Gearbox Oil

[Leo944]

Hi all,

I plan to change the oil on my 1986 NA type 016K - 5S gearbox and have read many posts on this site regarding which oil is the most suited and recommended.

It appears that Redline MT-90 is the preferred oil of choice for many on this forum and had planned to use it until I read the following disclaimer on Redline's website:

"MTL, MT-85 & MT-90 are not for use in differentials with hypoid gears"

Red Line Synthetic Oil - Gear Oil for Manual Transmissions - MT-90 75W90 GL-4 Gear Oil

I believe that the type 016K has hypoid gears (see shop manual below) and now I'm not sure if MT-90 is the correct oil for this gearbox.

What do you guys think? Thx!

Leo

[JRMock]

Look for Red Line 75W90 NS GL-5 Gear Oil.

From their site:
Designed for transmissions and transaxles - helps to slow synchros for easier
shifting across a broad temperature range
Popular in Ferrari, Porsche and Subaru transaxles

[DannoXYZ]

Strange as popular opinion shows GL-5 being more corrosive for brass-synchros than GL-4.

Anyway, I've had good success with Redline Heavy Shockproof gear oil. I used to get a whining sound when coasting in gear with regular 75w90 oil like Swepco or Mobil-1. The Redline Schockproof really quieted down the transmission. Easier shifting too, was kinda notchy after I installed the 944only short-shift kit.

[thomasryan]

The factory recommended Mobil PTX works very well.

[kevingross]

The factory approved, actually insisted on, use of GL-5 spec transmission fluid in all manual gearboxes in a service bulletin many years ago. I posted a note on this topic some months back. So no fears on the concerns regarding brass / bronze synchronizers.

Yes, your transmission has a hypoid pinion gear, which induces much greater sliding stresses than a spiral bevel pinion gear. The hypoid design accommodates the offset of the pinion rotational axis from the differential's.

Yes, do not use a Red Line or any fluid which the manufacturer does not endorse for a hypoid pinion. There's really no discussion to be had here: just don't do it. There are lots of great fluids out there, no need to use one that isn't appropriate.

Danno, you haven't said which Redline Shockproof fluid you're using. I'd be somewhat concerned that you've just masked a problem with a fluid that, long term, will accelerate wear and damage to your transmission. Redline doesn't call out the weights for the three versions, and that makes me uncomfortable. Good to hear, though, that you find the shifting improved.

[OPRN]

Back in about '84 I pulled the transaxle apart on my Ford Escort and was shocked to find ATF oil in it. Ford told me that was the factory fill fluid for those standard transmissions. At the time I was modifying a VW Rabbit with propane fuel and turbocharger and finding shifting very stiff in cold weather. I switched it over from 80/90Wt gear oil to Dextron II and never looked back! When you think about it the abuse that happens in an automatic and the oil takes it and does it's job for hundreds of thousands of miles... and I believe with the lower viscosity it will cool better too.

I haven't changed my 944s over yet as I rarely drive them in the winter.

This may not work with a limited slip diff, I haven't tried it.

[mattdavis11]

You'll probably notice a difference if you change it and replace with anything new. That said, I replaced with Amsoil and the recommended weight. Shifting was as smooth as cutting through warm butter.

[Leo944]

One of this forum's members contacted Redline regarding the suitability of MT-90 for use in the 944's gearbox and sent me the email trail in a private message. Thank you so much! (not sure if you wished your ID posted???)

Forum Member: “I have been reading various Porsche forums and there is a debate about which Redline oil is recommended for 1984 Porsche 944 transaxles. Some say MT-90, but others say 75w90 NS because of hypoid gears. Your oil selector on your website comes up with MT-90. Can you please clarify why MT-90 is what you recommend while it isn’t recommended for hypoid gears, which I think the Porsche 944 does have? Some people also talk about needing friction modifier. Thanks.”

Redline: “Thank you for contacting Red Line Oil, on your 944 transaxle the MT-90 would be recommended. The 944 transaxle doesn't contain a high offset hypoid gear and as a result a GL-4 is originally specified. A friction modifier wouldn't be recommended as that could make the fluid too slippery for the synchros.”

Forum Member: “Thank you for your quick reply. This makes sense. You may want to adjust your information on your website to mention the distinction between high offset hypoid gears and regular hypoid gears. I have seen some people on some forums decide not to purchase MT-90 after reading this warning on your site. Thanks.”

Redline: “We have discussed that here, it seems that owners assume their transaxle contains hypoid gears when it actually doesn’t.”

So, according to Redline, MT-90 is a suitable oil for 944 gearboxes.

[djnolan]

Interesting I have a Ford Explorer that uses Mercon ATF in the transfer case 2 pints and then I had a Pontiac Firebird 5 speed that use Dexron in the transmission and those things shifted so crisply and smoothly and all of that and everything handled by a 10 weight oil or whatever ATF is

[dgcantrell]

Whatever you go with, if you have an LSD, be sure to add an LSD additive to the oil. Mine herked and jerked (Chatter) on pull-out in turns until I added some.. I used the Swepco synthetic when I had me ring gear and pinion rebuilt about 16 years ago. Got tired of the chatter and popped in a tube not too long afterwards... Quietened it down nicely... No issues since.

[Chris944-1]

Personally running Amsoil GL-4 Manual Transmission & Transaxle Gear Lube 75w-90 in mine and it seems quite happy. Non-turbo LSD tranny.

AMSOIL Manual Transmission & Transaxle Gear Lube 75W-90

[88Silver924S]

My 88 924S owners manual clearly specifies use hypoid oil SAE 80 GL-4 or MIL-L 2105. As far as I can tell no such oil is available; I have never seen nor heard of this spec oil. Then Porsche comes out in October 1988 and says to use GL-5 in all cars (Service bulletin 3-8813, link in section 9.5: 9.0 Clutch and Transmission). Was Porsche just throwing in the towel knowing their dealers service departments want things simple, i.e. they don't want to stock GL-4 for the few classic cars that may rarely show up in their service department?

Redline quote: "owners assume their transaxle contains hypoid gears when it actually doesn’t.” This makes me suspect that Redline hasn't really done their homework on the 944 transaxle and, since they don't sell a truely compatible oil they knuckle under to marketing and recommend a "suitable" oil they do make. But then why the "MT-90" and not the Redline MTL which is a 75w80 GL-4? Is it because the multi weights are now available when they weren't in 1988 or earlier when my owner's manual was written and if they were available they would have been recommended over a straight-weight 80?

There are few hypoid gear oils out there, just how critical is that requirement for my rear end?

I'm more confused than a baby in a topless bar.

[Rasta Monsta]

I run MT90 in my 931 (Getrag G31) and in my 924S race car (Audi 016), and both boxes have shifted wonderfully for years. Not really an answer to your question, but maybe peace of mind if you elect to go this way.

Sent from my Nexus 6P using Tapatalk

[Leo944]

I just came across this TSB: