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The ultimate gearbox thread!

craig8585

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Gearbox failure is relatively common and the information about it seems to be scattered all over the forum, so here it is, all condensed into one thread. Thanks to _Wing_ for suggesting the idea.


The options are..


Replace 6-speed box

Convert to S14 5-speed box

Uprated gear sets for the above boxes

Convert to Z32 box

Convert to RB25 box

Convert to other, very expensive options (HKS etc)



Please keep all information and advice here FACTUAL, preferably from personal experience. None of the 'I've heard this', or 'my mate said that'.

Links to websites offering parts and services on this topic are welcome, along with links to other threads but no business plugs. Keep that in the traders section.



Related links..

Changing oil in a SR20 gearbox
S15 gearbox diagram
S15 to S14 gearbox conversion
Cryogenically freezing gearbox internals
Z32 and RB25 conversion chat



Companies/services

PAR-Engineering - uprated gear sets
AO-PS - gearbox conversions
S-Body Automotive - Garage services in UK


^ - Additional recommendations will be added.
 

craig8585

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I'll get the ball rolling.

S15 gearboxes always have had a reputation of being weak, but they are no weaker than a S14 5 speed box. S14 owners generally accept it when a gearbox fails as a replacement is only £150 or so, but 6-speed boxes are 3-4 times the cost.

I would never be satisfied with a 5-speed box in my car after using a 6-speed for so long, but if you run serious power then a conversion or uprated gearset will be the only option available..
 

DeanS15

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is it also worth mentioning that the 6spd box may commonly suffer from a noisy input shaft? some people (myself included) think/thought thier box was on its way out when they start to hear a whine or a feint grind when off the clutch pedal that dissappears with the clutch pressed. this is a noisy input shaft (not clutch thrust bearing - which would be noisy with the clutch pressed instead). this is probably due to bearing wear, but it's by no means the end of the box, mine has gone on for almost 2 years problem free despite having this noise.......
 

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Having just read the RB25/Z32 conversion thread (linked above), I can see why it's a safe upgrade, but I'm presuming the gear ratios are very different and will effect the drivability of the S15.

I too am a fan of the 6speed box and wouldn't want to loose it. Are there no 6speed alternatives? R34?
 

craig8585

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I think the only 6-speed solution is an uprated gear set in the S15 box
 
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If you but a uprated gear set in a S15 box you will waste your money and IT WILL blow again! and I have been advised this by Polo from S-body Automotive this inc gear sets from the likes of PPG etc

The Z32 and RB25 gearbox's are the same apart from input shaft and out lengths the gears and internals are the same, main reason I am doing a z32 rb25 box is so I have a perfect shift alinement with out needing to butcher the shifter space already in the s15 if I was just to put a RB25 box in, as for affecting the drivability I cant see how it will apart from changing the fact it will be a 5 speed instead of 6, its will just take some getting used to for not going for 6th gear lol
IF (and i mean if considering one of the guys I know down 2 seasons on the bdc on a rb25 stock box till it failed) the gearbox does fail you can always put a gearset in that and it will be 10x's what a S15 box with a gearset would be reliability wise :)

If anyone has doubts or questions : S-Body Automotive
 
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craig8585

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If you but a uprated gear set in a S15 box you will waste your money and IT WILL blow again! and I have been advised this by Polo from S-body Automotive this inc gear sets from the likes of PPG etc
I'd like to know why he has said this. People on SXOC are running OS Giken gearsets with silly power without problems. All of the failings I have heard of on these boxes are either shafts snapping or circlip failure which would surely be ironed out by a gearset?
 
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Has anyone ever investigated fitting a 5 speed box from a JDM S15 Silvia spec S (SR20DE engine model)? Assuming the internal strength is the same as the s14 K's gearbox (maybe someone knows?); you'd assume it would be a straight forward swap without some of the adaptations required for the s14 K's conversion. I'll see if I can find out from some locals.
 

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A complete reinforced nismo gearbox for the bargain price of £3500, plus shipping, duty and tax.

http://www.rhdjapan.com/nismo-silvia-180sx-reinforced-cross-6-speed-transmission-set
don't forget this - taken from the nismo website on the s15 nismo gearbox information:

{Durability Serviceability performance}

Durability of Engine torque design value: 40kgfm (392N•m)
Durability of Engine power: 350ps (257kW)
Recommended Clutch: NISMO SINGLE PLATE CLUTCH
*Please note: gears may be damaged by input beyond the design values.

^^if this is the case, then it's a pointless purchase. the standard gearbox copes with those figures comfortably......
 

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....... as for affecting the drivability I cant see how it will apart from changing the fact it will be a 5 speed instead of 6........
Thats exaclty my point, the ratios will be different. 6speeds are better for off the line and have the top end, 5speed compress the same length of gearing from 6 into 5speeds.

The reduced number of gears and adjust ratios are going to effect the way the car drives, without a doubt.

Dean, do we know the design values of the stock gearbox? i guess its only a pointless purchase is running power higher than those stated, if your stock box goes and you've no intention of running higher power, this is probably a fit and forget solution - although very expensive!
 
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don't forget this - taken from the nismo website on the s15 nismo gearbox information:

{Durability Serviceability performance}

Durability of Engine torque design value: 40kgfm (392N•m)
Durability of Engine power: 350ps (257kW)
Recommended Clutch: NISMO SINGLE PLATE CLUTCH
*Please note: gears may be damaged by input beyond the design values.

^^if this is the case, then it's a pointless purchase. the standard gearbox copes with those figures comfortably......

Nissan probably say the Durability of engine power for standard gearbox is 300ps, but it's generally considered as you said to be allright to 350 so in turn the nismo should cope with 400.

But lets be honest, who here is really gonna pay in the region of 4.5 grand for a nismo box. Especially if its only good for 100 brake horse power more than standard.

I'd take my £4500 save a little bit extra and go to a gearbox engineering specialist in the uk.

I think the quaife sequential bren had for his sr was 5.5k, so i'm sure you could get a 6 speed synchro box capable of decent power for that kind of money.
 
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I'd like to know why he has said this. People on SXOC are running OS Giken gearsets with silly power without problems. All of the failings I have heard of on these boxes are either shafts snapping or circlip failure which would surely be ironed out by a gearset?
What Polo said to me Craig was the face there is not enough oil getting round the box this is why even the uprated gear sets fail, he has custom fitted a 7L sump onto the bottom on his gearbox so its running well more oil that it would be standerd
 
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Thats exaclty my point, the ratios will be different. 6speeds are better for off the line and have the top end, 5speed compress the same length of gearing from 6 into 5speeds.

The reduced number of gears and adjust ratios are going to effect the way the car drives, without a doubt.

Dean, do we know the design values of the stock gearbox? i guess its only a pointless purchase is running power higher than those stated, if your stock box goes and you've no intention of running higher power, this is probably a fit and forget solution - although very expensive!
Yea thats true though for the set up I am going for I would prefer to have a solid gearbox even if it has to be a 6speed as I wont be running the car on the strip its build to go sideways rather than a fast road + its hard enough these days to find a quiet road with out a speed camera to hit the limmiter so I dont think it will be that much of an issue :p
 

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Amazing Guide - http://forums.nicoclub.com/rb25-trans-mated-to-z32-trans-lots-of-pics-explanations-t226812.html

This shows how you mate a RB25 to a Z32 Rear Gearbox Case meaning you down need to cut any of the shifter hole as you would do with just a RB25 conversion :)
This has been my bedtime reading the last few nights
Not exactly... swapping around the parts as much as you can will still leave you with the same shifter problems as a straight rb25 or z32 conversion - that's because the bellhousing lengths are practically the same. You'd only what to do that if you had 2 broken gearboxes and wanting to make 1 good one. Otherwise it's a complete waste of time.

EDIT: the z32 shifter problem can be solved if you use the alpha omega conversion kit
 
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_Wing_

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I'd like to know why he has said this. People on SXOC are running OS Giken gearsets with silly power without problems. All of the failings I have heard of on these boxes are either shafts snapping or circlip failure which would surely be ironed out by a gearset?
OS Giken don't make a gearset for the 6spd, neither does PPG and I have a OS Giken s14 box at work that's stripped a gear :( The 2 main players for 6spd gearsets are PAR and NISMO (there's also HPI that does an upgraded version of NISMO), and for the money you spend the results are... not what you'd expect.
 

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Has anyone ever investigated fitting a 5 speed box from a JDM S15 Silvia spec S (SR20DE engine model)? Assuming the internal strength is the same as the s14 K's gearbox (maybe someone knows?); you'd assume it would be a straight forward swap without some of the adaptations required for the s14 K's conversion. I'll see if I can find out from some locals.
The flywheel is the major difference between these boxes and the flywheel part numbers are different between non turbo 5 and turbo 6 - so highly unlikely. Besides, a s14/s15 5spd is a downgrade without the strength :p
 
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Not exactly... swapping around the parts as much as you can will still leave you with the same shifter problems as a straight rb25 or z32 conversion - that's because the bellhousing lengths are practically the same. You'd only what to do that if you had 2 broken gearboxes and wanting to make 1 good one. Otherwise it's a complete waste of time.

EDIT: the z32 shifter problem can be solved if you use the alpha omega conversion kit
Not exactly true because I am taking the rear of the Z32 casing and putting it on the RB25 bellhousing with RB25 internals and using Mazworx's short shifter kit for the Z32 rear casing means I wont need to trim any of the shifter housing where it comes through on the standerd 6 speed as their kit makes it come through at the same angle, I have been told this will work by one of the leading guys in the UK as he has done this before but will keep an up date on my members thread of how it goes :)
 
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