4th Gear is gone :/

[JK21]

Originally Posted by stugray

You are not really telling us what really happened.
So you shifted to 4th.
Did it go in?
When you released the clutch did it begin to catch then made a noise, then nothing?
Or did you get in and just nothing?

Now that it is "gone" what happens?
Can you get through the gate to where it use to be and nothing?
Now is there noise where 4th used to be?
Was it grinding a lot before this?
Has it ever slipped out of gear?

I have just spent the last 4 days disassembling & rebuilding a man trans for my other car, so I have a very good picture of what it looks like inside.

And 4th is usually not the gear that gives up first if you drive you car hard.

The gear engagement has always been fine and it has never slipped out. I was in 3rd and I was at 45. When I shifted I was at about 7K and when it went into 4th I heard a boom. The car still drives fine and I can engage all my other gears (1st, 2nd, 3rd, 5th, and 6th). When I drove it back to San Antonio today I drove it 1st, 2nd, 3rd, and then 6th.

Originally Posted by Deadspool

you'll have to crack the case and see what damage is done. If you an get a print out of the transmission internals from the dealer, they can order the pieces you need individually.

If you just sheared 4th, might not be too bad. I would however be careful how much you drive it with shavings and loose bits floating around in there.

Indeed. I am dropping it off at the shop tomorrow. I didn't have a trailer down in Houston so I drove the car back home to SA.

Originally Posted by stugray

That's why I said it is nearly impossible to break the actual drive gear.
Those dogteeth will break first.
And if the shift fork breaks you will lose two gears because each shift fork moves one slider to engage one of two gears.

In fact if the shift fork broke, you could conceivably be stuck in one gear unable to move the slider out.

Hmmm. Makes me wonder because I can engage it into 5th but I was told not to do that and just go 1,2,3,6. It catches in 5th but it seems sketchy to me personally.

[Dipstik-sportech]

Originally Posted by Hawaiian

How much power were you running?

That's from @FullBlown 's tranny, 700+ whp I believe. My tranny has messed up synchros but I'm sure I'll shear a tooth

The Frozen North

[wparsons]

Originally Posted by OmarGC

Your entire post comes off as ignorant.

Not all manual transmissions are the same, however I will say it's safe to say with the size of the frs/brz housing that the gear diameters aren't going to be very large by any means. Smaller gears, smaller teeth, weaker... Similar to how most Subaru 5 speed transmissions go(along with 1st gear launches). Shredding 3rd gear while on heavy(max) load due to limited housing space and having to use small gear sizes.

Gear diameter doesn't really affect overall strength... width and pitch of the teeth are much more important in the strength of the gear.

Diameter does have a slight affect on it because it can limit the pitch you can use, but you would need extremely small diameters before that comes into play.

[Boss Paco]

Sorry to hear about the trans letting go, @JK21. The FRS is a beast! I really can't wait for you to turn it up. Sucks that the tranny will be a delay but I'm sure it will be back better than ever.

Oh, btw, I'm the Asian dude who troubled you while swapping on your radials and was amazed that you actually fit a 275 on the back.

[mike the snake]

An oil cooler and pump would go a long way towards making our transmissions hold up with big power on track days, where the trans does get hot/heat soaked.

Years ago when I was researching transaxles for a racecar I was building, I found info on the old Porsche 911 gearbox (model 915) which had a torque max of like 180 ft/lbs, but the higher up gearbox was rated for something like 225 ft/lbs, and the only difference was a cooler and pump.

With gearboxes, bad things happen when they get hot.

[JK21]

Originally Posted by Boss Paco

Sorry to hear about the trans letting go, @JK21. The FRS is a beast! I really can't wait for you to turn it up. Sucks that the tranny will be a delay but I'm sure it will be back better than ever.

Oh, btw, I'm the Asian dude who troubled you while swapping on your radials and was amazed that you actually fit a 275 on the back.

Lol it is no problem man. And yeah we will have this car up and going even stronger than ever.

[stugray]

Originally Posted by wheelhaus

The 2006 Evo MR was shearing the teeth off 4th from even slightly modified power levels after being heat soaked from 20 minute track sessions. They didn't have problems at the strip because 1st, 2nd, and 3rd were more stout, and there's not enough time to strain the tranny and heat soak it..

Thanks for that explanation.

One of the reasons I stated that 4th is less likely to fail is that (in this car at least) 4th & 5th are the two gears closest to 1:1 ratio (4th = 1.213, 5th = 1), so in those two gears the drive shaft gear and the lay shaft gears are almost the same size so they share almost equal stress. (5th may not have any "gears" as it might just connect the drive shaft to the input shaft directly - that is one case where different trannys can be different).
If that is the case, then 4th has the lowest stress on gear teeth than any other gear (in this tranny)

1st is 3.626, so the smaller of the two gears in that pair would have the greatest stress of any gear in the stack.
2nd is 2.19 so would have the 2nd higest stress, etc.

Sorry to continue to show my ignorance of the subject

[mike the snake]

Placement of the gears on the shafts has a lot to do with failures too. If the gears are far away from the bearings or supports, then under load the shafts can flex, causing the gears to push away from each other.

[OrbitalEllipses]

Originally Posted by Knshro13

Only....? That's pretty good power. You probably made no mistake.

I was about to say...cause for 4th gear grenade found. LOL

[Hawaiian]

With all of these transmission failures above 400 hp (300ish tq) it seems that I am on borrowed time. I'm starting a project to come up with an inexpensive (not v160) that will hold sufficient power. I have a plan of attack, and hopefully I get some good news after my trip to the you-pull-it tomorrow.

[stugray]

Originally Posted by JK21

And yeah we will have this car up and going even stronger than ever.

Did you crack open that tranny yet? I want some more blown tranny porn...

[stugray]

Originally Posted by JK21

Lol it is no problem man. And yeah we will have this car up and going even stronger than ever.

Still no word on what happened?

[kiichiro]

Enjoying 300+ hp at the track as well
INDE this weekend
and realizing this is a ticking time bomb for us all

[King Tut]

Originally Posted by Hawaiian

With all of these transmission failures above 400 hp (300ish tq) it seems that I am on borrowed time. I'm starting a project to come up with an inexpensive (not v160) that will hold sufficient power. I have a plan of attack, and hopefully I get some good news after my trip to the you-pull-it tomorrow.

How did that trip go?