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Time for a 915 Gearbox oil change, recommendations please.


Ant7

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Motul semi synthetic 75/90.

https://www.opieoils.co.uk/p-897-motul-motylgear-75w-90-technosynthese-transmission-differential-oil.aspx

Don't be tempted to go for the fully synthetic.

Even if you have an LSD fitted don't use LSD oil or additives.

The correct oil won't fix a knackered gearbox but it will help it work correctly.

The wrong oil will wreck a tired gearbox.

 

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I read a lot and chose Motul Motyl Gear 75W/90 for my ‘79 resto.  No personal experience or idea of how it compares to others, but I’m happy with it.

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On 23/09/2023 at 20:13, Leicestershire said:

 

Even if you have an LSD fitted don't use LSD oil or additives.

 

I had heard that before, but Mike B recommended this mineral oil for mine, that was rebuilt with a Kaaz LSD...

Castrol B373 is a 90w mineral based extreme pressure gear oil which combines limited slip performance with excellent load carrying ability

Edited by RivieraBob
grammar
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Hi All,

Thanks for all your input, much appreciated, although I have to say I'm not sure what to go for now, obviously there seems to be a good following for the Motul, however I am intrigued to know Type 911 Recommendation. According to my car's history, the gearbox had work done to it around 18,000 miles before I purchased it, [some 12 years ago now] its not done a huge amount since, probably no more than about 3,000 miles since I changed the oil last time. There isn't anything  untoward with the box, just the usual quirks of the 915, just want to make sure it stays that way!

 

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25 minutes ago, RivieraBob said:

I had heard that before, but Mike B recommended this mineral oil for mine, that was rebuilt with a Kaaz LSD...

Castrol B373 is a 90w mineral based extreme pressure gear oil which combines limited slip performance with excellent load carrying ability

I know I will get shot down but Mr B doesn't always get it right. 

LSD lubricant has friction modifiers (added slipperiness) to make the plates slip without chatter.

Fine in a conventional differential housing but in a transaxle with the gearbox and differential sharing the same oil the friction modifiers prevent the synchro mechanism from working correctly / cause accelerated wear.

 

The OP asked for advice on type of gearbox oil.

In my opinion the Motul is the best match for a 915. However, like most oil threads everyone has an opinion so please feel free to use what you want. Even the blue smurf blood has its followers. 

https://azupim01.motul.com/media/motulData/DO/base/MOTYLGEAR_75W-90_en_FR_motul_45000_20220616.pdf

5 minutes ago, proporsche said:

honestly ,no need to mineral oil last for at least 50k miles mine is just perfect..

ivan

No need for the Motul due to cost or something else?

Would you consider the Motul product to be detrimental to the health of a 915 gearbox? 

The OP asked for information on a suitable product - what product (brand, specification) do you reccomend?

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36 minutes ago, Leicestershire said:

I know I will get shot down but Mr B doesn't always get it right. 

LSD lubricant has friction modifiers (added slipperiness) to make the plates slip without chatter.

Fine in a conventional differential housing but in a transaxle with the gearbox and differential sharing the same oil the friction modifiers prevent the synchro mechanism from working correctly / cause accelerated wear.

 

The OP asked for advice on type of gearbox oil.

In my opinion the Motul is the best match for a 915. However, like most oil threads everyone has an opinion so please feel free to use what you want. Even the blue smurf blood has its followers. 

https://azupim01.motul.com/media/motulData/DO/base/MOTYLGEAR_75W-90_en_FR_motul_45000_20220616.pdf

No need for the Motul due to cost or something else?

Would you consider the Motul product to be detrimental to the health of a 915 gearbox? 

The OP asked for information on a suitable product - what product (brand, specification) do you reccomend?

well..since i rebuild my trans about 16 years ago there is nada wrong with it..have been using swepco on clients car in LA ....but i still prefer 80w90 mineral no brand name necessary.Plus if i would like motul ,if is not avaiable in every country and shipping oil is a pita....so it is 80w90 any brand of mineral from my side;-)

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1 hour ago, Leicestershire said:

I know I will get shot down but Mr B doesn't always get it right. 

LSD lubricant has friction modifiers (added slipperiness) to make the plates slip without chatter.

Fine in a conventional differential housing but in a transaxle with the gearbox and differential sharing the same oil the friction modifiers prevent the synchro mechanism from working correctly / cause accelerated wear.

The OP asked for advice on type of gearbox oil.

I only commented because the statement was at odds with what he told me....I believe his view was if you have a plate LSD and a 915 it was a compromise for the two. But maybe he's just trying to drum up business with broken gearboxes! 🤣

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Swepco all day long, because it’s blue and @Type911likes it :D

Seriously though, for a moment, I had Swepco and it was great…….and then the gearbox broke. Don’t know if it was linked but you never know.

Edited by Phill
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Thanks again to all who contributed, I really do appreciate all your input,  I used conventional mineral based oil the last time I changed it, but I think I will go with the majority recommendation here which is the Motul Motyl Gear 75W/90, 

Thanks again!

Ant

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I read this post on Pelican with interest, any thoughts ?

Which oil to use in a 1978 915 gearbox?

I used Porsche spec. gear oil in my 915 the first year of owning it, 2012 to 2013.
But because the gearbox had some minor syncro issues between 2 and 3 gear I changed to Swepco 201, which I have used since.
I found a great improvement using the latter one, also together with my newly built 283PS, 343Nm 3.2 SS engine.
But I still have a question to the forum here: what is the best all purpose oil for my gearbox?
I like to run the car hard but it never sees the track.

Regards
Eskild


Steve Weiner:

For 915's, the only one I use is Swepco #201. Its a non-synthetic, GL-5 rated oil and the best one I've used since 1978.

Solved our ring & pinion issues in our 935 and RSR back in the day. NEVER, ever use any synthetic oil in those things.
Steve Weiner

 

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And there's this,

https://www.opieoils.co.uk/p-1017-red-line-synthetic-gear-oil-75w-90ns-gl5-non-limited-slip.aspx

A quote from one converted user;

I did all the other fixes, including rebuilding my shifter assembly, replacing all the bushings, going overboard with some brass bushings in my coupler, and adjusting the coupler to the sweet spot for all gears. My shifting now has near rifle bolt precision, but you know what that didn’t fix? My tired 1st and 2nd gear synchros.

Initially I changed my fluid to Swepco 201, the gold standard gear oil for the Porsche 915, according to the old timers on the Pelican Parts forums. It made a huge improvement in my shifting. However my 1st and 2nd gear engagement was still unpredictable, to the point that I did not want to drive my 911 in bumper to bumper traffic. I thought my synchros were simply too far gone.

Then a close friend who builds Porsches recommended I try Red Line 75W90NS. Looking for any option that would buy me more time before a rebuild, I gave it a shot.

I saw noticeable improvement right away. I kept this to myself and drove the car to evaluate its long term performance. I drove it through the full range of SoCal ambient temperatures, from the low 40s to 100 degrees. I covered a couple of thousand miles in everything from long canyon runs to bumper-to-bumper LA commuter traffic.

 

The entire time my shifting has improved by about 90% in first and second gear. Its easy to just get in and go and not even think about shifting issues. Based on my experience so far, I highly recommend it! In fact Ill probably put it in my new box once I rebuild it.

My situation is only one data point for a high mileage, driver quality gearbox operating in a mild climate. However for relatively little time and money it could result in a huge improvement.

 

 

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HI All,

As stated, I decided to go with the Motul, I remembered last time I changed the oil, I couldn't get the drain plug out, so managed to suck out what I could through the fill plug, Obviously that wasn't ideal, as there was quite a bit of the old oil left in there, that's why its been on my mind to change it properly, anyway, long story short, I managed to make a slightly tighter fitting hex bit, and with some patience and the use of a trolley jack to keep the hex bit and socket securely in the drain plug, it finally gave way, and I was able to see just how bad the oil was, safe to say it was quite dirty!

Anyway, after re-filling with the correct quantity of the Motul gear oil, a quick test drive, and I have to say; the box has never felt better, much easier changes, no issues going into first gear now, which could be quite embarrassing at the lights at times, and over-all the box seems quieter, and smoother, so cheers all for you intake, hopefully I won't need to change it now for a good few years.

Ant

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Thanks great news and a nice cheap improvement.  How dirty was the oil?  If really bad I would consider changing it again after a few miles and using the change you have just done as a flush to lift as much crap out of the box as possible.  Just a thought.  

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35 minutes ago, Ian Comerford said:

Thanks great news and a nice cheap improvement.  How dirty was the oil?  If really bad I would consider changing it again after a few miles and using the change you have just done as a flush to lift as much crap out of the box as possible.  Just a thought.  

Hi Ian,

Its hard to say how bad it was, when it was draining out, it still looked quite transparent looking through it, however; when it was in the tray, it was a different story, so I am going to run it for a while, and as you sugested; maybe drain it again after a few hundred miles or so.

Ant

Edited by Ant7
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On 30/09/2023 at 17:11, Ian Comerford said:

Thanks great news and a nice cheap improvement.  How dirty was the oil?  If really bad I would consider changing it again after a few miles and using the change you have just done as a flush to lift as much crap out of the box as possible.  Just a thought.  

+1. 

Cheap insurance for the cost of 3 litres of gear oil.

Did you fit a new drain plug?

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15 hours ago, Leicestershire said:

+1. 

Cheap insurance for the cost of 3 litres of gear oil.

Did you fit a new drain plug?

Indeed!

Not yet, obviously I need to order a new one,  Type 911 ???

Edited by Ant7
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