synthetic transmission oil-educate me!

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Peter C in Canberra
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synthetic transmission oil-educate me!

Post by Peter C in Canberra » Sat, 02 Apr 2011, 14:14

Hi,
The book with my Daihatsu charade says to change the gearbox/transmission oil every 2 years. I am approaching 2 years of electric driving so it is time to change the oil in the gear box. At conversion time I just put in some oil from the local car parts shop that seemed to have about the right numbers on it. Since then I occasionally seen reference to using synthetic oils in the gearbox for improved economy. I gather that there are around 10% energy losses through the gear box/transmission and that these can be reduced by a few percent with the right oil. I know almost nothing about fancy oil but I might as well have an extra km or two of range if I can have it from choosing the right oil. The original book says to use "API GL-3 or API GL-4, SAE 75W-90 or 80W-90". Can anyone suggest a particular make and grade of oil I should choose and why?
Thanks
Peter.
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Post by T1 Terry » Sat, 02 Apr 2011, 15:35

Tricky one Peter,
do you change gears like when driving with a ICE or is it more a gear selection from stationary to suit the conditions? Basically, do you rely on the syncros for gear matching?
If syncro function is not needed then either auto trans fluid or a super dooper synthetic oil that I'll need to find the the name for. I think the brand name is Redline or something similar.

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Post by Peter C in Canberra » Sat, 02 Apr 2011, 16:08

I use the gears and would want the sycros to work but I do not change nearly as much as I would in an ICE. On a typical trip I might use 2nd gear once or twice for a quicker take off and to more quickly reach 60kph up a hill. Most of the time I start and stay in 3rd. I only change down from 3rd to 2nd when almost stopped in anticipation of starting up certain hills. Infrequently I have trips with sustained 100kph for which I change to 4th while moving from 3rd and need to change down to 3rd while still moving when returning to suburban streets.
Gear changes are not as easy as they might be but are adequate but I would not want them to get worse. I do wonder if perhaps the 3rd gear syncro doesn't work as well as it should anyway. It is much easier to avoid a crunch going into 2nd than 3rd.
Thanks for your comments. Perhaps I should change the query to what could I put in to make the syncros work better without disassembling the car and getting the gearbox overhauled?
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Post by Tritium_James » Sat, 02 Apr 2011, 17:42

Peter, you probably should be using a *much* thinner oil than what is recommended in the manual. This is because when it was petrol powered, the engine heated up the gearbox significantly, making the oil less viscous. So the recommended viscosity would be assuming that the gearbox was operating at some fairly high temperature.

Since you no longer have an ICE dumping bulk amounts of energy into the gearbox, you should be using an oil that's lower viscosity to start with. However, picking which one to use is a bit harder, as it all depends on what the assumption was for the ICE-powered temperature, and what it operates at now it's an EV.

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Post by Peter C in Canberra » Sat, 02 Apr 2011, 19:44

Tritium_James wrote: Peter, you probably should be using a *much* thinner oil than what is recommended in the manual. This is because when it was petrol powered, the engine heated up the gearbox significantly, making the oil less viscous. So the recommended viscosity would be assuming that the gearbox was operating at some fairly high temperature.

Since you no longer have an ICE dumping bulk amounts of energy into the gearbox, you should be using an oil that's lower viscosity to start with. However, picking which one to use is a bit harder, as it all depends on what the assumption was for the ICE-powered temperature, and what it operates at now it's an EV.


Good point about the oil staying cooler and hence more viscous all else being equal. I reminded myself what the 75W-90 means via a web search. So, thinking out loud-tell me where the logic is wrong!:
The number is the viscosity of the oil at 100oC. The W is for Winter. This number means the oil acts like a 75-at-100oC viscosity oil would do when it is cold but like a 90 viscosity oil would do when warmed up to 100oC as a consequence of various clever additives that stop the 75-type oil from thinning as much as would be expected. If we assume my gearbox is staying pretty cool all the time then I would need an oil that is similar when cool to the viscosity of a 90-at-100oC oil at whatever is the assumed operating temperature of the gear box. I guess the rating is also telling me that a 75-at-100oC oil is not too viscous when it is cold. If a simple, oil without additives were 75W-75 I guess I could use that and know I was not doing much damage. It would be like always driving a cold gearbox and transmission. It would not get too hot and consequently too thin.
Another relevant difference from the ICE perhaps is that I might be putting more torque into the gearbox because I start in 2nd or 3rd gear so I might need something thicker on the cogs. On the other hand I am rotating the cogs smoothly, not with a huge thumps when an explosion goes off twice per rotation.
Would a thinner oil make the syncros work better or worse, particularly if they are a bit worn as they are likely to be in this older car?
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Post by T1 Terry » Sat, 02 Apr 2011, 22:05

This is where it all gets tricky. Gearbox oil acts different to engine oil. A 75w-90 gearbox oil when at operating temp is about the thickness of ICE engine oil. Because long runs and heat are not involved I made the suggestion of auto trans fluid. It has the lubricating properties and shear strength of gearbox oil but doesn't foam and remains at about the same consistency hot or cold. The syncros may be the issue here, if the oil is too thin the gears won't slow enough so some crunching may occur but as the whole driving/gear shifting thing is different it really is an unknown. Auto trans fluid is cheap, why not try it and see how it goes. Could you post a report back here if you do try it?
Don’t be tempted to use hydraulic oil, it has virtually no lubricating qualities.

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Peter C in Canberra
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Post by Peter C in Canberra » Sat, 02 Apr 2011, 22:46

Hmm. Is it relevant to that advice that mine is a front wheel drive car where the same oil is lubrication for the gears and differential bits?
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Post by T1 Terry » Sun, 03 Apr 2011, 08:57

With an auto FWD the diff is part of the transmission as well so it's lubricated with the same oil. FWD differentials are different to RWD diferentials in the way the gears mess, a RWD differential the pinnion is at 90deg to the crown wheel where a FWD the two are parallel so the same forces are not applied.

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Post by Peter C in Canberra » Sun, 03 Apr 2011, 14:13

Mine is a manual front wheel drive, not auto.
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Post by T1 Terry » Sun, 03 Apr 2011, 20:34

Same crown wheel pinnion principle with a manual or auto FWD, different deal for an all wheel drive though.

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Post by T1 Terry » Sun, 03 Apr 2011, 20:39

I will contact the mate with the bus that is converted to a motorhome regarding the name of the synthetic oil he is using in his truck size gearbox. That oil is about the same consistency as auto trans fluid. From there you will have the contact info to talk to the oil company engineers directly and they can advise the most suitable oil they have for you application. Better feed up the wallet good though, it ain't cheap oil.

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Last edited by T1 Terry on Sun, 03 Apr 2011, 10:41, edited 1 time in total.
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Peter C in Canberra
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Post by Peter C in Canberra » Sun, 03 Apr 2011, 23:18

Thanks again. I put my hand on the gearbox after taking the car for a typical local trip. The metal casing was warm to touch but no where near uncomfortable or anything that you could call hot.
I checked the Castrol site. They have tool where you put in your make and model. Following is what came up:
CASTROL VMX 80
Mild extreme pressure gear oil with special viscosity stabilisers to overcome shift problems. Recommended for use in transaxles of most front wheel drive vehicles with a transverse engine and manual transmissions experiencing low temperature shift problems. SAE 75W/80, API GL4.
May also use:
CASTROL SYNTRANS 75W-85
For competition applications where superior synchroniser performance is required. Also recommended for passenger car and light commercial vehicle transmission, transaxles and transfer cases. SAE 75W-85, GL-
or CASTROL SYNTRANS 75W/85
For competition applications where superior synchroniser performance is required. Also recommended for passenger car and light commercial vehicle transmission, transaxles and transfer cases. SAE 75W-85, GL-

I notice the first particularly mentions having the synchonisers working well at low temp which is my situation all the time. Perhaps I should just get that?
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Post by Electrocycle » Mon, 04 Apr 2011, 03:56

Some manual gearboxes use auto trans fluid from the factory, and I've heard of people using it in other boxes without issues.

It's still an extreme pressure lubricant, but much lower viscosity.
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Post by bga » Mon, 04 Apr 2011, 16:50

I was thinking high viscosity for the journal bearings, but auto transmissions also have journals and use much thinner ATF.

Motocycles usually use (hot) engine oil in the gearbox.

Some other considerations may be what gear is being used most of the time. If you are able to run mostly in the sraight through gear (usu. 4th), then the gearbox isn't doing anything.

If you have a rear wheel drive (or subaru?), the differential is likely to have bigger losses than the gearbox. Front wheel E-W drives don't have hypoids and are more efficient because of it.

It would be my expectation that thick oil is more needed in the hypoid differential where there is a sliding gear mesh. Most often there is only one type of gear oil used in the vehicle.

While fiddling around with the BMW diff recenty, I was surprised by the amount static friction it has. I suspect that this has a lot to do with the age and wear of the input bearings and the large amount of preload on them. I was thinking that a mitigation strategy may be to change the bearings and reduce the preload by 50% or so. Putting in a teflon modifier may also help.
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Post by Peter C in Canberra » Mon, 04 Apr 2011, 17:31

bga wrote: Some other considerations may be what gear is being used most of the time. If you are able to run mostly in the sraight through gear (usu. 4th), then the gearbox isn't doing anything.

If you have a rear wheel drive (or subaru?), the differential is likely to have bigger losses than the gearbox. Front wheel E-W drives don't have hypoids and are more efficient because of it.


Most of the time I am in 3rd, occasionally 2nd for uphill from stationary, occasionally 4th if anticipating sustained 100kph.
None of the ratios are 1:1.
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Post by woody » Thu, 07 Apr 2011, 07:11

Just correcting most of the above mentions for "front wheel drive" should refer to "transverse" or "east-west" layout which no 90 degree bend in the drive train like a traditional "north-south". 95% of FWD cars are "east-west", 99% of RWD cars are "north-south", but there are exceptions...

examples of east west cars:
Nearly all modern japanese + french cars, including the RWD Toyota MR2.
Some soft road 4wds
Magna

examples of north-south cars:
BMW
Porsche
Mercedes (not A or B)
Subaru
Nissan Pintara/Skyline
Most pre-80s cars
Saab 99 (Front wheel drive, gearbox at the front)
Commodore
Falcon
Sigma
Cressida
I can't think of a Front engine rear wheel drive car which isn't north south...
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Post by Alex_Brooy » Thu, 28 Apr 2011, 01:31

may be offtopic, but
Peter, how much km did you covered on your TS-LFP batteries?

Peter C in Canberra
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Post by Peter C in Canberra » Fri, 29 Apr 2011, 04:14

Alex_Brooy wrote: may be offtopic, but
Peter, how much km did you covered on your TS-LFP batteries?

20,000km in two years so far. No sign yet that they are behaving any differently from new. I hope for many more years.
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Post by Sunkosi » Fri, 26 Aug 2011, 04:23

Personally I'd be putting in a PM Lubricants product.

And you'd most likely never need to ever replace it and also gain advantages of lower friction losses at the same time.

http://www.pmlubricants.com.au/

Yes it's expensive - but it has it's advantages.

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Post by Johny » Fri, 26 Aug 2011, 15:12

Here is a corrected link:
http://www.pmlubricants.com.au/
Why do I get the feeling that there are claims here that can not be proven - or haven't been proven?
Has anyone subjected these products to a scientific method?

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Post by gannet » Mon, 10 Oct 2011, 03:15

Peter C in Canberra wrote:
... CASTROL SYNTRANS 75W/85
For competition applications where superior synchroniser performance ...


Don't know if it applies to trans oil, but some competition motor oils might lubricate better, but don't have any additives (or whatever) that help with long life. - they really are for one race day only.
Given you're looking for 2 years or more, might be worth checking.

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Post by Jeff Owen » Thu, 30 Oct 2014, 23:48

woody wrote: I can't think of a Front engine rear wheel drive car which isn't north south...


Ford Thunderbird with transverse, in line 6 cylinder engine and RWD.
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Post by reecho » Fri, 31 Oct 2014, 05:27

In a previous job a looked after a fleet of buses that were doing extreme duty urban running. The final drive transfer case normally had gear oil but overheating was a big issue. Replacing the gear oil with synthetic ATF improved temps and noise quite a bit with no noticeable breakdown from the gear sets. I agree if the syncros are not being used all the time then a high quality synthetic ATF like Transmax Z or TransSynd will work a treat and have a reduction in parasitic drag.

We used redline shockproof in the testing...

Redline
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