Dragi colegi,
Am nevoie de ajutorul celor dintre voi care au un background tehnic si/sau o buna cunoastere a transmisiilor Subaru - mai exact diferentialul central cu visco-cuplaj.
Situatia in care ma gasesc e urmatoarea: am vandut diferentialul central de 12 kgf acum vreo luna jumate unui tip din Australia, pe eBay. Omul n-a pus nici o intrebare in prealabil, a platit si eu i-am trimis piesa – iar piesa inseamna intreaga cutie de transfer cu tot cu diferentialul central. Deci vreo 15 kilograme de fieratanii, cu un tarif de transport substantial – vreo 900 de lei.
Ne-am mai conversat dupa ce i-am trimis pachetul, mi-a aratat pentru ce avea nevoie de ea – construia un Forester pentru off-road hardcore, cu tot soiul de goodies gen diff spate R180 4.44 sau bare stabilizatoare decuplabile, custom made – deci parea ca stie cu ce se mananca toata povestea asta. Spun asta pentru ca dupa vreo 3 saptamani mi-a scris ca a primit piesa si diferentialul central e prajit, nu poate sa faca nimic cu el, l-a testat cu o dinamometrica si e mai slab si decat un diferential central standard, de 4 kgf. Vazand ca nu e un newbie in materie de Subaru, am luat de bune cele spuse si am cautat o solutie prin care sa ma achit fata de el. Pentru ca returnarea pachetului nu era in interesul nimanui si eu nu eram dispus sa fac un full refund si sa raman si fara piese si cu transportul platit degeaba, i-am propus mai multe alternative, din care el a ales un diferential de 12 kgf, de tip phase 2. In mod ultra-mega-ironic, solutia acestui diferential a venit tot din Australia – sunt tipii de la la CorgiWerx care reconstruiesc diferentiale centrale si care pot combina diverse viscozitati de ulei siliconic pentru a obtine ce cuplu se doreste. Am platit pentru toata distractia asta si Craig (cumparatorul) a intrat in posesia lui week-end-ul trecut. Asa ca i-am scris si l-am rugat sa-mi trimita si mie un video cu testul pe care l-a facut, ca macar sa nu mor prost si sa vad cum se testeaza un diferential central cu visco-cuplaj.
Si iata ce am primit:
Mie mi se pare ca metoda este gresita, motiv pentru care i-am trimis urmatorul e-mail azi:
“Hi, Craig!
And thank you very much for your effort of documenting the process!
There are a couple of things I'd like to point out and, please, take each and everyone as a "maybe" - I'm no engineer so I cannot pretend to have an expert opinion on the matter.
1. You said "A 12kg diff should have 120Nm resistance" - I think there's an additional condition to be met - the rotational difference. As I understand it, this 120 Nm force is applied for a 100 rpm difference of rotation between the front axle and the rear axle, because it's this difference of the rate of turn between the inside splined discs and the outside splined discs in the core of the diff that drives the silicone oil to turn from its gel-like state into solid, thus forcing both axles to turn at the same speed. This is how the diff is rated by STI, as you can see from the attached print screen of the catalogue (picture 1 - position 12).
2. Accordingly, I think the test should be performed in a slightly different manner: try to engage the second row of splines on the inside of the diff's "neck", the ones on the viscous coupler unit, and lock them in the vice, and turn the transfer driven gear with a speed higher than 100 rpm - with a drilling machine, perhaps. In my opinion, this kind of replicates the conditions that would occur in case one of the axles is slipping.
3. As I see from the schematics of the older type of center diff, being able to turn by hand the transfer driven gear is absolutely normal because there's nothing to stop it from rotating, since the VC is mounted on needle bearings inside the case (picture 2).
So, do you think you could try to perform the test again and see how it turns out?
Cheers”
Va dati si voi cu parerea, va rog, ca tare as vrea sa stiu cum sta treaba in realitate.
Va multumesc anticipat pentru sprijin!
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