Tranny Rebuild - Serious Questions

[Wrecked944]

Okay, all kidding aside, I have this 1974 tranny mostly disassembled and it occurs to me that the casing is painted (?) a bronzish color. A small amount has scratched off over time and revealed bare metal underneath. Does anyone know why this thing is coated or painted or whatever? Is it important and should I have it repainted?

Oh yeah, and I also noticed that a number of the nuts are very difficult to remove (especially the 12mm nuts that hold the input/output shafts to the differential case). The nuts were in areas with very little clearance. I was able to remove them with a combo wrench slid in sideways but...how in the world am I going to re-torque them properly on re-assembly?

Oh, and lastly, I know this tranny is supposed to be made of magnesium....so is the entire thing magnesium including the shafts, gears and synchro-teeth? And what about the nuts made of? I was thinking of putting new hardware all around but I am suspecting that I can't just run down to Home Depot and buy a bag of 13mm nuts. Do I need to get special hardware from some obscure German source (not that there's anything wrong with that)?

[JWest]

Only the case is magnesium. Magnesium is very light - lighter than aluminum, but it corrodes quickly. That is why there is a coating (I assume) on the case. Mag has been run bare on VW engine cases and trans cases for years with no protection - if you keep salt off of it it will just look dull gray and does not really need a paint or other coating.

The gears and shafts are steel. The nuts are steel also. I have only rebuilt 901 transmissions - the mag cased 901s have funny nuts with what looks like a helicoil in it. I have never seen nuts like that anywhere else. I don't know that continued with the 915, but either way you should be fine just getting 8mm -1.25 nuts from any fastener supplier. The magnesium is much weaker than even the cheapest nut you may get. Just reuse the originals if they are not rusty, though.

James

[724doorE]

Bare magnesium corrodes faily easily in the elements so some people will paint the engine case or trans housing for protection. Usually a clearcoat so it doesn't look goofy?

If you can't get your torque wrench on the nut/bolt, you must simply use your best judgement. Make them, by feel, as tight as others of a similar size you already torqued. Only the case is mag, the shafts and gears are different grades of steel alloys(based on application and strength/loading). As far as replacing hardware, I'd suggest you find a local business that specializes in fasteners. They will surely have all the funny (to you) sizes and the price will be pennies compared to buying them elseware.

Hope you kept track of any shims and the general tolerances of the various parts like gear clusters.

Others will chime in and shed more light for you.

Good luck.

[Jim Sims]

As I recall the only internal 915 fasteners one must replace per the factory shop manual are the helical lock washers under the 12mm nuts and the pinion shaft (output shaft as you call it) flange nut. I would order OEM parts for these to ensure you get the correct, quality parts. Yes, it is impossible to get a standard torque wrench with a socket on some of these 12 mm nuts that secure the bearings to the transmission housing. The use of a crowsfoot wrench on the torque wrench (with suitable reduction in torque value) allows a couple more of the nuts to be torqued but as I recall five of them just have to be tightened by feel based on the feel of the the torque wrench on the other nuts. Besides the standard recommendations of replacing brake bands, synchro rings, dogteeth, operating sleeves (some say to replace the anchor and energizer blocks too) one should also check bearings, thrust washers, and the forks which move the operating slesves. Be careful you do not mix up the needle bearing cages and races and don't lose any needles; the needle located at the cage seam is really easy to lose. Also, replace every seal and gasket while you're in the transmission. The factory coated (sprayed?) the exteriors of the magnesium transmissions with various types of preservatives: some are like wax or tar like. The factory shop manual recommends these coatings be renewed to retain corrosion protection. Cheers, Jim

[Wrecked944]

Holy Cow !! I can not thank you guys enough for this info. The depth of knowledge and generosity on this bulletin board always exceeds my expectations. I wish I could invite all of you guys over for some German beer !!

Thanks again,

[pwd72s]

Janus? We wish you well...