73-up A-body versus 73-up B,F,J,M,R-body spindle

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 disk brakes. 5th Ave's and Diplomats are a common site in the junkyards, providing all the disk brake spindles we could ever need. Chassis classification chart.

The rumor is that these spindles cause all sorts of problems, which will lead to the untimely demise of you and your car. Having used these spindles with no problems, we decided to study the specific differences, and document it all. We're directly comparing the 73-76 A-body/70-74 E-body disk spindle to the late B spindle. We'll simply call them the A or B spindle.

Swapping to these spindles in some cars requires other parts, such as new upper control arms. See the Disk Brake page for all of that info

The B spindle is about 3/8" taller than the A, and has a more shapely profile, making it 3lbs 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.

  
Above, the B-spindle is on the left in each photo.

Next, we noticed the lower balljoints are different. On the A spindle, the balljoint is integral to the steering arms, while the B spindle has a balljoint in the control arm, having just a tapered hole in the steering arm. The late A-body lower balljoint is actually used in 73-76 A-bodies, 70-74 E-bodies, and 62-72 B-bodies. They carry Moog #K781 for left and K783 for right. These numbers can be crossed at most any local auto parts store. The late B spindles do use the same mounting holes, so the solution is to use the A-spindle balljoint. The only hang-up is the bolt length. The B spindles use a shorter bolt, so you'll need to get your own bolts. Use 5/8" X 18TPI X 2.5" long bolts, grade 8. They're readily available at any fastener store. It's best to use squish-type lock nuts as well. If you prefer the OEM bolts, you can find them on any of the above mentioned cars using the 781/783 balljoints.

 

The last items are caliper location and rotor size. Some cars had the calipers mounted in the rear, while others have it in the front. Some had 11.75" rotors and others 11". The spindles are the same, and simply swapped from one side to the other in certain cars to provide clearance where needed. You can swap between the two rotor sizes by using the correct caliper brackets. Shown below are the two different brackets. The bracket for the 11" rotor is on the left, with 3 3/8" to the hole centers. The 11.75" bracket has 3.75" to the hole centers. Although all these rotors have the bigger bolt circle, you can at least keep 14" wheels by using the smaller 11" rotors. The 11.75" rotors can be found on 76-79 B-bodies and 79-81 R-bodies. Also, try to avoid the pin-type calipers, as they tend to flex more than the slider-type. 70-74 E-bodies and 70-72 B-bodies used the pin-type.

We then assembled an A-body suspension, and compared both spindles with suspension software from Performance Trends.

First, we found no binding of the balljoints with either spindle in their full range of travel, and no alignment issues with the B spindle. The factory eccentric bolts did provide enough adjustment for both of these spindles. If more is needed, offset control arm bushings can be used to get more adjustment out of the stock arms. We started with 1.18 degrees of caster and zero camber. After swapping spindles and readjusting to zero camber, we found 1.32 degrees of caster. Nearly the same, but a slight improvement.

We found the A-spindle provided us with 1.22 degrees of camber gain, while the B-spindle provided 1.69 degrees. Another slight improvement. Roll center with the A-spindle was 6.73" above the ground, while the B-spindle was 8.14" above the ground. This is step backwards from a racing standpoint, but will provide a little more roll resistance in a street car. And finally, toe-change did increase with the B-spindle. Toe change with the A-spindle remained(barely) within tolerances throughout the travel range. With the B-spindle, toe change is slightly excessive during extension, but well within range in compression, which is much more important - How often is your suspension fully extended on main street?

Overall, using the B-spindle will result in geometry changes that are unnoticeable with all but the most aggressive drivers running against a stopwatch. Even at that, there's a good argument that the increased camber gain will have a positive impact on cornering while the increased toe-in through extension will go undetected.

The only word of warning we could come up with concerning this swap would be initial alignment. After installation, it's necessary to rotate the eccentric bolts a little further back to re-align it, and if your car is already at the inside edge of the adjustment range, you may have to use offset control arm bushings to increase the range. Lowered cars may actually find the difference beneficial. The offset bushings(called Problem Solvers - Moog#K7103) can be purchased from us if needed. Call for details. The K7103 fits all A and E bodies, and all B-bodies from 62-72.

Geometry Reports

73-76 A-body Spindle

Static alignment - 0 camber, 1.18 caster, 0.059 toe-in

Dive

Caster

Camber

Roll Ctr.

Toe-In

2.25

4.892

-1.226

5.608

0.041

2.00

4.502

-1.020

5.756

0.042

1.75

4.108

-0.830

5.901

0.042

1.50

3.707

-0.657

6.043

0.043

1.25

3.302

-0.500

6.180

0.045

1.00

2.890

-0.361

6.312

0.047

0.75

2.473

-0.241

6.435

0.049

0.50

2.048

-0.140

6.549

0.052

0.25

1.617

-0.059

6.650

0.055

0.00

1.177

0.000

6.735

0.059

-0.25

0.730

0.036

6.800

0.064

-0.50

0.273

0.046

6.840

0.069

-0.75

-0.194

0.028

6.849

0.075

-1.00

-0.672

-0.020

6.816

0.081

-1.25

-1.163

-0.103

6.730

0.089

-1.50

-1.669

-0.225

6.574

0.096

-1.75

-2.191

-0.392

6.323

0.105

-2.00

-2.734

-0.612

5.94

0.113

-2.25

-3.300

-0.895

5.366

0.122

73-up B Spindle

Static alignment - 0 camber, 1.32 caster, 0.059 toe-in

Dive

>

Caster

Camber

Roll Ctr.

Toe-In

2.25

4.77

-1.697

6.678

-0.013

2.00

4.407

-1.448

6.848

-0.007

1.75

4.039

-1.213

7.017

0.000

1.50

3.666

-0.993

7.187

0.007

1.25

3.289

-0.787

7.355

0.014

1.00

2.906

-0.597

7.521

0.022

0.75

2.518

-0.422

7.684

0.031

0.50

2.125

-0.264

7.843

0.039

0.25

1.725

-0.123

7.995

0.049

0.00

1.319

0.000

8.141

0.059

-0.25

0.906

0.104

8.276

0.070

-0.50

0.486

0.188

8.399

0.081

-0.75

0.057

0.250

8.505

0.094

-1.00

-0.380

0.288

8.591

0.107

-1.25

-0.827

0.300

8.651

0.121

-1.50

-1.284

0.284

8.677

0.136

-1.75

-1.754

0.236

8.658

0.151

-2.00

-2.237

0.151

8.580

0.168

-2.25

-2.737

0.025

8.421

0.186