StretchGSK

Hi
I know a lot has been written about oil and I have read most of it.
One topic that has not come up is what affect oil can have on your synchros. My mechanic has suggested that using synthetic oil staight after replacing synchros could lead to them getting galzed like a engine bore or bearings and thus prevent them from working correctly and failing again.
He thus recomends using regular oil for a while before swapping to synthetic.

Comments would be greatly appreciated.

Stretch

oilman

iTrader: (9)

Indeed there is a lot of talk about this but it mainly relates to GL5 gear oils however there are GL4 / GL5 Gear oils that don't harm the synchros.

These normally consist of GL4 gear oil with GL5 loadbearing capability.

Oils with this specification would normally read something like this:

"Suitable for use in synchromesh gearboxes and final drives - embraces traditional synchromesh gear oil performance (GL4) and hypoid axle performance (GL5) in one product".

Silkolene do a product called Silktran Syn 5 75w-90 which has this capability and will not damage your synchros. It's a fully synthetic ester based oil.

Hope this helps

Cheers
Simon

JohnD

iTrader: (5)

My experience of using Silkolene Syn5 in my previous Subaru (99my) is not good! As a firm believer in not leaving a gear oil in for 30k I changed to the above oil and began to experience poor synchro performance - crunching from 4th to 5th at relatively high revs (4k +) I changed to Castrol Syntrax (now called Driveline) and the problem disappeared completely. Perhaps the Full synth is simply too slippy? (It now resides in the gearbox of the wifes Primera!) I believe I am not the only one to experience this problem using full synth gear oil in a Subaru box. It turned out to be an expensive exercise that I won't repeat in my current STi
JohnD

StretchGSK

The people you speak to in the oil business all say that fully synth is ok.
I spent quite a while talking to a very helpfull guy from a business that repairs gearboxes etc. He said that in his experience the fully synth causes the surface of the cone clutch that the synchro bites up agains to become glazed and it thus no longer has the ability to slow the gear down to allow the gear to engage as it should.
Now I tend to believe him as he is never going to get any business from me and I am sure as this is his speciality field he would/should know. And now that I think about it my 4th gear only started crunching about 5000km after putting in Royal Purple Max Gear. Could this be a coincedence in a car with only 60000km??

I will spend a bit more time researching the GL 4 and 5 spec and post anything I find