Gearbox oil, sorry! 80w90 or 75w

[Ads1987]

Hi All,

Sorry it looks like this is one of those debated topics, I've searched and read a few threads but still stuck!

My gearbox broke, I've found a second hand 4 speed that's done 77,000 miles (not ideal but can't afford rebuild atm) and i'm ordering a new set of side seals, input seal and fluid etc. I've ordered from brickwerks and chose the ep80w90 gl4 spec 5litre bottle, I gather GL4 spec is needed as GL5 can damage internals but i'm not sure if I should be using the 75w80 stuff instead?

Some people seems to say the 80w90 isn't great and the 75w80 gives better shifting, does anyone have experience of this or shall I just go with what I've ordered?

https://www.brickwerks.co.uk/t3-parts/d ... litre.html#" onclick="window.open(this.href);return false;
https://www.brickwerks.co.uk/t3-parts/d ... litre.html" onclick="window.open(this.href);return false;

Cheers all,

Adam.

[Aidan]

At the moment I am using the Smith and Allan 75w/90 fully synthetic oil from ebay (actually cheaper on ebay than over the phone direct) it is dual spec GL4 GL5 and meets all the specs for our oil back in the day according to Smith and Allan tech dept.
The 75W element helps a little with the cold shift while still providing the full temp 90 protection
I recommend a Molyslip treatment GM6RA as well every two oil changes it definitely helps to protect the moly coating on the synchrorings
You still have to be careful when cold with the first shift of the day 1st to second and 2nd to 3rd on a 5 speed because the cold oil baulks the rings but after a mile it will generally be good, slow careful shifts, don't try and rush it or 'beat' the synchro as all you do is bang the dog teeth on the synchroniser slider and ring and gear making the shift worse and worse over time

[Ads1987]

That's great thanks Aidan, mines a four speed but I imagine that still applies about the cold shifting?
I normally try to match the engine revs when changing but again from reading other threads it sounds like that doesn't actually help much as double de clutching will match the gears speed to the engine whereas a bit of throttle doesn't really help?
Ordered the moly slip too so will put that in and hope the replacement box isn't in too bad condition!

[R0B]

Aidan

[Ads1987]

Ah good spot, sorry Aidan!