another gearbox oil question

[ZsZ]

Hi all! It is decision time.

I have an 1.9 mtdi with a modified AAP box.In the summer I have added factory 40% limited slip diff., Weddle 0.74 5th.
For oil I used Fuchs Titan Gear LS 90 regarding to the OE given FORD M2C104-A spec. Now as the weather gets colder it is really difficult to change the gears in the mornings.

Searched through the internet, the wiki, the archives, the forums and I now really confused without any useful infos.

What should I use for new oil? I have two locally available candidates: Fuchs Titan Sintopoid LS 75W90 vs Castrol Syntrax limited slip 75w-140.
Which one? Total different? Do I need 75w-140 vs 75w-90? Any advice?

THX!

[Aidan]

go with the 140 with Weddle HD gear and TDi

[ZsZ]

Thanks Aidan!
The 75w-140 is marked as an axle oil and not as gearbox oil. Is it missing the synchomesh protecting additives? Does it matter anyway?

I think I need to consult a tribologist

[silverbullet]

I was going to ask a similar question
Slight aside but the turbo variants of the UN1 specced a different oil to n/a versions, a Mobil fully synthetic 90 iirc and that was in the mid 1980's

75W140 would be great for hard working hot transmissions in cramped spaces i.e. syncro with a skid plate (we have a diff sharing its oil with the gearbox anyway) but...
Rear engine placement means a lot less heat wash from the engine and radiator compared to a front engined installation, although most longitudinal inlines & vees have the transmission enclosed in a tunnel with the exhaust downpipes running close by

[ZsZ]

In the end I ordered a third one, a Fuchs Titan Syntopoid LS 75W140. Marked as axle and transfer gearbox oil.
I was thinking about a fourth. The MOTUL Gear FF Competition 75W-140 is described as a gearbox oil for racing purposes, but its price is almost the double here.
Maybe next summer

[ZsZ]

Changed the oil.

The magnet after ~2000 kms with SAE 90 looks like this: