Gearbox Oil - Should I Change?

[meestapeta]

Hey folks, thanks in advance for any advice. So I realized the other day that the oil in my gearbox (78 280Z 5 speed) probably hasn't ever been changed. Right now its at about 127k total mileage and it shifts fine, actually quite well for such an old car, but I was just wondering about that oil. Is it complicated to change it? Expensive? Is it worth it? And have any of you changed it and noticed an improvement in shifting quality?

[2ManyZs]

Easy to do and it's rather inexpensive insurance. Pull the drian plug out of the bottom and drain it, pull the plug on the passengers side to fill it. The hardest part is getting the lube back in it, most times I use a clear neoprene hose and run it from the engine compartment down into the fill hole and re-fill it. The diff is done the same way, as the mustache bar makes it a little difficult to pour directly from the container, pull the drain plug, and re-fill through the top plug. Changing both will cost you in the neighborhood of 25-40 dollars depending on which brand of lube you choose if you switch over to synthetic, even less if you go with non-synthetic lube.

If you want some imprevement, go to a synthetic lube such as Red-Line MTL for the tans, and 75-90 for the diff. You'll get a bit slicker shifts and it will last much longer than regular lube.

You don't have a filter on the trans or diff to get the contaminants out of the lube like you do an engine, but you still change your engine oil regularly right? So why not change the lube in the trans and diff both and get longer life out of the bearings,synchro's and gears? All the fine metal particles in the diff and trans have no place to go excpet to keep getting dissolved in the lube and spread throught out the case. Once the drain plug magnet builds up to a certian point with shavings, it is no longer going to pull the shavings out of the lube.

[260DET]

Caution re using Redline oil in the gearbox. I filled my recond box with MT-90 and immediately noticed that the shifts were harsh. So the oil was drained and was found full of tiny brass particles. Now it could be that there is an oil unrelated problem so the jury is out until the box is stripped.

[mwz]

One last thing worth noting might be to make sure you succeed at getting the fill plug out first, then the drain plug. That way, if you have trouble getting the fill plug out, you're not stuck with an empty gearbox. Been there, done that :stupid:

[Victor Laury]

One last thing worth noting might be to make sure you succeed at getting the fill plug out first, then the drain plug. That way, if you have trouble getting the fill plug out, you're not stuck with an empty gearbox. Been there, done that

When this happens, all is not lost. You'll notice that very close to the abso-Friccken-lutly fused fill plug, that you've rounded off, ruining your best 17mm, a knuckle or two and your throat from yelling obsenities at, is the reverse light switch.

Ah Ha!

Pull the switch (it never gets stuck) and fill. It's a tad bit lower than the filler plug, so you'll be 4 oz shy of full. Big deal.

[meestapeta]

So what kind of gearbox oil is the best? I think the manual recommends Castrol GTX or something, is that stuff any good? I'll avoid the Redline after hearing that story.

[260DET]

If you want to use a full synthetic, Castrol recommend Syntrans although I put the slightly heavier Syntrax in mine which now works beautifully. In a cold climate though Syntrans may be the better choice.

[meestapeta]

So I changed the gearbox oil tonight. I refilled it with Castrol Hypoy C, which apparently is the uprated version of Castrol Hypoy, which is what was recommended in the repair manual I have. Interestingly enough, I found 5 or so 1/2 inch long strips of metal stuck to the magnet on the plug, along with plenty of metallic dust. Refilled it, let it off the jack so it could drain to the right level, and then put it back up and capped it. Now it shifts smoother and doesn't buzz in 3rd gear anymore. Yay! I'll probably do the diff in the next few days.