A/T - A4LD 4-3 Gear Flare, No Engagement in O/D
TECHNICAL BULLETIN # 163DATE: April 1993
TRANSMISSION: A4LD
SUBJECT: INPUT SPRAG PROBLEMS
APPLICATION: FORD BRONCO, RANGER, AEROSTAR, MERKUR
A4LD Input Sprag Problems
4-3 Flare, No Engagement in O/D, Exploded Overrun Clutch Return Spring
Assembly - Broken O/D Planet/Race
The A4LD input sprag connects the O/D planet to the O/D ring gear hub (see Figure 1). It engages in 1st, 2nd and 3rd gears, as wet as reverse. In the O/D shifter position, it is the only engaging element that connects the converter turbine to the forward drum in 1st, 2nd & 3rd gears, and if it can't engage properly it can cause all of the above problems.
The inner race for the input sprag is part of the O/D planet assembly. This race can be mis-machined or worn to an undersized diameter, and can allow the sprag to freewheel, slip or flip over instead of engage. You have to check the inner race diameter to make sure it can lock the sprag.
A4LD-Input Sprag Problems
4-3 Flare, No Engagement in O/.D ,Exploded Overrun Clutch Return Spring
Assembly - Broken 0/D Planet/Race
The blueprint specifications through 1992 are:
Minimum Diameter: 54.757 mm (2.155788")
Maximum Diameter: 54.777 mm (2.156576")
The blueprint specifications through 1993 are:
Minimum Diameter: 54.777 mm (2.156576")
Maximum Diameter: 54.797 mm (2.157363")
A good working inner race will typically measure at least 2.1556".
Using an ACCURATE 2.3" micrometer with a resolution to .0001", make sure your race is above 2.1556" (see Figure 2).
If your measurement is less, replace the O/D planet assembly.
The O/D ring gear hub bore acts as the sprag outer race. Although there have not been reports of mis-machining of the bore to the wrong diameter, any observable wear means replace the hub,
It is also advisable to change the input sprag on a unit that has over 50,000 miles, or experiences any of the above problems.
The micro-finish specification on the inner and outer races is .6 microns. Use 320-360 grit emery cloth to sand used inner & outer races.