Over the years, the Honda transmission has evolved from a simple, two-speed automatic, to a solenoid-laden behemoth. It’s the most unusual automatic trans-mission on the market, and it scares many builders off because of its non-traditional design. But it shares some basic characteristics that we’ve grown accustomed to with other units. One of those characteristics is the low sprag assembly.
The clutch apply chart (figure 1) doesn’t encourage the use of a low sprag. The first gear clutch is applied directly to the geartrain, without the use of a sprag assembly in 4-cylinder applications. So why even use an additional component that could eventually fail? Maybe because a sprag helps eliminate shift-timing issues that can cause clunks on coast-down into 1st.
So units that use a low sprag keepthe low clutch applied in all forwardgears. The sprag freewheels while the transmission is in other gears.This prevents the need for complex programming to accommodate multiple downshift timing scenarios into first gear, such as those used for theA604/41TE.
Now that we know what the low sprag does in the Honda unit, it’s easier to appreciate its presence. In the earliest years, the low sprag took on several different dimensions, based on application. Finally, in the early 2000s, the sprag element became a standard size across the board.
Even though the elements are the same, the races differ from one application to the next. The inner races become part of the low gear itself, and are usually the part that fails. The inner sprag surface becomes worn by the low sprag element dogs free-wheeling on its surface (figure 2). This wear creates symptoms such as no forward movement, falling out of gear when coming to a stop, and neutral-bang when accelerating after slowing to around 5 to 15 MPH. (For more, check out Mike Souza’s article in the October 2009 issue of GEARS).
You many need to check the first clutch pressures to make sure the issue is the sprag. Sometimes these symptoms can be intermittent and you may not be able to duplicate them easily.
While the inner race is relatively similar across the board, the outer races differ widely. From the supporting bearing’s outer dimensions to the inner lube retaining washers, there’s a wide variety of designs.
One thing that remains constant is that the outer sprag race surface is normally intact and doesn’t show signs of wear. So replacing the worn parts — the sprag element and the low gear — would be the proper repair for this unit. These parts are normally available through the dealer or your regular parts supplier.
Now for the dilemma: Not all parts are created equal. It’s been a common repair technique to use a 1982–86 (early) 700R4 input sprag element without the washers as a direct replacement for the OEM Honda element. This repair works in most cases, but we’re seeing some failures in specific applications (figure 3). The common thread appears to be the high torque 3.5L V-6 engine applications. Your best bet is to use the OEM sprag and outer race assembly in these applications, as opposed to the early 700R4 sprag element.
Let’s take a closer look at why this has become a problem:
First, there’s a dimension-al difference between the OEM versus the 700R4 early element figure 4). The 700R4 sprag is 0.045” taller; a substantial difference. This can allow the 700R4 element cage to bind, preload-ing the dogs and preventing them from locking. This effectively puts the unit in neutral.
Another noticeable difference between the 700R4 and the Honda elements is there are no centering tabs on the outer cage (figure 5). These tabs not only center the sprag inside the outer race, but they also keep the element from rotating, relative to the outer race.
If you use the 700R4 sprag, it’ll float between the two races until it locks. That’s like a game of musical chairs, where it may or may not lock, depending on the sprag orientation. Remember that the washers you discard when using the 700R4 sprag keep the races an equal distance apart as well as control lubrication to the element.
The 700R4 element works well in most applications, but, since the Honda elements are available from many resources other than the OEM, substitution makes little sense. You’re better off using the Honda sprag, particularly when working with high torque, high horsepower applications.
Then again, maybe the 700R4 sprags have been working just fine for you. In that case, keep doing what you’re doing. But if you’ve run into any of these problems, consider making a change.
Sometimes it’s necessary to take a closer look at your building habits, especially when dealing with come-backs and no-goes. The parts playing field is constantly changing. From time to time, it’s a good idea to review your processes and change them to make sure you’re getting the best results in your rebuilds.
In this case, until an OEM-quality, drop-in element is available, use the OEM sprag assembly to make sure your rebuilds work as designed. Special thanks to H and A Transmissions, Inc. in Rancho Cucamonga for helping with this article.
