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Old 12-17-2012, 02:44 PM
chrisn7 chrisn7 is offline
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Location: Huddersfield, West Yorks
Join Date: Oct 2011
Posts: 706
Mein Auto: 750iL
Originally Posted by Dalmat3 View Post
I've replaced 2 or 3 times trans fluid -admittedly not on 7 series. Each time tranny quit short time after. If it says "lifetime" -trust it is
Seals in the original tranny become quite acidic due to fluid wear. By putting low ph (new) fluid into tranny, we cause more trouble by allowing those old seals to suddenly get exposed to new fluid with radically opposite ph factor. This is what screw them seals up. If I had to change I'd change half fluid only, so that chock of new fluid wouldn't ruin the tranny too soon
Depends what you meant by 'replaced 2 or 3 times trans fluid'. If this was done by draining the fluid via the gearbox drain plug only, then you certainly didn't change even half the fluid, since this action doesn't drain the torque converter. For example a 5HP30 box fills from dry with about 13 litres, yet only some 5.5 litres can be drained as above..
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