How can I completely drain gearbox oil?

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RichardF
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How can I completely drain gearbox oil?

Post by RichardF »

Now I have the gearbox off, I would like to drain all the oil, including the 1.5 litres usually trapped.

Can I do this by just tilting the box with the drain plug removed, or will I get more oil out by removing the shaft drive flange and seal and draining via that end?
Don't force it - get a bigger hammer!

'87 2.1 Syncro, '96 Audi A4 Avant, '94 Alfa 33.

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Re: How can I completely drain gearbox oil?

Post by Aidan »

because of the one way valve inside it's pretty much impossible to completely drain the box and if you stand it on the nosecone you will cause the oil to drain through the bearings and any debris in the oil can be trapped in the bearings causing potential damage so short of stripping the box you can't get it all out so don't worry about getting every drop out, and don't incline the box by more than 15degrees down at the clutch end and you'll get most of it out through the drain plug leaving probably 10% inside

TONYT25T25
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Re: How can I completely drain gearbox oil?

Post by TONYT25T25 »

When I recently changed the oil in mine all be it still fitted to the van, I filled the box with a bit of the new oil with the drain plug still off as a flush to get rid of some more of the old stuff.
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RichardF
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Re: How can I completely drain gearbox oil?

Post by RichardF »

Thank you both very much :D
Don't force it - get a bigger hammer!

'87 2.1 Syncro, '96 Audi A4 Avant, '94 Alfa 33.

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Re: How can I completely drain gearbox oil?

Post by silverbullet »

How does the 15 degree rule work when driving off-road? Steep ascents and descents result in sludge being run through the bearings regardless?
A good reason to change the oil regularly, especially after wading.
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Re: How can I completely drain gearbox oil?

Post by Aidan »

silverbullet wrote:
31 Jul 2020, 16:45
How does the 15 degree rule work when driving off-road? Steep ascents and descents result in sludge being run through the bearings regardless?
A good reason to change the oil regularly, especially after wading.

'snot a rule just a suggestion to get optimal drainage without disturbing any larger debris which will mostly stay on the bottom of the case; generally any gross debris in the nosecone will stay in that section and similarly any gross debris from the reduction housing will stay in front of the one way valve, debris in the main case will generally be flowing under gravity towards the diff housing and will be driven sideways by the oil flow from first gear and will be lifted over the internal sill through the large opening and into the diff housing where the differential and crown wheel flings it at the magnet where if steel it will be captured

I have seen many instances of damage to in particular the input shaft from I think gearboxes have been stored on their end standing on the bellhousing in which case the oil and residues will over time make it's way to that end and some of it will drain and filter through the bearings, any that gets trapped in the input bearing will as soon as the box is put back into use be spun at engine speed in a close tolerance space, similarly gross debris from the reduction housing may become trapped in the mainshaft bearing which is blocked by the ring which is there to keep the bearing oiled when climbing, and again will be instantly spun at engine revs if still trapped in there, and any that is trapped in the 3rd 4th or R and G selector fork bearings may cause splits in the bearing shells when operated if not pushed out as the ball bearings move to and fro

In operation with all the gears spinning any debris will mostly be flung away from mating surfaces and bearings; regular oil changes will help reduce wear and circulation of debris and observation of the drainplug help to suggest timely repair before catastrophic failure

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