Whats it takes to break the main shaft in a 901 transaxle

[theKbStockpiler]

Hi, I might swap a converted 914 transaxle in a beetle and I'm interested in what circumstances the main shaft will twist in first gear. Let's say I use 195-65r15 tires and stock half shafts, would the weakest link still be the main shaft? I would never purposely dump the clutch at high rpms at a standstill because there is too much weight in the rear but is this the primary way the transaxle is damaged?

Thanks in advance!

[aircooledtechguy]

The main shaft will be just fine. People routinely plug Chevy 350s and even larger up to them without issues.

The only issue that these trannys have is that 1st gear is only supported by a bearing on one side since its in the nose cone. It will handle all the abuse an aircooled VW can give it. If you run above around 200hp, I wouldn't so dumping the clutch with wide tires, but your skinny tires with that much hp to them would just spin anyways. Most guys running really big hp motors don't even bother using 1st gear.

901s are good boxes that can handle whatever you can throw at them.

[theKbStockpiler]

I meant 'twisting first gear off the shaft' but thought it was connected to the main shaft. A 915 transaxle is nowhere to be found in my locale and are about 4 times the price of a 901 else where. I'm only planning on having 120 hp so I should be good.

[aircooledtechguy]

I meant 'twisting first gear off the shaft' but thought it was connected to the main shaft. A 915 transaxle is nowhere to be found in my locale and are about 4 times the price of a 901 else where. I'm only planning on having 120 hp so I should be good.

The internet "parrots" have again greatly exagerated and perpetuated wrong info. Hopefully I can clear this issue up once and for all.

1st/Rev gear will never twist off. That is not the issue. Since they are only suported on one side by a bearing, if you have crazy HP and dump the clutch, the main shaft and the pinion shaft will naturally want to be forced apart. So over time the bearing on the one side fails and gets sloppy. This in turn causes bad shifting and ultimately the destruction of the box internals including the intermediate plate.

Honestly, I would recommend searching for a 915 series box since this is not an issue and they are just a better box. Virtually ANY 901 box will need a rebuild before it can be used reliably. Count on $1k - $1.5k+ in parts alone plus labor unless you get really lucky. If you start with a 915 trans, chances are it's not in need of rebuilding and it has a modern 5-speed shift pattern w/5th and reverse on the right. Either way, you gotta pay to play. . . I'd rather end up with a 915 if I'm gonna pay. . .