4th Gear is gone :/

[OmarGC]

Originally Posted by stugray

By not telling me what part of my post "comes off as ignorant" makes you sound ignorant.

Each "gear" is actually TWO gears. One on the lay shaft and one on the drive shaft. If you are in a gear that is "smaller", then the gear on the opposite shaft is "bigger".

So EVERY gear has one smaller and on larger gear, so I fail to see your point.
What is the smallest gear in a gear stack? Usually the one opposite 1st gear (which is the largest diameter gear).
So if you think the "smallest" gear would break first, then the gear opposite the large gear on first is the smallest in the tranny.

And the actual "gears" that do the driving are far less likely to fail than the dog teeth that engage them.

The gear that usually gives out first in a manual trans is 2nd because the synchros and the dog teeth take the most abuse.

Is that ignorant enough for you?

If you read the first line of my post, I said ENTIRE.

And I'm sorry I didn't go into enough detail for you on my phone. But this week? None. Entire life? Likely more.

It's okay to be butthurt...

[EZWood]

Probably broke a shift fork. Its not the first to happen. Accelerated performance did the same thing, slightly different situation.

[mike the snake]

I think Full Blown blew a 4th gear at around 600 or 700 whp on the dyno.

That cutout of the BRZ tranny, the gears look pretty stout to me!

[stugray]

Originally Posted by mike the snake

That cutout of the BRZ tranny, the gears look pretty stout to me!

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.

[mike the snake]

One could zing the teeth off one of the 4th gear gears and lose only 4th and still have the rest of the gears function though, correct?

[stugray]

Originally Posted by mike the snake

One could zing the teeth off one of the 4th gear gears and lose only 4th and still have the rest of the gears function though, correct?

Yes, but breaking the actual drive teeth off (all lof them) would have been extremely noisy. From the OPs description there was very little excitement.

Here is a pic that shows the various parts I am talking about:


You can see that the drive teeth are much larger than the dogteeth.
As you shift into gear the dogteeth are what make the grinding sound as the shift fork moves the slider from one gear to the next.
The slider has the matching set of dogteeth inside where you can barely see them in this pic.
The dogteeth are more delicate than the gear teeth.
For the trannys I work on, I have never heard of a drive gear breaking but I have plenty of ruined dogteeth gears and sliders.

[stugray]

Originally Posted by OmarGC

If you read the first line of my post, I said ENTIRE.

Oh I'm sorry I was not aware that you are posting from Bizzaro world where Ignorant means the exact opposite of what normal people think.

My BAD ( Oh I mean My GOOD)...

[mike the snake]

Ahhh, I see. Before the gear teeth go, all the dog teeth would go, which would then not engage, leaving that gear not working?

I once had a trans where the shift fork got bent and would shift into 3rd, but not 4th, or was it 1st and not 2nd, well, you get the idea.

Originally Posted by stugray

Yes, but breaking the actual drive teeth off (all lof them) would have been extremely noisy. From the OPs description there was very little excitement.

Here is a pic that shows the various parts I am talking about:


You can see that the drive teeth are much larger than the dogteeth.
As you shift into gear the dogteeth are what make the grinding sound as the shift fork moves the slider from one gear to the next.
The slider has the matching set of dogteeth inside where you can barely see them in this pic.
The dogteeth are more delicate than the gear teeth.
For the trannys I work on, I have never heard of a drive gear breaking but I have plenty of ruined dogteeth gears and sliders.

[stugray]

Originally Posted by mike the snake

Ahhh, I see. Before the gear teeth go, all the dog teeth would go, which would then not engage, leaving that gear not working?

Exactly. and grinding off enough of the dogteeth to not even be able to make grinding sounds is not likely.

Originally Posted by mike the snake

I once had a trans where the shift fork got bent and would shift into 3rd, but not 4th, or was it 1st and not 2nd, well, you get the idea.

That is what I suspect in the OPs case and why I asked for more details of how the failure occurred.
If you are in the middle of a hard pull and you have violent "non-linear catastrophic structural exasperation" (D. Adams), then it is pretty obvious what happened.

If OTOH the tranny just refused to engage and never made any nasty sounds then that is something else.

If the tranny refuses to let you even TRY to go through the gates, then it is likely to be the detent system that keeps you from engaging more than one gear at a time.

[Dipstik-sportech]

Dog teeth are still there, but none of the teeth on the gear are lol

The Frozen North

[Dipstik-sportech]

Originally Posted by Dipstik-sportech

Attachment 70840

Dog teeth are still there, but none of the teeth on the gear are lol.

I got quoted 650$ Canadian to replace just 4th gear and the synchro in my trans and that's with me changing it. You're better off to find a low mileage stocker. Oh and to the guy that said the gears are beefy, heeelllll no they're f@#£ing tiny!!!

The Frozen North

The Frozen North

[Hawaiian]

Originally Posted by Dipstik-sportech

The Frozen North

How much power were you running?

[stugray]

That is awesome! But that is the kind failure that you would definitely notice.
It looks like it was all the way in gear so the dog teeth are fully engaged.

The way the teeth are broken it suggests that the main shaft bearing failed first and allowed the two gears to slip apart.

Which gear was that?

[wheelhaus]

Originally Posted by stugray

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

With Subies, in the mid 2000's the 5sp has been known to be a weak link with the "glass gears" used for 1st/2nd, but other designs are simply different, even made by Aisin, they can all be unique.

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. It was the heat soak and higher torque levels under constant load that would cause the failure. It's sad, the 6sp gear spacing was great and felt spectacular, but unfortunately the notchy and clunky 5sp was much stronger. It was because the 6sp 4th gear was only 14mm wide, and frequently used at nearly any track. If the gears were larger diameter, 14mm wouldn't be a concern, but the small diameter meant higher tooth face pressure. Tnhe solution was supposed to be a oil cooler, but I had since sold the car and haven't looked back into it.

The 86 transmission is pretty light, so I'm curious about the gear widths and diameters. I haven't heard of too many tranny failures but those that have, I'm wondering if there's any trending.