ATF auto transmission fluid change

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littlepolo
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Joined: Thu Jul 21, 2011 9:47 pm

ATF auto transmission fluid change

Post by littlepolo »

I've had the parts and fluid at hand for some time and the warm weather is encouraging me to do the job.

Just wanted to check in in case anyone has any tips or suggestions for the job.

I've been trying to pinpoint the problem that causes transmission snatch after slowing/stopping and then taking off again. It's worse in the warmer weather, for some reason. I did read some comments about the ECU cutting fuel but the engine picks up and revs freely from slow/standstill whereas the transmission does not - so not sure about that as a possible explanation.

While doing some other repairs recently, I did notice 'oil' around the transmission as per photos. I'll have a closer look to try and determine if the oil is indeed oil or if it could be ATF fluid. Unlikely that engine oil would be deposited on the outside (near side) of the transmission case? On the inboard side, maybe?
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littlepolo
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Posts: 778
Joined: Thu Jul 21, 2011 9:47 pm

Re: ATF auto transmission fluid change

Post by littlepolo »

Started the job and found the ATF to be dark in colour with an odour that is not fresh.

I'm not sure there is a leak from the sump but the sealant around one of the bolt holes looks a little suspect. I was surprised to find sealant as I had purchased a rubber seal for the job and it's not correct. Does anyone have an idea what sealant/mastic is needed for this job?

I dropped the strainer and more fluid came out. The strainer itself looks OK, though I have a new one at hand.

Can the sump bolts be reused?

Presumably the strainer bolts (very long) can be re-used, at the right torque setting.

There is a deposit aft of the auto box and I wonder if there is anything leaking around there. Will clean it up and try to find out. Does anyone know what the big nut/plug seal is back there (see photo below)?

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littlepolo
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Posts: 778
Joined: Thu Jul 21, 2011 9:47 pm

Re: ATF auto transmission fluid change

Post by littlepolo »

IN looking through my old Haynes manual, I noticed there are two speed sensors - road speed and transmission speed. Does anyone have any history of these sensors being problematic? I will connect my diagnostics laptop and look through for any issues/codes.
littlepolo
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Re: ATF auto transmission fluid change

Post by littlepolo »

I see the Haynes manual specifies torque for the sump to transmission shield of 45Nm/33 lb ft, yet nothing for the sump pan to transmission (18 x 10mm hex bolts) or strainer to transmission (11 long hex bolts). The strainer bolts 'felt' like they are around 33 lb ft grunt when I undid them but it would be helpful if anyone has the correct spec ;-). I read elsewhere that the sump pan bolts are 7 lb ft (on a 5 speed box) tighten diagonally then 11 lb ft final torque (so I guess these are similar).
littlepolo
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Re: ATF auto transmission fluid change

Post by littlepolo »

Posting this which might help anyone doing this job with torques!

Interestingly, the schematic shows the 'plug' I spotted from the underside. It looks like this might well be the final drive/differential drain plug? Since, like the auto box these are 'sealed for life' I can find no information at all on what it is, or how to drain and refill the final drive, or the gear oil specification.

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littlepolo
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Re: ATF auto transmission fluid change

Post by littlepolo »

For anyone doing this job, the hex plug is the lowest drain point for the ATF. Another 100ml or so of ATF dropped when I opened this.
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littlepolo
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Re: ATF auto transmission fluid change

Post by littlepolo »

After purchasing an additional 2l of ATF to go with the 2l I had at hand I thought I'd be OK for the refill. I firstly poured in 3l. When the transmission temp reported 40C I ran through the gears, into park and then added ATF from the last litre bottle and with the drain plug removed expected to see an overflow. Nothing. I had poured all of the 4l in and it was below level. 3l was the volume I had taken out - possibly a little more than that allowing for absorption of spills into rags, etc

Ordered another 1l bottle from Amazon and waited until next day.

Set up funnel into the transmission sump filler again, brought the transmission up to temp, ran through the gears, back to park and poured from the 1l bottle. After about half the contents emptied I started to see some drips below! The ATF coming out was still dark in colour and there was still an odour (though not as bad as before). I put the remainder of the bottle in to force more out. Waited for the fluid to start dripping, checked the temp (41C) and replaced the drain plug.

In total I had purchased 5l of new ATF and poured it in. The total capacity is reported to be 5.7l (residual ATF would have been in the torque converter). My best estimate is that I firstly drained a max of 3.1-3.2l and when pouring in the fifth litre an additional 500ml came out. So, a total of 5l in and max 3.7l out, leaves a shortfall of at least 1.3l. Likely evaporative loss over a 20 year period, and possibly minor seepage (still investigating - I degreased the entire under engine area and will monitor).

Went for a test drive and all seems to be well. I think the low fluid and its poor condition might account for the difficulties I had experienced, namely slow take up on drive after changing gear (e.g. D to R and back to D), and in particular the clunk when resuming from slowing down to about 5-10mph and pulling away from standstill after a long run (particularly in hot weather). I had the 'clunk' problem since 50,000 miles. I've not had a chance to see if the clunk problem has cleared as I have not yet driven on a long run. Otherwise, the drive seems to take up very well.

My plan is to drive for a couple of hundred miles or so then drop whatever comes out cold from the transmission sump, measure it, and replace the same volume/weight with new fluid. I'll report back on the symptoms (hopefully a lack of them) in due course.

So much for sealed for life.
littlepolo
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Re: ATF auto transmission fluid change

Post by littlepolo »

Just in case anyone ever takes on this job, I used Dirko HT (red) to seal the transmission sump pan after cleaning and refitting. I had a tube of Dirko grey at hand from when I did the top end overhaul back in Dec 2018/Jan 2019 but did not want to risk it being up to spec. I think there is only 20C difference between regular Dirko and the HT version (so of no import here). It's not that difficult a job really, just a bit messy. Also, you don't need a computer since you can use an IR thermometer to check the transmission sump pan (which will likely read a degree or two low from outside). The temp range is 35C to 45C and I went for 40C. I would not measure out and refill fluid if it has not had a service before, especially when the overall volume could be low like mine was!
littlepolo
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Re: ATF auto transmission fluid change

Post by littlepolo »

After several long journeys (including some in warmish weather) I am quite convinced the problem with the transmission snatch on restart after slowing down and stopping is solved. Reason - low ATF fluid.

If anyone is experiencing the symptoms it's worth checking your ATF fluid.
4aceman
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Drives: Polo 9n 1.4 auto BKY
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Re: ATF auto transmission fluid change

Post by 4aceman »

Hey littlepolo.

Thanks for the writeup, I’ve been meaning to do an atf change on my sisters polo just as general maintenance, and I couldn’t find any information online, and the Haynes manual is pretty s**t for the gearbox. It’s good you got your low level sorted out, low level burns up the clutches pretty easily but it seems like these boxes are pretty robust.

I couldn’t get much info on how much fluid I needed, from my experience doing a valve body rebuild and fluid changes on my E46 auto a filter off drain only gets about 5.5L of the 9.2L it holds. I thought the Polo would be similar but interestingly not. Seems like it holds 4.5L of the 5.7L. The E46 holds about another litre above the valve body, which dropping it releases, and the rest in the torque converter.

How was the strainer and sump when you took the pan off? Did they look really clogged/dirty?

I only bought 4L of fluid to be honest, I found a febi atf which referenced to this gearbox on their website and went with that. G052990 spec / febi 29934.

I’m tempted to just drain and fill. If I do drop the sump I’ll probably reuse the remaining 500ml from the old fluid. I’m not sure if that crappy mesh filter is worth dropping the sump for.

I’m assuming the car was level when you did the final fill? And how did you manage with the funnel, had a look the other day and it looks like a pita reaching that filler neck.

Also for future use of anyone watching here’s a little trick https://youtu.be/-VTnxVlw4Ls
littlepolo
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Re: ATF auto transmission fluid change

Post by littlepolo »

I would drop ATF from the pan and inspect its condition. Likely no need to change the strainer (but it's cheap and easy to do) and the pan is easy remove to inspect the magnet for evidence of wear and drop another litre.

You did not say what engine, year, and mileage and I would be curious to know about any ATF losses. My 2002 has 122,000 miles and no issues with the ATF change. In fact, it's better than it ever was and I like the reassuring downshift on slowing from a high speed run!

I've had my Polo from about 29,000 miles and it's been treated well (aside from the unwitting operation at low ATF levels due to VW's 'sealed for life' ruse). That said, these transmissions seem to be quite resilient.

One other thing, I seem to be getting better mpg since I did this work. I guess >30% down on ATF might have caused some inefficiencies, friction losses, etc.
4aceman
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Re: ATF auto transmission fluid change

Post by 4aceman »

I have the strainer so might as well change it out. I have a 1.4 BKY, 2007 but with the old 4 speed GJG auto like you have. It's on a hair over 100k miles and I just got it a few weeks ago, I strongly believe in maintenance so I'm trying to change all belts, fluids, filters etc. just to have a clean slate.

No current issues with shifting but an ounce of prevention is worth a pound of cure. Gearboxes aren't cheap, but fluid is. I have a tiny seep from the pan, but not much to cause low fluid issues, and it shifts well. I snugged up that bolt a hair and I think that will sort that seep out.

Perhaps at higher speeds with the gearbox pump drawing more fluid there wasn't enough fluid pressure to activate the torque converter lockup properly, that'll account for about 15% mpg at cruising speeds ish.
littlepolo
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Re: ATF auto transmission fluid change

Post by littlepolo »

Good timing at 100K for an ATF refresh, I reckon. Oddly, the shift problems I had only materialised on hot days and/or warm days after long runs. Lately, it did start to get worse though, and as I mentioned, delays in selecting FWD and REV gears.

If you are careful, it's possible to re-use the fill plug (but likely not the locking cap) though I bought new.

I'm not sure if the BKY uses an ATF sump gasket or sealant. If latter, Dirko is a good product to use. If the former, I have a Febi rubber gasket that I didn't use :-)

After refill, and fluid level checks, you'll be able to calculate what volume of ATF was in it.

BTW, I used Febi 29934 ATF fluid. I'm going to check it again soon (drop a little to check condition).

For filling, I used one of those oil filter funnels with the corrugated tube (nozzle is around 10mm and just fits in the filler cap tube). I seem to recall that the orange plastic funnel once had a Draper label on it. I see many similar for sale online, but they have a tapered nozzle - mine has a (more or less) parallel section at the nozzle. You can use some spare tubing to size the filler port.

Just as an example, this would probably do (though find a local seller!)

https://www.ebay.co.uk/itm/165665740808 ... BM6LCy8PRg
4aceman
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Re: ATF auto transmission fluid change

Post by 4aceman »

I once had low fluid on my bmw gearbox and again problems would only really come after driving a while when the atf heats up. Which is weird because the fluid should expand as it heats up?

What happens to damage the fill plug when you remove it?

It uses sealant like your gearbox, and I have bunch of Mannol sealant which I think should get the job done. Smells pretty potent while it’s drying so it must be good stuff :D . Theres a lot of wiring and radiator piping over the fill tube so I’ll see what i can do with the funnel hose. I can always pump it from below if I need.

Could you estimate the amount of time it took idling to get up to the right temp? It’s the same fill procedure for most autos and up to now my method is just putting my hand on the pan and feeling when its “kinda warm. Worked pretty good so far
littlepolo
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Re: ATF auto transmission fluid change

Post by littlepolo »

Nothing much happens to the fill plug itself, thought it's difficult to take the locking cap off without breaking it. I had a new one at hand so butchered the old one!

I did the job in warmer weather and it didn't take long, at a guess 15 mins (probably an increase of 15-20C over ambient). I used a diagnostics software to monitor the temp and once I reached 40C it slowly increased by a degree or two by the time I was finished (within 5 mins or so - though I stopped and restarted the engine due to the shock at the lack of fluid and the need to uncork more).

The risk is you will over or underfill if too far off on temp. If your experienced hand is close enough then it might be OK.

It's easy to drop a bendy funnel into the filler tube from above.
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