A/T - 700R4 4-3 Downshift On Slight Acceleration

TSB 87-35 (June)

SUBJECT: 700 R4

PROBLEM:

In 4th gear, at approximately 40 to 50 miles per hour, the slightest acceleration gives a 4-3 downshift on the L4 and V-6 versions. This is a common cause of internal spline wear on the forward clutch friction plates.

CAUSE:

When the transmission is in 4th gear, the input sprag is freewheeling (overrunning). When the transmission shifts to 3rd gear, the input sprag must lock, causing the outer race to change direction against the forward clutch splines. The busyness of the 4-3-4 shifts cause a back and forth motion of the input sprag outer race against the forward clutch splines, and may wear the forward clutch splines.

CURE:







Remove the spring from the T.V. modulator downshift valve (see Figure 1) and install a spring that weighs approximately two pounds more than the original. To weigh springs, compress spring, using the valve, on a scale until stem of valve is just touching the scale, then read the scale (see Figure 2). After installing the stronger spring, L4 and V6 versions will require more acceleration before the transmission will make a 4-3 downshift at approximately 40-50 MPH.