That hub and shifter plates are definitely completely worn out
Double clutch does save the blocking rings when the driver knows what he is doing.
Those that do not have lot's of experience on unsynchronized gearboxes should NOT double clutch a synchronized gearbox
A T84 can be driven with the blocking rings removed if the driver can double clutch.
The blocking rings are not really necessary to make a T84 working.
Am going to try to explain how things work.
It won’t be easy to understand, and it is difficult to explain.
It is for the die hard only.
To understand the synchronizer one must know that everything on this planet is in motion, simply because earth is turning constantly.
When 2 objects move in the same direction with the same speed they are standing still against each other, even while they are both in motion.
It is possible to step from one driving car into another if they both have the same speed in the same direction.
Also the force from inertia is a major player in the synchronizing process.
An object in motion want to stay in motion.
It needs a force to bring it to another direction or another speed.
The clutch cone must accelerate or decelerate the gear to the same speed as the clutch hub.
Inertia is the force that the synchro must overcome
The cones from the gears and the blocking rings are a brake system, they are cone clutches.
Just as the clutch between engine and gearbox, the cone clutch from the synchronizer is there for a smooth transition from 2 different speeding parts.
Therefore one must shift smooth and in one gentle move.
The synchronizer works in 2 steps.
The shifter plates are involved in the first step.
The bobble from the shifter plates are held in the clutch hub groove by the 2 wire springs.
When the driver shift, the clutch hub is moving towards the blocking ring and takes the shifter plates along.
The shifter plates push against the blocking ring, and the blocking ring makes contact with the cone from the gear.
The gear has a different speed than the clutch hub, hence the blocking ring want to turn the same speed as the tapers create friction.
The notches in the blocking rings and the shifter plates prevent the blocking ring from turning with the gear.
But they bring the teeth from both the blocking ring and clutch hub in the right position.
There are 3 positions that the blocking ring takes during the synchronizing process.
When down shifting the gear is turning faster than the clutch hub.
Position 1 ) Then the blocking ring notches are held against one side from the shifter plates.
When up shifting the gear turns slower than the clutch hub.
Position 2 ) Now the blocking ring notches are held against the other side from the shifter plates.
As the driver moves the clutch hub forward, the second step is taking action.
As long as the gears are not turning the same speed, hence stand still against each other the blocking ring will not allow to shift.
The teeth from the blocking ring and clutch hub are now in the right position and held against each other.
The teeth are point shaped, they are exactly the same on both parts.
This means that when the clutch hub want to slide over the teeth from the blocking ring, it must turn the blocking ring in the opposite direction from the turning gear, to allow the teeth sliding in the splines from the clutch hub.
The driver is now putting more force on the shifter stick, and the bobbles from the shifter plates are forced to leave the groove in the clutch hub.
From now on step one is finished, and the shifter plates have no force on the blocking ring anymore.
They just keep the blocking ring from turning with the gear.
The pressure that the driver is building up on the shifter stick is the force that the clutch cone needs to slow down or accelerate the gear allowing it to mesh with the clutch hub.
As long as there is inertia, the teeth cant line up and mesh.
No matter how much force the driver is putting on the shifter stick.
One that let the engine run on a parked car, will not be able to make the gearbox grind when pushing the shifter into a synchronized gear.
The shifter stick will push back on your hand until the blocking ring is failing.
If the wheels are off the ground they will start to spin.
The clutch cone is making drag under the pressure from the shifter stick and the gear is brought to the same speed as the clutch hub.
The inertia is fading away as the speed from both parts become equal.
The blocking ring has no inertia anymore to keep the teeth from sliding against each other, and now allowing it to slightly turn in the opposite direction that the teeth can mesh.
The blocking ring is losing its friction with the taper from the gear and let go.
It is now in the 3th position, sitting loose inside the clutch hub.
The gear is no longer held by the friction from the blocking ring and for a split second it want to start to turn a different speed than the clutch hub.
But the clutch hub is moving forward and now the pointy teeth from the gear and clutch hub are sliding and positioning with the clutch hub splines and mesh.
The process is at the end and the gear is engaged.
All this happens when one shift second or third gear.
The driver can feel the process in the shifter stick as he has to supply the power for the braking action between both…with a different speed… moving parts.
When the inertia is fading away the shifter stick can move forward.
When a driver want to shift to fast, the clutch cone is under great stress and shall wear fast.
A good driver put a given pressure on the stick, and give time to the clutch cone doing its job.
When shifting very slow, the second step can fail and make the gearbox grind.
When shifting back to neutral, the bobbles from the shifter plates are back in the groove and the process can be repeated.
Hope someone read and understood all this.