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Brand new RB25 big box notchy shifting

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Just put in a brand new RB25DET big box, auto conversion.

Last time I drove manual was my 260Z, 15 years ago. But this box seems a bit notchy shifting up. Are new gearboxes like this? Do they have a break in period?

Also noticed a vibration on the clutch pedal when shifting close to red line. It is R34 box, with a pull clutch. I installed a new Nismo sports clutch with a slightly lighter flywheel.

I am running Penrite Pro Gear 75W-90.


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Yes, a brand new box needs to wear in a little, and the "big box" is actually pretty beefy compared to most.

Just treat it nice for 500klm then change the oil, see if it improves

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  • 2 months later...

Or to be a bit more specific. The 5 speed gearboxes that are built to take the RB25DET (turbo engines). The R33 GTS-T and the R34 GT-T came with them. Also the 300ZX Twin turbos, came with a similar gearset. A modern version is the CD009, which comes on the 350-370Z, 6 speed. They physically look stronger better made with extra gussets etc.

Basically these are the go to gearbox for people wanting a reliable gearbox for high HP applications. 

By the way I had mine checked by a local mechanic and he thinks it is fine, just needs some more miles to be clocked up on it.

The vibration was due the the Nismo pressure plate being out of balance. Had to pull it out and get it balanced along with the brand new billet steel flywheel. I would have thought they should be good from the factory already.

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I am running Penrite 85-90 full synthetic. 

He reckoned I should not play with difference oils. As I saw someone comment that they think the synchro's in these like mineral oil more. 

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You beat me to it while I was typing this. Regarding mineral, Duncan mentioned somewhere in another thread about Terry at Award diff and gearbox recommending mineral with more frequent changes. I can definitely see the merit in that, getting rid of any excess metal in the box frequently. The same recommendation of changing gear oil after every event is for the same reason in dog engagement transmissions, to purge the metal shavings, regardless of oil type used. Obviously dog boxes shed more metal that synchro boxes but idea is the same for prevention of gear pitting and whatnot.

The main advantage of using synthetic is the higher operating temperature break down point of lubrication, leading to longer interval changes which can be good or bad depending on how frequently you change transmissions oil. We generally break in / flush the synchro boxes with Castrol VMX-M mineral. Actually in our white 32 it still has it in it after 2500km including a 1500km drive to Adelaide on a rebuilt box and the shift quality is excellent.

On 07/10/2021 at 1:36 PM, elohim_imanu said:

I am running Penrite 85-90 full synthetic. 

You mean

On 31/07/2021 at 7:32 PM, elohim_imanu said:

I am running Penrite Pro Gear 75W-90.

If so I hope it's this one


Not this one,  it's GL-5


On 07/10/2021 at 12:46 PM, Dose Pipe Sutututu said:

(this is my opinion, please feel free to ignore) whatever you do, don't put Redline Shockproof into the box. Great for old, worn and thrashed boxes - has no place in new tight boxes.

Gee.. that sounded wrong.

 I wanted to both like and laugh at that one 😄

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Actually I mean this one, after a check. (the 90 was for the diff) 🤣


Is this bad?

I was surprised to see the amount of tiny steel shavings when I drained it after about 150ks, due to the clutch balance problem. Since I do not race and I am not pumping high HP through, it is this oil a good choice and how often do I change it? We are only talking a few thousand ks a year.


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Nah should be spot on 👍

Your box is new yes ? It will shed a fair bit from new, a balance problem wouldn't have had an influence on gear to gear mesh, which is where most if the material comes from.

Change intervals ? Change it in a year and see what it looks like. When new a good 500 -1000km first oil drop is generally the go.

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