Moving UCA mount rearward with stock UCA & LCA & G-mod

[TheBandit]

I am doing the Gulstrand mod on my Nova using the cut & reweld method of lowering the stock formed tower. I bought the templates directly from Guldstrand and will be buliding a jig for this. Because I'm using stock upper & lower control arms, I'm also considering moving the frame tower rearward to increase caster (correct me if I'm wrong, but the G-Mod template seems to move the mounts only vertically down). Is this a reasonable approach or am I overlooking something?

I am not sure how far to go back yet, but I was thinking to target +2deg delta from stock caster resulting from the move. I will check the BJ seperation at the spindle to determine the needed distance.

Thanks in advance for any advice / opinions / links.

[67zo6Camaro]

Yes, you are on the right tract. Typically by movement of the upper control arm back, at the frame pivot piont and/or at the ball joint point will give you additional caster with minimal conflicts with other piviot points. If, you are not using a suspension geometry program such as Suspension Pro, then you will need to error on the side of causion and do a tack in place mock up first. Then move the suspension in travel from ride height to verify your critical numbers. Most likely you will want more caster, in my opinion, closer to the 5 degree mark without shims.

Basically if you build your caster into the frame piviot point and/or upper A arm ball joint, you will reduce the chances of effecting your camber prior to shimming the upper arm. Normally when shimming the upper arm to get more caster you typically push the upper arm slightly inward causing more camber unless you shimm it back out. This can make for a messy attachment point (longer bolts and more shims).

In my opinion, if you are going to do modifications, then set your base suspension closer to your desired suspension settings first (ie.. negative 1.5 degree on camber and 5 degree on caster).

I just did a similar modification on a 72' Nova, See "The FAB53 72' Nova" thread.

Good luck, and feel free PM me.

Brett

[TheBandit]

Brett, thanks for the reply.


Most likely you will want more caster, in my opinion, closer to the 5 degree mark without shims.

I was thinking to target a 2* degree caster change from stock. From what I've read, you can get about 3* caster out of the stock location, so this would get me to 5*, although I'm not sure if the 3* is assuming maximum shimming on the stock location. I was going to use simple trig and assume small angles on the balljoint seperation at the spindle to determine how far to move the UCA mount rearward (if the spindle BJ seperation was 10", it would be 10*2*2pi/360=.349in)

Looking at David Pozzi's site, he says the Speed Tech arms increased caster by 3.5* from stock, so perhaps that's a better target.


In my opinion, if you are going to do modifications, then set your base suspension closer to your desired suspension settings first (ie.. negative 1.5 degree on camber and 5 degree on caster).

I have also thought about the idea of moving the towers toward the center of the car (slightly) so fewer shims are required to increase static camber, but I don't have a good idea of how much I would want to move them in. It would depend on how many shims were needed in the stock location and whether or not that is a problem.


I just did a similar modification on a 72' Nova, See "The FAB53 72' Nova" thread.

Thanks, I have seen your thread and was looking forward to hearing about your results at RTTC.

[TheBandit]

I did my best to measure the BJ seperation at the spindle and it looks to be around 10" from the pivot points (hard to tell exactly where the center of the BJ rotation is). If this is the case, for 3.5 degrees of additional caster, I'd need to move the UCA mounts rearward 0.610in. This is pretty close to what Pozzi estimated for his Speedtech arms (he says on his site the upper BJ moves back about 9/16" or .5625 from stock with those arms and he got 3.5* additional caster).

Some of my concerns if move the tower rearward:
- header clearance: no idea if this will be a problem since I'm swapping in an LSx and headers are undecided
- tire-to-firewall/fenderwell clearance: probably not an issue if it isn't for aftermarket arms
- nearly irreversible change: I don't want to be cutting and welding after the car is back together, just something to consider
- can't go to tubular arms in the future: I don't see any advantage to doing so anyway if I can get the same geometry out of stock arms
- can't go to tall spindles in the future: the theme is budget anyway, so I don't see this as much of a problem and I'd have this problem with the G-mod by itself anyway
- inner fender clearance with arm: I can notch the opening if this is a problem, no big deal
- bumpsteer: can't really model this w/o software, but I don't see it being any different than a car with aftermarket arms.

Overall I think this makes sense. With the arms back, I'll need less shiming to get the caster I want which should give more room for camber adjustment via shims. Hopefully no movement inboard is necessary to get 0-2* negative static camber (I think this is the range I'll be using for street & track).

Any other comments/input would be greatly appreciated!

[JRouche]

I did my best to measure the BJ seperation at the spindle and it looks to be around 10" from the pivot points (hard to tell exactly where the center of the BJ rotation is). If this is the case, for 3.5 degrees of additional caster, I'd need to move the UCA mounts rearward 0.610in. This is pretty close to what Pozzi estimated for his Speedtech arms (he says on his site the upper BJ moves back about 9/16" or .5625 from stock with those arms and he got 3.5* additional caster).

Some of my concerns if move the tower rearward:
- header clearance: no idea if this will be a problem since I'm swapping in an LSx and headers are undecided
- tire-to-firewall/fenderwell clearance: probably not an issue if it isn't for aftermarket arms
- nearly irreversible change: I don't want to be cutting and welding after the car is back together, just something to consider
- can't go to tubular arms in the future: I don't see any advantage to doing so anyway if I can get the same geometry out of stock arms
- can't go to tall spindles in the future: the theme is budget anyway, so I don't see this as much of a problem and I'd have this problem with the G-mod by itself anyway
- inner fender clearance with arm: I can notch the opening if this is a problem, no big deal
- bumpsteer: can't really model this w/o software, but I don't see it being any different than a car with aftermarket arms.

Overall I think this makes sense. With the arms back, I'll need less shiming to get the caster I want which should give more room for camber adjustment via shims. Hopefully no movement inboard is necessary to get 0-2* negative static camber (I think this is the range I'll be using for street & track).

Any other comments/input would be greatly appreciated!

Ummm, yeah, I think you pretty much did all the head work and 5/8" backwards for the mounts is not huge so header clearance might not be bad.

The biggy for me is the no going back without some of the same work to cut and weld. But you really arent moving it far, so if push comes to shove you can fix it. With alot of work. But I dont think you will have any major issues.

Now!! On a side note. Why all the hate for shims. Not just on this post. But Ive seen it alot here and on other sites. I just dont get it. I look at shims as being a really simple tuning aid and not a problem. The way I see it is if I have the uppers hard set (welded position) in the center of my needed adjustment with a good 1/2" (or more) shim stack under the mount then I can change some camber easily by removing a shim or two or adding some shim.

Solly, I just dont understand the dislike for shims when tuning the upper control arms. And whats cool is you can get a certain amount of caster adjustment with the shims also. What am I missing? Im learning all the time. School is in session!! School me up... JR

[TheBandit]

Thanks for the additional feedback. The dislike on the shims is that as you shim for caster (adding on one stud, removing on the other), you start to encroach on your camber. There is only so much practical adjustment range with shims, so being able to use fewer for one means more room to shim for the other.

I hope to hear from others on this subject. Appreciate any experience.

[David Pozzi]

I'd offset it by 7/8" or so.
You'd like to see 5 deg positive caster with equal shims on the bolts.

[JRouche]

Thanks for the additional feedback. The dislike on the shims is that as you shim for caster (adding on one stud, removing on the other), you start to encroach on your camber. There is only so much practical adjustment range with shims, so being able to use fewer for one means more room to shim for the other.

I hope to hear from others on this subject. Appreciate any experience.

Oh, I guess I kinda see it.

I welded my mounts for my upper control arms to give a decent static setting for the mid point of the camber I wanted with a 1/2" shim stack in place. I also have adjustable upper arms (great arms) to fine tune it once the final shim use was in place. I like adjustability. So in my case I like shims for an adjustable shim stack along with an adjustable arm. I can adjust it with some heavy handed caster and still have a decent camber curve. It took ALOT of measurements to map it all out. But I saved it all on paper so I can dial in a large variety of suspension alignments by using a certain shim stack and so many turns for the adjustable arms. And I did all my mapping with the car on turn tables and a special alignment rig. So now that the hard work is out of the way I can dial in the alignment I want with the numbers I have. And yes, I would still double check it on the tables to make sure it was correct.

And as far as I am concerned a decent camber curve is more important than the caster numbers.

But... With alot of adjustability I can keep a similar camber curve throughout the caster settings. Ive measured it from zero caster all the way up to 8* of caster and I can still keep my camber curve the same with some shim adjustments then arm adjustments.

Oh, but there is a problem for my car with 8* of caster. The tire moves back too far and interferes with the fender and inner fender. So I wont ever need to go that far. JR

[TheBandit]

I'd offset it by 7/8" or so.
You'd like to see 5 deg positive caster with equal shims on the bolts.

Thanks for the input David.

Assuming I make this change, do you see any advantage to an aftermarket/tubular arm over this setup? As far as I can tell, it's making an equivalent change in geometry.

[TheBandit]

After laying things out, I decided against moving the UCA tower rearward using the stock arms. It looked like the UCA might not clear some features on the frame in the droop position unless I did some clearancing to the frame or arm. There are some other little things involved like moving brakelines and whatnot that also put me off to doing this. I have decided to just do the vanilla Guldstrand mod, see how much caster I can get, and go aftermarket arms in the future if I want to spend the money. For what it's worth my plan WAS to dual drill mounting plates for the motor mounts, with one pattern setup at normal position and a second pattern 3/4 to 7/8" back.