There are four of these selector rings inside the GR6; three double sided and one single sided. Currently, only the double side ones are made by Dodson, and only one of them typically fails (first/reverse.) So, you can purchase all three of them if you like, however typically only one is needed if you just want to upgrade the first/reverse selector ring.
When the TCM pre selects a gear it operates a solinoid to allow fluid from the main valve body to push the selector piston from one position to another. When it reaches the calibrated positon it stops operating that particular solinoid.
The selected gear is held in place by a selector detent. It is also held in place when under power by the taper on the selector/dog ring and reverse taper on the dog teeth on the gear. It is actually pulled in when under power.
If for some reason you prevent the selector/dog ring from reaching it's designed stops then the selector/dog ring will continue to try to engage when under power.
This thrusting will then be applied to what is holding it, the selector fork thrust faces, the select piston and the main valve body which they are not designed for.
These thrust faces are only designed to select a gear not to hold the selector/dog ring from it's designed stopped position. They are generally made from alloys and will generate heat and/or wear quickly.
The selector/dog ring stops also have another function which is to help hold the selector/dog ring parallel to the splined drive hub. When the stops are damaged they no longer can hold the selector/dog ring evenly and tilt sideways and eventually jam in position.
A few reasons for the selector/dog ring stoppers/guides breaking are:
- Material failure. Incorrect heat treatment process.
- Poor design. Economizing on machining processes.
- Incorrect clutch gear learning. Operator error or being driven with a partial learn.
- Poor syncro engagement. Thick slippery fluids not allowing syncros to match speeds quickly and then smashing them home at the last minute.
- Proper clutch/gear learning procedure.
- Correct fluid matching.
- Replace with superior parts that rectify mentioned faults.