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Toploader thoughts...

December 3 2017 at 2:04 PM
John  (Login jetstuff)

Response to O/T, catastrophic trans failure redux.

A few thoughts on your trans from a guy whose built more than a few...

1st, spinning the trans to 7K in first gear wouldn't cause first gear to seize on the mainshaft, because when the shifter is in 1st, first gear is already locked to the mainshaft by the sliding ring.

2nd, I've used a lot of the currently produced parts, and never had a clearance issue where I had to modify anything due to out of tolerance parts.

My thoughts on what went wrong?

It's hard to tell without having the trans in front of me, but I'd look real close at what's left of the blocking ring and the syncro assembly. If the 1-2 syncro assembly is assembled or installed wrong, you can have a situation where the blocking ring is constantly forced against the cone on 1st gear. From the looks of your 1st gear it looks like the synchronizer cone got real hot, which could cause either the lubricant film to break down or the gear to bite the shaft and gall, then seize. Once 1st welds itself to the mainshaft, If the trans is in any other gear it will lock up and push the cluster sideways, splitting the case just as yours broke.

If the failure was caused by out of tolerance parts (another possibility) I would expect the whole gear to show some heat discoloration , not just the syncro cone.

If the gear wasn't lubed properly on assembly, you could also cause damage to the gear or mainshaft bearing surfaces the first time you moved the car( before enough gear oil got between the parts). Once there was surface damage, the trans would fail in short order.

I've seen gears weld themselves to the mainshaft before, but it's usually second, and it's usually in endurance applications(road racing) where you can be in second under power extensively. Gears that are bronze bushed are available for these applications, in fact, I think the 67 Shelby transmissions (RUG-S) boxes were built with a bushed second gear from Ford.

I guess what I'm saying is that I can't imagine what you could do as an operator (driver) to cause a properly assembled toploader to fail like this. Generally, driver abuse results in beat up syncro teeth, a broken mainshaft (about 6" past the rear bearing), or a twisted input shaft.

JMHO (as always,)


This message has been edited by jetstuff on Dec 3, 2017 2:06 PM

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