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After changing my drive shaft and losing some transmission oil in the process (about 0.4L a related query open on this), being unable to undo the filler hole as it is stripped.

I can put oil through the breather/air hole (top). So I attempted this with a 10ml syringe and filled 30ml before getting fed up at how slow it was so got a cheap oil pump and pumped in 0.5L in a matter of seconds. It also pumped some air in with the process.

If I drain the transmission (drain hole) and measure the amount drained. Thereby pumping in the same amount via the breather/air hole this would be the equivalent of using the filler hole right?

I am just concerned it may introduce more than normal air/bubbles but then again the breather/air hole is there for that reason to settle thereafter?

Is there anything to advise me against doing so?

The pump I am using is a basic one but works for anyone interested.

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  • What is the year/make/model of the vehicle in question? Why are you changing it in the first place? Most manual transmissions don't need fluid changes. Commented Mar 10 at 2:43
  • @Pᴀᴜʟsᴛᴇʀ2 2006/Nissan/Almera N16. Recent months rough gear changes, ever since the loss of 0.4L which was over 1 months ago? Last week clicking when reverse gear is engaged. I do a LOT of gear shifts way over average over weekends so fluid change is least intrusive/cheapest and quickest if it may help with any of the symptoms mentioned if at all.
    – Dave1UK
    Commented Mar 10 at 3:19

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Yes, what you are doing is fine. I've changed many transmission fluids through the filler tube with a pump instead of opening a drain plug. Air bubbles are not an issue.

Total capacity of your gearbox is 2.3L. At only 0.5L per fluid change, you'll have to change the fluid approximately 12 times to completely remove all the oil fluid.

Here in America, old mechanics will add 1 oz. per liter of Lucas Oil Stabilizer to gearbox fluid to improve shifting on old gearboxes.

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  • I'm proposing to open the drain plug and drain all the oil. Measure amount drained. Pump back same amount through the breather/air hole. Wouldn't opening the drain plug drain all the oil from the system?
    – Dave1UK
    Commented Mar 10 at 7:52
  • In regards to the Lucas Oil Stabilizer thankfully can get it on Amazon here in the UK. So 1 oz. is 30ml, for 2.3L of transmission fluid would be ~70ml of Lucas?
    – Dave1UK
    Commented Mar 10 at 8:02
  • Yes, you're right about the drain plug. As for the Lucas, start with less. You can always add more.
    – Carguy
    Commented Mar 11 at 23:52

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