Torque Converter Alignment
Many of the rebuilders today face one common problem when building a torque converter. Alignment. When we think of a converter and how it functions in the vehicle we generally think about run-out between the flex plate, the converter pilot, and the impeller hub. But what is often overlooked is the internal alignment of parts and its relation to all of the external components.
When a torque converter is assembled there are four principles of concern with alignment. These principles are Concentricity, Parallelism, Perpendicularity, and Flatness. All four of these items must be addressed to achieve true converter alignment.
Two circles, one inside the other remaining an equal distance apart throughout the entire circumference.
Well that seems simple enough. Lets describe this definition in Torque Converter language. We will use an Impeller and its Hub for the description. If the distance between the outer diameter of the hub and the outer diameter of the impeller are the same at all points around the hub the part would be concentric. The same applies to the relationship of a hub from its inner diameter to its outer diameter. If the distance does not remain equal around the entire circumference of the hub then the part is not concentric.
Two lines of infinite distance running the same direction but remaining the same distance apart.
Another easy one. For a good example will use a front cover (bowl) for the description. If the lock-up (friction) surface and the face of the mounting pads (lugs or studs) are machined flat. The distance between the face of the lock-up surface and the face of the mounting pod will be the same at any point of measurement from all of the mounting pads. If the distance varies from one measurement to the next then the Front cover is not Parallel.
Two lines that cross each other at a perfect 90 degree angle.
Back to the Impeller and the Hub for this one. The angle between the outer diameter of the Hub and the bottom of the Impeller (this is the area that contacts the cover when assembling a converter) should be a perfect 90 degrees.
This should be pretty simple however it is commonly measured incorrectly or misinterpreted.
A flat object can be measured only by sweeping across the surface of the object with a gauge or other precision measuring device. If the lock-up surface of a Front cover or Piston is machined it should be flat. However there are a few common problems that can effect the flatness of these surfaces.
1. If the part is mounted in a chuck over tightening can cause the part to distort. When the part is machined and removed from the chuck it can spring back into shape.
2. If the part is being mounted to a face plate using bolts over tightening and have the same effect.
What are the effects of poor Alignment on each converter component?Inside a torque converter there are many moving parts. Each part must be in alignment for the converter to function at its peak efficiency. Alignment also effects the longevity (life) of the converter. Many converter failures can be blamed on poor alignment. Lets talk about some of the effects of poor alignement and how ech of the previous torpics we've discussed relates to each part of the torque converter.
The Impeller and Hub
When a hub is not concentric to the Impeller multiple problems can occur.
- Static (Single Plane) unbalance occurs. When the hub is aligned to the Pilot on the front cover, the Impeller will now rotate out ofcenter.
- The outer diamter of the Stator may come in contact with the Torus Ring inside the Impeller. Most of you have seen the smallor sometimes quite large cuts and scrapes on the Stator. This can cause debris and noise inside a converter.
- Heavy Side loading can occur on the race and rollers inside the stator causing early stator failure.
When a hub is not Perpendicular to the Impeller multiple problems can occur.
- Dynamic (Multiple Plane) imbalance occurs. When the Hub is aligned perpendicular to the Front Cover, the Impeller is no longer parallel to the Front cover.
- Fluid unbalance occurs, allowing a greater amount of fluid to be in a geometric area then in the other areas of the converter.
- Fluid cavitarion occurs. Fluid in one geometric area has to travel further through the pump varies before returning to the Stator. That fluid is then quickly compressed into a shorter distance of travel by the other areas.
- Excessive Pump Bushing wear can occur and often does.
- Impeller vane contact with the turbine assembly can occur causing major failure