Synchronizer wear

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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Greencom
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Synchronizer wear

Post by Greencom » Sat Apr 24, 2010 8:41 pm

I started my throwout bearing replacement chore, I decided to remove the transfer case first then the tranny, the transfer came off with no great problem but I wasn't quite careful enough and the tranny shaft came out part way along with it, at first I was upset about it but upon looking at the tranny's guts I noticed that the synchronizer hub's splines are rather chewed up looking so It has to be taken apart anyway. What would cause the hub's splines to get like that? When I drove the jeep the only trouble that showed up was going into second gear, it went in smoothly but if you move the stick a little too far forward a bad grinding can be heard. Anybody know how a synchro gets like that and how it causes the noise after it already is in gear? I am going to upload some pics of it later. Thank you for your time.
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Re: Synchronizer wear

Post by Lew Ladwig » Sat Apr 24, 2010 8:55 pm

Very often when a tranny is rebuilt, the input an output shafts look fine. What is not noticed is that the roller bearings between the two wear out. From a visual inspection you can't tell. But the two shafts are worn. This then causes poor alignment of the 2nd gear and syncro. Much of the root cause of poping out of 2nd and rapid wear on the syncro. I would take a carefull check of these parts. You would need a mic to measure them.
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Greencom
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Re: Synchronizer wear

Post by Greencom » Sat Apr 24, 2010 9:25 pm

Thank you, it looks like I'll need more than just a synchro.

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Re: Synchronizer wear

Post by 41jeeps » Sat Apr 24, 2010 10:46 pm

Let's first have a look at the pictures :wink:

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Re: Synchronizer wear

Post by Ed Menees » Sun Apr 25, 2010 2:33 am

While we are talking about synchronizers, Does anybody sell a synchronizer that can be shifted into second at a reasonable speed without grinding a little. I know they can't be speed shifted and need to be double clutched when down shifting at moderate speeds. I always replace them anytime the tranny is out but they all have to be shifted very slowly to not grind a little. Third gear can be shifted very quickly with no grind. Next time (hopefully a long time from now) I'm going to swap the 2nd and 3rd blocking rings and see if it's actually the synchronizer or just the way it is.
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Re: Synchronizer wear

Post by Joe Gopan » Sun Apr 25, 2010 5:04 am

Beas longevity medicine for the T-84 or any Jeep transmission is to avoid double clutching downshifts or and downshifting for compression braking, it eats up the synchronizer blocking rings and is equally tough on the 2nd gear bushing which causes premature wear and eventually the jumping out of 2nd that many experience. Best to just let up on the gas or use the brakes more often. The blocking rings available today do not seem to have the quality of the original Borg Warner brand.
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Re: Synchronizer wear

Post by 41jeeps » Sun Apr 25, 2010 11:02 am

When understanding how a synchronizer works one knows that the gearbox should be shifted smooth.
95% from the mechanics do not know how it actually works.
It is a very ingenious system 8)

A good synchronizer will not allow the gearbox to grind, fast or slow shifting.
As Ben said, the "good" ones are scarce.

Double clutch a synchronizer gearbox does not harm, if the operator knows what he is doing.
Shifting without using the clutch is murder on a synchronized gearbox, while it is common practice on unsynchronized gearboxes by those that have enough miles on them.

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Re: Synchronizer wear

Post by Ed Menees » Sun Apr 25, 2010 11:15 am

I would love to fully understand how a synchronizer works. I don't understand how a "good" synchronizer prevents engagement until the two gears are at the same speed. I imagine that it has to do with the dogs, spring pressure and centrifugal force. This would be a good place for someone to explain it.
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Re: Synchronizer wear

Post by Joe Gopan » Sun Apr 25, 2010 11:36 am

They act as a brake to stop the MC and 2nd Speed Gear from turning when selecting 2nd and 3rd Speed.
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Re: Synchronizer wear

Post by Greencom » Sun Apr 25, 2010 12:44 pm

Double clutching actually keeps the synchro from wearing out by matching the speed of the gears manually instead of the synchro having to rub against the gear to speed it up of slow it down.

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Re: Synchronizer wear

Post by Joe Gopan » Sun Apr 25, 2010 1:10 pm

Not on the small Jeep Transmission, it won't take the pounding, it is not built for the extra shock of dropping into second or low. The drivers that baby theT-84 enjoy many more happy miles that those who do not.
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Re: Synchronizer wear

Post by Greencom » Sun Apr 25, 2010 6:53 pm

When I mean double clutching I mean at a reasonable speed that would be normal for a particular gear, like downshifting from third into second at around 20 MPH, not to slow the jeep down but to get going again after a slowdown. I don't double clutch to shift faster, I do it to help the synchros, that IS babying it, the synchro does not have to work, just lock the gear to the shaft. Anyway here's a couple of pics of the synchro hub and the inserts, notice the hub splines look kind of rough and the insert at the left is partially crushed.
Image
Image

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Re: Synchronizer wear

Post by Joe Gopan » Mon Apr 26, 2010 3:42 am

Years of moisture and neglect, there is a reason for timely checking gear box level and scheduled draining. What do the rest of the gears look like, how do the shafts fit, and are the thrust areas worn?
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Re: Synchronizer wear

Post by gearhead » Mon Apr 26, 2010 5:23 am

Moisture, oh yeah. How many of us have found as much water as lube in the trans, transfer and axles!
The old car rule applies, 3=1, average of three used trans etc. to get enough good parts, and still need to buy parts kits.
Any pitting like shown on internal parts gets replaced. Use any marginal parts and they will wear other things with the debris generated.
I have taken manual transmissions apart that looked Ok from the top and the cluster gear was trashed from water in the case.


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Re: Synchronizer wear

Post by Joe Gopan » Mon Apr 26, 2010 5:36 am

And it is not wise to use old gears from transmisions that have gears with broken teeth, there is danger that the teeth on mating gears have been weakened.
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