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Tranny and Final Drive Oil


fritz1

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I have a 2000 R1100RT and a '93 R100GS.

For the last 6 years and over 200,000 km I've used Maxima 75\140 GL-5 rated 100% synthetic gear oil in my trannies and final drives without any problems!!

Here is my dilema.....Maxima no longer makes this oil and has only the 75\90 100% synthetic viscosity! Not enough demand for the 75\140, is what I'm told by Maxima!

What is an equivalent or better substitute???

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Your friendly neighborhood BMW dealer sells a BMW-branded 75W/140 synthetic gear oil. Made by Spectro, I believe, so you might look for the Spectro stuff elsewhere.

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How does one read the weightings for gear oil? In other words, what is the difference between 90w and 75w90?

 

And while we are at it, has anyone heard of synthetic blends? I seem to have two bottles of the stuff.

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My BMW manual calls up standard SAE 90W

doesn't anyone use this grade anymore?

 

Can't seem to get it if you want to go with synthetic. All the major synth brands only seem to offer a multi-weight gear oil - 75W90 or 75W140.

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My BMW manual calls up standard SAE 90W

doesn't anyone use this grade anymore?

 

Arbee:

Yeah, I run straight 90 in both. I noticed significant improvement in my old K75C and I believe my "new" R also shifts better especially after a hard run on a hot day.

Tipover Bob

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BMW told me not to use synthetics in the transmission as it permeates the seals and leaks

 

 

Who at your dealership told you this and did they give a reason why synthetics would do this versus dino oil?

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BMW told me not to use synthetics in the transmission as it permeates the seals and leaks

 

Arbee:

I don't believe synthetics permeate seals as much as they can remove deposits of parafin in and around old seals that opens them up to leakage. I expect that if this happens you can probably just go back to the dino oil you were using previously and the leaks will stop.

 

Tipover Bob

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BMW told me not to use synthetics in the transmission as it permeates the seals and leaks

 

Arbee, I sure wouldn’t trust that dealer to do anything important if that is what they told you.. Maybe it was just the service manager spouting off to sound important to you..

 

What the gear oil is derived from (Synthetic or Dino) has little to do with how it seeps through seals or permeates the seal material.. In fact the majority of modern Synthetic oil’s are derived from the very same oil stock as their Dino cousins..

 

Probably the biggest factor in how ANY gear oil interfaces with a seal is the amount of seal conditioner in the gear oil.. Some Synthetics contain more than others but that can be said of Dino bases as well.. In some high end Synthetics the oil molecules are closer to the same size with fewer outliers & less debris in the oil so that can have some effect on what size hole the oil will leak through..

 

My guess here is: the reason most Synthetics seem to leak out easier than their Dino counterparts is due to their flow ratings.. Most Synthetic based gear oil are a 75Wxx & most conventional Dino base gear oil are a 80Wxx or 85Wxx.. That low number is the cold flow rating so the easier the oil flows out when cold the thinner it is when cold.. Plus I’m betting the paraffin content of the conventional gear oil is higher & that in itself will make the oil leak out less as paraffin tends to block small opening..

 

Twisty

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