API GL-4 and GL-5

[DakDak]

Hi all,

I know this isnt a Honda but I'd really appreciate some knowledge.

My SR20 GB feels really notchy. I know they are known for not being the smoothest of gearboxes. But mine makes noises when cold. With taking off from a stop, and gear changes. I've had it inspected by my mechanic and he says just give it a fluid change.

So I began my research.

Everyone rants and raves about Redline Shockproof, how it is the bomb-diggety. But I am concerned that it isnt fixing the problems but putting a guise over them.

I know this much, an SR20 is a syncro box, and some additives in Redline Shockproof [which is really designed for dog boxes] dont react well with the yellow metals in the gb e.g syncros. This is because it is GL-5 I believe. Its designed for diffs and contains sulphur as an additive which attacks brass and copper used in syncros and bushes?

On the service manual it states to use 75-90w GL4. Im leaning towards Motul 300.

But is it safe to use a GL-5 oil for my gb provided it says something like "safe for yellow metals'? Is there even such thing?

Can anyone give their two cents?

[wastingtime]

I think mainly when people use the wrong oil is when they use LSD diff oil in the actual gearbox as it has friction modifiers or something. Id say as long as its any 75-90w you should be fine.

I tried redline in my rex and wasn't happy for how much it cost, motul I've heard very good things about.

I've tried a few cheapos too and nulon and valvoline sucked. Penrite gear oil is really good for the price and great if you're on a tight budget.

[mocchi]

i thought gl5 was too slippery for synchros
thats why theyre in the gl5 category

[DakDak]

I think mainly when people use the wrong oil is when they use LSD diff oil in the actual gearbox as it has friction modifiers or something. Id say as long as its any 75-90w you should be fine.

I tried redline in my rex and wasn't happy for how much it cost, motul I've heard very good things about.

I've tried a few cheapos too and nulon and valvoline sucked. Penrite gear oil is really good for the price and great if you're on a tight budget.

Im going to try Nulon. Sulphur is added into gl5 stuff, and that eats yellow metals. I dont hink they are designed for syncro boxes only dog boxes.


i thought gl5 was too slippery for synchros
thats why theyre in the gl5 category

Any idea why some oils list themselves as gl4 and 5?

[dougie_504]

Dude if your synchros are rooted then using a superior GBox oil will only buy you some more time before the rebuild.

Consider just biting the bullet IMO.

[DakDak]

I changed it yesterday using Nulon GB additive and Castrol VMX 80.

Feels great now. I was confident it was just the inferior quality GB oil it previously had.

Im really just trying to diagnose things. I dont want a fluid that will mask things up. Just something that will do its job.

Anyways I called up the GB specialist guy. And he doesnt rate Redline shockproof. It gums up after awhile and its additives eat yellow metals. He confirmed this.

[dougie_504]

Feels great by comparison, or is it fixed/perfect?

Reckon you still have synchro issues?

[DakDak]

Driving feels good. No more resistance shifting. So problem solved. I dont think I really had any synchro issues to begin with. It was just crappy oil making second gear hard and causing crunches.
My sr20 gb will never shift as smooth as my DC5R's. But its in really good health compared to other s15's.

[wastingtime]

I heard redline is a rebuilders nightmare and just gums everything up like you said.

When the fluid gets a bit older you will notice grinds more try nulon gear treatment, I tried that for syncro problems in the past and it completely fixed it for about 10k lol.

[DakDak]

--Update--

The Castrol VMX 80 and Nulon treatment so far is going very well in my GB.

Been about 1000 km now.

I'll regularly update. At service intervals.

[bboyzell]

Personally Iv used Castrol VMX80 in my Cable Driven B16A Gear box, And i found it had pretty good results.
Went from being difficult to engaging first and second gear, to sliding in nice and easy.

Still have a problem with 4th, if im coasting along at low speeds it tends to kick me out of it :( happens once in a blue moon tho