allencr wrote:The synthetics seem to be too slippery for syncros to do their friction bit and live a long life, and the 'thicker is better' attitude definitely doesn't help their life. That syncro has to grab & turn not only the selected gear & clutch disk to the driveshaft/road speed, it has to turn ALL those other gears at the same time too.
It's gears but not Hypoid so it doesn't need any Hypoid type lube.
It's gears and doesn't need any of the additives for blowby smegma & all the other stuff that's in engine type lube.
So it's gear lube or ATF, both recommended by all manufacturers for all their transmissions that are all the same basic design & materials for bearings, gears, seals, syncronizers that need friction or clutchs shedding material.
Please tell me if the synthetic oil is bad for synchroes, why then Toyota recommends GL5 oil (which usually comes as synthetic) for their E series GT4 gearboxes? If the oil was a problem, then obviously there would be a massive problem with synchroes on those vehicles?
Castrol Syntrax 75W-90
Full synthetic SAE 75W/90, API GL5. manual transmission, transaxle and rear axle lubricant with outstanding extreme pressure, synchroniser and high temperature performance. For vehicles that combine gearbox and hypoid diffs, rear axles of light cars and secondary drive axles of 4WD vehicles.
from here
http://www.castrol.com/castrol/multipleproductsection.do?categoryId=8000016&contentId=7000384PRODUCT APPLICATION
Manual transaxles, manual transmissions where API GL4 or 5 is recommended, eg
Subaru, Porsche, Alfa Romeo, various VW and Audi models
Car and light commercial differential for competition applications and reduced viscous
drag.
Most competition transmissions and transaxles, NOT recommended for 6 speed
Hollinger transmission in V8 Super-Car
Jaguar XJ 220 transaxle, Sportscar, Formula Ford + VEE Transaxles
Selected MB, MAN, ZF, DAF, Eaton and Scania applications
PRODUCT FEATURES & BENEFITS
Continued lubrication effectiveness over a broad range of operating temperatures.
A special formulation for a range of European truck driveline applications
Outstanding Extreme Pressure gear oil synchronizer performance
May be used throughout the entire temperature range normally specified to SAE 75W-80,
SAE 80W-90 and SAE 90
Superior thermal and oxidation stability
http://www.tds.castrol.com.au/pdf/10082_Syntrax%2075W-90.pdfTYPEOFUSE
Specially designed for FF (Front-engine/Front-drive) type transmission with mechanical LSD (Limited
Slip Differential) system.
Suitable for all transmission (synchronized or non-synchronized), 6-speed transmission, gearbox with
differential, transfer gearbox and hypoid differentials with or without LSD.
All types of cars: Circuit, Group A, Rally, Gymkhana, Tuned, 4WD,.....
from here:
http://www.motul.com/system/product_des ... _75W90_(GB).pdf?1339467706
Smooth shift feel for the life of the oil
Enhanced oxidation stability, reducing harmful deposits
Improved load carrying capacity
Contains synthetic base oils for longer life
Will not harm brass or bronze
Compatible with synchro materials
Very fast flow at start up for slick gear shifts
from here:
http://www.penriteoil.com.au/products/manual-gear-&-differential-oils/pro_gear_70w-75_full_syn