Synchronizer testing

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old_chopper
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Synchronizer testing

Post by old_chopper » Fri Jul 24, 2015 11:55 am

I developed an extreme duty transmission for the demolition derby crowd. They have troubles with breaking the cast cases so we designed a welded steel case using the heavy duty Muncie 3 speed internals. One I put together would not shift into first when the engine is running. It appears the synchronizer for first is wore out. Going forward I would like to check these before a customer has it installed in the car. Can you give me some advice on how to check the synchronizers? I do not remove the gears from the output shaft as they are a major pain.

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Baprace
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Re: Synchronizer testing

Post by Baprace » Fri Jul 24, 2015 6:59 pm

Did it shift into any other gears when running ? If no then the clutch is dragging, if yes the syncro is bad, If all the teeth look OK on slider and gear , I just hold gear in one hand and apply the brass by hand onto the gear, if it locks and looks like it has more room to go before it hits the gear face then it should be OK, a hand test on the inside of the brass ring is slide your finger in and out over the inside grooves, it should almost feel like it is shaving the skin off if your finger slides easily then the brass is probably no good. that's all I know.

ChevyEFI
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Re: Synchronizer testing

Post by ChevyEFI » Fri Jul 24, 2015 7:29 pm

On basic synchronizers, the 3 internal notches inside the slider push the keys (struts) into the blocker ring.

This pushes the ring onto the cone on the gear, matching its speed to the mainshaft. This allows the slider to push past the teeth of the blocker and mesh with the speed gear teeth without clashing.

You gotta look at the blocker to cone relationship; blocker could be worn past it's measurable lifespan. I don't know on the Muncie, but some models have bottomed out = replace. Others, you gotta break out the feeler gauges. Keep notes on the bad units and you'll find what generally works. And blockers are cheap all things considered.

Try and keep the slider to hub relationship the same. Make sure key springs are opposing (clockwise when you look at each, so opposite directions,) and starting from the same key (like 12:00)

And the joy of going through a unit a ham-fist rookie used a puller on, twisting the hub of the synchro is a whole other ball of fun.

old_chopper
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Re: Synchronizer testing

Post by old_chopper » Mon Jul 27, 2015 1:41 pm

I can't say if it would go into any other gear as they only use 1st and reverse. I don't think the cluth wasn't dragging, it would go into reverse fine. I have two that have proven to work, I'll pull one of them apart and measure the clearance on it versus the one that didn't shift. Fortunately we found this one before it was shipped to a customer.

old_chopper
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Re: Synchronizer testing

Post by old_chopper » Mon Aug 03, 2015 12:16 pm

I tore the trans apart and found the hardened steel dogs on the synchronizer drum were damaged. The friction cone looked good but I swapped it out for another. We built a "test stand" so we can spin the input shaft with an electric motor and test shifting the trans. I'll report back when I have the results.

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