901 transaxle shifting from 1st to second truths and myths.

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theKbStockpiler
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901 transaxle shifting from 1st to second truths and myths.

Post by theKbStockpiler » Mon Feb 02, 2015 6:20 pm

Hi, Is the shift from 1st to 2nd gear in a 901 all mental difficutlty or is part of it reverse is a straight gear with no syncro? If in 1st and you make sure you are in between 1st and reverse before going sideways, is it still easy to grind it into reverse? Is the 1st to second shift in a 901 harder than a (HI) pattern transmission going from 2nd to 3rd?

Thanks for your expertise!
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aircooledtechguy
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Re: 901 transaxle shifting from 1st to second truths and myt

Post by aircooledtechguy » Wed Feb 04, 2015 11:11 am

There's two reasons for the slight "grind" shifting into reverse:

1. There is no syncro on the reverse side of the 1st/Rev slider/gear. Half of each gear set is solidly mounted to the main shaft and spins at engine speed. Syncros and the brake bands in all other gears allow the half of each gear set that is floating on the main shaft via bearings to monetarily match speeds so the syncro teeth can engage the sliders teeth mounted solid to the main shaft and thus locking the floating gears to the main shaft via the slider. When you depress the clutch, it allows the main shaft to UN-torque from the motor and spin freely so everything can match speeds via the brake bands and the syncros. I know that this can be a bit confusing to read without actually seeing it in action so you may want to read that again. :wink:

2. On the reverse gear it only has the straight cut teeth which must engage the reverse idler gear. These teeth on the Rev/1st slider have a cone profile on the edge to aid them in sliding into place and engaging the reverse idler gear.

With both of these conditions happening, it's easy to understand why if you push in the clutch and slide it immediately into Reverse, you will sometimes here a "grind" as the two gears mesh.

As for the 1st to 2nd shift, if you feel a slight "grind" as you shift into second, that is due to the brake band being worn on the 2nd gear syncro. Since this is worn, it can't match speeds as well causing the syncro teeth to jam into the slider teeth which in time rounds them down. So it leaves you with a worn 2nd gear syncro AND equally worn 2nd/3rd gear slider.

If you think you have a trans that is in need of rebuilding, I highly recommend picking up a spare trans on Craigslist for a couple hundred bucks. The internal parts are expensive(!!!) but with a spare trans you will likely have most everything you need. You can use 2nd-5th gear syncros on the second gear. They can also replace the 1st gear syncro provided you use the 2nd-5th gear brake bands on 1st. The 2nd/3rd slider is the same as the 4th/5th slider. The 901s are good boxes, but I would still count on having to replace the 1st/Rev slider (which is about a $550 part alone!!). This slider however is a literal marvel of machining and you'll soon see why it cost to much. :lol:

Hope this helps. . . Good Luck!!

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Re: 901 transaxle shifting from 1st to second truths and myt

Post by theKbStockpiler » Wed Feb 04, 2015 1:55 pm

Thanks for your expertise! :D

I read experiences with people putting the 901 in a beetle; which are my plans as well, and they all sound like it's impossible to shift the car to 2nd from 1st without grinding it.

My transaxle came from a rust bucket 1.7 so hopefully it has not been abused. :D
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Re: 901 transaxle shifting from 1st to second truths and myt

Post by aircooledtechguy » Wed Feb 04, 2015 4:12 pm

No problem; glad to help.

If your trans is out of a 1.7L 914, you are going to have to convert it to the 911 configuration using 911 shift rod set and the 911 nose cone & mount. This is the time to go through the box and refresh the worn parts anyway. Believe me, they ALL suffer from the same issues mentioned above. A lot of those issues went away with the 915 trans.

If people are having shifting problems there's a couple things that they probably did/didn't do.

1. They didn't rebuild the box before it was installed, so they inherited all the shifting ailments of the last owner. Not the 901's fault; this is common with cheap (myself included) VW owners. :wink: :lol:

2. You can introduce a lot of shifting problems depending on how the trans is installed. I learned this all too well when I installed the 923 5-speed out of a '76 912E into my '67 Squareback. Many, many issues had to be addressed due to how I decided to install it in the car. It took 4 months and countless re-configurations and re-designs before I fully identified and understood the problems I had created by the install and how to overcome them. When you get it right, it shifts like a factory Porsche and nothing is sweeter!!

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