BMR Introductory Sale Thread Split (G-Mod Discussion)

[sinned]

The guys at BMR might want to consider making a front a-arm set that incorporates the Gulstrand mod.

I suggest doing a search, we have discussed this in length several times as it comes it. The "G" mod repositions the upper control arm pivot point to improve a more favorable amount of negative camber gain during bump. It is impossible to accomplish this by changing the arm design. ANY arm can be used with the "G" mod, it is amazing how misunderstood this simple mod seems to have become.



BMR, sorry for the thread hi-jack. I saw an opportunity to make some quick and painless "corrections".

[vanzuuk1]

Dennis, if the bracket for the upper arm moved the control arm into the spot where it would be with the gmod, wouldnt that do it? The c/a wouldnt "know" where the bolts were but the geometry would be the same. I assume I am missing something, thats why I am asking.

[sinned]

The "bracket" you speak of is welded to the subframe, there is no "moving" it. The "G" mod is simply a matter of re-drilling the holes that attach the cross shaft to the subframe. The point that needs to move is the actual bushing, I suppose one could get real creative and try to design a cross shaft that drops the bushings to a more ideal location but that would compromise the strength of this very crucial area.

[vanzuuk1]

I meant changing the way the cross shaft mounts, like a cross shaft with the offset built in. I guess I will eyeball my front end tomorow to see if the c/a would have room to move.I am sure if it was easy it would have been done before.

[Nine Ball]

that would be a sweet deal, to have the cross-shafts made to relocate the rotation angle of the A-arms to simulate the Guldstrand mod, without us having to cut the frame mounts and re-drill holes.

[derekf]

In order to make cross shafts that were offset like that, wouldn't the holes need to be moved higher on the shaft? If so, with enough "meat" around the hole to be safe on the street, would the new and improved shaft even fit through the bushing holes in the UCA?

[Chevy350]

I don't think there's a problem with it not fitting through the bushing holes - think of changing a u-joint: There's no way for it to go through from just one side, but you place the u-joint in the yoke, then mount the cups with the bearings afterwards. (as one would the bushings on the a-arms)



This way it could be made quite beefy, and have built-in caster/camber/anti-dive changes with the stock UCA's and of course change the inner pivot location for the G-mod.

There are several offset crosshafts for other makes out there, it's strange (to me) that nobody has done this before.

Edit: Except for cost of this vs the G-mod, I would love a simple bolt-in mod on an already "finished" car, with no more hassle involved than what changing UCA bushings normally has.

[rattus]

"that would be a sweet deal, to have the cross-shafts made to relocate the rotation angle of the A-arms to simulate the Guldstrand mod, without us having to cut the frame mounts and re-drill holes."

I posted a thread awhile back of a SolidWorks model cross-shaft that could do just that, but it didn't generate much interest:

https://www.pro-touring.com/forum/showthread.php?t=8559

[Nine Ball]

It also might be possible just to make an offset bracket and custom cross-shaft that bolts to it. Doing the G-mod on a car that has a painted frame and the car is assembled already is a pain in the butt. Having some sort of bolt-in way of doing it would rock.

[vanzuuk1]

Rattus , thats what I meant, I may have even seen your thread and had it in the back of my mind.

[David Pozzi]

GULDSTRAND MOD
The problem is, the shaft when offset in height, would put a bending load on the bolts and since there are shims between the bolts and the subframe bracket, they might loosen up and fall out.

ADDED CASTER
If better handling is the goal, the upper arms should be made to accomodate 5 degrees positive caster setting. Power steering will probably be needed to reduce steering effort.

[sinned]

GULDSTRAND MOD
The problem is, the shaft when offset in height, would put a bending load on the bolts and since there are shims between the bolts and the subframe bracket, they might loosen up and fall out.

Assuming they don't break entirely. This also assumes someone finds a way to do what no other has in 30+ years and build a cross shaft that fits in the space requirements, doesn't limit arm movement, and keeps the arm itself a safe distance from the sub frame itself. Guys, there s a reason the greatest racing minds in history drilled new holes to locate the arm, there is no other way.

[Marcus SC&C]

Lots of work (and money) to avoid drilling 4 holes... Marcus

[vanzuuk1]

I agree, its not worth it to avoid drilling a few holes.I thought it would be an option for people shy about drilling and templates (not me) or the guys who are obsessed with being able to go back to stock (I could care less, I am about to trim off my rear seat brackets). I was more curious than anything.

The good thing about my car is that the suspension is so worn that even a rebuild will seem dramatically better. Air shocks, bent mono leafs, clunking front end, my car will be happy in a week, new qa1s and leaf springs etc.

Bit by bit...

Ps thanks for shedding light on a subject thats probably been beat to death.

[zman1969]

they have made offset upper control arm shafts to give more camber adjustment on cars with sagged frames - why not then? maybe too much offset is needed hmmm........

[David Pozzi]

I should note, long ago I bought the Guldstrand steel eccentric upper bushings and used them to raise the arm for better clearance to the frame mount. I was hoping to reduce the amount I'd have to cut off the mount, but it didn't help much at all.