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Old 16-03-2016, 12:08 AM   #1
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Help with RB25DET transmission

I have a 240sx with a RB25det. The 4th gear synchronizer is gone. Anybody know where I can find parts to rebuild this? Or anybody around PA or MD willing to rebuild and install? Or does anyone have one they are willing to sell? Or does anybody know if I can use parts from a different vehicle for this transmission? Any and all help would be appreciated. Just got this car and I am at a loss as to how to get it fixed.
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Old 16-03-2016, 03:44 AM   #2
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The 300ZX, RB25, and RB26 transmissions are supposed to share similar internals. Since the RB26 tranny has pretty much the same internals as a Z32 tranny except for a couple of the shafts and the AWD splitter I was able to get a transmission shop in San Diego to rebuild and fix the 4th gear synchros on my R32 tranny.

If you find a good trans shop that knows their way around a 300ZX transmission you should be good to go.
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Old 16-03-2016, 03:17 PM   #3
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Whatever you do don't use that redline shockproof oil that everyone raves about lol

I've been told by two local transmission rebuild shops that most gl5/6 has activates that contain sulfate in the oil and it can eat brass synchros over time
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Old 16-03-2016, 04:19 PM   #4
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Quote:
Originally Posted by KarlosR33 View Post
Whatever you do don't use that redline shockproof oil that everyone raves about lol

I've been told by two local transmission rebuild shops that most gl5/6 has activates that contain sulfate in the oil and it can eat brass synchros over time
Redline themselves refuted not using shockproof because of synchros. Go to this link and scroll down to a post by a user named "cameronevans" who works for Redline. He says and I quote "It's not accurate that you should never run Shockproof in a synchro box. Thousands use it without issue. By theory, it is too thick for the synchros, Mayhem is right. But, it often works and we have lots of happy customers running Lightweight."

Redline Heavy Shock Proof Gear Oil Question - Technical Discussions - ChumpCar World Series
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Old 17-03-2016, 02:03 PM   #5
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You're on the other side of the pond, I'll rather take first hand experience ( getting a box rebuilt hopefully Monday onwards ) and the advise from a transmission company. One been in business for 50+ years, and another one that's been around for 20+ when they rebuilt a old v6 fords gearbox.

Of course "Redline themselves refuted" they wouldn't say use our oil to get you by for a while.

Your car, your bills
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Old 17-03-2016, 04:20 PM   #6
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Originally Posted by KarlosR33 View Post
You're on the other side of the pond, I'll rather take first hand experience ( getting a box rebuilt hopefully Monday onwards ) and the advise from a transmission company. One been in business for 50+ years, and another one that's been around for 20+ when they rebuilt a old v6 fords gearbox.

Of course "Redline themselves refuted" they wouldn't say use our oil to get you by for a while.

Your car, your bills
Believe what you want man. If you want to believe a couple of shops over the actual manufacturer then that's your choice. Good luck with your tranny rebuild - I already had mine bench built and they didn't find any issue with the Redline fluid that was in it. And this is a shop that's been around since 1978 and with experience doing anything and everything, not some two-bit corner repair shop.
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Old 17-03-2016, 07:38 PM   #7
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And since I'm not a fan of the "Well, this shop told me..." approach to justifying any decisions I'll just leave this link here from another person endorsing Redline Shockproof. He's just a guy I know who's been working on Skylines for decades, tried all the different tranny options (PPG, dog boxes, OS Giken, etc), and crew-chiefed a Speed World Challenge GT-R team:

Nissan Skyline GT-R s in the USA Blog: Nissan Skyline GT-R Transmissions and Upgrades
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Old 17-03-2016, 10:41 PM   #8
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^^
gtr box, I dare say a complete different ball game

gtst hear
As wikiwouldsay

Quote:
GL-5 is not necessarily backward-compatible in synchro-mesh transmissions which are designed for a GL-4 oil: GL-5 has a lower coefficient of friction due to the higher concentration of EP additives over GL-4, and thus synchros can not engage as effectively. Also, transmissions which explicitly call for GL-4 oil may have been designed around this lower concentration of EP additives and thus may contain yellow metal parts which GL-5 will corrode
I swapped over to a gl4 based lube as recommended by nissan ;)
mt-xz gear oil 75w-gl4 part no KE916-99932

Nissan MT-XZ 75W80 Passenger Vehicles (1-Litre) - KE91699932

But if we did everything the same, well where's the fun in that


But anyway Getting back to the OP question
Depending if they post overseas a trader hear called Conceptua Tuning sell a rebuild kit for a 33 with a rb25det Both the spec 1 and 2
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Old 17-03-2016, 11:40 PM   #9
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I never said you couldn't or shouldn't use a GL4 oil in an R32/33 GT-R or RB25 trans (which btw have similar synchros - the part the OP was asking about, not a "totally different ballgame" as you say - its the shafts and AWD splitter that are different) but you said you couldn't use Redline Shockproof AT ALL based on what two transmission shops said.

I pointed you to the manufacturer rep's statement that yes, you can use Shockproof on a transmission with synchros and your response is just "well, these two shops told me" and "this random generic Wikipedia quote says...".

If you don't want to listen to their rep's forum post or my friend with all the Skyline experience (which is on all types btw since he has a warehouse full of them from Hako's to GTS-Ts to R34s, not just GT-Rs as you seem to think) then how about this quote from the manufacturer's website directly:

Appropriate coefficient of friction for most manual transmission synchronizers (other's synthetic gear oils are often too slippery for proper synchro engagement)


Excellent gear and synchro protection, balanced slipperiness for easier shifting in cold climates

Taken from here:

Red Line Synthetic Oil - Gear Oil for Manual Transmissions - Lightweight ShockProof®

To put it simply: GL4 such as Redline MT90 is the normal oil to use, Lightweight Shockproof for higher demand applications, Heavy CAN be used but recommended mainly for racing applications.

Since I don't want to beat a dead horse, let's just agree to disagree on this and you can believe your tranny shops while I'll believe the manufacturer, thousands of other happy owners, and a guy with extensive Skyline experience.
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Old 18-03-2016, 02:03 PM   #10
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We can all post up links from the net lol
Shockproof and there stockiest will not say "don't use our crap" lol

The spare box I'm getting rebuilt had redline crap inside.
It's a public forum so I won't quote what he said lol. He's not some back yard garage either, as when I worked at a main-dealer's some 25+ years back he was out gearbox rebuild guy, quicker and cheaper than a inhouse repair, the shops has been going for 50+ year's. Now the younger son runs the place.
If he didn't know his/there s**t he off closed his doors, or been sued by now lol

See the photos?
That's what happens with gl5 and brass synco's. Over time the black crap eats into the brass. If you look you can see it happening already.

Quote:
A traditional GL-4 gear oil of any given viscosity has about ½ of the level of sulfur/phosphorous additive that would be in the GL-5 product, so the bond is not as strong, and therefore can be peeled off without peeling a layer of brass (or less brass). This means that the GL-4 product provides a little less extreme pressure protection, so in the differential of a high-powered car, it would not be the ideal product in the differential. To understand this need we should be aware of the fact that the differential is where the final torque is applied to the wheels (in most applications)
Quote:
When we use a GL-5 product in a transmission that requires GL-4, we normally find 2 to 4 times as
much copper in the used oil as we would with a GL-4 product (with used oil analysis). Eventually the synchronizers wear to the point that they no longer make contact with the other half of the cone, bottoming out before stopping the opposing gear
. (Refer to the picture below.)

A good 90% of UK owners use Nissan own gl4 based lube, Hence why there was only 10 litres in stock, and I had to wait for 9 litres ( yes I'm replacing the oil in two boxes )
Do what you want, think what you like

If this forum wasn't dead there be loads of people saying they use KE916-99932
Just google redline or nissans KE916-99932

I'll do mine my way, you do whatever you want to yours
Mines never missed a beat in the last 7 years I've owned this one.
Only been to a garage 8 times for a mot, and one retest.
Only broke down once ( touch wood ) when my autobox went bang, after 3 years of stage one mod's, so I must be doing something right.
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Old 18-03-2016, 04:10 PM   #11
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Yep, we can all post links but it sounds better than "My mate said this but I won't reveal who it is..." lol.
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