Well the tranny housing is the same, I believe, so it should just be the brackets, cables, shifter, and such, I think...

 

Yeah, everything else should be identical. But that's a discouraging argument, because the 6sp is one of the MAIN reasons I bought the MR!

I'm trying to see if there's a pattern, or at least combination of elements.. Is the breakage caused solely by overheating? Is it caused solely by a thin gear seeing too much shock or stress? I don't think it's either alone, though in and of themselves they each could easily cause failures...

It seems more like a combination of these things, or a chain reaction where the heat begins to break down the lubricant, and it then causes too much friction, then more heat, then more friction, the lube breaks down completely, then it's metal on metal and the teeth simply get destroyed. Maybe the GL4 lubes aren't slippery enough to prevent this friction, but anything slicker will affect the synchros.

What trans lube have you guys used during the life of the original trans? Factory ONLY, BG I or II, Redline, etc...

I still wonder if the unshielded exhaust is part of the "heat" culprit.

I believe the excessive heat can be avoided by using a better lubricant because it will prevent excessive friction buildup and thus, reduce the overall heat. Smoother shifting can reduce the shock load. There has to be a better solution than "It's a crap design, deal with it or buy a 5sp."
That NEO RHD stuff sounds interesting..

 

Wheelhaus I agree its a combination of things that probably caused the issue. Both these guys were using BG Synchroshift 2 when their trannies went bad, both have decently mod'ed cars, both have grippier clutches ... The 6 speed is ultimately a weaker design but a lot depends on how much torque/power you are outputting and what kinds of fluid you are using.

My main concern is whether my 6 speed tranny will be able to hold the amount of power I have planned for it (which isn't much). If it does then I really don't care but if it doesn't then I'll probably just replace it with a 5 speed. The EVO9 SE is starting to catch my eye

Warr and Razor with the power levels you guys are outputting you should give the 5 speed serious consideration ...

 

I was running the stock clutch and BG2. I really think its the heat that did it in.

Here is a quote from Jon@TRE after I saw the photos and asked if it could have been from a misshift earlier in the boxes life:

"No the stock clutch wouldn't do that but when the gears get hot they go plastic and bend further which leads to thermal runaway...which makes them bend more and the further they bend the sooner they will break. The fatigue cycle curve becomes a steep slope as bending increases."

Then I asked if he has ever seen a 5spd box look like mine:

"Never or should I say hardly ever...

I've seen a few 5 speeds lay the teeth down but it's worlds stronger than the 6 speed."

 

A little off topic, but didn't I mention how I hated this fluid in the 6 speed?

 

Yep, you and others. I haven't been bothered by it as I've been able to powershift with ease on the drag strip and shift cleanly on the road course (no powershifting), but I did not choose it from preference. I chose it since it was all I could find locally. The local Mitsu dealer doesn't even USE SUPER DIAQUEEN on local MRs. They just use a huge 100-gallon vat of generic tranny fluid for all Evo servicing. Scary, eh?

When I have my free 30k mile service done, they will be ordering the proper fluids per my request. They agreed to do that, but it scares me that they don't already stock all the required fluids for the tranny/t-case/acd/rear.

 

You are overthinking this. It is really very simple. Inorder to make six gears fit in the same tranny housing, Mitsu had to make the gears SMALLER. According to Jon @ TRE the high gears in the 6 speed are significantly smaller than those of the 5 speed. The heat generated by the drivetrain stayed about the same, but the gear became smaller. While the same heat had little impact on the beefy high gears of the 5 speed, the same heat tends to destroy smaller and hence weaker gears in the 6 speed. IT IS A DESIGN FLAW. Mitsu did this to please those who wanted a 6 speed just like the STI had. It was a marketing gimmick. The Evo never needed a 6 speed. It is what the marketing guys wanted.

So what are your options:

1. Start using Redline Shock Proof heavy gear oil especially if you track your car.
2. Use a pp plate that is only marginally stronger than stock. Use an organic clutch disk.
3. Send your tranny in to Jon and have him cryotreat and shotpeen the gears. This will add some strength to them. Have him also installed an oil cooler. This will help somewaht, but I believe your tranny will still break.
4. Remove the 6 speed and install a 5 speed and pay the money now and get it over with. Number 4 is your BEST solution.

 

Razor,

Jon is really telling you what you have to do w/o directly telling you Listen to him and me and get rid of the 6 speed and get a 5 speed in there. If you are going to track this car, then you more than likely will break the 6 speed one more time. Pay once now rather than have to pay TWICE. It makes sense to me and I think it makes sense to you.

 

It's a different housing, you can tell just by looking at both of them. Different design of the shifter area, casing, cooling fins, etc.

 

Believe me I know, I am just waiting for the quote, then I gotta figure out what body organ to sell.

 

The MR 6MT is strong as long as it doesn't get too hot. Look at Warrtalon's numberous (125?) 1/4 mi passes. If the tranny was inheriently weak, he would have busted a gear long ago. And driving on the track is not quite as rough as attacking a 1/4 mile run. Sure, people go WOT on the track, but I think they are smoother with the gear shifts and do not generate the same kind of impulse stresses that are generated during a 1/4 run. If you want to see an inheriently weak tranny, look at the 2002-2003 WRX 5MT. People were (are still are) routinely breaking gears just driving aggressively on the street.

The issue with MR 6MT breaking on the track has got to be the temperature. The fatigue resistance and strength of steels begins to drop as the temperature rises from room temperature. The heat of the engine combined with the frictional heat of the gear faces undergoing metal-to-metal sliding because the gear oil had overheated probably generated the heat that weakened the gears enough to fatigue fail under track racing conditions.

Get a good oil pump and cooler on that 6MT, monitor the tranny oil temperature, and I think it will do just fine on the track.

 

Agreed. But it will still be much weaker than th 5spd which is what people are getting at, hence the reason why everyone is suggesting razor get a 5spd rather than take the risk of breaking the 6spd again, and breaking his wallet.

 

This is what I'm getting at. There has to be some solutions besides the easy but expensive "just replace it with a 5sp" response everyone is falling back on.

Something has to be done to reduce the heat buildup, because WITHOUT THE HEAT, THERE'S NO PROBLEM. The heat buildup overcomes the gear's ability to sustain stress. Maybe an active oil cooler will accomplish this along with a better lubricant. The oil breaks down and the friction increases. METAL DOESN'T TURN SOFT FROM A FEW HUNDRED DEGREES. The oil is failing and it's allowing the friction of the gear teeth to build some incredible heat. This is where the problem lies. Keep the oil cool, and use an oil that can withstand much higher heat so the friction can't develop.

Jon is right, it's a thermal runaway, the hotter the oil gets the less it can lube, the more friction you have. Well, more friction means more heat. More heat, more friction. This builds up until something fails. If we can prevent this "thermal" reaction, the transmissions weakness is never allowed to develop.

The gears aren't weak by themselves, hell Warr has proven that. But when the heat exceeds the oil's capability, the gears turn soft because of the excess friction. Prevent heat, that prevents friction, this prevents the problem.

 

Talk to WORKS. Jamie posted this a while back on the evomr forum:

 

Dude,

I know you have an emotional investment in the MR, but face the facts. This is a design flaw. When someone like Jon URGES track driven MRs to swap to the 5 speed (just re-read his comments to Razor), there is no more room for debate. The 6 speed tranny CANNOT withstand the abuse of the track and it WILL break sooner or later. An oil cooler, better oil etc...are all BANDAID solutions. The 5 speed tranny is the ONLY solution short of making straight cut gears for the 6 speed tranny.

I have lived through this with my race prepped SE-R. I broke 4 trannies and I guarantee you that I will break the current one in the not-to-distant future. I am running the BEST tranny fluid money can buy (Shockproof Heavy) and I use a stock like clutch and PP, but the tranny has a WEAK design and it will break.

The road course puts MORE stress on a tranny than drag racing. The roadcourse session is 20-25 min long. Drag racing is just 11-12 sec long for the average Evo. Warr's Evo MR withstood drag racing, but it only took him a relatively small number of roadcourse sessions to break his tranny. I believe Razor broke his tranny on his 9 roadcourse event. That is not a lot of track time, but the tranny is inherently weak and breaks. It has more moving parts than the 5 speed, weaker gears than the 5 speed and generates as much heat as the 5 speed.