QUESTION ON GEAR OIL

I am soon going to try Motul Gear 300 LS 75W90 in my 348. The reason why I decided to use Motul is my excellent experience with it in my race car (BMW E30 M3, Getrag 265). With the unknown oil in it, the gearbox had the usual somewhat difficult shift 1-2 when cold and rattled a bit in neutral when really hot (after a longer highway drive or after the race). I first decided to try Redline MTL but it was worse than the previous "whatever" oil. Very notchy gear changes cold or warm so I only kept it for some 10km (driving back home from the workshop) and threw it out the next day. What I then put in was Motul Gear Competition 75W140 - perfect, when totally cold I have easy engagement into 1 or R, shift 1-2 and all other shifts up or down. Same when hot or very hot and the hot rattle completely disappeared.

This experience is with a totally different gearbox but it tells something about Motul compared with Redline MTL - huge difference. Otherwise, Motul 75W90 and 75W140 are quite similar in quality; 75W90 is also a racing grade and it is recommended instead of 75W140 when greater transmission efficiency is desired. One may say 140 is "too thick". Not at all, surprisingly thin when cold despite the number. I believe that the number 140 does not mean thicker when cold (compared to 90) but that it can hold its viscosity at extremely high temperatures better than 90.

A related info - I have seen mentions on this forum that the Allen key size for the 348 transmission fill plug is 20mm; just checked the new fill plug I have and found that a 19mm (3/4) Allen bit fits tight, same when I checked the old plug on the transmission. I guess 20mm was just somebody's wrong info.

 

They don't really have a problem with engine oil but they have had a problem with gear oil since the very beginning. We have been seeing this problem since before 2000 was over. The motor oil gets very hot on a track, sometimes to the end of the temp gauge but I have never seen a lubrication failure from it.

Any name brand GL5 that gets changed annually.

 

Interesting as that's been my experience...I've started changing it annually as it seems to get notchy after a year.

And as long as I remember to uncap the drain tub its pretty easy and quick and not messy. Unlike the last time

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20mm is definitely wrong.

Here is exactly what you will need:

19mm Allen for the fill plug underneath the airbox

10mm Allen for the drain plug underneath the car at the bottom of gearbox

17mm socket for dipstick, which some people also use to fill instead of the 19mm plug under the airbox.

 

My 348 gearbox was frustratingly obstructive, so I came here looking for info and decided to try Redline, on recommendation of other 348 owners here.

I collected the car today with Redline Lightweight Shockproof 75W140.

The gearchange is transformed!

It remains a little recalcitrant when engaging 1st or reverse from standstill, though less than before. When up and running, the gearchange has gone from being a real PITA to a real joy! Wow! It's now a firmer version of my 512 TR gearchange - lovely.

Very happy. Thanks guys!