Author Topic: Adventures with transmission fluid  (Read 1048 times)

FordPrefect8

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Adventures with transmission fluid
« on: May 13, 2020, 09:51:40 PM »
Finally got new jack today, after breaking halfords advanced 3T one last week (with 1 tonne car!), managed to find decent example. Having car lifted on 4 axle stands enabled me to have a go at changing transmissions fluid, which was in the pipeline for a while.
To my surprise, what came out looked almost new! But anyway, the point is whatever car I have a look at (Honda Jazzes atmo exclusively) I keep finding bolts over-tightened by 2 or maybe even 3 fold, it that current fashion amongst Honda dealership mechanics? Did they develop torque wrench allergy? Maybe they're used to things made of steel?
Can anyone explain?

My set of aviation spanners turns out to be best investment ever!

Jocko

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Re: Adventures with transmission fluid
« Reply #1 on: May 13, 2020, 09:59:55 PM »
Transmission oil should always "look" new. Probably never been changed, so plugs were more than likely tightened at the factory!

FordPrefect8

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Re: Adventures with transmission fluid
« Reply #2 on: May 14, 2020, 07:54:01 AM »
Transmission oil should always "look" new. Probably never been changed, so plugs were more than likely tightened at the factory!

Transmission fluid was changed but I had my reasons to doubt it was filled with MTF-3, hence I wanted to put new one in anyway. We’re talking even engine oil bolt which must have been tightened to at least 100 Nm :S
I’m guessing most mechanics do it “by hand”

culzean

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Re: Adventures with transmission fluid
« Reply #3 on: May 14, 2020, 08:33:51 AM »
Transmission oil should always "look" new. Probably never been changed, so plugs were more than likely tightened at the factory!

Transmission fluid was changed but I had my reasons to doubt it was filled with MTF-3, hence I wanted to put new one in anyway. We’re talking even engine oil bolt which must have been tightened to at least 100 Nm :S
I’m guessing most mechanics do it “by hand”

It can take more torque to unscrew a fastener that took to tighten it,  especially after it has been in place for a long time - a bolt may get rusted in,  but bolts can stretch over time and may need less torque, there is no stretch in a drain plug but the washer can stick and make it seem tighter than it is.

When I change transmission fluid I always make sure I can get the 'fill' plug unscrewed before I take the drain plug out,  this is after struggling with the fill plug on some cars - don't want to find yourself in the situation where the oil is drained out and you cannot refill it  :o  it is good practice to replace the washer on plugs when refitting them ( they harden over time and may not deform properly when re-tightened )  I bought a load of different sized copper washers years ago - but you can anneal ( soften ) both copper and aluminium washers for re-use but copper ones are easier to anneal - just get them red hot and drop in cold water - polish any scale off sealing faces with wet and dry paper on glass surface and can be reused many times.

The plugs do tend to get harder to undo the longer they have been left in,  same with sparkplugs - the longer life iridium and platinum plus have a special thread coating to stop them sticking ( they are expected to be in place for 70,000 miles + ) the normal plugs are just passivated zinc coating which can get a bit hard to move if plugs not changed on time ( like the rear plugs on i-DSi which can be ignored and be in for many years ).  With spark plugs though it should be hand tight and then about half a turn - just to seal the crush washer - or about 25 NM IIRC.

Remember if you have lubricated a thread it alters the torque value - ( which is why the 'hand tight + 1/2 turn may be better for spark plug ) and you should lower torque by 25% - so the thread of a drain plug is pretty much always gonna be lubricated by residual oil in the thread. so is the rated torque for a dry or lubed thread ? ).
« Last Edit: May 14, 2020, 09:10:04 AM by culzean »
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FordPrefect8

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Re: Adventures with transmission fluid
« Reply #4 on: May 14, 2020, 09:13:54 AM »
That is precisely what I did, so the fill plug was fine, thanks to an angle my 17mm aviation spanner had protruding flange just long enough. The fill plug however is a wee awkward so had to work with extensions, then gave up, removed half passenger side underneath plastic paneling and started the ol' penetrant + rubber mullet tapping + prayers, curses and small animal sacrifice routine until 2 hours later, with a LOUD creak the nut gave up :D

FordPrefect8

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Re: Adventures with transmission fluid
« Reply #5 on: May 14, 2020, 09:30:48 AM »
Quote
Remember if you have lubricated a thread it alters the torque value - ( which is why the 'hand tight + 1/2 turn may be better for spark plug ) and you should lower torque by 25% - so the thread of a drain plug is pretty much always gonna be lubricated by residual oil in the thread. so is the rated torque for a dry or lubed thread ? ).

An excellent point, my approach to this is I would always use recommended torque settings in any case. I don't put any lube or copper paste on spark plugs but I always use Iridium ones.

Btw. on this occasion I tried half a tube of Molyslip in transmission, curious if it'll improve things...

culzean

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Re: Adventures with transmission fluid
« Reply #6 on: May 14, 2020, 10:47:09 AM »
That is precisely what I did, so the fill plug was fine, thanks to an angle my 17mm aviation spanner had protruding flange just long enough. The fill plug however is a wee awkward so had to work with extensions, then gave up, removed half passenger side underneath plastic paneling and started the ol' penetrant + rubber mullet tapping + prayers, curses and small animal sacrifice routine until 2 hours later, with a LOUD creak the nut gave up :D

IIRC the thread on the fill plug is larger diameter than drain,  may explain why fill plugs are often harder to unscrew than drain ones,  and on the Jazz harder to access  :(    not done this for a while so cannot remember if the fill or drain has the 3/8" square hole in it   - I had to pull the plastic guarding out of the way to get to gearbox plugs on both Jazz and Civic,  may as well do it up-front as it makes life easier.

On the plus side modern transmission oil is thin enough to pour down a funnel and tube ( older stuff was like treacle and on a cold day needed warming up to pour ) and you cannot overfill gearbox as when it has enough it just overflows out of fill hole ( as long as car is level ).
« Last Edit: May 14, 2020, 10:49:59 AM by culzean »
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

casper1240

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Re: Adventures with transmission fluid
« Reply #7 on: May 14, 2020, 01:02:27 PM »
Transmission oil should always "look" new. Probably never been changed, so plugs were more than likely tightened at the factory!

Transmission fluid was changed but I had my reasons to doubt it was filled with MTF-3, hence I wanted to put new one in anyway. We’re talking even engine oil bolt which must have been tightened to at least 100 Nm :S
I’m guessing most mechanics do it “by hand”

It can take more torque to unscrew a fastener that took to tighten it,  especially after it has been in place for a long time - a bolt may get rusted in,  but bolts can stretch over time and may need less torque, there is no stretch in a drain plug but the washer can stick and make it seem tighter than it is.

When I change transmission fluid I always make sure I can get the 'fill' plug unscrewed before I take the drain plug out,  this is after struggling with the fill plug on some cars - don't want to find yourself in the situation where the oil is drained out and you cannot refill it  :o  it is good practice to replace the washer on plugs when refitting them ( they harden over time and may not deform properly when re-tightened )  I bought a load of different sized copper washers years ago - but you can anneal ( soften ) both copper and aluminium washers for re-use but copper ones are easier to anneal - just get them red hot and drop in cold water - polish any scale off sealing faces with wet and dry paper on glass surface and can be reused many times.

The plugs do tend to get harder to undo the longer they have been left in,  same with sparkplugs - the longer life iridium and platinum plus have a special thread coating to stop them sticking ( they are expected to be in place for 70,000 miles + ) the normal plugs are just passivated zinc coating which can get a bit hard to move if plugs not changed on time ( like the rear plugs on i-DSi which can be ignored and be in for many years ).  With spark plugs though it should be hand tight and then about half a turn - just to seal the crush washer - or about 25 NM IIRC.

Remember if you have lubricated a thread it alters the torque value - ( which is why the 'hand tight + 1/2 turn may be better for spark plug ) and you should lower torque by 25% - so the thread of a drain plug is pretty much always gonna be lubricated by residual oil in the thread. so is the rated torque for a dry or lubed thread ? ).

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