synthetic gearbox oil

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Mon 8 Nov 2004 12:18
synthetic gearbox oil - Alan
I know synthetic oil greatly reduces wear but would it improve the gearchange quality.
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Mon 8 Nov 2004 13:46
synthetic gearbox oil - Peter D
Depends on the car. I have a MKIII Golf Driver and the Diff bearings failed. VW rebuilt the box but put EP80 oil it and when the engine/gearbox was cold you could not get first gear and very difficult second. Warm it was OK. They saw the error of their ways and replaced it with correct synthetic gearbox oil which is thinner and problem sorted. I think without knowledge of which is the correct oil for your box you should leave alone but the car makers may tell you what they suggest. Regards Peter
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Mon 8 Nov 2004 15:02
synthetic gearbox oil - RichardW
On the flip side, Citroen / Pug boxes do not like synthetic oil, and perform much better on the recommended TOTAL BV oil. I wouldn't change to a synthetic oil, unless the box was not very old, or it was recommended by the maker.


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RichardW

Is it illogical? It must be Citroen....
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Mon 8 Nov 2004 15:35
synthetic gearbox oil - Number_Cruncher
I would tend to agree with the position as given by RichardW.

Wheras in an engine, all friction is unwanted, synchromesh action depends on generating certain levels of friction between parts rotating at differing speeds. Therefore, the oil used during the development of the synchromesh, and hence that recommended for the gearbox should be used to get the best results.

It is, however, worth checking that there have been no bulletins, or changes in the spec of your gearbox oil since your owners manual was published.

number_cruncher
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Mon 8 Nov 2004 16:41
synthetic gearbox oil - Aprilia
Whilst some of the above answers are correct 'in principle', most modern synthetic gear oils are actually 'fricition modified' to enhance synchromesh action and will enable faster and smoother gearchanges for this reason. Most saloon car racers run friction modified synthetics for this reason.

A good 'cooking' semi-synthetic is Castrol Syntrax 75W-90.

Total-Elf 'Synthease' is a good 75W-90 that works well in most 'boxes that use an 80-90 EP - its also GL-5 rated but without the corrosive EP additives that other oils use (so OK for boxes with yellow metal or fibre synchro). This oil is also quite cheap (about £25 for 5l).

Castrol's top fully synth oil for gearboxes is Castrol SMS-X, but its only available in 25 litre drums so you'd have to find a stockist who would sell you just a few litres. Its a good oil for cold climates and is excellent for high power cars with 'difficult' gearboxes (e.g. Skyline's and Mitsu Evo etc.).

Alternatively you can try one of the oils from Redline (e.g. MT or MTL) or Motul. These will set you back about £10-12 a litre - but they are all good oils.
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Mon 8 Nov 2004 22:27
synthetic gearbox oil - mark999
I've had problems with gearboxes on 2 cars after changing the oil.

The First was a Merc V-Class due to the Spec of the oil reccomended by castrol being wrong. The correct oil was a dealer only oil and the gearbox returned to normal when the correct oil was used.

The second is the Yaris which still has problems with poor gearchange when cold. The reccomended Toyota 75w-90 was used.
My dealer eventually changed the oil for ATF (Shell Donax TA)
which improved things slightly.

Overall I wish I'd just left alone.
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