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Gearbox self destructed for Christmas - thanks Santa. Sound like circlip failure?

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I'm 100% sure my 3rd / 4th gear circlip has let go. There is talk some people weld the gear in place vs regrooving and fitting a larger circlip. Has anyone had experience with either method?
 
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_Wing_

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I've done it long ago but there were too many risks, I never ended up using the built 6spd gearbox as it's only a matter of WHEN, not IF, it'll break. I ended up going with a gearbox conversion......... with me ending up on my 3rd gearbox conversion. Do it once and do it right.
 
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I've done it long ago but there were too many risks, I never ended up using the built 6spd gearbox as it's only a matter of WHEN, not IF, it'll break. I ended up going with a gearbox conversion......... with me ending up on my 3rd gearbox conversion. Do it once and do it right.
Thanks for the feedback, I recognised your comments on the nissansilvia.com site. I'm trying to locate somewhere in Auckland that has done the circlip mod. I'm hoping someonw knows what to do as the exact technique is not clear to me. Some people refer to making a newly located deeper groove, however I assumed you'd just make the existing groove deeper and fit a tighter circlip - could you confirm? My car makes 210rwkw, I haven't gone to a GTRS turbo etc partly because I didn't want to kill the gearbox and have to upgrade my clutch etc. I'm going to keep the power where it is so a conversion is probably overkill for me. That and I'm pretty sympathetic towards my gearbox, so I'm pretty surprised mine gave way (only 70k's on the clock too). Because of the low k's and known history, I'll definitely fix mine - it's just a matter of whether I try this circlip mod.
 

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There's 2 main techniques:

1 - deepen and/or widen the grove the circlip sits in and replace with a larger circlip: this will weaken the shaft as the surface hardening process is now removed, and the shaft is now physically weaker at that point.

2 - weld the circlip in place so it never comes off: welding is extreme heat which will alter the metallurgy of the components, and will never ever be rebuildable.


Of all the people that I know and/or have reported on the famous circlip mod, everybody eventually breaks the gearbox. You may consider yourself sympathetic towards the gearbox by shifting slower and softer, no launches or clutch kicks but you have to bear in mind "on/off/on/off/on/off" throttle is a big reason why the circlip fails. Helical cut gears by design are always forcing each other apart which loads and unloads the circlip until it fails.


Personally, I'm only running the standard turbo but I will get to test out a few turbos soon. Regardless of power I wouldn't want to granny around a sports car...
 

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Just a note on the costs, I don't know how it is around the globe but in Australia a 6spd gearbox is around $1000, less if you have the time to hunt around and wait for a crash, more if you buy it from a wrecker.

So you broke a gearbox, $1000
Pick up another gearbox, $1000
Labour to swap them around, $400
Downtime, depends how quick you find a replacement gearbox

TOTAL: $2400. Add a few hundred dollars and you get a good gearbox conversion. And I say GOOD because there is expensive and there is cheap stuff out there that are bad; ask me how I know and why I'm on my 3rd gearbox conversion lol
 
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Sorry to hear about your troubles mate! :(

Wing what gearbox set up are you running now? This is something I will no doubt do in the next few years..RB25 with single plate Excedy sounds good to me.
 

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I first used a z32 gearbox + a mazworx copy kit + a OS GIKEN twin, then went to rb25 gearbox + a pt kit + a FULL CARBON twin, now back to z32 gearbox + alpha omega kit + FULL CARBON single. Other than the gearboxes, all parts were brand new... which is scary because I reckon the money I spent on these lessons is enough to buy me another s15 :annoyed:

Here's the parts I'm now using: www.ao-ps.com


Between RB25 and Z32, the Z32 gearbox is the better pick (which is why I went back to it) as they're both internally the same so same strength, z32 is cheaper, z32 usually in better condition and as i'm using the ALPHA OMEGA setup, the shifter comes out of the standard shifter hole (no cutting or bashing).
Also, the rb25 gearbox is actually too short so people do all sorts of "interesting" things like flywheel spacers, bending the shifter so it sits at a 45 degree angle, adding a dogleg into it or not addressing the issue at all and giving you a nice surprise when you go to install it (I had that happen to me and still have a pic of it somewhere :mad:).

Actually, it wasn't the gearbox itself that was the problem it was the conversion kits that let me down the most. When I bought all my conversions I had no other choice as there was nothing else available, but it was very obvious just looking at the products that there were issues: only half the gearbox is bolted on, adapter that is as thin as my pinky finger, spacing a heavy flywheel spinning at 7000rpm, why use a rb25 gearbox that's too short when you can use the same gearbox in a different housing (z32) that will do the job?

I'll try not to talk your eyes off so will only touch on the last point - like most things it's not so straight forward... you see, the z32 gearbox has what is known as a "remote shifter" design whereby the shifter is external to the gearbox itself - the shifter is connect via a long linkage which when used with a mazworx style of kit will make the shifter sit too far out, effectively making the gearbox too long.
The beauty of this "remote shifter" is that ALPHA OMEGA makes all the right parts so the shifter comes out the standard hole. So with the right kit you can have a good fitting, strong, reliable and economical gearbox conversion.


If you have an s15 still running the 6spd gearbox, the alpha omega s15 conversion allows you to keep your s15 flywheel/clutch setup whereas other conversions require you to change to a s14 setup, so good money to be saved there, if you're already running a 5spd gearbox in your s15 then the alpha omega s13/s14 conversion is the one you want.


There's heaaaaaps of things to consider and talk about, I just hope that nobody makes the same expensive mistakes that I have. Maybe we can sticky a thread to gearbox conversions so that people can find all the info in one place?
 

craig8585

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So you broke a gearbox, $1000
Pick up another gearbox, $1000
Labour to swap them around, $400
Downtime, depends how quick you find a replacement gearbox

TOTAL: $2400
I don't get this.. how does it cost $1000 to break your own gearbox? I thought that was the free bit! If I break a box I see it costing £450 for a box and £50 to borrow a ramp and a mate to help do the work. Plus the best part of a day to change it.

I know the SR20 gearboxes are weak but personally I would never want to loose the 6-speed box - hence why I've got 2 replacment boxes just incase. Yeah they are a lot of money but it's a price I'm willing to pay. If your running serious power then a conversion probably is the only way to go unless you change the entire gearset..?

I like the idea of an all-in-one gearbox thread Wing, I'll get one going shortly. You clearly have a lot of experience with this yourself so look forward to reading your input.
 
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Thanks again Wing. You're running a pretty serious driveline for a stock turbo car - drift action I'm guessing? I was hoping stock turbo and clutch would lead to gearbox longevity - but I guess not. I just put in some magic Amsoil gearbox fluid too about 2 months ago so that'll go to waste.

I was quoted today $1800 NZD for the circlip mod. I'm still shopping but expected it to be around that. Unlike some, I have no noises from the gearbox so I'm hoping internal damage is minimal and the bill may be lighter.

I want to keep the original gearbox in play so I think I'll be going for option 1 - wish me luck! I'll let you guys know how it goes.
 

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I don't get this.. how does it cost $1000 to break your own gearbox? I thought that was the free bit! If I break a box I see it costing £450 for a box ...
Free? So when can I come around to pick up that perfectly working gearbox for free? :p Or would you want 450gbp for it? :)


And I 100% agree, if the 6spd gearbox was as strong as a z32, then I would never ever ever want to lose it (which is why I did the circlip mod before). But wasting money on replacing broken 6spd gearboxes for the better ratios is not practical or feasible.
 

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Thanks again Wing. You're running a pretty serious driveline for a stock turbo car - drift action I'm guessing? I was hoping stock turbo and clutch would lead to gearbox longevity - but I guess not. I just put in some magic Amsoil gearbox fluid too about 2 months ago so that'll go to waste.

I was quoted today $1800 NZD for the circlip mod. I'm still shopping but expected it to be around that. Unlike some, I have no noises from the gearbox so I'm hoping internal damage is minimal and the bill may be lighter.

I want to keep the original gearbox in play so I think I'll be going for option 1 - wish me luck! I'll let you guys know how it goes.
I do drift :D Although I'm sh!t at it, and I also circuit race and daily it too hehe I go by the "prevention is better than cure" mantra, so now that it's upgraded I was going to install my GT-RS, but actually had to sell it to fix my motor. At work we're developing new turbos for SR20, so I'll get to test them out without fear of breaking the drivetrain.

Amsoil is a good oil, I like it (and use it) too! Remember that when the box blew, metal chunks started flying around inside but hopefully they didn't cause any damage! Good luck and keep us posted :thumbs:
 
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Has anyone tried the Z33 six speed gearbox? I was thinking about this as I 'heard' that it has the same gearing as the Z32 but with a six speed factor that would operate like the S15 six speed keeping the rpms higher between shifts. If I had the extra cash I would experiment but currently I will stick to my unmodded S15 six speed until it says bye bye.
 

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Free? So when can I come around to pick up that perfectly working gearbox for free? :p Or would you want 450gbp for it? :)
Ok.. My gearbox blows so I spend £450 on a new box and am I'm the same position as before. Hence the cost is £450, not £900. :) there are different ways of looking at it I suppose.

BTW Wing, as you have trader status why not advertise and describe the conversion kits you sell in the traders section? I know you have a web link in your sig but it would be nice if you would do that to as it may interest a lot of people
 

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Yeah different points of view, the way I see it is you can take out your unbroken gearbox and sell it off to recoup the money which you can't if the box is broken :)

My interest and job is in tech and development as opposed to sales, but sure I can do that no probs; the website and pics need updating so when the web guy gets back to work I'll post up details with nice big pics...
 
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Well my gearbox is out and the news is all bad. The counter shaft has been chewed around the dreaded 4th gear circlip so the shaft is a throwaway item according to the gearbox mechanic. In addition, the 3rd and 4th gear syncros are recommended for replacement along with a host of other parts. The end bill is looking like $2000 NZD for parts alone and then a further $1000 for labour.

Option 2 is to fit a second hand 6spd gearbox which incidentally are as rare as rocking horse sh1t. I've managed to find one for $1800 and then I incur the $1000 odd for labour.

So either way - I'm going to take a bath to the tune of $3k. My particular gearbox specialist had never seen this kind of damage before to the circlip area. It seems many rebuilds had been just syncro and bearing replacements. I guess I just got lucky with a bonafide circlip failure - yay!

The 5 speed conversion had never appealed to me but given the costs of repairing the 6spd - although the 5spd conversion will also cost $2500 odd, at least repairs from there will be cheap.

I know it makes sense to repair the current box rather than replace with a second hand unit; but I also hear people who get rebuilds done often have to go back many times to get it right. I've heard this from 2 people who went to 2 different places. I want to avoid any unnecessary remedial work. At least with the second hand box - you know it'll be assembled right (although it may be a grenade waiting to happen).

What do you guys all think? I thought the decision would be easy but now I'm not so sure. I'm trying to think ahead as I plan to keep the car for a while yet.

ps - Skyline conversions etc are not on the agenda.
 

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I've been down this path and I even had my 6spd gearbox rebuilt with the circlip mod, but in the end I knew deep down inside that it'll only be a matter of time before it breaks. They break sooner or later, stock or modified... you get a bit of success then it breaks, in fact a mate just broke his circlipped-6spd box. If you're set on the 6spd box with the circlip mod, then might as well rebuild what you have, because either way your box or a 2nd hand box is going to need to be fully stripped down to carry out the work - just pick a transmission specialist that you can trust because as you know, getting something checked is a big, time consuming, annoying job.

The 6spd gearing is excellent! I believe it's a big part of what makes a s15 mechanically so great and if I could keep it I would have - I actually did everything I could to keep it like buying a soft clutch and the circlip mod. If you're considering going to a SR20 5spd box for $2500 odd then you might as well get a z32 gearbox conversion. That's the best solution to keeping similar ratios with the required strength; a z32 gearbox + 4.3 final drive. I did the calculations. And you're lucky because now there is bolt-on z32 gearbox conversions for the s15... back when I did it the first time I had to spend more money to convert to a s14 flywheel/clutch setup, chop this and dodge that.

Good luck with it, I know your pain well :|
 
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Wing - I reckon Nissan should have ensured we never have to feel this pain! You would think surely the engineers who designed the box would have known the implications of having the circlip where it is positioned how it is. Worst case scenario Nissan should have a rebuild / strengthening kit available for victims of this damage. I guess that would be them admitting liability to poor design which would explain why they wouldn't.

You know - I'm actually in 2 minds now as to whether to even attempt this circlip mod. The new counter shaft is around $1300 NZD and I'm nervous about having someone butcher it and me having to buy another one with another 2 week's wait from Japan. There seem to be plenty of places in Oz that do this work but in Auckland at least, no one seems to know much about it. I don't really want to risk it.

Some guys seem to be getting by on just stock rebuilds with up to 250rwkw so maybe I'll just rebuild back to stock specifications and just cross my fingers. I figure with my 210rwkw, stock driveline and some mechanical sympathy; I have a better chance than most (I hope!).

I actually saw the damaged components and the infamous groove where the circlip fits. The groove is actually quite large already. Some people say they make the groove wider, others say make the groove deeper. What I'd like to know is what exactly causes them to fail? I've heard the helical gearing forces cause the clip to dislodge - if so, then it's the torque / power of the engine that determines the failure rate. I've also heard the circlip can be "clipped" during changes causing the circlip to fracture and fail. If this is the case, then recessing the circlip makes sense and explains why even low power cars can experience this fault.

Either way, if the mod works or helps then I'd like to try it, but with the costs involved and inexperience I've found - sh1t it's like Russian roulette with 1 chamber empty! You can imagine if someone machined the shaft incorrectly or used the wrong sized circlip – the failure rate would be increased by this modification.

So lack of experienced "circlip" modifiers and the costs involved mean I'll probably be going down the rebuild to stock specification route. Wish me luck as I spin the barrel!!

ps - I avoided buying an Rx7 due to reliability issues - I shake my head at you Mr Nissan!!! haha.

pps - to add insult to injury, the towing firm lead me to damage my front bumper loading the car onto the truck (directing me to drive into an incline that would not allow me to load safely! What was the guy looking at when directing me to drive further forward??!).

But worse still; I wanted to be towed to the garage to avoid damaging the gearbox further. Up until that point, all gears but 3rd worked and there was no grinding, noise etc - all fully functional. The towing firm had me drive the car onto the street, and onto the truck (approx 50m). Upon driving off the truck, reverse and 1st (the only gears I used to load, unload) sounded awful, grinding and munching away.

I reckon this was where the shaft damage was done. I saved $20 on the towing charge vs more expensive competitor firms; but it potentially cost me $2500 more in damages. There's a lesson to be learnt in that story for everyone.

To anyone who suspects circlip failure – have the car towed, and make sure the tow company uses a slide deck truck to preserve your body kit, and have them use a winch so you don’t have to drive the car onto the truck. This was always my plan but when the wrong type of truck turned up, I figured my gearbox wasn’t making any noises and should be fine to travel 50 odd metres. 5m can be the difference between internal carnage and not – so play it safe people.
 

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I guess Nissan wasn't expecting or caring that we'll be modifying the car to pump out double to almost tripple the factory power levels... afterall the car only makes out about ~110wkw from the factory, or they didn't want to over-engineer everything (more money) like Toyota has in their supras. These boxes break because of a combination of power, driving style, clutch, physical size and design.

I touched on the helical design - regardless of power/torque the gears are constantly forcing each other apart under load. You take your foot off the gas it unloads, you apply gas it loads. Obviously more power/torque = more load but even at today's "low" power levels (remember that 200wkw is almost double factory power) it's enough to cause issues. You can widen the circlip, deepen it, or both. Widening will allow for a fatter circlip and the bigger it is the more it can handle, deepening the groove allows for the same + more surface area BUT at the expense of shaft diameter. Choice is there to do one or the other or both. I wouldn't recommend welding.

I think if the combination of things you've done to come to this point resulted in a broken gearbox, then with a standard rebuild it'll only be a matter of time... unless you (un)modify the car or modify your driving style. I wasn't prepared to drive a sports car granny shifting.

IMO there's 2 fails from Nissan in their Silvia's; the gearbox, and the rocker arms... I've replaced both :(

Damn that sux with the tow! It's like getting kicked when you're down :annoyed:
 
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My gearbox broke at 72,000km’s; now if the rebuild lasts me another 72,000km's, then that's probably acceptable to me if that’s the price to pay to maintain the 6spd. I don't plan on increasing power or changing my driving habits etc so this assumption should hold true if the break is just fatigue related.

The conditions in which these gearboxes break seem to be variable. Wing, you mentioned your friend's circlip modded box recently broke. Do you know whether the failure was circlip related again - ie the modification failed? When people mention a circlip modded box blew; are we sure the problem was the same as the original failure or maybe it was due to something else?

One thing’s for sure; keeping below 250rwkw, maintaining the stock driveline, maintaining your fluids and exhibiting some mechanical sympathy doesn’t guarantee a long and prosperous relationship with your gearbox. Just like Rx7 owners accept engine rebuilds are a part of rotary ownership; we S15 drivers have to unfortunately accept gearbox rebuilds are a part of 6spd ownership…
 
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