901 vs 915 Tranny

[vujade]

What are the differences between the 901 & the 915 trannies?

Does the 915 have the same shift patter as the 901?

[jhelgesen]

fogot to put in my email, 901 and 915 have diffent patterns, which also means different shifters.

[chigger]

Here is slight overview on the differences.
The 901 is not much bigger or stronger or heavier than a bugs tran, uses the same CVs and axles. The front mount is different and the rear is close to a bugs. Clutch operates as a push instead of a pull.
The 915 is a different animal. There are three different models and they are heavier, stronger and longer than a bugs. The clutch operates the same as a bug, but the cable goes into the bottom and not the top. The CVs are 930 fine spline and require custom axles to mate to a bug CV. The case is the same width as a bug. The rear can be modified to use bug mounts , but the front has to be custom.
Getting a trans with the right gear ratios is the most important item as they are very expensive to change. The clutch flywheel combo is based on the engine you use, however both require the use of a Porsche starter or an VW autostick starter (much cheaper with the same part number).
The bug shift coupler will bolt up.
Due to the differences in the trans I would say they are about same difficulty to install. I would rate it a moderate modification with welding and fabrication skills needed.
Michel Ghia's site has been very helpful.
My configuration is a 911/901 (915) with a padded offroad rear mount (so I would have some thing to bolt my Kafer bars to), custom front, reversed bowen tube clutch release, redrilled to 915 CV flanges, 914 clutch and pressure plate, thing shift rod bent to mate to the trans shift rod, and a Scat dragfast with modified reverse lockout plate to allow first gear with a locked out reverse. It took longer to run a new fuel line down the tunnel than it did to modify the trans. Hope it helps.

[Shad Laws]

Hello-

The 915 is a different animal. There are three different models and they are heavier, stronger and longer than a bugs. The clutch operates the same as a bug, but the cable goes into the bottom and not the top. The CVs are 930 fine spline and require custom axles to mate to a bug CV.

Not true. *Some* had 930 flanges, but many had 915 flanges. A 915 CV is the SAME bolt pattern as a T2/T4/944 CV, only with different splines (and different internal parts). So, while the 915 CVs themselves are fairly useless, their flanges are perfect.

Also, you can get the earlier 915-sized flanges and put them on a later box.


The case is the same width as a bug. The rear can be modified to use bug mounts , but the front has to be custom.
Getting a trans with the right gear ratios is the most important item as they are very expensive to change. The clutch flywheel combo is based on the engine you use, however both require the use of a Porsche starter or an VW autostick starter (much cheaper with the same part number).

Or, an IMI high-torque starter. For $180-200, you'll never burn up a starter again. I went through 4 automatic VW starters before I learned :-).

Take care,

[kdanie]

I bought a 915 a couple of years ago to use with my type 4 but sold it when I realized the clutch setup alone would cost $500 and the 930 CVs/axles/stub axles was another $500 on top of the $800 I spent on the trans. Big $$ but bullet proof, certainly not necessary for my little 125hp!

I then bought a 902 from a '69 912 for $200, just like a 901 but with slightly different gear ratios. I thought it would have type 1/901/914 size drive flanges but it also had 930 size flanges! I picked up a pair of 914 flanges and I'm back in business. My 914 clutch/flywheel/release bearing work well. The 915 included a Porsche starter so I kept that too.

The reference chigger made to the clutch actuation can get confusing, VW's/914/901 use a push type clutch- that is the release bearing pushes on the pressure plate to release the clutch disk. 915 trans use a pull type clutch-the release bearing is attached to the pressure plate and the arm pulls release bearing that pulls the pressure plate to release the clutch disk. These references have nothing to do with the clutch arm and the way the cable acts on the arm. Now to confuse things more, I understand the 912E used a 923(?) trans that is like the 915 but uses a 914 style clutch (push). Pretty rare and I have not seen one in person.

I did some careful measurements and found my 914 clutch/flywheel would not work in my 915 trans. It would require a custom flywheel from Kennedy eng. I have heard that someone converted a 915 to use a 901 clutch arm but I don't remember who.

We still haven't talked about the 911/01 trans, it's a mix of the 901 and 915 for '70-'71 only. As I understand it, it's a 915 with a 901 bellhousing so it's a good way to go but much harder to find.

So, to answer some of your questions: 901 trans sell for $200-$1000 depending on condition and your luck. I was very lucky. 915 trans sell for much more- $600-$2000 depending on condition. What to look for? Well, be sure you know what drive flange size you are getting so you know how expensive the rest of the parts will be. Check the oil for metal and hope for the best.

ken

[Shad Laws]

Hello-

The reference chigger made to the clutch actuation can get confusing, VW's/914/901 use a push type clutch- that is the release bearing pushes on the pressure plate to release the clutch disk. 915 trans use a pull type clutch-the release bearing is attached to the pressure plate and the arm pulls release bearing that pulls the pressure plate to release the clutch disk. These references have nothing to do with the clutch arm and the way the cable acts on the arm. Now to confuse things more, I understand the 912E used a 923(?) trans that is like the 915 but uses a 914 style clutch (push). Pretty rare and I have not seen one in person.

You are correct about the 923. I have one of them in my T3 - it's a nice thing to have :-).


We still haven't talked about the 911/01 trans, it's a mix of the 901 and 915 for '70-'71 only. As I understand it, it's a 915 with a 901 bellhousing so it's a good way to go but much harder to find.

Not quite.

Beginning in Aug. 1969, Porsche did use an updated transmission from the 901 called the 911. However, it is basically a 901 with a slightly reinfornced casing. Not *that* huge of an improvement in the durability/strength/etc. department, but notable nevertheless.

The 915 (which started in Aug. 1971) is a _totally_ different animal. It is _not_ based on the 901, but rather on the 916 racing transmission. The shaft center-to-center spacing is perhaps the biggest difference - it is 76mm instead of 68mm, making larger, stronger, and more durable gear fitment possible. The bearings are significantly larger and have significantly more reinforcement, too.

The 1976 912E, with the 923 transmission, is based on the 915 transmission. However, as pointed out, rather than using a 225mm pull-type clutch, it uses a 215mm push-type clutch from a 914, making it one of the perfect transmissions for a T4 engine.

Take care,

[MdR]

Originally posted by Shad Laws

We still haven't talked about the 911/01 trans, it's a mix of the 901 and 915 for '70-'71 only. As I understand it, it's a 915 with a 901 bellhousing so it's a good way to go but much harder to find.

Not quite.

Beginning in Aug. 1969, Porsche did use an updated transmission from the 901 called the 911. However, it is basically a 901 with a slightly reinfornced casing. Not *that* huge of an improvement in the durability/strength/etc. department, but notable nevertheless.


A useful difference between the 901 & the 911/01 is that the latter has a bellhousing similar to a T1 in that, unlike the circular 901 (or 915), it has 'flats' cast in (just like a 914/4) to allow easier fitment of the rear hanger.
This is a good thing.