Synchronizer wear

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Re: Synchronizer wear

Postby Greencom » Mon Apr 26, 2010 7:55 am

Everything looks clean and shiny except the synchro hub, I'm wondering if someone installed a a rusted one into the tranny in the past, it looks out of place with the rest of the tranny. The synchro sleeve looks great but the hub and insert springs are a mess, I thought the hub was worn but it looks like really bad pitting. :shock:
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Re: Synchronizer wear

Postby 41jeeps » Mon Apr 26, 2010 2:11 pm

That hub and shifter plates are definitely completely worn out :shock:

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.
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Re: Synchronizer wear

Postby Ben Dover » Mon Apr 26, 2010 3:20 pm

I understand.
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Re: Synchronizer wear

Postby Greencom » Mon Apr 26, 2010 11:51 pm

41jeeps,
That's great description of synchronizer function, you are better at putting it all into words than I could. I learned all about being my own manual synchronizer (double clutching) by driving my 1930 Ford Model A, it cannot be driven without double clutching either going up or down in gears, the owner's manual even explains the procedure, I can do it almost without thinking about it now, after studying transmission design and function I can visualize what is going on inside the gearbox now which makes learning what the synchro has to accomplish and how it does it. I'm ordering a new synchronizer assembly, blocking rings and new poppet springs for the shifter rods. I hope to be on the road again with a fresher tranny and new throwout bearing, man I'm getting too old for all of this but there's nobody around me that works on ancient Jeeps near me. Thanks to everyone for the advice and time you have given me.
Bob R
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Re: Synchronizer wear

Postby 41jeeps » Tue Apr 27, 2010 11:49 am

A Ford A has about the same gearbox as the GP.
So you are well prepared for if you would ever become a GP Jeep owner 8)

Double clutch gearboxes are fun. :D
I used to drive a Mack twin stick with splitter.
The clutch got barely used, actually it was only used to start from a stop.
There was a Jacobs brake system that was pretty convenient on a steep up hill.
No one wanted to drive the Mack as all other trucks in the company had synchronized gearboxes and all other luxury.
I was crazy about it and would not trade it for a European truck mostly for the brilliant gearbox and engine brake system.
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Re: Synchronizer wear

Postby Greencom » Tue Apr 27, 2010 3:21 pm

Slat grill MB parts are expensive enough, I wouldn't want to buy GP stuff.
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Re: Synchronizer wear

Postby Ben Dover » Tue Apr 27, 2010 5:42 pm

Remember, Synchronizer Blocking Rings wear as well as the mating cone surface on the Main Drive Gear and the 2nd Gear. If the front face of the toothed portion of the Synchronizer Blocking Ring contacts the face of the corresponding teeth on the Main Drive gear and the 2nd Gear, the Blocking Rings are worn and should be discarded9there ssould be a slight gap). To test the effectiveness of a blocking ring, it should not be able to be turned by hand when it is twisted against the tapered surface of the M.D. or Second Gear, if you can spin it under pressure, discard the synchronizer blocking ring.
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Re: Synchronizer wear

Postby 41jeeps » Tue Apr 27, 2010 10:04 pm

Synchronizer Blocking Rings wear as well as the mating cone surface on the Main Drive Gear and the 2nd Gear.

That's correct, when the cone on the gear has wear one can feel the uneven surface caused by the oil grooves inside the blocking ring.
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Re: Synchronizer wear

Postby Wolfy » Fri Sep 10, 2010 7:42 am

Folks,

I just rebuilt my T84 and put in new Synchro hub, plates and springs. Sleeve was ok.

When I try to simulate a gearchange the outer hub of the synchro wont hardly move from side to side. Is this normal?? Should the blocking rings be hidden under the sleeve on changing?

I put the gear lever on and tried and it popped the main shaft out the back. Can I assume that once the transmission is back in the Jeep that I will be able to shift normally? I was able to change gear ok on the bench before the rebuild but is it the case that everything is much tighter after a rebuild?

Please advise Thanks :)

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Re: Synchronizer wear

Postby 41jeeps » Fri Sep 10, 2010 3:05 pm

As you popped the main shaft out of the back it is advisable to check the main drive roller bearings before putting the gearbox back.
There is a good chance they fell out there place.
It is normal that the clutch hub is tighter with the new parts.
But there are longer shifter plates out there that can give you problems.
When everything is back together, check if the blocking rings sit loose in neutral.
It is normal that the blocking ring from the selected gear sit under the clutch hub.
Other than the drag from the cork seal the gearbox should turn free in any gear.
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Re: Synchronizer wear

Postby Wolfy » Sat Sep 11, 2010 8:52 am

Thanks for your reply, I've replaced the rear bearing with a new one I just needed to tie it down as the bearing was popping out.

The blocking ring towards the front of the box turns forwards and backwards ok (obviously not all the way round and only a bit as it locks in the cut outs for the plates) and with force I can cover it with the outer ring.

The ring to the rear seems to be the problem and is very tight, I cant move it and it looks like its slightly out of line with the teeth on the outer synchro ring. When its under load will it be more likely to move?

The shifter plates are the same size as those removed, presumably as the dealer I used sells lots of them they are ok...

Thanks
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Re: Synchronizer wear

Postby Ben Dover » Sat Sep 11, 2010 9:04 am

If the edge of the teeth on the blocking rings contact the edge of the corresponding teeth on the gear they mate up with, they are worn out. The blocking rings are like brake shoes and stop the gear from spinning during shifts if you can turn the blocking ring while it is on the tapered portion of the gear, it is worn out and no longer effective.
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Re: Synchronizer wear

Postby 41jeeps » Sat Sep 11, 2010 2:14 pm

Both synchro rings should sit loose when in neutral.
This picture shows a good shifter plate and a longer one that give problems.
The only way to find out if they are right is to measure them.
shifter plate differences.jpg
shifter plate differences.jpg (185.86 KiB) Viewed 671 times
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Re: Synchronizer wear

Postby Wolfy » Sun Sep 12, 2010 9:12 am

Interesting, thanks. My old plates measure .747 of an inch, I cant check the new ones without removing.

Guys below is a photo of my box, it would help me if you could answer one question....you can see the gold coloured Blocking rings either side of the Synchro sleeve, should I be able to move the sleeve over the rings easily by hand as it is or is it normal for it to be too tight after a rebuild using new synchro rings, hub and countershaft washers? I'm hoping with the shift lever connected it will work.

Image

I think I'll hook it up to the Transfer box and try shifting it....

Thanks
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Re: Synchronizer wear

Postby 41jeeps » Sun Sep 12, 2010 10:49 am

The poppet ball and spring will not allow easy movement.
You will need a lever to shift it.
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