Tech FAQ

Q: How do I determine which rear brake kit fits my axle?

A: Magnum manufacturers a variety of rear disc brake kits for popular Ford rearends used in hot rods. This chart will give you critical dimensions to help you identify which housing ends you have and what rotor offset you will require.


Q: My brakes are dragging, what are the most common causes of this?

A: Most brake dragging problems can be traced down to one of the following issues:

  1. Residual check valve left in the master cylinder. You will need to remove the valve from the master cylinder. If you have drum brakes you will need a 10-12# inline residual check valve installed on the rear brake line. For front disc brake applications, a 2# inline residual check valve is recommended on applications where the master cylinder is mounted below the level from the front calipers to prevent brake fluid from running back into the master cylinder when the vehicle is not being operated.
  2. Inadequate master cylinder pushrod free-play. Adjust the pushrod free-play for optimum clearance and remove excessive play without depressing the master cylinder.
  3. Air trapped in the hydraulic system which expands with heat. It is critical to remove all the air from your brake system to ensure it is operating at peak performance. Also, remember to periodically inspect the fluid level and condition and flush the fluid semi-annually.
  4. Caliper not mounted square to the brake rotor. Check the mounting position in relation to the rotor to determine if there is an out-of-square condition. Check and correct as necessary. Call our tech department for additional information. After a short test drive, raise and spin the tires. If they drag, don’t operate the car until the problem has been corrected.


Q: How do I determine which axle I need for my build?

A: Magnum manufacturers a wide variety of axles for most early Ford and some other custom applications. Our narrower, 46" Tube and 46" and 46 1/2" I-Beams are well suited for '28-'34 fendered cars, offering improved tire clearance combined with a perfect stance and a great fit. Our 48" axles are popular on fenderless hi-boy style cars for a low, wide stance. We also offer narrower 47 3/4" and 50" axles for '37-'41 and '42-'48 Ford cars and trucks. If you need assistance, just call our technical department for more information.


Q: How do I determine the drop on an I-beam or tube axle?

A: Stock axles generally have about 1 1/4" of drop built-in, and our dropped I-beam and tube axles drop a given amount (4"– 6") beyond the factory axle. The drop is calculated from the top of the king pin boss to the top of the perch boss.


Q: What makes Magnum axles better than the knock-off products I see advertised online?

A: Magnum Axles are produced to the highest standards in the industry and recognized by professional street rod builders worldwide. Here are just some of the reasons to buy Magnum:

  1. Magnum Tube axle ends are forged from premium 1018 steel, not cast.
  2. Magnum Tubes are precision welded to the forged ends with deep penetration.
  3. Available in a wider range of sizes to fit most builds.
  4. Magnum axles are precision machined right here in the USA to exacting dimensions!


Q: Do I need a power booster for my application?

A: For most applications with a curb weight of under 3,000 lbs. using Magnum brake kits with 11" rotors and a matched master cylinder, you will generally not need a power booster, saving valuable space.