[ND] a proposito della fragilità del cambio ND

[LupoTHP]

Sembra che la Walter Motorsports stia sviluppando dei cambi per ND "irrobustiti". Il tutto è ancora in fase di sviluppo e sperimentazione, in ogni caso propongono due step, qui di seguito quanto riportato sul loro sito:

NOTE: BUILT ND TRANSMISSIONS ARE AVAILABLE TO THOSE WHO NEED THEM NOW, BUT ARE STILL UNDER DEVELOPMENT. IF YOU CAN WAIT FOR OUR FINAL TWEAKS, PLEASE DO SO. IF NEEDING A TRANSMISSION IS TIME SENSITIVE, WE WILL BUILD YOU ONE WITHOUT THE FINAL UPDATES. IT WILL STILL BE SIGNIFICANTLY BETTER THAN OE AND PROBABLY ALL MOST CARS WILL NEED, BUT WILL JUST NOT BE OUR STANDARD OF A TRANSMISSION. 

Currently, we provide two options for ND transmission builds. Prices listed include a useable core exchange or rebuilding your current transmission. A core charge of $1000 is applied in addition if no core is provided.

Stage 1 - $1650 plus shipping
Stage 2 - $1950 plus shipping

Stage 1:
-Gearboxes are completely torn down, go through an extremely detailed qualification process, cleaned, and rebuilt, replacing seals, synchros, any failing gears/parts and are built with upgraded bearings.
-Modifications are done to improve oiling and cooling of problem areas.
-Machining is done to gear engagement teeth to improve gear engagement feel. Most race boxes get different engagement teeth timing to improve ability to shift for specific gears, so racing style and applications are important to disclose prior to rebuilds.
-Gear tooth machining to reduce temps, noise, and improve oil evacuation.
-Shift-bias modification for better shift feel and help to ensure proper gear engagement.
-Upgraded bearings to handle higher performance and higher speed applications.
-Stage 1 gearboxes are built using hardened bolts.  This provides a stronger and more reliable clamping force of the transmission case which results in maintained gear alignment and dynamics creating a stronger, higher power capacity transmission that will last longer.
-Partial break in on a bench dyno for verification.

Stage 2:
Highly recommended for racing/track applications using an aftermarket limited slip and or using slicks, for higher powered applications, and for applications using a lightweight flywheel and/or and unsprung clutch disk. Note: We do not recommend the use of lightweight flywheels and unsprung clutch disks. Both severely increase shock loads on the gear train with little to no measurable increases in performance.
-Includes all of stage 1
-In house heat treatment of gears to significantly increase gear strength
-Case is modified to accept larger 10mm case hardware.  This provides even more clamping force and reduced case flex over the stock 8mm size.

-Emco 3rd and 4th gear option: Emco has 3rd and 4th gear pairs available for the ND transmission.  While they are not perfect and require modification out of the box, they are still stronger gears for those who track and are recommend.  They are not cheap though, or even close to reasonably priced.  Still we highly suggest them for track use.

Please note these transmissions are built to order, and as such, they come with a lead time of about 8 weeks. If you will not be providing a working transmission to be rebuilt, please select the 'no core' option when purchasing. If you are providing a core, you will be responsible for shipping or delivering the transmission to our shop before we will ship the built transmission out. If you would like to receive a transmission before you ship your existing transmission, you will have to select the 'no core' option. Once the new transmission is installed, please contact us to arrange a core charge refund. We reserve the right to adjust the core price depending on condition of transmission. While most transmissions that are replaced in working condition will receive the full core refund, transmissions with sheared teeth, or other catastrophic damage will be refunded at a reduce value.

Al di la del fatto che essendo loro di base in USA, e che è richiesto il fatto di spedire il cambio completo, quindi direi cosa piuttosto impraticabile a partire dall'Europa. Quello che mi pare interessante è che di fatto sembrerebbe che loro abbiano identificato il problema in una generale pochezza di precisione negli assemblaggi oltre che bassa qualità dei componenti, qui di seguito un altro estratto trovato su un forum USA:

"[We have seen] a good bit of [repeat ND transmission failure under stock power]. It’s why our recommendations for our suggested builds -- for [the] type of use -- aren’t exactly what customers would want to hear. The boxes are very poorly built. A gear giving way during acceleration after [a] full engagement is part of the poor gearbox blueprinting, poor tolerance of parts, and cheap bearings causing gears to misalign and pinpoint gear tooth contact instead of mesh across the teeth. Pinpointed tooth contact shears through the crap gear oil, which makes it worse. Good gear oil is only a bandaid for this. It’s why we highly suggest [built Walter Motorsports ND] stage 1s for normal -- even just daily -- driving.

We are offering [ND] rebuilds to those who need them now, but if you [can] wait for the last few bits of development, please do. But in the meantime, our [ND] transmission rebuild without the final tweaks is still massively more reliable than stock and might even be all most people need, but it’s just not to the level we want to say is our standard."

Inoltre sembrerebbe che loro affermino che la rottura avviene quando questi accoppiamenti errati generano delle flessioni negli alberi della trasmissione tali per cui gli ingranaggi si impuntino e da qui la rottura.

Ora tenendo conto che vengono riportate rotture anche su cambi con i recenti aggiornamenti, anche sull'ultima "V5" e che invece la mia è una delle primissime (immatricolata Ottobre 2015), che ho già percorso più di 53k Km con uso in pista etc. insomma, non una vita tranquilla e per ora tutto sta in piedi. La mia ipotesi è che effettivamente al di la degli aggiornamenti, alcune trasmissioni vengano assemblate male a causa di tolleranze di progetto errate etc... Mentre può essere che altre trasmissioni, pur della primissima versione, se sono state (a questo punto a fortuna) assemblate "bene" dovrebbero essere relativamente più longeve.

Che ne pensate? Di seguito link alle pagine da cui ho tratto i quote.

https://walter-motorsports.com/

https://forum.miata.net/vb/showthread.php?t=711347