9" drum to disc conversion confusion
For years, it's been a common recommendation to use the '73-and-up A-Body disc-brake spindles as a starting point, and up until recently, this wasn't an issue. Now, however, the question is if you can find them, not where. Original A-Body disc brake setups are almost impossible to find in the yard as everything's getting crushed to make way for the profitable late-model wrecks. Of course, you can also use the identical '70-'74 E-Body disc spindles, but we all know there aren't any E-Bodies in junkyards.
http://www.moparmusclemagazine.com/...ing_a_and_b_disc_brake_spindles/photo_02.html
Above, the B spindle is on the left.
So what are we to do? There's a fierce debate going on about the so-called B-Body spindle. This one spindle is actually used in all '73-and-up B-, F-, J-, M- and R-Body cars, which is a huge source for cheap disc brakes. Fifth Avenues and Diplomats are a common site in the junkyards, providing all the disc-brake spindles we could ever need. See the accompanying chart for a list of all the cars in this group.
The rumor is that these spindles cause poor geometry, binding balljoints and other problems, which will lead to the untimely demise of you and your car
. Having used these spindles in various A- and B-Bodies with no problems at all, we decided to study the differences, analyze the geometry with some good software and document the honest differences. We're directly comparing the '73-'76 A-Body/'70-'74 E-Body disc spindles to the late B spindle. We'll simply call them the A or B spindle.
If you have a '63-'72 A-Body, you'll need new upper control arms from a '73-'76 A-Body, which uses the bigger K772 balljoint. Aftermarket tubular a-arms also use this bigger balljoint. Upon inspection, the first thing you'll notice is the height difference. The B spindle is about 3/8-inch taller than the A, and has a more shapely profile, making it 3 poundss lighter, helping unsprung weight. One other item of interest is the SAI, or Steering Axis Inclination. This angle is the major reason for self-centering steering on cars, more so than caster, and within limits, more is better. The A-Body spindle has a cast-in SAI of 7.5 degrees, while the B-spindle has an SAI of 8 degrees, further aiding in stability.
If you have a '63-'72 A-Body, you'll need new upper control arms from a '73-'76 A-Body, wh
To explain these differences, a little geometry background is required. There are many issues concerning front suspension, but we'll only touch on the major items that are affected by this spindle change.
Toe change can also be called "bump steer," and is the most commonly known term, and the least understood. All suspension systems exhibit some amount of bump steer, because the tie rod does not follow the same arc as the spindle in a double a-arm system. A strut suspension is much easier to work with, but that doesn't apply here. The goal is merely to minimize bump steer and to keep it within an acceptable range. Race car builders try for as little bump steer as possible, but it's basically accepted that it does not affect handling if kept below approx. 0.031-inch or 1/10 of a degree per inch of travel. Factory street cars have a much larger tolerance, usually double this amount. In basic terms, less than 1/16-inch of toe change per inch of travel is acceptable.
Also important to know is how toe-change affects the driver. In a straight line, with the nose moving up or down, both tires change the same amount, essentially canceling out the effects. Through a corner, however, the outside tire carries most of the weight, and determines most of the driver's control of the car. This means toe-change in compression is most important, as it has a bigger affect on handling. If the wheels toe-out slightly under compression, the car will turn less into the corner, called under-steer. This is typically more stable, as the driver will continue turning the wheel into the turn, which is a natural response. If the wheels toe-in substantially under compression, the car will turn more, called over-steer. The driver is forced to turn the wheel out of the turn to correct, which is not natural, causing an unstable feeling.
Read more: http://www.moparmusclemagazine.com/...isc_brake_spindles/viewall.html#ixzz2lrxkh5hl
I think this is why I had to use the Moog offset bushing. My alignment mechanic couldn't align the Cuda properly until I replaced the bushings.
Treblig
For years, it's been a common recommendation to use the '73-and-up A-Body disc-brake spindles as a starting point, and up until recently, this wasn't an issue. Now, however, the question is if you can find them, not where. Original A-Body disc brake setups are almost impossible to find in the yard as everything's getting crushed to make way for the profitable late-model wrecks. Of course, you can also use the identical '70-'74 E-Body disc spindles, but we all know there aren't any E-Bodies in junkyards.
http://www.moparmusclemagazine.com/...ing_a_and_b_disc_brake_spindles/photo_02.html
Above, the B spindle is on the left.
So what are we to do? There's a fierce debate going on about the so-called B-Body spindle. This one spindle is actually used in all '73-and-up B-, F-, J-, M- and R-Body cars, which is a huge source for cheap disc brakes. Fifth Avenues and Diplomats are a common site in the junkyards, providing all the disc-brake spindles we could ever need. See the accompanying chart for a list of all the cars in this group.
The rumor is that these spindles cause poor geometry, binding balljoints and other problems, which will lead to the untimely demise of you and your car
. Having used these spindles in various A- and B-Bodies with no problems at all, we decided to study the differences, analyze the geometry with some good software and document the honest differences. We're directly comparing the '73-'76 A-Body/'70-'74 E-Body disc spindles to the late B spindle. We'll simply call them the A or B spindle. If you have a '63-'72 A-Body, you'll need new upper control arms from a '73-'76 A-Body, which uses the bigger K772 balljoint. Aftermarket tubular a-arms also use this bigger balljoint. Upon inspection, the first thing you'll notice is the height difference. The B spindle is about 3/8-inch taller than the A, and has a more shapely profile, making it 3 poundss lighter, helping unsprung weight. One other item of interest is the SAI, or Steering Axis Inclination. This angle is the major reason for self-centering steering on cars, more so than caster, and within limits, more is better. The A-Body spindle has a cast-in SAI of 7.5 degrees, while the B-spindle has an SAI of 8 degrees, further aiding in stability. If you have a '63-'72 A-Body, you'll need new upper control arms from a '73-'76 A-Body, whTo explain these differences, a little geometry background is required. There are many issues concerning front suspension
, but we'll only touch on the major items that are affected by this spindle change. Toe change can also be called "bump steer," and is the most commonly known term, and the least understood. All suspension systems exhibit some amount of bump steer, because the tie rod does not follow the same arc as the spindle in a double a-arm system. A strut suspension is much easier to work with, but that doesn't apply here. The goal is merely to minimize bump steer and to keep it within an acceptable range. Race car builders try for as little bump steer as possible, but it's basically accepted that it does not affect handling if kept below approx. 0.031-inch or 1/10 of a degree per inch of travel. Factory street cars have a much larger tolerance, usually double this amount. In basic terms, less than 1/16-inch of toe change per inch of travel is acceptable.
Also important to know is how toe-change affects the driver. In a straight line, with the nose moving up or down, both tires change the same amount, essentially canceling out the effects. Through a corner, however, the outside tire
carries most of the weight, and determines most of the driver's control of the car. This means toe-change in compression is most important, as it has a bigger affect on handling. If the wheels toe-out slightly under compression, the car will turn less into the corner, called under-steer. This is typically more stable, as the driver will continue turning the wheel into the turn, which is a natural response. If the wheels toe-in substantially under compression, the car will turn more, called over-steer. The driver is forced to turn the wheel out of the turn to correct, which is not natural, causing an unstable feeling. Read more: http://www.moparmusclemagazine.com/...isc_brake_spindles/viewall.html#ixzz2lrxkh5hl
I think this is why I had to use the Moog offset bushing. My alignment mechanic couldn't align the Cuda properly until I replaced the bushings.
Treblig
