Hi people,

It's time to change the oil in gearbox and diff of "little beastie" GT. The gearbox especially, whines like a turbo on acceleration, then grinds like a croc nashing it's teeth when decelerating from a reasonable speed Synchro is also a bit tricky in first and also difficult to put into reverse sometimes.

About 5 years ago a mechanic topped up the gbox with modern gearbox oil, 10- W90 i think. Recently, some of you good and knowledgable folk have informed me the correct oil is single wheight 40 oil. This explains the weird noises, and the need to change the oil to the correct sort.

Penrite make a specific W40 for older gboxes, selling at $18 per litre. Can any one tell me how much I would need to fill both the diff and gearbox in the GT, and anything else I should know before doing the job?

Cheers, B.

B i use a penrite 70/80 synthetic gearbox oil in mine.
reason is for the same prob u describe as with yours. has helped it but will never 'fix' it completely.
diff wise i use a penrite 90/140 diff oil to keep it quiet.
now i know these oils seem far heather than original, but remember that oils of today are designed for exactly this. and don't forget that ours cars have 100,000 miles or more on these components now so that has produced wear that the original oils won't keep up with...
that's my theory anyway and my GT has been fine.

Thanks for the quick response as usual PR91. So what you're saying is the oils you have recommended are better at coping with the amount of wear in a gearbox that has seen that many kilometres ?

Also, do you have some idea of the volume of oil in a GT gearbox and diff ? This would save me bying a heap of it if only using a few litres to do the job.

Cheers,

B.

I'am using Penrite 75 synthetic fortified sae 75w-80, was with the car
takes less than 2.5lt is this the same Brett?Have been told not to mix
some of these new oils,Lindsay was talking about Castrol Edge for engine
oil at the nationals I think,what engine oil are you using in the GT Brett?

Thanks Gerry. The good oil on the diff is it takes about 750ml apparently. Your right about mixing oils tho. I don't think thats a good idea, be it engine, gearbox or diff. Best to be on the safe side.........'cause oils ain't oils

B.