BMR Suspension – Adjusting S197 Mustang Driveline Angles



Having the right driveline angles on your Mustang is incredibly important when you’re trying to rip down the strip. Kelly Aiken, Mustang Suspension Specialist at BMR Suspension, gives us all the tools we need to measure and adjust the driveline angles on our S197 Mustang.

BMR Suspension offers suspension, chassis, and drivetrain products for over 16 different vehicles. They are the leading suspension manufacturer in many market segments. Whether you are interested in street performance, hard-core drag racing, or handling applications, BMR Suspension has the components that you need. All products are made in the USA. The products fit and work so well because they are street driven and track tested on BMR project vehicles before they make their way to you. Their love of racing is demonstrated every day in their customer service, design innovation, and manufacturing quality.

In this video, Kelly Aiken, Mustang Suspension Specialist at BMR Suspension explains and demonstrates how to accurately measure the angle of the engine and the transmission and how this relates to the pinion flange angle. To show just how much the pinion moves with the stock suspension, Kelly shows us BMR’s project turbocharged 2011 Mustang GT. With the exception of a spherical disc bearing, the rear suspension on this project car is stock. The stock bushings are soft and allow for massive amounts of movement under hard acceleration. When the pinion flange raises under load, it’s coming up about 3 to 4 degrees.

The angle you want to set the pinion to in relation to the transmission will vary depending on the bushing and the upper control arm. For example, with a stock rubber bushing, there is going to be a larger amount of pinion rise, as the soft rubber bushings let the rear end rotate more than harder bushings. With polyurethane bushings, the rear end is not going to rotate as much, so the difference in angles is will be less.

With a spherical bearing, the split will be even lower, as the rear end will rotate even less. Though the transmission and pinion are on different planes, you want them to maintain parallel angles when accelerating. This will eliminate any unwanted bind or vibrations.

When installing a new upper control arm, BMR recommends starting with the arm adjusting to the stock length of 9.5 inches for a Mustang 2011 or newer. If you have an earlier S197, your upper arm should be adjusted to 8.5 inches.

When measuring and correcting driveline angles, you’ll want to start at the front and work your way back. Even more importantly, make sure you stay on the same side of the car while taking your measurements.

Start by measuring the transmission angle. If the driveshaft is not installed on the car, you can measure off the flat surface of the front of the transmission bell housing or the flat of the front crankshaft pulley. The angle of the crankshaft and the transmission are the same.

The angle you get off of the transmission is a fixed angle and won’t be adjustable. This angle is going to be your starting point to set the angle of the pinion flange. When you get to the pinion flange, make sure your angle finder has the same orientation that it did on the transmission measurement. An easy way to do this is with a square since this will give you a true 90-degree angle and a flat surface to measure from.

For the pinion flange measurement, there are a few different places you can use to measure. The front of the pinion flange will be the easiest to use, but if the driveshaft is installed, you can use the flat surface on the back side or the bottom of the flange.

When the vehicle is accelerating, you’ll want the pinion flange angle to be parallel to the transmission angle. With the weight of the car on the tires, set the pinion flange angle between 1 and 3 degrees less than the transmission angle. With a spherical bearing, it’s recommended to use a 1 degree difference. For polyurethane, a 2 degree difference is recommended, and for OEM rubber bushing, use a 3 degree difference.

This BMR project Mustang had a transmission angle of -2 degrees, so they chose to run a -2 degree driveline angle difference, or a -2 degree pinion angle, which sets the pinion flange measurement to zero.

If you want to get the most out of your car, having your driveline angles perfect is incredibly important. The differences in bushing materials affect the way the suspension moves under heavy loads and hard acceleration, so make sure you know what type of bushing material is on your vehicle and measure and adjust your angles to make your suspension perfect.

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