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Gearbox question (yes, another one!)

craig8585

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Right then..

My box has begun making some rather unwanted noises over the last few weeks which are gradually geting louder and louder. Its a very hard noise to describe so I will add a video clip below (it is the high-pitch metallic ticking sort of noise).

I've searched through every thread related to gearboxes on the forum but cant find a definitive answer to a few questions I have regarding the notorious gearbox issues..


- When the counter rotating gear circlip comes off, is there any noise of notice prior to it happening?







My noise occurs when..
- Driving in all gears, on or off throttle
- Freewheeling in gears with clutch depressed or neutral with clutch in either position
- ONLY occurs after driving 4 or so miles, once the oil is warm I assume.

I recently changed the clutch for an ACT Heavy Duty Organic item, which went well. The old gearbox oil was Redline Lightweight Shockproof, but I refilled with OEM Nissan stuff as that was all I had at the time. Last weekend I had a last ditch effort at fixing it and refilled with the Redline Lightweight Shockproof again, but it has made no difference. There was not a particually large amount of swarf on the mag drain plug either, just the usual amount as to be expected (no chunks!)

My assumption is that it is some sort of output shaft bearing thats on its way out due to the noise and symptoms mentioned above, but cant be sure until the box is off and apart. Luckily I have got a spare 6-speed box lined up incase this one is toast, but would prefer to rebuild this one than fit the spare.

Any advice and experience is more than welcome, and hopefully we can build up a good profile of problems and symptoms people have occured.

Cheers, Craig
:)
 

craig8585

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I just played that vid clip on my computer and can barely hear any noise at all. It is definatly a fair bit louder than it appears in that vid!

Also, it doesnt get any louder with the gaiter removed either but can hear the general box noise a lot more. Maybe the sound is traveling through the metal shifter a lot more than the air...?
 

craig8585

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I've just found this on another Silvia forum, so have edited out the irrelevant bits, and left that of interest.

It'd be cool if people could share their own experiences too as to build up a better profile of potential problems..






If your gearbox is making some noises, check the fluid levels immediately. Checking the gear fluid requires removal of the filler plug and poking your finger in to check.

The S15 gearbox is known for making noise. These includes harmonic wines in certain gears (especially 6th) and some slight clonks when engaging.

The problem has been identified as the front two constant mesh gears. The input shaft and the lay shaft's both have a fixed gear that like to become noisy in the teeth over time. The biggest cause seems to be poor lubrication/oil quality (courtesy of NFI).

Replacing the gears and using a good quality oil will fix the noisy box issue. Its not nessisary to overhaul the box just to replace the gears. You can get away with just replacing the parts that are worn. Typically syncro's and majority of the bearings are re-usable.

Also the gear stick will shake since the shifter is directly in the gearbox and isn't cable shift like many other cars out there.

The S15 6 speed gearbox has a weakness in 3rd and 4th gear where the gears are attached by a circlip.

Click Here For Large Image

The common issue with them is the circlip/snap ring breaks out of the groove and causes all sorts of shift problems. The fix there is to machine the groove deeper and provide the ring more surface area to but up against.

Syncro failures are not common nor are gear set failures.

The S15 Flywheels is Dual Mass. Dual Mass Flywheels should not be machined, but replaced (it apparently says DO NOT MACHINE on the flywheel). Dual Mass Flywheels are designed to take a portion of load transferred form the engine to the gearbox.

Many change the Dual Mass Flywheel to a lightened Single Plate since I understand they are a lot cheaper. Changing to a single piece flywheel will increase nvh noise significantly compared to the stock dual mass (courtesy of ITCHY-GO)

The Standard Clutch in an S15 is designed to absorb some of the load transferred from the engine.

Upgrading to an extremley heavy duty race type of clutch such transfers more of the engine loads to the gearbox an therefore puts more strain on it.

The release (throw out, thrust) bearing is prone to failure. The release bearing is located along the gearbox input shaft (external) and should be changed when replacing a clutch. When a release bearing fails it generally makes a noise all the time (these usually come as part of a clutch kit and shoul be replaced).

Certain gearbox oils can make the box louder or smoother. I'd say redline would be better or just use factory recommended gearbox oil.
 
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did you check ur fluid on this and sort it?

i have a whiny noise coming from mine on tickover and little in lower gears, need to check the level!
 

meddler

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This has now been added to the useful threads. Great info in the 3rd post Craig.
 

craig8585

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My problem turned out to be nothing to do with the gearbox afterall. I'd definatly try new oil though first off.

I use the Redline lightweight shockproof stuff. It reduces noise a lot. Try overfilling slightly too (around 200ml) as this smooths gear changes too. :)
 
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My problem turned out to be nothing to do with the gearbox afterall. I'd definatly try new oil though first off.

I use the Redline lightweight shockproof stuff. It reduces noise a lot. Try overfilling slightly too (around 200ml) as this smooths gear changes too. :)
im running the lightweight redline craig, and have now topped it up a bit more but still seems whiny..

it ever since i put the redline in it started, im not bothered though as long as it kosher and doesnt mess up..
 

craig8585

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Thanks for the info Craig, so what was the issue then ?
Well, I havent got to the bottom of it yet as I haven't had time to look in depth, but I'm sure its not the box. It seems to be something under the carpet/behind the radio! It's really hard to pinpoint where it is coming from. I've even had my mate with his head in the passenger footwell trying to find what it is! Really strange though as it only seems to do it when it's warm.


im running the lightweight redline craig, and have now topped it up a bit more but still seems whiny..

it ever since i put the redline in it started, im not bothered though as long as it kosher and doesnt mess up..
Thats odd. The Redline oil does seem good to me. When I changed my clutch I had to refill it with OEM oil as I couldnt get any Redline in time, but when I changed it again the fresh Redline oil (that came out of the fill plug) stuck to the oil tray like s*** on your shoe. The OEM oil ran off and puddled in the bottom, but IIRC the viscosity is the same as the Redline lightweight. Have you got uprated gearbox mounts or locking collars etc?


I can´t open the larger image in the 3rd post :(
It's not working for me now either. I'll find it again and put it on here via my photobucket account :)
 

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I think that post on #3 is an old (but good) one from nissansilvia, good searching skills there hehe
 
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