G body spindle conversion

[sirstude]

Frank,

We talked about using the 12" brake setup from the Mid 80's Cad on my Olds, but I was wondering, with the taller spindle, do I have to change out the upper control arm?

Doug

[enjenjo]

That kind of depends.  As some of you may be aware, the GM frames tend to sag in over time, at the upper A frame mount. With a  good frame, one that is not sagged in, there is about 3/4" difference in the upper A frame length with a tall spindle. But I have seen frames that have moved enough that stock A frames work fine, without excessive shims. As long as you have clearance at the exhaust, you can make up 1/2" plate shims, and use the stock A frame on an unsagged frame. You may have to change the bolts. Or you can use a shorter A frame.

[1FATGMC]

That kind of depends.  As some of you may be aware, the GM frames tend to sag in over time, at the upper A frame mount.........

Funny you mentioned that.  When I put the camaro subframe in my truck in Wyoming I had a friend that had a frame machine (straightener??).  He said to bring the truck over and he would "de-sag" the front.  I never knew if it had a sag or not, but I figured he knew what he was talking about and it was free so I did it.  I have always had lots of room for shims if needed to align it and that was his concern that at some point it might run out of space.

I had forgotten all about this for years and never heard of anyone else doing it, so maybe something like that might also be an option Doug if you have a "sagging frame" .

c ya, Sum

[sirstude]

Sum,

I am not worried about the "sagging Frame" but I am still trying to get a rack and pinion to work on the Olds.  The big spindles have a much shorter (about 1.5 inches) steering arm on them than the stock spindles.  The shorter arms also shorten up the travel from lock to lock which allows for a rack and pinion that does not have so much travel.  The stock travel was almost 7 inches lock to lock and the most I could get in a custom rack was just under 6 inches.  I don't know if I will do this, but just getting ahead of the game.  

I am more wondering on the upper control arm that it will point too far up in the air with the longer spindle, thinking about the speedway engineering tubular a-arms, they are flat so also will not put so much angle on the ball joint.

Doug

[enjenjo]

I am more wondering on the upper control arm that it will point too far up in the air with the longer spindle, thinking about the speedway engineering tubular a-arms, they are flat so also will not put so much angle on the ball joint.

That has never been a problem on the ones I have done. You could bend the stock A arm if needed, which would also shorten the effective length a bit.

[jaybee]

"I am more wondering on the upper control arm that it will point too far up in the air with the longer spindle, thinking about the speedway engineering tubular a-arms, they are flat so also will not put so much angle on the ball joint."

Probably not, but it wouldn't be a bad idea to run the suspension through its full travel just to make sure.  The early Mustang and Camaro/Firebird guys will sometimes lower the point where the upper control arm cross shafts mount just so the control arm WILL point upward more.  Shelby did it with their Mustangs as did * Gulstrand with his Trans Am Camaros.  The purpose of this is to gain negative camber as the suspension travels so that the tread stays more flat under cornering.  The longer spindle duplicates that geometry by a slightly different mechanism.

[Bob Paulin]

"I am more wondering on the upper control arm that it will point too far up in the air with the longer spindle, thinking about the speedway engineering tubular a-arms, they are flat so also will not put so much angle on the ball joint."

Some oval-trackers (myself included) have carved up some wedges to go in between the upper ball joint and control arm to keep the ball joints from hitting the edges of their sockets due to the severe angle of the upper control arm - either from a taller spindle, lowering the inner pivot, or both.

There are also some aftermarket racing control arms that have the ball joint plate mounted in a way that levels the ball joint off a bit - but I cannot rationalize the expense when I can make up tapered shims fairly quickly - shims that can usually be salvaged and transferred from arm to arm when the inevitable crunches come along.

When installing spindles with taller uprights, you can easily run into problems with the upper ball joint hitting the side of the socket and popping itself apart.

Wedging the upper ball joint back towards level compensates for this nicely.

"Probably not, but it wouldn't be a bad idea to run the suspension through its full travel just to make sure.  The early Mustang and Camaro/Firebird guys will sometimes lower the point where the upper control arm cross shafts mount just so the control arm WILL point upward more.  Shelby did it with their Mustangs as did * Gulstrand with his Trans Am Camaros.  The purpose of this is to gain negative camber as the suspension travels so that the tread stays more flat under cornering.  The longer spindle duplicates that geometry by a slightly different mechanism.

Camber gain is, likely, NOT the reason for lowering the upper control arm's inner mounts as related to the outer pivot (ball joint).

Changing the front-end geometry to raise the roll center is more likely the reason why this is done.

While it is true that there is usually camber gain during roll from re-arranging the upper control arm angle, it is often necessary to offset this gain by starting out with less static camber.

When you raise the roll center - which running the upper control arm at a steeper angle does - you shorten the lever arm - aka "moment arm" - between the roll center and the Center of Gravity height.

With less leverage, the CoG cannot roll the car quite as far, resulting in a flatter footprint in the turns.

Probably a moot point in a Street Rod, but on the track, this allows a softer spring setup......which allows better conformity between the tires and track....which results in faster segment times through the turns.....which results in faster lap times.....etc.

One good result of a higher RC in a relatively high Street Rod would be less leaning in the turns.


B.P.