G'day all,
There are lots of handwavingly vague threads on A/T service life, fluid life and how Maxlife is the answer to a maidens prayer and makes all transmissions last forever. This is considerably more specific and comes about because I really don't know the answer and would appreciate some input from someone that does.
I drive old Volvos. Old Volvos have Aisin Warner transmissions as used in gazillions of Toyotas. These transmissions routinely run past 300,000 miles and the general consensus is the only wear items are o-rings, clutch frictions and check balls in the valve body. As a rule the transmissions tend to die because they run out of clutch friction material.
So, what contributes to clutch life? A common "performance" modification of these transmissions is to shim up the accumulators to reduce the clutch engagement time. I guess less slide, less heat, less wear but a harsher shift. I can see the point, the 1-2 & 2-3 shift in these trans can be long and slippy under hard load. Backing off the throttle during the shift makes it a lot more snappy. I suppose interaction between line pressure & throttle pressure pumps them up quicker. Anyway I digress..
Lubricant has the unenviable task of preventing friction in the transmission, yet allowing sufficient friction for the clutches to do their thing (like a wet clutch in a bike I guess). Does the lubricant have a part to play in allowing friction but minimising wear? How does that work? Is that a result of the 'friction modifiers' I hear discussed, and do they wear out? Would more frequent fluid changes facilitate longer clutch life?
Volvo specify A/T fluid replacement at 20,000 miles in the service schedule, but I've never met a Volvo mechanic who ever changes the fluid. I do mine every couple of years because it's cheap and easy to do when doing a service, but I wonder if they were maintained by the book from new how much (if at all) longer they might last?
So, who knows about the actual mechanics of a wet clutch and how it interacts with the lubricant?
There are lots of handwavingly vague threads on A/T service life, fluid life and how Maxlife is the answer to a maidens prayer and makes all transmissions last forever. This is considerably more specific and comes about because I really don't know the answer and would appreciate some input from someone that does.
I drive old Volvos. Old Volvos have Aisin Warner transmissions as used in gazillions of Toyotas. These transmissions routinely run past 300,000 miles and the general consensus is the only wear items are o-rings, clutch frictions and check balls in the valve body. As a rule the transmissions tend to die because they run out of clutch friction material.
So, what contributes to clutch life? A common "performance" modification of these transmissions is to shim up the accumulators to reduce the clutch engagement time. I guess less slide, less heat, less wear but a harsher shift. I can see the point, the 1-2 & 2-3 shift in these trans can be long and slippy under hard load. Backing off the throttle during the shift makes it a lot more snappy. I suppose interaction between line pressure & throttle pressure pumps them up quicker. Anyway I digress..
Lubricant has the unenviable task of preventing friction in the transmission, yet allowing sufficient friction for the clutches to do their thing (like a wet clutch in a bike I guess). Does the lubricant have a part to play in allowing friction but minimising wear? How does that work? Is that a result of the 'friction modifiers' I hear discussed, and do they wear out? Would more frequent fluid changes facilitate longer clutch life?
Volvo specify A/T fluid replacement at 20,000 miles in the service schedule, but I've never met a Volvo mechanic who ever changes the fluid. I do mine every couple of years because it's cheap and easy to do when doing a service, but I wonder if they were maintained by the book from new how much (if at all) longer they might last?
So, who knows about the actual mechanics of a wet clutch and how it interacts with the lubricant?
