FredR

A couple of thoughts I would like to bounce off the list:
1. ATF life- Porsche suggest 40k miles but did not pick up any timeline. My ATF has been in the car about 6 years and covered 20k miles [30k km to be more precise]. I am a bit paranoid about dropping the sump to replace the filter due to fears of dust contamination- my garage floor invariably has concrete dust on it never mind what is in the air. I am thinking of dropping the ATF and just filling without replacing the filter- the WSM says something about this at 20k miles for examples used heavily [not my case these days]- any thoughts?
2. To replace the fluid my intention would be to simply replace what I get out of the torque converter and sump volume for volume- any thoughts as the likely amount? I am expecting something in the region of 6 to 7 litres.
3. The process of filling the ATF is a bit daunting- I have a pressure brake bleed system that is unused and not likely to be used for brake bleeding. It has a cap that screws onto the reservoir- are these caps on the auto tranny reservoir same fitting as those found on brake reservoirs? The bottle holds about 2.5 litres - maybe a tad more if pushed. Two or three shots should do the job. I do not have a fitting to use the nozzle intended for the purpose- also wondered if the ATF could be introduced via the cooler connections?
4. Regarding reservoir level- I checked the level a couple of years ago and fully warmed and after cycling the lever through park and reverse the level was at the top mark. My understanding is that when car is stood still the level rises and fills the reservoir as the ATF flows out of the torque converter but does not overflow the reservoir when the cap is opened- is this a correct perception?

Thoughts/insights appreciated

skpyle

Hi FredR!

I think you are making this more daunting than it needs to be. Relax, you will be fine. If I can do it...

OK, Here are my thoughts, take them with whatever grain of salt is required:

1. There are several different targets to shoot for regarding ATF life. My personal vehicles get a full fluid change every 2 years, which equates to around 15k miles. When I only had one vehicle, its ATF got changed yearly. I grew up driving junk, and you did what you did to keep it running. I learned regular ATF changes were a relatively cheap way to keep an automatic transmission running happily. I don't think the base stock in ATF, in this case Dexron III, 'ages', but the additive package could deplete, and it might go acidic. I am not 100% sure. Having said that, 6 years and 20k miles, I'd say that is a good time to change the ATF in your A28.18 in your GTS. Do it.
Dexron III is a good, stable ATF. The Mercedes 722.3 transmission is quite robust. They can both take some abuse. For example, I bought the Red Witch knowing she had not had an ATF and filter change in 18 years. The fluid was a tad on the brown side when I changed it, but the transmission ran flawlessly.

2. For a proper dump and fill, you are looking at around 12 quarts of ATF (approx 11.3 L) from the sump and torque converter. Both take the same size crush ring. However, the filter kits Roger sends out has one copper crush ring and one aluminum crush ring. I am ashamed to admit I have not yet figured out which is for the sump and which is for the torque converter. The crush ring for the transmission sump drain plug is: 900 123 062 30. The crush ring for the torque converter drain plug is: 900 123 033 20.

3. There is no need to go to such extremes to fill your transmission fluid sump. The exhaust heat shields make it a pain to access the reservoir cap. More importantly, there is a MUCH easier way. There is a fill port in the passenger's side transmission oil cooling line, at the transmission. There is a male quick connect fitting under a metal cap. The corresponding female quick connector is a DN 7.2 Type 26 connector. I have determined that the Parker 26KBTF09MPN will work. However, I am STILL awaiting a response from Parker-Hannefin of France to my inquiry. You might have better luck finding one locally. It doesn't matter, because it is simple to just push a length of tubing over the male quick connect and secure it with a hose clamp. Pump away! The fitting is not under pressure, there is just a check ball held in place by gravity. Refer to Service Info Technical Manual for 1986 928S, page 32, for more details on the quick fill port for the automatic transmission. Refer to WSM Volume 3, Section 38, page 139 for the procedure to refill the ATF.
To access the male quick connect, you will need a 19mm spanner to remove the metal cap. There is an aluminum crush ring that seals the cap. It is 900 123 007 30.


Screenshot of page 32 from Service Information Technical Manual for 9186 928S regarding the new quick fill port for ATF.






Male quick connect fill port for ATF. (Note: metal cap has been removed from the fitting.)





Tubing connected to fill port.





First time I filled the transmission: hand pump and 1 gallon jug.





Tools of war for the sump and torque converter drain plug.





Rig for filling the last time: Garden sprayer.





Wand removed from the sprayer, replaced with tubing.





Filling transmission the last time, much easier. (Note, the exhaust and heat shields have not been installed at this time. Access is usually far more restricted to the reservoir.)




4. You are correct, and incorrect. As the fluid warms, when the level is correct, it is at the top mark on the reservoir. When the engine is shut off, the fluid level in the reservoir rises as the torque converter drains. However, I believe you are incorrect in that the level does not rise above the fill cap. I believe it will overflow if you remove the cap after the car has sat for a day or so. Just my belief.

Be aware that all of the reservoir parts, with the exception of the screen in the filler neck, are still readily available from Porsche. I replaced the reservoir, cap, cap seal, and sealing nut O-ring as mine were all past due. The vent hose is available from places like Belmetric.


Regardless, FredR, I don't think you will have much trouble changing the ATF in your GTS.
Good Luck!!!

FredR

Seth,

Many thanks for the excellent input.

My perception is that when the transmission is fully warm it might drain back and overflow if the cap were to be opened- I just do not know where the level sits. Logic says that Porsche worked on the premise that the thing would not be full hot when worked on but either way I would hope that if the reservoir cap is removed the ATF will not pee all over me when flat on my back under the car on jack stands [I envy those with a hoist].

I have a fitting similar to that for the fill connection [I am aware of that] but my presumption is that it will not be identical- I will probably give it a try tomorrow morning. We are on the same page with the weedkiller bottle- hoping to get something tomorrow in that regard.

Was a bit surprised at the quantity you quoted -for some reason I had the impression that a dry fill takes 8 litres- I have not done this previously when I was working- it was just too easy to sub it out when I was on the big bucks- retirement is not all that it is cracked up to be!

With anything I do I always plan for the worst on the basis that it will be much easier in practice- biggest problem is working on my back - age is catching up with me and of course the damage to my back sustained in my wreck 15 years ago is starting to kick in as the doctors warned me it would- fractured L1 vertebra! Pity it did not happen in your neck of the woods or the UK- over here you have to lose pretty big parts of one's anatomy get any compensation other than costs.

NoVector

Hi Fred -
Completely drained, it's about 2.5 gallons of ATF. I buy a case of quart bottles when I change mine and the bottle or two that are left are good for topping off later.

When you're feeding new fluid in, it will suck up the first 2 gallons pretty quickly - and then it will somewhat stabilize. When it gets to that point, that's when I get back in the car (with it running) and cycle it through the gears. You will get to the point where the fluid will be on the lower mark and then slowly rise to the top mark as the transmission gets warm/hot. So, you won't have to worry about it "peeing" all over you (as long as you don't overfill it )

I understand your concern about working above a dusty floor. I had the same issue with my garage floor in Germany. I had my pan off for a couple days while I re-zinced the bolts. To keep dust out, I wrapped the transmission in aluminum foil. That may help you too in case you need to order parts or it takes longer than expected.

No goop or sealant on the pan gasket. And be careful with the pan bolt torque as they're only 8 nm.

FredR

My original plan was to do the ATF as a complete service next year but the more I thought about it the more I figured it was time to have a go as it were. Good to bounce one's thoughts off the team if nothing else to ensure there are no misunderstandings preparation wise. My plans changed a little as I like to inspect in early January, order any parts I need for projects or maintenance and then execute in February. In December I started a cosmetic spruce up in my friends detailing shop that took a month longer than expected so I am behind schedule and in another couple of weeks or so the heat may be back so I may not do as much as I want. Some jobs I can do any time even in the heat but stuff under the car- it is now or not until next cool season. If I was to drop the pan I would put some plastic sheeting over the footprint of the car but given the mileage covered I will probably just change out the ATF and be done with it.

Whilst on the subject I may also change the diff oil- any one got any specific recommendations for the diff oil given the PSD system? Need to do a bit of research on that one!

StratfordShark

Hi Fred I have the same PSD and used a 75W90 gear oil for the diff — Halfords own brand actually but I doubt that's available where you are! The PSD runs on brake fluid so I doubt the PSD presence makes any difference to the diff oil spec anyway, or creates any special requirement.

FredR

Hi Adrian,

As I recall diffs with clutches require an oil with specific characteristics is required to stop the clutches slipping excessively. Know relatively little about this so just want to ensure I do not goof up just by sticking any old 75w90 in there if it is not wise to do so. Doubtless it will be my imagination running riot!

NoVector

In this thread (https://rennlist.com/forums/928-foru...d-for-psd.html) Greg mentions that 3 different kinds of friction disks were used with the PSD. In that thread, he recommended the owner of a 1991 S4 use 75/90 Mobil One LS. Kind of curious what he would recommend for your '93. Personally I used regular Royal Purple 75/90 (the non-LS) when I did mine.

StratfordShark

As usual I've learnt something new about my 928, but am reassured by comment that Greg Brown approved 75W90 (though I didn't use Mobil)!

FredR

Thanks for the link- I know I have read something about this but the detail escapes me. I could not find anything in the manuals about such but then maybe it is a development that came with time/experience. Sounds as though it is comparative as in good, better, best as opposed to "good and dammed awful". In my case I will be happy to get a good diff oil or so I suspect, variants with modifiers for LSD are probably a pipe dream.

Zirconocene

Hi Fred-

Here's a post I put together on the fitting to refill the ATF, if you use the one way valve provided on the transmission: https://rennlist.com/forums/928-foru...ure-heavy.html

Cheers

FredR

Thanks for the link- it all helps. I have several quick fit connector kits in the garage so that may also work for me. I also picked up today an 8 litre spray bottle for the princely sum of $10 or so. Need to pick up another gallon of Dexron 3 by the sound of it.

What I do not have at the moment are new sealing washers for the plugs. Maybe I can pick something up at the local dealers in the morning- anything special about these things?

I noted Seth saying he used a Loctite thread sealant- I would hope the washer does the sealing but a bit of reinforcement should do no harm.

Zirconocene

Full disclosure: due to other work on the car, I haven't actually refilled the transmission yet. I did not use Loctite on the plugs, as Seth suggests, so I'm now a little nervous

The recommendation that I have read in many places is to fill to the line indicated on the reservoir on the first fill, then go drive for a bit to warm things up. Only after about 10 - 20 minutes of driving do you come back and fill to the line, as things have settled by that point. This is what makes the valve so useful, as your exhaust will be quite warm and getting to the reservoir seems dicey, at best. You seem to be pretty experienced with these cars, so apologies if this is all old news to you.

Apart from my own confusion about which sealing ring goes where, they appear to be pretty standard crush washers. I took everything apart to clean what I could when I did this work and, honestly, the old ones still looked pretty good. I don't imagine that the stresses on the plugs, especially given the low torque values that are called for, are particularly large. Of course, I still went ahead and replaced them, along with the o rings which Seth called out.

Cheers

skpyle

Hi FredR!

There is nothing exotic about the sealing washers, they are just crush rings. I have sourced them from multi-size copper crush ring kits before in a pinch.
You just want to get the ID and OD as close as possible.

The Loctite sealant is nothing more than pipe dope teflon sealant. dr bob clued me in on this. A thin layer on each side of the crush ring improves the sealing of the ring and allows you to reduce the torque a hair. Important in some applications, but not as much in this one. The sealant is a nice touch, but not required. I do it because it seems like a good idea.

Good Luck!

FredR

Seth,

At a pinch the copper ring can be heated up and quenched- good to go again. Puzzled as to why one is copper and the other looks aluminium- do you remember which is which?

The liquid PTFE will do no harm. For years I had folks in the oil industry rabbit on about how PTFE tape is problematical- I reckon one would have to do something monumentally stupid to make it so.