rebuild 901 vs. 915 conversion

[RandyWebb]

Hayden et al.

Do you happen to know the actual length of the shift tubes?

I've got one that I'd like to ID.

Thanks!

[Hayden Burvill]

Randy,


The 915 version Porsche # 911 424 020 00 is 867mm +/- 1mm overall length.

From recollection, the 901 version is about 15mm longer and can not be easily confused when checked with a tape measure.

Regards

Hayden

[RandyWebb]

Thanks Hayden.

BTW, I am assuming that the 911 type tranny (as used in the 1970-71 cars) uses the 901 type longer shift tube (?)

[Hayden Burvill]

Randy,

That is correct, the part # above started with the 915 transmission. I would assume the 911 trans uses the 901 version.

Regards

Hayden

[nick-moss]

Hayden

Am I right in assuming that you can use a 915 instead of a 901/911 box without changing the shift tube if the 915 gearchange linkage is used?

[Hayden Burvill]

Nick,

It can be done, I am pretty sure Sherwood has that combo of parts, - Sherwood??

If the coupler can be correctly adjusted, the install might be OK. The potential problem is that if the coupler can not be correctly adjusted, you have to remove the engine / trans to swap the tube.

With a 915 installed with a 901 shift tube, the coupler will have to be inserted completely into the section where the pinch clamp is located.

The normal position of the coupler with the 915 tube allows adjustment both forwards and backwards of the lever position.

The 901 tube, with a 915 transmission is going to have very limited adjustment to move the lever forwards. It might be that the lever can not even be located in the O.E. intended position, where the lower section of the lever is vertical when the transmission is in neutral.

If you look at the coupler of a 901 car that has a 915 transmission upgrade (sic) and the splined stump of the coupler is pushed all the way into the shift tube, then look at the shift lever and see it seems to be part way towards 4th gear when it's really in neutral, then it's a fair bet that the 901 shift tube is still in the tunnel.

Success not guaranteed with the 901 shift tube, but you might be lucky - might be frustrated...

Regards

Hayden

[admin_old]

Nick,
I've noted Hayden's keen observation on the differences between 901 and 915 shift tubes. I can only speak from my experience with my gearbox upgrade. I used the existing 901 shift tube and I have no difficulties shifting with the 915 shift housing using either the factory stock or factory short shifter. MHO, if one can install the shift housing with the lever sitting vertical while in neutral, there shouldn't be any shifting issues. If my 15mm shorter shift tube is preventing adequate shift coupler engagement with the shift tube splines, it's transparent (so far) to me.

Sherwood

[Hayden Burvill]

Sherwood, excellent picture to illustrate that point.

Your 901 shift tube is actually about 15mm longer - not shorter, so the spline engagement will never be too short. Rather the range of adjustment will be compromised.

Here is a pic of a 915 in a O.E. install, showing the relative position of the coupler and the shift tube.

From this position, the coupler could be inserted deeper, or retracted, offering fore and aft adjustment of the shift lever.

In the photo of your coupler, you can see that no adjustment deeper into the shift tube remains. This is the adjustment that would move the lever forwards, should it be required.

With variations in chassis dimensions, tube dimensions, engine mounts etc, etc. There is no doubt it will work in some installations. Hopefully from a thread like this, awareness of the potential problem will allow sufficient planning to avoid it.

Regards

Hayden

[admin_old]

HI Hayden,
Thanks for the nice comparative photo and the shaft length correction. I think we've got the definitive photos; it's the length that's in question. But armed with this info, owners can decide what direction they want to go.

Regards,
Sherwood

[nick-moss]

Thanks guys.

If I do the conversion I will post pics