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Replacing transmission oil - best way to flush?


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I've been having trouble with my J-type O/D since I had it installed by my former mechanic (the trans w/overdrive was in working order and so wasn't rebuilt). It has all new wiring and switch (the car didn't have O/D previously) and after about 100 miles the O/D began hesitating with engagement and now will move in and out regardless of whether the switch is on or off. I know that usually means two separate issues of electrical problems and low oil level. BUT the wiring is all new and the fluid was, I hope, filled properly and I see no evidence of leaks.

I am planning on replacing the oil since I don't know what kind was put in and I don't trust the mechanic to tell me what was really put in there. I've been doing research here and came across the Quantumechanics article about trans. oil and the results of using 90 gear oil seem to explain the issues i'm having. So i'm going to use 30 w non-detergent engine oil when I refill the trans.

My question though is, should I do anything to flush the trans before adding the new oil?


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"I second Velocita. never run engine oil in a gearbox. Disasterous results."

Working on BMC boxes (non-overdrive), in the days when they recommend SAE 30 for them, sure revealed a lot of surface damage to the teeth, particularly the straight cut ones, in Australian conditions Tony.

If Redex's claims of the day are to be accepted, foaming could have been a factor.

Don't know how the Mini gears survived, running in the crank case, as I was out of it by then.

I used to put straight 90 (Shell) into them after overhauling, as used in American boxes at the time, no follow-up to see how they survived, but no complaints.  They did still synchromesh OK with straight 90.

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the use of ep90 or sae30 or engine oil depends on the tooth loading and basic design Rootes boxes run on engine oil there are designed too,  Triumph small chassis boxes are of very limited capacity and by design are
required to use an EP oil, or life can expire  , in fact they expire on ep90 without any more assistance in reducing the oil spec.

both A D J overdrives are deigned to run on engine oils but will happily work OK with EP oils

this has as said all the hall marks of  fussy inhibitor settings.  
but always check the levels on a flat surface , clean the filters and on J type may need new O rings on the sol valve .


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Some good news, I disconnected the toggle switch and after driving it about a quarter mile it seemed to pop into overdrive and then back out quickly once.  Drove it about 20 miles around town & country with no O/D engagement so hopefully it is a bad inhibitor.

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