First post, noob here! Hello all and thanks for letting me in on your fun.
I have a 74 Super Beetle.... ok you can all stop laughing now. (914 someday, but for now I like my Bug) I am in the process of upgrading from a stock VW trans and a 12A rotary engine to a turbo 13B (~300hp and 250ft/lb of torque) and a 901 transaxle. I am sending some engine parts out for nidriding and I would like to get in as many parts as I can while I am at it that may benifit from the treatment. I am aware of the first gears lack of support and was thinking that having the drive and pinion shaft nitrided to make them less prone to deflection (I will still be gentle, not a drag car). I am a little worried about the diff since it's only a 2 spider and a Quaife is not in the budget. I think nitriding the diff housing should help reduce flex and keep the pinion gears fully engaged. I will probably have the pinion gears done as well. Now I'll admit that this is the first trans I have had apart and I am not familiar with what is prone to failure and what is fine for these power levels. In the Type 1 world you always hear the welded keyed 3rd and 4th, super diff, heavy duty side cover, etc. So if any one has some good info on how to beef up a 901 that would be greeeeat
PS anyone have a 901 nose cone from a 911 laying around???
PPS who ever had the red 914 out at the woodward dream cruise yesterday very nice, very clean, kick ass.

Thanks!

What made you choose a 901 over a 915? With that kind of HP you might want to look at a 915 trans with a LSD already in it, as the 901 trans' intermediate plate will flex if it's not a smooth increase in torque/hp. Once that plate flexes... you've bought yourself another trans. The 915 is more robust and was re-designed from the ground up to fix the 901's faults.

Interesting. I am not sure thatyou will notice or recieve any benefit by nitriding anything. The weak point in the trannt is the owner first, and then the other parts

Seriously, the pinion is not prone to losing engaugment with the diff unless the pinion bearing fails as is common with too much torque. 250ft/lb is near the believed top end of 300. The gears are hardly a failure point and are in no need of keying or anything due to the shaft having flutes for them already. I have seen teeth completely stripped from a gear and it still did not rotate on the shaft.

There are billet aluminum intermediate plates that are touted as fixing case flex issues, but IMHO I do not believe that they are necessary and have never seen a tranny with a failed intermediate plate.

Not sure what else to tell you, I do not know much if anything about nitriding things.

Brando, have you actually ever SEEN a tranny with a flexed int plate? I woudl be curious as that would make you the first out of everyone I know. The failure point is the pinion shaft bearing which is the part holding the pinion onto the diff. More tq = more side load stress ont eh bearing and KAPOW!

The plate needs to flex very little, if at all to facilitate this small movement.

Oh ya, We take all types

i dont think nitriding will help with torsional stiffness or longetudenal flex.
looks like it's for anti-wear and reduces stress factures.

good read here

Nitriding is a surface treatment. You could think of it as being something akin to case hardening. It does produce a hard, wear resistant surface but nitriding won't change the deflection of the parts you are considering nitriding.

Good luck with your project. It sounds like fun!

Regards,
Kevin

Thanks for the replys guys, I had a couple hourse over a pint of the black stuff to mull my plans over.

There are a few reasons I did not go with a 915. Costs 3X what my 901 ran me, 901 in a beetle is pretty straight forward and bolts right up to my adaptor kit and flywheel (not sure the 915 would even fit in the limited space), I think my clutch, tires, and CV joints, and fear will all give way before I hurt the 901.

If the gears and diff themselves are plenty strong then I am not worried about it, these are just typical weak points in the type 1 and get a bit stuck in my head as things to look to impove. I have a bad habit of finding failure modes the hard way. If I can pick some experienced brains I might save myself the trouble and hopefully find a workable sollution.

As to the intermediate plate... I have seen the billet numbers on ebay and thought about just making my own (got the machine shop and a billet of 6061 big enough sittin on the rack... don't tempt me) The way I see it the suspected cause of the plate flexing is due to the bearing pivoting in it's seat as the drive shaft flexes because the loaded gears are trying to push away from eachother. If the force is great enough to flex that plate then a more rigid plate would just flex less and cause the bearing to bind even harder. The gears may not disengage as much but I would have to assume that bearing damage would still be done and the bearing seat would get pounded out in no time. I could be totaly wrong though, wouldn't be the first time or the last.

kdfoust you are correct it is a surface treatment that alters the surface structure of the metal. I have read that nitriding will help lower the elastic modulus and increase tensile strength in the affected region. If that is ture it should reduce the ability of the shaft to deflect (like a three point tensile test). On the other hand I reeeeealy don't want to pull the whole gear stack apart...

Oh god my ramblings are gettin long... I'll stop now haha have a good one

Hey Man, they bearing in the plate gives long before the plate in my experience. Its much easier for the cage in the bearing to fracture giving the small amount of movement necessary for a catastrophic failure then to have a press fit bearing pivot. The bearings destruction I have seen, the plate flex I have not (yet). I am still open to someone telling me they saw it, had it, but the only people to claim that is happens are the ones selling the plates. If that is good enough for anyone then I have some Big Foot repellent to sell them that is gauranteed to work


If you want some internal pics, click the tranny service link in my sig line.

Did you just pick that tranny up from me a few weeks ago in Livonia?

Jake has had a lot of good things to say about cryo treatment, I think regarding bug transmissions though. It's probably cheaper than nitriding and couldn't hurt.

Keep in mind the affected region is likely to be only a few thousandths of an inch deep from the surface of the part. Not likely enough to be of practical significance. I'd have a discussion with my supplier to see what recomendations they would make based on the known failure modes.

Good luck,
Kevin

i thought the ultimate weak link is the case itself which there is nothing short of casting a new case to take care of the problem......


the billet plate only takes care of one end of the gear cluster...

DORIGTT
Yep that's me. Oh yeah as to cleaning the case, I soaked it in mineral spirits and tied it up in a black garbage bag on one of those 90+ deg days. The grime just drools away.


kdfoust
The tech guy at the place I'm using is really knowledgable and isn't involved in the sales side of things. I'll talk to him some more tomorrow when I drop my parts off. He did say he can go up to .010" deep. Any words of wisdom from people who know thier poo is always cool though.

I keep playing with the idea of running a dual stage boost controller an just cut boost way down in first gear. (limit switch, boost controller, and a 4 way valve would work)

Dr Evil I've allready been lookin through your pics as well as the tech stuff on Pelican parts. Thanks for taking the time to shed some light on the subject. You take a transmission for granted untill it blows or you actually have to pull one apart. It's funny I have a buddy that is an engineer at a big drivetrain development and manufacturing company. He has never taken apart or put a transmission together. He did give me a ride in a Porsche Cayenne Turbo though so I can't bust his chops.