915 tranny, late T3 car, big T4 engine, help!

[Shad Laws]

Hey Guys-

I was hoping you could help me out...

I have tabs on a Porsche 923 gearbox, which is a 1976 912E item. Essentially, it's a 915 gearbox that accepts 901-like flywheel, clutch, TO bearing, etc. (i.e. use 914 parts for a T4). This means I won't have a problem with the TO mechanism going the wrong way.

The car is a 1972 T3 Fastback, and the engine will be a new 2800cc 350hp+ normally-aspirated monster with our new cylinder heads :-).

But, I think I have some other problems... namely size and CV/driveshafts.

SIZE:
I know it's bigger than the 901. From what I've read in previous posts, it appears that the common solution on a T1 is to kill the torsion bar housing and use coil-overs as the rear suspension system. I'd like not to do that if possible...

A late T3 has no frame horns and (I think) the torsion bar housing is *slightly* more out of the way. Remember that the big automatic tranny fit in there without a hitch. Here's my thought: clearance the torsion bar housing as much as possible without killing it, then mount the tranny as far forward as possible, although likely still further back than the stock box. The engine will be pushed back a little, but that's fine. And, as a result, the CV flanges may be pushed a little further back than normal. Do you think I could get away with this? Would the angle on the CVs be too much?

CVs/DRIVESHAFTS:
The manual-tranny late T3 uses the same CVs and driveshafts as a T1. What options do I have? Would some options allow a higher degree travel and make it easier to get away with having the tranny located too far back? I'd prefer using the stock outside stub axles *if possible.*

SHIFTING:
The T3 has the access plate for the shifter on the bottom of the car, unlike the T1. Now I just make it into the shifter entrance point, too :-). I'm sure that after fussing with this for awhile, maybe adding a second U-joint, I'll be able to knock it out. Do you think that I could get away with using a stock shift rod and shifter and simply modify the blockout plate?

Thanks much for your help!

Take care,

[Alex]

I believe you can use the same driveshaft but you have to get T2 CVs.

Somebody back this up please.

Alex

[Wally]

Shad,
I cannot help you on all questions, but I have a 915 4 speed at hand from 3-'76. CV's of a type 2 cannot be used here unfortunately. Your 915/923 tranny will probably have the same dimensions. These CV's are about 110 mm outer diameter. Type 2 CV's are about 100 mm and bug CV's are 90 mm. Not a problem if the splines in the porsche CV's were VW like, but I heared they were not.
Michel Ghia said that you can use 914 stud axles (with 100 mm CV's so you can use type 2 CV's), but 'opening up' the tranny is not for the faint at hart. To boot, a porsche mechanic said to me that the stub axles of a 914 trans and a 915 trans are NOT interchangeble !?
Although I haven't done the mod myself yet, I understood that can can have drive axles made for you at reasonable cost, so one side would accept porsche splines and the other end would use VW splines. Ans you can than have them in any desired length.

The relatively (1 inch or so I believe) small change in transmission placement is not a problem. as I found out. I have placed a standard box 1 inch forward as an experiment to be able to use a porsche 911 engine. With a 2 ltr type 4 to it held out fine. The 911 engine never went on, because it wasn't approved of legally (should be 4 cylinders as stated in vehicle documentation). Would (just) have fitted though, but for the fan...

Good luck, keep us informed as I (we) are interested in your solution/choice.
Walter

[Alex]

If the CVs meassure 110mm then you should be able to use 930 CVs which are 110mm and you would need to get new stub axles from Erco or Weddle for 930 CVs.

Alex

[ricola]

There are two different spline types for the 915 transmission, I think it is the coarse type which allows swapping the flanges for type 2 CVs, this is an easy job that you could even do with the trans in the car!
You don't have to run coil-overs, you could cut the centre section from the torsion housing, move the splined inner sections outwards and use swing axle torsion bars (shorter) with the IRS spring plates...

Rich

[Wally]

Rich,
The last part about shortening the torsion tubes to swing axle length, is sooooo cleverly thought of! Thanks!!!!
Walter

[typ4boy]

shad you have the ideal box for vw installation, ihave 2 cars with 915,s installed, 1303 with 1974 mag case 915- cut the rear mount off clearence the torsion tube a little, to sit the box back. concerning drive shafts this is what i did to overcome the problem. remove the 915 drive flanges , replace with 914 901,s not 911 901 flanges, use 914 cv gearbox end your type3/1 axels and type 3/1 cv,s brake end. or while your at it replace the brake end drive flanges with 944 (early arms) these are direct fit on i.r.s type 1 /3 this uprates to 944 cv or type2 cv which have the same inner size as your typ3 axels, you even have cable clutch i had to hydraulic mine cause it was push to release insted of pull on all vw,s, ialso have 1979 bug with 1986 3.2 911 915 box same install as 1303. all the best Lee L.A.P