Fitting a 915 Porsche transmission hasn't been covered very well on the web but I plan to have a go anyway!
I have chosen a 915 due to its strength in standard form and its conventional 5 speed shift pattern. The particular one I have gone for is from a Porsche 911 SC. This came with a pull type clutch and type 2 sized CV joints. I am going to use 944 drive shafts and CVs to mate up with the rear suspension which will be converted to IRS using 944 parts. Due to all the extra height I have above the engine and trans I am going to raise them in the chassis, I will use the standard hole in the chassis for the gear selector rod so I will not have to modify the chassis in any way, the selector rod exits the 911 trans at the bottom of the nosecone instead of the top as with the beetle, this is the amount I will raise the trans by.
I'm not going to use the Porsche front mount. I plan to make a bracket to use the stock Beetle rubber mount until I later also fit an intermediate mount from the case like the Gene Berg versions. |
Here you can see the clutch arm which is underneath the trans. |
I will be able to raise the trans by up to 8 inches if I want! Although I won't, I just want to drop the body over the engine, I will keep the same ground clearance as I find it is OK at 5 inches. |
The transmission raised into its approximate position. |
The body had to be cut away to allow it to be raised. |
First trial fit shows the bottom of the nose cone to be about flush with the top of the torsion tube |
With minimal cutting for clearance of the selector rod and reverse switch that protrude from the front of the nosecone. The stock front mount is in position here. I will make a bracket to go from the 915 to this for simplicity. |
A view showing how much higher the transmission will be. I plan to move it further forwards than shown with some more clearancing at the front above the torsion tube. It will be a lot of work to make up a new rear mount, going from the frame horns up to the Subaru mounts on the engine. I am not fitting the rear mount to the transmission with welded pads, as other people have done. |
The transmission is approximately 5 1/2" higher than standard... |
Here is the front mount once welded up. It is made of 5mm thick plate with extra bracing. With the rear of the transmission supported on a jack it all looks nice and centered. I will concentrate on the linkage 911 shifter next. The old rod guide tube needs to be cut out and a plate welded into the tunnel to support the new shifter base plate. |
These two are of the new KEP flywheel I just received to mate the Subaru engine to the 915 transmission. It uses the standard 911 clutch (which incorporates the ring gear). |
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Another one of those measure twice and cut once jobs! The top of the tunnel isn't wide enough for the base of the 911 shifter as well as the fact that this was the only way to remove the old shift rod with the body on as the guide is welded onto the underneath of the tunnel. If I'd known where the spot weld were I could have drilled them out... |
This will allow a bit of misalignment. The 911 rear shift coupling is adjustable in both length and rotation so I will fix the shifter assembly in the mid point of adjustment. Incidentally, I am using the shift rod completely unmodified. As the speedster is based on a shortened VW pan, it just so happens that my wheel base is very similar to a 911 now. |
I've started making up the engine cradle using the stock Subaru rubber mounts. Some 40mm square tube and angle welded onto it allows everything to sit nicely. I will next join the engine and gearbox and hoist them into position with the front mount now done. I will then create the rest of the frame going onto the frame in the car's body. |
Here is the new assembly. With the front mount supporting the transmission almost exactly level, the bottom of it indicates the new lowest position of the engine sump. |
I made up a new base plate for the 911 shifter and here I am checking for size and clearance, next step is to weld it into the tunnel. The threads that hold the shifter in place are tapped into the plate, an alternative would be to weld nuts underneath. |
Here is the shifter in place and everything seems OK. This is just a dummy shifter I am using for sizing etc, the correct one is being sourced. |
Here is the plate welded in position and finished in POR-15. The front and back of the tunnel have been 'pie-cut' and tapered down to the new top for a neater appearance (even though it will be covered in carpet!). |
915 clutch in place, fitted to the KEP flywheel. |
Getting the engine into place wasn't as easy as I had hoped! The Chesil has a frame which goes around the back of the engine bay and there is only a couple of inches clearance between this and the alternator belt. This meant that with the extra length of the shift rod I couldn't get the gearbox and engine assembly into place. The final solution after much swearing was to cut out the back section of the frame and make it removable with a new bolt in section. |
This is the right hand side of the new engine mount. |
On the left side I moved the vertical inwards to allow more space for the exhaust system. |
Here is the finished frame, I have now painted it so it lasts. Note I have triangulated all corners for extra rigidity. |
A few pictures above you can see that the right side deck lid hinge would foul the intercooler in its new raised position. So I extended it to the side, the base part of the hinge had to be kinked as the bulkhead is not flat all the way across. |
I still need to do a bit of fitting but it's more or less in properly now. |
Thankfully with the engine cradle vertical pushed across, I haven't had to modify the exhaust at all apart from putting a bend in the outlet of the muffler. |
The K&N filter now pushes through the engine bay above the rear frame. I will make another shield for it. |
Hopefully I will be able to fit my battery back here! I will have to remake the complete area though. The base of the rear seat will be raised too. |
I received the proper aluminium towered 911SC shifter today, from Mike Ghia. It is incredibly precise and has a reverse lockout so you can't accidentally go into it from 5th on a downchange. The one seen in earlier pictures was kindly lent to me by Simon at Pro-9 Porsche breakers. |
I had to fit the clutch cable with a small amount of pre-tension due to the smaller stroke of the VW pedal. Now that the engine and trans are out again for the trans rebuild I thought I would take the opportunity to extend the pedal to solve this annoying problem... Here you can see the extended version, the pivot centre has been increased by just over 10mm |
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Time for a rebuild! The synchros were knackered and if
I was ever to truly realise the potential of the car the transmission
had to be rebuilt...
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Here it is all going back together... |
5 synchros, 2 selector sleeves and various other parts adding up to £750 were fitted before re-assembly. |
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This guides the selector rod inside the transmission case. Lucky I did the rebuild now as this was loose and one of the studs had been broken off and was inside the case! Luckily, I managed to extract the broken stud with a bit of ingenuity and all is fine now. The car is much nicer to drive with positive and quick shifts. Oh, and a big thanks to Simon at Pro-9 who helped me and did all the tricky stuff... |