Hey guys, thanks for the question.
When Toyota introduced the 4cyl t/case for the 1979 model year (MY), it came with what we call "
Noisy" gear sets. These were just ordinary helical gears with no bells attached (because that would be even more noisy
).
Starting with the 1984 MY vehicles, Toyota altered the low speed and counter shaft gears to include a new gear the thickness of a thin plate that is mounted right next each main gear with a shimmed fit that resists movement. This thin plate gear is designed with one less tooth count, so as the main gears mesh the thin plate spins at a different angular velocity. This difference of speed puts a load to the shimed gear which keeps a preload on all teeth resulting in what we call "
Run Quiet" gears as it prevents gear chatter during the unloaded state between drive and coast.
Here are pics from the Repair Manual for reference:
While this reduced gear chatter noise, it introduced a new problem during assembly in that as you gentlemen noted both low speed and counter shaft gears are able to move and slide out the front of the t/case. The problem with this is that if they are (1) allowed to slide out which disengages the thin metal gears, then (2) rotated and meshed some, and then (3) pushed back in, then it is likely that the thin plates are no longer in mesh with the main gear.
In such case, when the t/case is mated to the transmission while the thin plates are out of mesh, then when the vehicle is driven the teeth on both thin plate gears will be worn down and bent over, throwing metal into the gear oil and eventually thin gear teeth snapping off and then moving through the box causing havoc.
To prevent this, for the 1985 MY Toyota added a Bearing Retainer Clip that is supposed to hold the bearings to the housing prior to being mated to the transmission. Once mated, the machined face of the transmission tail housing keeps the bearing race in place
If you look at our
Transfer Case Bible, you'll see that from August of 1983 until April of 1984, Run Quiet gears were used on housings that did not have a Retainer Clip. Possibly either this was during a crossover period until inventory was consumed, or it took a while until dealerships were doing warranties where the issue of the thin gear plate not being in mesh were discovered.
On our own 4.70:1 gear sets, we omitted the Run Quiet plates for simplicity and maximum gear tooth strength as each tooth is the full maximum width that can fit into the housing.
Regards,
BigMike
