Does this influence anything, I thought only one end indexed in the the frame member?

[BMERDOC]

Only one does from the factory. What box did those shafts come in?

[jnickell41]

So these will be going on a 1/2 ton '87 R10 so will have the rubber bushings.

The holes are 8.75 inches apart, 4.375 inches from the centerline of the shaft. I have included a picture of the box they came in.

I checked the shafts that came out of these lower control arms and they appear to be the exact same measurements, distance from the ends as well as distance from each other.

Am I missing something here, are the majority of the 1.5 inch measurements I've seen on this site from 72 and older trucks, or 3/4 ton trucks with steel bushings?

Any insight would be greatly appreciated.

[69gmcc10]

Originally Posted by jnickell41

So these will be going on a 1/2 ton '87 R10 so will have the rubber bushings.

The holes are 8.75 inches apart, 4.375 inches from the centerline of the shaft. I have included a picture of the box they came in.

I checked the shafts that came out of these lower control arms and they appear to be the exact same measurements, distance from the ends as well as distance from each other.

Am I missing something here, are the majority of the 1.5 inch measurements I've seen on this site from 72 and older trucks, or 3/4 ton trucks with steel bushings?

Any insight would be greatly appreciated.

That is one of the things we are trying to figure out right now and why everyone is trying to add as much info as possible. Thanks for adding your information to the thread. Hopefully, with guidance from BMERDOC and others of his caliber on this thread, we can make some sense of things.

[The Rocknrod]

I have a 64 with Steel Bushings, here are my measurements before drilling on a stock unit:

[crakarjax]

I got my bag mocked up, but it looks like it'll have stress in bad places. Then again, I've never run bags. Anyone know if the offset pictured will cause more than a marginal decrease in bag life? I also have no idea what the internal bumpstops on these bags look like. I'm a little worried that they aren't making solid contact as pictured.

[SCOTI]

Originally Posted by crakarjax

I got my bag mocked up, but it looks like it'll have stress in bad places. Then again, I've never run bags. Anyone know if the offset pictured will cause more than a marginal decrease in bag life? I also have no idea what the internal bumpstops on these bags look like. I'm a little worried that they aren't making solid contact as pictured.

I made my own upper plates & shifted the mounting holes forward when I did the caster mod for my lowers. I then had to shift them back (drill more holes) when I swapped in the PB lowers.

I would make new uppers or re-drill the holes accordingly to keep the bag as straight as possible @ ride height.

[crakarjax]

Originally Posted by BMERDOC

Have you put air in them (cycled them) to see if they settled out correctly?

No, my crossmember isn't installed yet so I'm just mocking things up. I contoured my lower cups though and they're inthe spot where they are going to land.

Yeah, shifting them forward seems like the best option at this point -- I should have waited on painting the plates! I wish I had just fabbed up some plates for the lower control arms now though, because then I could put the bags wherever I wanted them. I did find a cutaway of the SS bags though and the bumpstop looks like it covers the entirety of the bag top/bottom, being a non-issue.

[Slowguy]

Originally Posted by crakarjax

I got my bag mocked up, but it looks like it'll have stress in bad places. Then again, I've never run bags. Anyone know if the offset pictured will cause more than a marginal decrease in bag life? I also have no idea what the internal bumpstops on these bags look like. I'm a little worried that they aren't making solid contact as pictured.

I didn’t even know about this mod until reading a build thread on “green Gus” since I have everything apart for my nut and bolt build I figured I had better do this now or I may regret it.

Anyway, you were one of the only ones to mention bags. I too am using air and wondered how well you solved the issue of the crooked bag? Did you just relocate the mount holes in the top bag bracket? I actually cut out the lower indent section of my lca and welded in pockets to the entire bag will now sit in the pocket when completely deflated. This also allows me to run with more air in the bags at a lowered ride height. I’m wondering if this is going to affect or alter my attempt at this modification?