5-Speed Tranny Cracks Under Pressure.

For The Second Time...

I blew the guts out of my first differential several years ago, my guess is around 1994. It happened while accelerating at a green light. At the time I took it as a fluke, shit happens, maybe a bad forging or something was left loose during the previous rebuild. Who knows? Later I was to find that there were other reported cases of this happening, mainly to X1/9 racers. This, and other reasons, where why the 4-speed was the tranny of choice for race cars.

Well, it happened again. Different green light, same results.

The light turned green, the clutch was dopped, a fraction of a second of acceleration ensued but was followed by a very loud bang and immediately followed by buzzing and grinding sounds from the gearbox. Luckily there was just enough momentum built up before the explosion to coast across the intersection. In my wake was left a trail of gear oil (that is still visible at that intersection) and a couple of metal fragments that were launched from the hole in the casing.

What appears to be happeing here is that the forging that holds the differential together breaks apart. This lets the pinion gears inside wedge themselves in the carrier resulting in huge expansion loads on the now two piece differential which blows the casing apart. There seems to be no warning, though my wife did make the comment that my tranny was making odd sounds the day before it blew. I didn't notice anything different from before.

Here's the speculation: The transmissions that are susceptible to this form of catastrophic failure are from 1987 cars. BOTH of the transmissions that I have exploded are out of 1987 cars. Two other cases that I know of were also in 1987 cars. This is looking like a trend. So if you happen to have a 1987 X1/9 with the original transmission, I recommend you keep those Autocross launches to a minimum lest you suffer the same fate.

The gruesome details of the explosion follow:

	Here's the view from below. Not good. I was reminded to look at the bright side of this situation, at least I didn't have to drain the gear oil to get the tranny out...
Here's the view from the trunk access panel. The only thing that kept that chunk of casing from falling to the ground was the speedometer cable.
	The carnage is clear with the transmission out of the car. The fractured differential is visible through the gaping hole in the casing...
And one more shot of the internal carnage for those who can't get enough of senseless violence and utter destruction. Note the pinion gears laying at the bottom of the casing...

To replace this transmission I had a spare 5-speed that I was going to go through and rebuild. But as luck would have it, a freshly rebuilt transmission fell into my lap recently. Several months ago I rebuilt a 5-speed transmission for a friend. New synchros, a couple of new gears and sliders, etc. Well, during our last big winter storm the car was left in a parking lot with clogged drains and was flooded up to the side scoops. The car was declared a total loss and I was fortunate to have the chance to buy it back from the insurance for let's just say the less than the cost of the parts to rebuild that transmission. Thankfully the water never entered the transmission nor the engine. That transmission is now in my car.

Now for the bad news, the car of which I speak is an '87...

If you're interested in what it takes to replace and rebuild a transmission, click HERE.

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