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I have read multiple threads on what to use in my 1989 6 speed for fluid, but I'm more confused than ever. Some say GM fluid, some say Amsoil, some say BMW oil, etc. What is the REAL story on what is safe to use?
I've had this car for a couple of years, almost 80k on it now, and it runs and shifts great, but I want to perform this service, and do not want to use improper fluid.
I use Amsoil Synchromesh... Some use Pennzoil... I've generally read the BMW should not be used. Honestly, you will get varying opinions on what works...so don't expect anything definitive in this thread...because it is likely multiple are completely viable options that will work fine so I wouldn't overthink it....
If you thought the 80K was all on the 'original' fill I might be inclined to maybe use one of the lesser expensive recommended fills/fluids and service it again in maybe a few thousand miles. Buy 2 fill/drain plugs ahead of time, get it warm do the drain, fill and drive. The Amsoil gets many/most recommends but I'd think to expensive for the service I mentioned. Maybe for the fill after the few thousand mile drive.
The fill/drain plug if there's VW/Audi dealers in the vicinity are quite inexpensive. WHT-001-937 is a part # VW and Audi should be able to help you with. Ask for M17 hex as that part # was replaced at some point with a different that's not desirable. I'd think if still available from 'locals' maybe 7$ each - less expensive are available but then there's the ship.
If Royal Purple or Redline are available locally I'd think either would do, maybe even for the 'next'.
This is what I'm presently using. I switched from an expensive synthetic to this after chasing GM part numbers awhile. Butt dyno/ operator perceptions only, I prefer the fluid I'm using now. Seems easier, smoother shifting. Good advice above regarding buying new plugs prior to undertaking fluid exchange.
If you thought the 80K was all on the 'original' fill I might be inclined to maybe use one of the lesser expensive recommended fills/fluids and service it again in maybe a few thousand miles. Buy 2 fill/drain plugs ahead of time, get it warm do the drain, fill and drive. The Amsoil gets many/most recommends but I'd think to expensive for the service I mentioned. Maybe for the fill after the few thousand mile drive.
The fill/drain plug if there's VW/Audi dealers in the vicinity are quite inexpensive. WHT-001-937 is a part # VW and Audi should be able to help you with. Ask for M17 hex as that part # was replaced at some point with a different that's not desirable. I'd think if still available from 'locals' maybe 7$ each - less expensive are available but then there's the ship.
If Royal Purple or Redline are available locally I'd think either would do, maybe even for the 'next'.
further to the recommendation here of getting two new plugs and the 17mm hex socket to remove/install said plugs, ....if your bottom plug is mangled....high probability....you can grab a bolt with a bolt head that is big enough to fit in the hex plug even in its mangled condition and use two nuts jammed together to back the plug out. then replace. this worked for me. i got replacement plugs from a vw dealer up in canada
Here is what I have found on the zfdoc.com website. I have never contacted them or used them, but this guy seems to be the authority based on his reputation on this forum. This was in the FAQ section on that site. The confusion in information comes from people on here saying they've tried the 10w-60 and their transmissions not shifting as well. (Q.) I just bought, at the local BMW dealership, 3 liters of the Castrol TWS 10W60 oil. I was surprised to see that it is motor oil. Not being a lubrication engineer myself, who did the investigation and determination that this product is compatible with and good for our ZF transmissions? Jim – Grand Sport Registry (A.) Jim, the C4 Corvette ZF S6-40 6-speed transmission uses engine oil for lubrication. I was told by Jeff Henning, Warranty Administrator of ZF Industries North America, that Engineering of ZF Industries in Germany determined that the BMW imported Castrol (RS superseded by TWS) 10W-60 oil was the recommended alternative to the (GM P/N 1052931) factory-fill oil for use in the ZF S6-40 transmission. In effort to verify ZF Industries alternative lubricant recommendation, we ran our own test series on the BMW imported Castrol TWS 10W-60 oil. Independent testing of the transmission oil samples was sub-contracted out to CTC Analytical Services. The test series went as follows:
<1> Spectrographic analysis indicated that it is has full synthetic composition.
<2> After 2 hours of operation, approximately 100 miles, oil sample analysis tests indicated that the viscosity rating was reduced from 60 down to a 43 level. No need to worry, this is a normal occurrence for this heavier type of oil. I attribute this to microscopic-level lubricant-strand trimming through operational loading where all of the oil contents has been passed through gear pressure-loading regions at least a few times.
<3> At 200 miles, the viscosity level stabilized at a 42 level viscosity since the 100 mile oil analysis test results.
<4> At 5000 miles, the oil analysis test results indicated a 40 level viscosity.
The test-transmission was completely disassembled and checked for wear. There were no signs of carbon film like experienced with the factory-fill oil. The phosphor-bronze lined synchronizers had no glazing and experienced an average mass loss of approximately 4% based on reserve-wear-range mass equivalency between 0.062"(new) and 0.048"(spent)
gap wear/mass measurements.
<5> At 10,000 miles, the oil analysis test results indicated a 39 level viscosity.
<6> At 12,500 miles, the oil analysis test results indicated a 37 level viscosity.
<7> At 15,000 miles, the oil analysis test results indicated a 34 level viscosity.
The test-transmission was again completely disassembled and checked for wear. There were no signs of carbon film like experienced with the factory-fill 30 oil. The phosphor-bronze lined synchronizers had no glazing and experienced an average mass loss of approximately 17% based on reserve-wear-range mass equivalency between 0.062"(new) and 0.048"(spent) gap wear/mass measurements.
<8> At 15,000 miles the oil had enough phosphor-bronze particles suspended
in it that deposits began building up inside of the synchronizer sliding
sleeves from the normal centrifuge-like rotational occurrence.
In Conclusion, until someone invents a copper magnet, we recommend that the ZF S6-40 6-speed transmission oil be changed at 10,000 - 12,000 mile intervals so as to minimize the amount of deposits of the suspended spent synchronizer material from collecting in critical component contact surface areas.
There is no "real story". You'll get about as many answers as people who post. One may get the most "votes", but there is ZERO data to back up, the opinions.
EDIT: It appears that ZF doc has some actual data! Just saw topfuel67's post.
There is no "real story". You'll get about as many answers as people who post. One may get the most "votes", but there is ZERO data to back up, the opinions.
EDIT: It appears that ZF doc has some actual data! Just saw topfuel67's post.
Totally agree. It's mostly anecdotal. I've heard people complain about shifting with the BMW stuff...but again, that's hearsay. I think the main takeaway though is change it... and change it every 10k or so miles, every other year or whatever works for you...I don't think it matters a ton which brand, find one with the right properties that works for you and stick with it. If after you change it you notice shifting is immediately worse, then try another one. Amsoil works for me, so I have no reason to change to something else. Is it just the brand name? IDK...but it works...for me.
Similar to engine oil, as long as you change it regularly you are ok. If you are a super aggressive racer, then maybe some more thinking is needed.
I have not seen anyone say that they used a particular oil in the ZF and it toasted their transmission on this forum(I could be wrong here???)...IMO the minor variations between these different oils matters a lot less than driving habits, frequency of maintenance and a PROPERLY functioning clutch hydraulic system.
As some said above, there is anecdotal evidence from many sources. I generally try to look for test data , but not too much exists.
All I can offer is more anecdotal evidence on my history. I had an issue where the 1st to 2nd shift was not smooth when cold on my '95. It clicked when it would go into gear. I suspect it was a lack of synchronizing on the shift. I changed the fluid to the AMSOIL fluid and it immediately went back to a good shift. It was slightly better on other shifts too, but really noticeable on my 1-2 shift. It has remained a good shift for 5 or 6 years now.
Zf fluid change
