changing upper a-arm mount locations. Wanting input please

[Custom 68]

Front suspension: I have noticed most if not all the aftermarket performance cross member swaps have the upper a-arm mounts are level as opposed to the factory mounts having the rear mount lower than the front.
I have replaced my upper a-arms with a set from CPP and with that I have gained quite a bit of caster so that part is good. I also swapped out to coil overs and that all is good. I am going to redo my mounts for the upper shock mount since after the 3000 mile power tour the upper mount may have shifted a little, I will know more after I start tearing into it again. This mount also incorporates my upper a-arm mounting points which I kept at the stock location.
That all said during my revamp I can move these locations. I can move them level or both up and down . Since I have good caster I don't necessarily need to move them forward or backward.
I am studying suspension geometry to learn but was looking for knowledge here if there is an ideal location to be found? I am just trying to work with what I have as money is tight Any changes I can do as I go would be ideal.
Thanks
David

[lolife99]

Any of the "suspension geometry" experts want to chime in?

[Custom 68]

Thanks Keith, I may be better off leaving it alone but I figured if I was going to rebuild part of this and could get some gains from an easy change or modification I figured I would.

I hope my questions or thoughts are understandable.

[Dano69c10]

Maybe pm Rob at NoLimit and Nate at Porterbuilt

[Custom 68]

Yea I had hoped they might chime in here but understand they have also gone to a lot of design work to get their suspensions correct. I was just thinking of what I could do next and maybe even make some improvements. I also didn't understand the differences from the stock mounts to those that are level.
Thanks
David

[Custom 68]

I am going to get started on fixing my mounts, I have not had any chance to draw or layout any different configurations so to play it safe I will probably follow what GM originally did and leave the mounts where they are currently.
If there are any other thoughts then please chime in.

[Bigdav160]

The tilting of the upper control arms is part of the "anti dive geometry". Changes can be made but spring rates, pitch and yaw all have to taken in consideration.

[Custom 68]

very cool info, that gives me something to look at and study. I had not found what that angle did. I just found it curious why the aftermarket performance suspension configurations did not have as much angle. Since I am lowered (like most) this might be something to look deeper into.
Thanks for the great info.

[tubbedII]

I don't understand any of this, but changing this mounting point made me think of the Guldstrand mod done in camaros/novas. Moving the upper a-arm mount (in this clip at least) is said to gain some negative camber and a higher front roll center. The mod looks like it moves the mount down and a hair back...don't know if this can be applied to the truck's front geometery, but I figured it's worth posting for some experts to chime in:
http://www.pozziracing.com/first_gen...sion_geome.htm

[Custom 68]

Hey Tubbed, that is some good reading. I will look it over when I have more time. So the changing of the upper mount is not completely new. So far it changes the antidive adn looks like some camber gain. They are also moving back for more caster. I have that covered with my upper a-arms already.
Fun stuff, I am sure these can be improved but I am not going to just jump into this without understanding the changes.

[robnolimit]

the 'rake' on the upper arm, as to the pivit shaft, does creat the "anti dive". I am surprised to see that a lot of aftermarket IFS crossmembers have very little, or none. Remember that most IFS kits were built for 32-40 fords, copying must.II geometry, and these cars don't need much anti dive. They have good front to rear balance, and a low CG. Corvette stuff is also copied a lot, again, good balance and LOW CG, therefor, low anti dive. High anti-dive angles cancreate there own problems, as they create "caster gain" during suspension compression, and this can cause some bumpsteer.
So, back to the world of trucks. First, don't rely much on any geometryfrom the OEM pre-1988. ALL of these trucks were pure utilitarian. "Tractors with windows". Handling and ride quality were not too high on the spec list. How much anti-dive do you want now? I'd say 6 to 8 degrees total. That would be the total gain in angle between the UCA pivit axis and the LCA pivit axis. Now, since the LCA axis is basically level to the rail, you can set the anti dive in the upper mount.
The Guldstrand mod, or the Shelby mod, was simply to lower the UCA pivit shaft appx 1". This mod increases the amount of camber gain per inch of compression. Remember that these guys had to follow a certain set of rules for their class of racing, and OEM parts had to be used. Lowering the UCA shaft on a C10 can mean a lot of fab work to create clearance for the A-arm. Save you time and headaches, and buy some tall ball joints from Howe Racing, or Speedway. It6 gives you the same result.

[Custom 68]

Rob, thanks for jumping in here for your input, it is appreciated.
First I will measure my anti-dive angle based on your info above to see where it currently is. I was not sure again just looking at pictures but the aftermarket stuff did look like a pretty shallow angle.
I will look and measure to see how much trouble it would be for me to lower my upper mounts. I have fabed custom mounts for some coil over shocks that incorporates a stock mount configuration for the upper a-arm.
I had looked before for some "tall" ball joints and seemed to hit a dead end. After looking again it appears like maybe in the 1973 and newer they may have some? http://www.speedwaymotors.com/Speedw...oint,3522.html
I recently returned from a 2800 plus mile long haul on the hot rod power tour. About half way thru my journey I blew out one of my outer wheel bearings, I limped it to a shop and they were able to "get me going" it was a thrash to cut the friction welded bearing off. I made it the rest of the way and home and have yet to tear into it to resurvey the damage but I am going to assume my spindles are in need of replacement. That said I can go with this newer spindle if a taller ball joint is in deed available.
I will be asking for spindle recommendations also... Currently I have the CPP modular spindles but am using the Wilwood stock d52 replacement calipers so I am not using the larger brake option.
Thanks for everybodys input so far.

[bdiamond]

The balljoint speedway is selling looks to be a Moog K6136. That is a stock 77 Chevy C10 balljoint. Maybe a tall ball joint for a car based suspension but not us. Howe has a 22301 they look to be about $100 a side and are available in .10" longer lengths than the K6136 up to .5"
Posted via Mobile Device

[Custom 68]

Their description was a little confusing I didn't know if it was a "taller" one or not. I may just be able to lower my mounts some to get the same effect. I am still studying. It seems like I have been doing maintenance on my other stuff so no time to play yet. Still got to get this think apart and figure what all needs updated and strengthened.

[Custom 68]

Ok just some updates, I removed my suspension stuff and did some measuring.
Currently these stock suspensions have almost 10 degrees of antidive or slope on upper pivot mount. I removed my spring and left the upper and lower mount and spindle attached and ran this thru some up and down travel to get some measurements.
currently I have about 7 degrees of static Caster. As Rob stated above with this high angle I get alot of additional caster gain when going thru a bump. By lowering the front my caster gain is minimized. So to find that happy medium on antidive and minimizing the caster gain. Since I am building this I will shoot for 6 to 7 degrees angle which still seems like quite a bit but I dont want to over shoot it.
My calculations are at home but I believe I can lower the rear mount about 1/2 inch and the front can go down that 1/2 inch plus a 3 degree change on the piviot angle is an additional 1/4 inch for a total of 3/4 inches.
I don't have the tools to measure caster and camber changes when moving up[ and down and adding a turn. I have a digital angle gage I attached to measure the changes during my up and down movement.
I cant afford the bolt in front cross members so I am having fun building and modifying my own stuff. If anybody sees anything blatantly wrong let me know, I think these changes are minimal.
Thanks
Dave

[robnolimit]

be carefull here, I would never give up any anti-dive. If it came with 10*, keep it. Try lowering the front and rear mount points the same 1/2".

[Custom 68]

Rob it seems you are the master at this so I will step away from the torch and drill... lol
I was basing on what you said earlier thinking I could get away with less antidive. you mentioned maybe between 6 to 8 degrees.
I have also noticed most of these aftermarket front cross members that are set up for handling have a much less angle. I was trying to get less caster gain by bringing the front down a little more than the rear point. It seemed that was the general direction to go. I will go out and do some more measuring to see what i might find.
Again I dont want to do anything to make my truck unsafe I don't want make it handle worse my only goals are to learn more about the suspension plus make some modifications which I also enjoy and save a couple bucks. Anyway if you have any other inputs or thoughts please let me know. I dont want to reinvent the wheel so to speak
Holler if I can get anything else to make sense of this
Thanks
Dave

[INSIDIOUS '86]

I have some qa1 ball joints on my truck. You can by longer studs to put in to change your roll centers and such. I was thinking of making the ball joints "taller" on my upper arms to increase camber gain and change the roll center some. May be worth looking into
Posted via Mobile Device

[GEARBOXGARAGE]

When Hotchkis created their upper A-Arms, they incorporated offset shafts (approximately 1/2") for better camber gain, much like what you are attempting by lowering your mounting point. Check out this photo of an install in progress, you can see how the ends of the shaft are offset from the centerline of the mounting point.

[Custom 68]

Yes I found that a couple days off when I was looking around and thought it was pretty cool. They have a better shot when looking at their install instructions it shows this off set goes for correct placement. I appreciate you posting this. I have mine off and ready for the modifications. I am also going to brace up the front side rails to help the flex.
I will keep you posted. If you find any more cool info post up.
thanks a ton
Dave

[Jon @ Hotchkis]

Hey Dave! Its good to see you tinkering with the geometry on your truck. Some fairly simple changes can really wake these trucks up!

I agree with Rob, you won't want to lose any of the anti-dive built into the suspension. Don't be afraid to add in some extra caster too (static around 9*), as this will help fight the KPI (king pin inclination) on the spindle; this will help keep the inside front tire flatter on the ground during cornering; you can also run less static camber this way so your grip under braking will be improved.

If you have any questions feel free to ask!

[theastronaut]

Great info here! I've been wondering about upper control arm mount relocation and if there were any benefits... Now I know!

[Custom 68]

awesome guys We have the top 2 suspension builders on here sharing great information. Thanks.
So you both say not to mess with the antidive so I better leave it alone, I wanted to change it but now I wont.
I was planning on lowering the upper mounts 1/2 inch does that sound about right? I dont want to over do it but thought that sounded about right.
again thanks for the great info.
Dave

[robnolimit]

Yep. dropping the pivit shaft 1/2" will help. combine that with a tall ball joint later. While some performance cars will have less anti-dive, they also have a MUCH lower CG, and are WAY closer to 50/50 fr/rr balance. Keep in mind we're on the truck forum, not the 'vette forum You'll need all the anti-dive you've got. the caster gain won't hurt.

[Custom 68]

ok so first off I know I need pictures so they will come soon. I have been reworking my mounts and have them re drilled and dropped 1/2 inch (both pivots) I have a measured antidive of 9.5 degrees. My upper a-arms have additional caster built into them but I noticed I had a few of the spacers on the front mount to get as much caster as I had (around 7 degrees) so I removed the lower and drilled the pin location 1/2 inch back. I will measure and see what that nets me. I didn't want to over shoot this so I only moved it 1/2 inch. I am stiffening up this upper mount and my lower mount on the lower a-arm.
I am having fun and hope it will make this all the better.
Thanks to all who have made this an interesting thread.