We live in a time where modern cars don’t have to sacrifice ride and luxury for performance. The newest generation Chevrolet Camaro is able to drive to a black-tie dinner one night and the local drag strip the next. They exude luxury, style, and ride comfort, without sacrificing their ability to rip down the track. That’s one of the benefits that comes with modern computer controls, high-end automatic transmissions, and the precision of the modern engines designed for the newer cars.
A big-block engine was never an option in 1955, but Tom Brown squeezed one into his Bel Air. A swap like this involves a lot more than just dropping in the engine, he also had to do work to the crossmember, driveline, and rearend, meaning he had to consider the angles that we're going to be talking about.
We’ve seen people apply these modern drivetrains to classic cars to achieve the same performance and luxury driving conditions. There’s a lot to be said about the performance of a 1967 Camaro, but their rigid structure and outdated suspension construction leave something to be desired.
This '68 C10 wasn't offered with an LS drivetrain, another example of a custom vehicle that was modified in a way that required modifying the driveline dynamics, and therefore, working to create new angles.
Fuel injection, overdrive transmissions, and computer controls provide the power and reliability that people want from modern cars, but we’re talking about equipment that was never an option in a classic vehicle: LS and LT engines paired with 700R4, 4L60E, 4L80E, and any number of Tremec or Muncie manual-transmissions. There are a lot of things that need attention when swapping a modern drivetrain into a classic car, and one important measurement that makes a big difference in ride quality and reliability is your driveshaft angle.
An Expert Opinion, And Why Driveline Angles Matter
We know enough about driveshaft angles and transmission swaps to get ourselves into trouble, but we aren’t experts like the folks over at Silver Sport Transmission. So, we reached out and got their input about driveshaft angles. We talked to Dick McCord, vice president of engineering and operations, and got his thoughts on driveline angles for a street car setup – what can go wrong, and how to make sure your angles are within acceptable tolerances.
“If your driveshaft operating angle is too small, there will not be enough rotation of the needles in the u-joint caps and you’ll wear out your bearings due to lack of lubrication,” Dick explained. “You have to have some angle, a minimum of 1/2-degree, or the needles will brinell the surface of the u-joint, cross-bearing journal. U-joints were designed to operate at an angle, and if they don’t have an operating angle, they will wear out prematurely.”
This is what your driveline might look like with too small an angle. The transmission, driveshaft, and rearend are all lined up straight across. (keep in mind, none of these illustrations are drawn to scale.)
“Conversely,” Dick continued, “If the driveshaft operating angle is too great (more than 3 1/2 degrees), then the u-joint will produce torsional vibrations as the u-joint rotates, and will tend to bind as the internal clearance for the needle bearings is eliminated. This will cause extensive wear of the needle bearing. If the angle is too great, you also have to be concerned when driveshaft RPM are high. That’s probably the most common problem we see when guys try to set their angles.”
Here’s an illustration of what things might look like with too much angle, it’s exaggerated for effect, but imagine that’s 5 degrees on each end.
So, with too little of an angle you’ll wear out your u-joints, but too much of an angle you’ll wear out your u-joints and end up with some nasty vibrations. Sounds a little intimidating, right? Well, with proper planning and just a few measurements, you can make sure things are lined up and that you’re angles are within acceptable tolerances.
Here are two angles that could be considered within acceptable tolerances. There's not too much of an angle, roughly 2 degrees on each end, but still enough of an angle to keep things running smoothly.
One of the things we wanted to get cleared up with Dick is when to start considering your driveline angle and the resulting driveshaft operating angles. When to measure, and how to measure are crucial. “When you buy a kit from us, there are only a limited number of standard driveline lengths we provide for cars with an independent rear suspension,” Dick explained. “A customer is likely going to need a custom driveshaft made. A good time to get a preliminary measurement is when you measure for the driveshaft that is included as part of the SST kit.”
Dick recommends using a digital protractor like this one, so you can get the most accurate measurements possible.
That new LS engine and 4L80E automatic transmission are not going to fit in a ’67 Camaro just like the factory small-block and Powerglide did. The engine, mounts, bellhousing, transmission, transmission mount, and crossmember are all going to be sized and fit differently from factory specs. When measuring the fit of your driveshaft, also make the first measurement for the angles so you can get an idea of where you’re at.
“A trick that I like to use when measuring the pinion angle, is to hold a piece of sheet metal across the rearend yoke,” Dick explained. “That gives you a flat surface to work with for a nice square measurement of the angle. It only needs to be large enough to contact all four posts on the yoke.”
Dick also recommends using a digital protractor for finding your angles, because they are smaller and more accurate than their analogue counterparts. “When you are close to the driveshaft operating-angle limits and you try to use a carpenter angle-finder or a spirit level, that’s not really accurate enough,” Dick told us.
Once you have your measurements, you need to calculate the operating angles. Dick recommended this online calculator on the Spicer Parts website. He told us that while some of the smart-phone apps available for measuring angles might also include a calculator, he would recommend sticking with the Spicer calculator. The Spicer website also includes a chart of values for vibration free performance, showing driveshaft RPM vs operating angle when the operating angles exceed the 3 1/2-degree limit.
This is an example of an analogue angle measure that can be used, but only when a digital meter is not available.
Dialing In The Angle
How do you dial things in if the angle is off? Let’s say you have 3 1/2 degrees on the transmission end and zero degrees on the pinion end. How do you get things adjusted? “On the pinion end, you buy wedge shaped shims,” Dick explained. “You get 1/2 or 1-degree shims to insert into your rear suspension mounting locations. On the front end, when you’re working with the crossmember mount and isolator, you’re looking at installing 1/4 or 1/2-inch shims. It depends a little on the vehicle and the distance from the engine mounts to the crossmember mount for what angle change you get from adding each shim.”
The Spicer calculator is an invaluable tool when setting up driveline angles and troubleshooting.
It’s also important to note that most of the adjusting will likely be done at the pinion end of the driveline. If you start adding shims to the crossmember, you’re going to run out of space real quick and end up with the transmission hitting the floor of the car.
The Spicer calculator is also a versatile tool when troubleshooting angles. As Dick explained, “Once you have the values entered into the calculator, it’s very easy to change the values to see what you need to adjust in order to dial in the operating angles.” You can simply adjust the numbers in the calculator to see where you need to add or remove shims. Ideally, the transmission angle and the pinion angle will be parallel, and the resulting driveshaft operating angles will be within 1-degree of each other to cancel out torsional vibrations produced by the U-joints.
These are the three angles you'll need to measure for the Spicer calculator: the angle at the driven member of the transmission, the driveshaft angle, and the pinion angle.
“I probably made it sound harder than it is,” Dick said. “I don’t think the typical hot-rodder would have any problems as long as their angle measuring tool is accurate and they understand what is an UP angle and what is a DOWN angle. If you use the Spicer calculator, there is a definition for up and down angles that may be a little different than standard nomenclature when speaking of pinion angles.” According to the Spicer calculator definition, up is when the measured component rises from the front to the rear of the vehicle, and down is when the measured component descends from the front to the rear of the vehicle. “Driveshaft operating angles can also go up or down depending on the relative height of the engine and differential pinion.”
The driveline angle itself can go up or down depending on the application. As long as the angles are within acceptable tolerances, you're good to go.
We actually felt that Dick’s explanation made things sound simple and easy, and the more we talked to him, the more sense everything made. Luckily you don’t have to figure this all from scratch and you can buy kits from Silver Sport Transmission that include bell housings, flywheels, clutches, and crossmembers. “We sell the transmission and all parts that fit that transmission,” Dick explained. “We sell a crossmember that has been designed to setup the transmission driveline angle. It doesn’t always match the factory crossmember specs, and we don’t always match the original driveline angle in order to gain tunnel clearance, but the crossmember is designed to give the customer the ability to setup good working driveshaft operating angles.”
This is a more detailed example of ideal driveline angles.
If you’re working with Silver Sport Transmission, they also emphasize that their customer service agents will work closely with you to get the right angles. They’ll help you figure out if you need more or less shims, and where. They’ll also walk you through the process. It’s just good to remember that when working with Silver Sport, you’ve got a team of experts at your disposal to answer any questions you might have.
If you are considering an engine and/or transmission swap, get in touch with the folks at Silver Sport Transmission and they’ll take good care of you. Their kits will help simplify the process and make sure that you’re getting your engine and transmission mounted into the car in the ideal position, with the ideal driveshaft operating angles.