Is this a good gearbox oil?

[Ali-Mk2]

I'm about to fill my new gearbox with 150ml of STP Oil Treatment For Gearboxes, and 2L of Halfords 75W/90 GL5 Part Synthetic Gear Oil. Good stuff? I'm not aquainted with either of these products.

I'm pleased to see that there are reassuringly few fragments of metal in the old oil, especially considering it's been in there for about 15 years. The old one died from an oil leak, starting with the 5th gear popout. 

I'll be filling it tomorrow so if I'm about to balls it up would someone please let me know?

Many thanks!

Ali

[Agreeable Slick]

STP oil treatment is fine.

Personally i would go for 80/90 hypoid gear oil for the box though.

[Barnzyuk]

im no mechanic, but im sure i heard somewhere that u should use mineral stuff, as the part synthetic stuff rots the gearbox's seals. i could be wrong though

[Ali-Mk2]

STP oil treatment is fine.

Personally i would go for 80/90 hypoid gear oil for the box though.

Can you tell me a little about that oil? The Halfords stuff is unopened so I can probably blag a refund.

Also, is there such a thing as overfilling the box? I was just gonna have it "clutch end down" and fill it up by the hole at the green end until it was completely full.

I've had a look through the past posts and those are the only 2 questions I have.

[Agreeable Slick]

It's basically just a slightly more viscous oil for the box. Coats the gears, and synchros better, and provides a slightly smoother gear change.

From what i remember the box takes about 2.3 litres of oil, there are two plugs on the side of the gearbox, one is fill hole, and one is the drain plug, easiest way to fill it it is to take the top fill plug out and then fill up from the speedo cable hole. once oil comes out of the fill hole you know it is full. 

[Godzilla]

I want to change my gearbox oil too! I had a look behind the front passenger wheel and saw one huge allen key looking thing which i think must be the gearbox oil plug. I could not find another one?? Mine is a 1991 16v GTI.

[Gambit]

easiest way to fill the gearbox is thru the speedo cable hole.

1. drain the box completly, and refit drain plug obviously!
2. remove the top allen key nut on the side of the gearbox (behind passenger side wheel)
3. remove speedo cable
4. Fill box through speedo hole until oil starts to seep out the allen key hole on side
(note: if your car is pre88 you need to slightly raise the gearbox by jacking underneath it, only a few cms or an inch)
5. once its full. refit the fill bolt & speedo cable

to fill the box you need 2 quarts of gearbox oil

[jezza16v]

I wouldn't advise removing the speedo cable except as a last resort, so many have ended up loosing the speedo drive into the box, a real pain. You have to take the filler plug out of the end of the gearbox to check the level either way, so why not use it to fill the box. The drain plug by the way is a big allen bolt at the lowest point on the gearbox/diff casing. Also, don't drain the box before you can be sure of getting the filler plug out, they're f......... tight sometimes. 2 quarts = 2 litres NAMND. 

[Gambit]

you'll only lose the speedo drive if you yank the cable out. remove it carefully. just for those who dont have a wee bottle/applicator for getting it into the side hole.

1 imperial quart = 1.13652297litres - so u need slighlty over 2 litres

[Agreeable Slick]

so rounded up to 2.3 then