Stock is not a word used very often in the performance industry. LS engine swaps, transmission changes, beefy rear axles, major suspension mods, and ride height modifications are all part of this complex game. This is especially true when it comes to engines and transmissions, as it’s not unusual for drivetrain angles to change slightly, especially if we are trying to clear the floor with a larger trans. These may seem to be insignificant changes, but they can have big effects when it comes to running the car down the road. Tremec is in the business of selling high-performance manual transmissions and through the years, customers run into driveline vibration issues that are often blamed on the transmission or poorly balanced driveshafts. Closer diagnosis revealed that most of these problems were related to driveline angle issues.
This motivated Tremec to create a simple driveline angle finder program that anyone could use. The idea is to measure the angle of the engine and transmission, the driveshaft, and the pinion angle separately and then combine them mathematically to determine the system’s proper overall angle. Virtually all passenger car engines are installed in production vehicles with a slight tail-down angle of 1 to 3 degrees. If we look at the drivetrain from a side view, in order to maintain the proper U-joint operating angles, the pinion needs to be roughly parallel (one or two degrees) to the angle created by the engine and transmission. When this happens, the relative angle of the engine to the front U-joint and the pinion to the rear U-joint allow the joints to operate within their intended range of motion. This is the goal of a proper driveline angle. If you take a minute to study Tremec’s side view illustration, it speaks volumes on how the two angles should be oriented.
So what happens when these angles are not correct? Sometimes nothing happens. We’ve actually tested two of our Chevelles with non-stock drivetrains and both were severely out of spec and yet neither exhibited a driveline vibration. That means that if or when a car exhibits a vibration, there are some components that are way out of spec. The most common issue is a driveline vibration that occurs at higher vehicle cruise speeds or during acceleration or deceleration. Perhaps the biggest variable that can cause a vibration is a change to ride height. We experienced this when we drove our ’65 Chevelle on the Hot Rod Power Tour a few years ago. The Chevelle exhibited a severe vibration that occurred when decelerating from 70 mph but it only occurred during Power Tour. We realized that we were carrying more weight in the trunk with tools, spare parts, and luggage, which lowered the ride height by more than an inch. This changed the pinion angle, which created the vibration. At the time the car did not have adjustable upper control arms, so we opted for the next best solution and raised the back of the transmission roughly 1/2 inch. This solved our vibration issue. We rechecked the car with the Tremec app and discovered our modified transmission crossmember had sagged, creating a much greater tail-down engine/trans angle, which we repaired with a new crossmember from American Powertrain. So even if your car does not exhibit problems, that doesn’t mean the driveline is optimized. The Tremec app has revealed that none of our cars were right.
All smart phones come with an internal sensor that monitors the phone’s horizontal or vertical orientation. Among the common smart phone apps is one that converts this sensor to a digital angle finder. Tremec’s Nate Tovey told us that Tremec created a simple app that uses this sensor to measure and record three angles: the engine/trans, the driveshaft, and the pinion angle, and quickly computes the system’s overall operating angle. If your numbers are good, the results appear in green. If one or more angle is out of spec, the results will be in red. We’ve used this app on four different cars, and once we figured out all the details with this app, it works really well. Are you out of luck if you don’t own a smart phone? No, we’ll also show you how to compute these angles using a more traditional angle finder—and don’t worry—the math is easy.
The easiest way to check your driveline angle will be on a drive-on hoist. You can do this on a level driveway but when jacking up the car, make sure the frame is level and that the rear axle is at normal ride height. Our two-post hoist lifts the car by the frame, so we had to remove the rear springs and jack the rearend up until it sat at ride height. This is critical because ride height has a major effect on pinion angle. This brings up another point relative to drag cars. With a leaf spring car, drag racers often will place the pinion angle 4 or 5 degrees nose down in order to compensate for spring wrap-up under acceleration. This means that with a major nose-down pinion angle, measuring it with the Tremec app will indicate a fail. This is where you might have to apply additional logic. The problem is making the assumption as to how far the pinion travels upward under hard acceleration. Pinion angle could also be estimated (or limited) with the help of a pinion snubber. Plus, the use of CalTracs bars or other traction control devices will also limit pinion movement.
For street cars, you will need to set the pinion angle based on how the car is used. For leaf spring cars like early Camaros or Novas, it’s best to set the angles based on normal highway driving because that is where the vibration is likely to occur. To modify the pinion angle for a leaf spring car, Lakewood sells an angled pinion shim spacer that is placed between the leaf springs and the axlehousing. For coil-spring cars like Chevelles and fullsize cars, the only way to adjust the pinion angle will be by using adjustable upper control arms from companies like Global West, Hotchkis, and others. Often, just changing the pinion angle will solve a driveline vibration.
01. Checking driveline angles with the new Tremec smart phone app is a quick way to determine your actual U-joint operating angles. If you’re experiencing a vibration and have been unsuccessful in your diagnosis—this might just help you identify the issue.
02. This Tremec diagram is a great explanation for what the app is measuring. The goal is for the pinion angle to be roughly parallel with the engine/transmission angle. Generally this will require a nose-up pinion angle. What we want to avoid is opposing angles where the engine/trans is tail down and the pinion is nose down, which would create lines that would cross.
03. Here’s how the free Tremec app home page appears on your smart phone. You can find it by logging onto tremec.com and then clicking on the Aftermarket logo in the lower right corner. Under Motorsports & Aftermarket, click on Driveline Angle Finder App. The phone automatically compensates for switching from vertical to horizontal.
04. Our ’66 Chevelle test subject was loaded with a 4.8L LS truck engine and a California Performance Transmissions 200-4R trans. The app confirmed that the engine appeared to be at a steep angle with a 5.8 degree slope. We used the machined flat of the oil filter adapter and confirmed this with another point on the trans.
05. Step 2 is to measure the driveshaft angle. Make sure the phone is completely parallel to the shaft—use the edge of the phone without the buttons. The app indicated a near zero, 0.2 degree, angle so we knew we had a problem because the app calls for no more than a 2-degree difference in U-joint angle and 5.8 – 0.2 = 5.6 degrees.
06. Measuring the pinion angle can be difficult. Tovey says laying the phone across two rear cover bolts works. We compared that reading to a machined surface we found next to the rear cover. They were within 0.1 degree so we felt that our 0 degree pinion angle was accurate. But this was also not going to work with the steep engine/trans angle.
07. You may notice that the Results screen lists Angle 1 and 2, which are not the same as the readings you recorded. This is because this screen displays the calculated operating angles of the front and rear U-joints. The overall Driveline Operating Angle is the difference between Angle 1 and 2. We obviously had work to do since the whole system was way out of spec.
Using the App
There are several things about this app that might seem confusing at first. But once you understand how the app works and what it is telling you, it all makes sense. Start by measuring all three positions called for by the app. When the results screen is displayed, you may see some or all of these angles displayed in red. Angles indicated in red are out of spec. Green numbers mean you are good. The beauty of this app is that you don’t even really need to understand what the angles are telling you. All you really have to do is know that if the numbers are green, you’re good. But if the numbers are red, you have work to do.
The Results screen will also indicate Angles 1 and 2—but these numbers will not be what you measured for the engine/trans and driveshaft. Instead, the Results screen displays Angle 1 as the operating U-joint angle that is the result of subtracting Reading 2 (driveshaft angle) from Reading 1 (engine/transmission angle). Angle 2 on the Tremec Results screen is the rear U-joint operating angle that is the result of the driveshaft angle (Reading 2) subtracted from the pinion angle (Reading 3).
Finally, the Results screen will also display a third, overall Driveline Operating Angle. This is determined by subtracting Angle 2 from Angle 1. This is also the same as subtracting the pinion angle from the engine/trans angle. If both U-joint operating angles are in the green, the overall angle will also be good. This probably sounds confusing, but it really isn’t that bad once you think about it and use the app. Again, the goal is to have the pinion angle roughly parallel to the engine/trans angle. The key is to avoid overlapping angles between the engine/trans and the pinion.
The Old-School Way
If you don’t have a smart phone or are just ornery enough to want to do it the old fashioned way, the process is pretty easy especially if you understand the process behind the Tremec app. First, you’ll need either a digital angle finder or a simple analog angle finder. The least expensive analog tool we found was at Harbor Freight (PN 34214, $4.95). Using an angle finder, record all three angles if you want to, but the two important ones are the engine/trans and the pinion angle. Make sure you record not just the physical angle, but the directions that the engine/trans and the pinion are pointing. This is especially important for the pinion angle. As an example, let’s use 3.0 degrees, tail-down angle for the engine/trans, 1.1 degree (nose-up) for the driveshaft, and 1.9 degrees nose-up for the pinion angle. Remember, these are angles viewed from the side. By subtracting 3.0 – 1.9 = 1.1 degrees, this result is within the maximum overall operating angle of 2 degrees with a maximum driveshaft speed of 5,000 rpm. These are Tremec’s recommendations. It’s entirely possible that if driveshaft speeds for a daily driver never exceed 4,000 rpm, then a 3-degree overall driveline-operating angle is acceptable.
It’s also worth mentioning that this app is intended only to measure the operating angle as viewed from the side. There is also a second operating angle as view from the top. There is some complex math involved with calculating the combined operating angle that we won’t get into here. It’s possible that this second, overhead angle may exceed its recommended total operating angle and cause a problem, but for production cars where the rear axle has not been changed, then the combined angle will most likely be acceptable. Where you could get into trouble is with a custom chassis and drivetrain application where the driveline is an amalgam of different parts.
All of this might sound a bit complicated, but once you understand the concept, it’s all fairly straightforward. Knowing more about how your car is set up is always a good thing, and this app may be very enlightening as to what that annoying vibration is that you can feel in the seat of your pants or through your feet on the floorboard. You might just try believing your driveshaft guy when he tells you that he’s checked that driveshaft twice and it doesn’t need balancing!
08. We had to raise the rear of the trans with these spacers in order to get the engine/trans angle down to a more reasonable 3.2-degree angle.
09. Next, we lengthened the Global West rear upper control arms to raise the pinion angle to 2.2 degrees nose-up. This also changed the driveshaft angle slightly so that the rear U-joint operating angle is now within spec.
10. This is our results screen after changing the engine/trans and pinion angles. As you can see, we now have all green results because the front U-joint angle (Angle 1) and rear U-joint angle (Angle 2) are now within spec and the total operating angle is 3.2 – 2.2 = 1.0 degrees.
11. Of course, you don’t need a smart phone app to do this job. This is a typical analog angle finder. You can get one from Harbor Freight or Summit for around $5.
12. The large angle finder base makes finding a suitable spot to measure a challenge. On a different Chevelle with a T-56, we removed the driveshaft and used the machined end of the output shaft.
13. You can also use the end of the pinion yoke as a suitable position to find pinion angle. You must keep track of the relative angles to make sure the pinion angle is parallel to the engine angle. Then it’s just a matter of subtracting the angles.
14. This quickie drawing might help you visualize what’s going on when doing the analog calculations. Our engine/trans angle was 3.0 degrees, the driveshaft was 1.1 degrees, and the pinion angle was 1.9 degrees. This creates a passing overall operating angle of 1.1 degrees.