6MT Gearbox circlip

[Silverstreak]

Right, as I'm sure your all aware, the S15's 6 speed gearbox is subject to alot of hearsay about how weak it is. And I'm sure you are all aware if you have read through all the threads regarding this issue, there are alot of different opinions on how to overcome this problem and the actual quality of the box itself.

If you like me, don't fancy the prospect of changing to a 5MT with uprated internals such as the OS Gilken etc for around 3k, then your only real route is gettin the circlip between the 3rd and 4th gears sorted by machining the counter shaft and fitting a larger, stronger snap ring.

As no one has been able to post images on this fix, I thought as I'm in the prosess of building a powerful engine that I better get this sorted. I'm going to strip the whole box, get it cleaned, then with the help of a custom gearbox builder (I will let you know who once I decide who to use) get the machining done and source a new circlip. But the clever bit will be that I will be getting the whole lot cryogenically treated, which in theory will leave me with a very strong box indeed.

I am also going to look into getting the whole engine cryogenically treated as well.

I will post all pictures of all the stages of the build, who I use and hopefully be able to let you know if this ingenious solution will help those of us running big power witout having to spend megabucks on other gearbox solutions.......

 

[Adam L]

There was a thread I read last week on boxes on the sxoc... The 6 speed box had varying comments, some even said the later models were fitted with rectified internals?... True or not, I don't know, but there's some drift guys using them on big power engines with no problems. I've never believed the spiel about weak Nissan boxes, I ran nearly 450bhp on my Pulsar with a stock box, which never let me down, I just didn't launch it.

Obviously hard lanuching or sudden impacts of large amounts of torque are going to destroy your gears.

I've also got a very high spec SR20, which is ready to build, but unless the stock box broke I wasn't going to do anything.

Mobnes S13 even runs a stock transmission on 500bhp, ok it breaks after severe useage, but he lanuches it with drag radials.

 

[craig8585]

This would be very interesting to see. I've heard of Pulsar owners getting their box cases cryogenically frozen with impressive results. Not sure how true it is though as it's probably 10th hand information. Defiantly keep us updated with this one mate, this is one thing that no-one seems to know a huge amount about.

The only other option I have considered is a 6MT gear set from Australia (rated to 600bhp), but it works out at around £3000 too once you've factored in the postage etc. Theres a few threads in the useful threads section about gearboxes. They may or may not be of use to you but is there is any other information you need, just post it up and we'll do our best to help

 

[Silverstreak]

Cheers Craig, much appreciated. Hopefully I can get something useful together that will benifit you guys too! :nod: Hadn't heard about the gearbox from Aus though, got any more info on that? It would be interesting to get as many options together in one place as we can for viewing

 

[craig8585]

It's not a gearbox, it's a gear set (just the internals). I made a thread about it a while ago so will try and dig it out.

Have you looked into the cryogenics part of it yet? I've had a bit of a look and understand the principle, just need somewhere that actually does it now! I've got a spare box that I'd like to get done too, so if you find somewhere that does it let us know! Are you planning on freezing the internals or the whole lot including the case etc?

 

[Silverstreak]

yeah, have looked into it, there seems to be two companies in the uk that do it, I will post details on monday once I have spoken with them regarding price etc and which parts they are willing to do. I also need to find out weather they can do certain parts like the engine crank shaft because of its special coating to find out if the process would damage it etc.... I am planning on getting the internals of the gearbox done for deffinate, but will get the case done if I have the funds. There are companies in the US that will do the whole engine gearbox and clutch for around $560.

The following is a explanation of deep Cryogenics and how it is used on an engine and its components as well as other automotive related parts as well as parts that should not be cryogenically treated;

If you look at the machined parts of an engine they appear very smooth to the naked eye and to the touch. But if you were to look at them through a high powered microscope you could see that they are not smooth at all. If you can envision your hand with your fingers spread apart, that is much like the machine areas before the Cryogenic treatment is performed. During the Cryo treatment the grain structure closes much like taking your other hand and squeezing your fingers together, thus making a better bearing surface with less drag and friction and therefore improved performance.

Normally you will experience a slight increase in Rockwell of a point or two, not much of a change, but still improvement in the right direction. The big improvement is stress relief and stabilization. Engine parts, transmission parts , or any non cryogenic treated parts you are thinking about are full of stress and just waiting to distort when it reaches racing temperatures. All machined parts can distort if they have not been stress relieved. Pistons can change from round to oval due to stress and temperature. When this happens the piston drags the cylinder wall which takes horsepower away, creates heat, and wears the cylinder walls. It then requires the engine builder to rebore the cylinders by 2 to 3 thousandths. Cylinders that have been Cryogenic treated will normally be out of round only a 1/4 to a 1/2 of a thousandths, a big decrease in wear from a non treated cylinder.

The end result of Cryogenics treatment of your engine is improved performance with far less wear and less breakage. What parts should be Cryo treated? All parts that wear, break, or distort. Sheet metal, electrical parts, water pumps, oil pumps, or fuel pumps should not be treated.

The following are various parts of an engine and what you can expect to occur after the Cryogenic treatment:

BLOCKS: The treatment of the engine blocks should not only result in improved performance with less wear and breakage, but the stress relief and stabilization of the block should result in reduced distortion in other parts such as crankshafts and camshafts since they are no longer flexing and distorting.

CRANKSHAFTS AND RODS: Reducing the stress from the large mass made up of the crankshaft and rods can help them stay more in balance allowing for improved performance with reduced wear and breakage.

PISTON ASSEMBLIES: The piston assemblies should not be treated with the rings installed on the pistons. Wrist pins should not be treated at all. Treating the piston assembly will help the pistons and rings remain round therefore maintaining a better seal which translates to more constant compression , improved performance and reduced breakage.

HEADS: Heads both cast and aluminum are less prone to distortion and breakage following the Cryogenic treatment.

CAMSHAFTS: Although camshafts don’t seem to suffer breakage, wear can be a problem With Cryogenic treatment this wear can be greatly reduced.

VALVE SPRINGS: Often show an increase in pressure (5-15%) and improved life of 100% or more. Automotive valve springs as well as Top Fuel drag cars have shown an increase in life.

PUSHRODS, LIFTERS, VALVES: These should all be treated but do not have any real advantages.

ROCKER ARMS: Stock automotive to high quality rocker arms with bearings are good candidates for Cryogenics.

INTAKE MANIFOLDS: You should have the intake manifolds Cryogenic treated. If you have the block, head, and all the internals Cryo treated, and thus stress relieved, it only makes sence to have the intake done as well. Bolting a non-Cryo intake to an engine that has been Cryogenic treated is only introducing stress back into the picture.

RING AND PINIONS: Cryogenic treated these parts will show less wear and last longer.

INPUT SHAFTS: By Cryogenic treating of the input shafts wear and alignment can be a huge benefit.

STANDARD TRANSMISSIONS: Operation with less wear and breakage. You should do the entire transmission completely disassembled, including the case.

BRAKE ROTORS: Cryogenic treatment closes the grain structure of the rotors resulting in an increased contact area for the pad to touch against and also reduces the abrasiveness of the rotor against the pad therefore increasing pad life.

I hope this gives a bit of an insight to this topic :thumbs:

 

[DeanS15]

what about bearings though? the gear circlip causes failure, but the bearings seem to be a weak point too, i have never had actual mechanical failure on my box, but as others, get input shaft noise due to perhaps the layshaft bearing worn. it would be good to know if a rebuilt box would come back as new and hold up to the extra power we put through them please keep us informed.

 

[Auss15]

You would be talking about PAR Engineering Craig, and yes they are great gear sets but not cheap.

You get the choice of dog gears or helical cut gears

http://www.par-engineering.com/products.htm
Nissan 200SX/Silvia 6MT Dog Engagement (FS6R92A)
$6,640 AUD (plus GST)

The Nissan FS6R92A transmission is fitted to S15 200sx/Silvia vehicles along with the SR20DET powerplant. Although much stronger than the earlier FS5W71C transmission, the FS6R92A starts to have durability issues with vehicles sporting over 220kw of power. With many modified vehicles passing the 240~280kw mark, gear breakages are not an uncommon occurance.
Available as an off the shelf model is a 1st~6th straight cut dog engagement gearset with the strength and durability required for dedicated circuit and drag racing vehicles.

Features:
- Tooth profiles that reduce noise, wear and load forces on the standard OEM transmission housing
- Multiple piece layshaft for ease of assembly, strength and ratio changes
- Single piece billet output shaft for maximum strength and durability
- Billet shift forks included
- No extra cost helical gears
- No extra cost custom ratios
- Also available in 1st~4th dog engagement, 5th synchromesh engagement configuration ($4,960 AUD)


Ratios:
- 1st: 2.92
- 2nd: 2.00
- 3rd: 1.45
- 4th: 1.17
- 5th: 1.00
- 6th: 0.88 (Optional)


Applications:
- S15 SR20DET






Nissan 200SX/Silvia 6MT Synchromesh Engagement (FS6R92A)
$4,240 AUD (plus GST)

The Nissan FS6R92A transmission is fitted to S15 200sx/Silvia vehicles along with the SR20DET powerplant. Although much stronger than the earlier FS5W71C transmission, the FS6R92A starts to have durability issues with vehicles sporting over 220kw of power. With many modified vehicles passing the 240~280kw mark, gear breakages are not an uncommon occurance.
Available as an off the shelf model is a 1st~5th helical cut synchromesh engagement gearset with the strength and durability required for tough street and racing vehicles.
Features:
- Tooth profiles that reduce noise, wear and load forces on the standard OEM transmission housing
- Multiple piece layshaft for ease of assembly, strength and ratio changes
- Shift retaining rings incorporated into design to eliminate over selection and synchronizer baulking
- Retension of OEM 6th gear assembly provides OEM NVH levels during cruise and freeway driving
- Helical cut gears (1st~4th) for the best balance of strength and refinement
- Billet single piece output shaft
- No extra cost straight cut gears
- No extra cost custom ratios


Ratios:
- 1st: 3.61
- 2nd: 2.16
- 3rd: 1.57
- 4th: 1.11
- 5th: 1.00
- 6th: 0.88(Optional)


Applications:
- S15 SR20DET

 

[Silverstreak]

what about bearings though? the gear circlip causes failure, but the bearings seem to be a weak point too, i have never had actual mechanical failure on my box, but as others, get input shaft noise due to perhaps the layshaft bearing worn. it would be good to know if a rebuilt box would come back as new and hold up to the extra power we put through them please keep us informed.

When I speak with the custom gearbox builder I shall ask the question, they should be able to source a uprated replacement or some solution. Will keep you posted...

 

[andeep]

Surely a Z32 box conversion would be cheaper? The boxes are very strong too.

 

[Silverstreak]

Surely a Z32 box conversion would be cheaper? The boxes are very strong too.

Its still a pricy option, although cheaper than some, here is a link for the Mazworx convertion kit;

http://www.mazworx.com/index.php?l=product_list&c=107

You will also need to buy a used Z32 box and get it reconditioned also adding to the price, There is also the option of going for the Z33. You could consider skyline boxes, although these also suffer from durability concerns.... This is why I am seeing if I can do something cheaper than the current crop of options that will work well.

 

[DeanS15]

z32 box is still a bodge - ratios dont work that great with the s15 hlsd apparently and you would need to change for a new clutch and flywheel setup afaik, along with the conversion kit. the shifter also hits the interior trims as it comes throuhg in the wrong location.......

 

[craig8585]

Surely a Z32 box conversion would be cheaper? The boxes are very strong too.

This thread was started as an alternative for people who don't want to do down the conversion route. Yeah, you can get Z32 or RB25 boxes to fit, but they will be a bodge one way or another whatever people say (as Dean also mentioned above). I don't know how the ratio's pan out but I imagine they aren't ideal. And they are 5 speed.

Probably a good option for people who use their cars for drifting, but not for us who like them to be pristine and how they should be.

 

[craig8585]

You would be talking about PAR Engineering Craig, and yes they are great gear sets but not cheap.

Yeah, thats the one mate

I'd go for a synchromeshed straight cut box myself if I went down that route. Would sound crazy!

 

[Silverstreak]

A quick update, I now have a specialist race car builder on board to build a prototype gearbox using a 'virgin' 6MT. we will be focusing mainly on resolving the issue with the weak snap ring as well as the other bits previously in this thread. We will be carrying out a complete photo casebook on the box and I will post to this tread once complete. If we are successful, this conversion will be available to the public through myself and my specialist.

Watch this space!!!

 

[craig8585]

Sounds good

What company are you using to do the work??

 

[TriniGT]

Sweet, wonder what sort of pricing and also what stress testing will be done to ensure it standing up to the thrashing of a daily and weekend runner.

 

[Silverstreak]

Sounds good

What company are you using to do the work??

I'm keeping my cards close to my chest, but he is well known in silvia and skyline circles. and yes, we will still be freezing the internals, but this will be a very specific list of bits, hopefully will be doing the case as well..

 

[Silverstreak]

Sweet, wonder what sort of pricing and also what stress testing will be done to ensure it standing up to the thrashing of a daily and weekend runner.

we won't know until we have built the prototype box, it will depend on the way we fix the problem. Testing will mainly be done using a real time daily runner used every day runing 400+bhp.

 

[craig8585]

I'm keeping my cards close to my chest, but he is well known in silvia and skyline circles. and yes, we will still be freezing the internals, but this will be a very specific list of bits, hopefully will be doing the case as well..

Oh right.. why don't you want to say? Other people may want to use them to have work done too. Surely it won't impact you if this happens?

I thought this thread was going to be really useful but unless you share information about what your doing and how your doing it, then its pretty useless.