My transmission is reported to have a broken 1st gear. Not uncommon.
I've taken one pass through the EvilWerks videos (I bought the series) and as best as my memory can provide - the 1st and reverse gears are under the outer cover and not nested inside with the rest of the gear clusters. So, here's the question: If the damage is limited to just those components can one do a diagnosis and repair without cracking open the whole gearbox? Obviously if upon inspection things like synchros, etc are worn I'm all in, but this trans is reported to be sound other than the broken 1st, but yeah, race car...
Any transmission repair advice welcomed.
Thx.

Broken..? First start with issue/symptoms what it doing/not doing?
To your question more broadly, Yes if isolated to 1st/reverse you can service in the car w/o removal of the trans.

Popping out of gear I assume?

Not sure. Engine and trans were both out when I got it. It’s a race car with slicks and a LSD so I’m assuming the PO got overeager off the line and twisted something off.

It’s false economy to just look at part of the transmission. I would pull the stack and inspect the diff.
Track days are too expensive and time consuming to go when your equipment may not be up to snuff.

Once you pull the back of it
It’s not much more work, to open the front

Plus the last one I actually blew something up on. I found tons of metal bits under the diff in the front of the case. Much easier to clean that with the side cover off

It's easy to pop the rear cover off the trans to look at first gear. The synchro hub or the slider could be badly worn to the point that they no longer engage properly. Another possibility - the spline on the 901/914 first gear is small and can strip is first gear is abused.

I'd have to agree with other comments above, that once you're that far it's easy to pull the intermediate plate and gear stack. They come out as a unit and you can look at the gear stack and ring & pinion.

You probably know this, but keep the gasket that goes between and the main case - it is used to set pinion depth, so you'll want to replace it with one of the same thickness.

My suspicion is the latter - likely stripped spline. It has / had a rather sizable engine. I'll start by breaking open the rear case, but in all likelihood will do a full tear down. There is a rather expert gear guy here in town that I can tap for coaching. Thx all.

Well... I tore it apart today with the help of a local expert.
Bit of a mess. Not LSD but welded diff, very odd gear ratios ( A, HA, M, S, V ), which explains some other things, namely over revving.

One little bit of good news is it has a 904 main shaft.

I'm working on a parts list now which I'll post here when it's complete. Meanwhile taking suggestions on sources. Aware of Dr. Evil and CA motorsports, but welcome to other suggestions.

Cool find on the 904 main shaft.

Aaaaand the carnage:
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1st/Rev stack destroyed
So is the 1st /Rev carrier
couple of other sliders,
all the synchros and the ring gear is iffy... not to mention the main case is getting sloppy (main shaft bearing race not secure)

Yeah, gonna cost...

Yep...I've come to the realization that the transmission on a track car with over 200hp has become another consumable....

Certainly a number of components within..

Trans going back together.
The only parts salvageable from the old one are the main shaft, intermediate plate and 3 of the forward gears. The old case, all consumables were done. Even the ring and pinion were trashed. If anyone ever tells you a welded diff is a good idea, turn around and walk away...

We changed the gearing a bit to better suit our road courses 'round here. Going with A, HA,N, S. X. We'll see how that all feels.

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Master tech Gordon giving the parts a good talking to:

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The huge advantage of getting help from a pro is he's got pretty much every conceivable shim and spacer on hand. No stopping and waiting to order fiddly little parts.

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Shafts are assembled, Pinion depth set, pr-load and RP lash all set. Final assembly tomorrow. Wavetrac is on order and will go in later this summer or over the winter. There's a worldwide shortage of diffs at the moment.

I went from knowing very little about transmissions (I've understood the basic principles, but never torn one down before) to having at least a rudimentary understanding of how a Porsche synchro box works. After I've done it a dozen more times I'll feel comfortable taking one on myself. When you see it done right you begin to understand how precise they actually are. The notion that you can tear it down, measure a couple gaskets and re-assemble isn't true. Maybe if it was less than 10 or even 20 years old, but a 40 plus collection of parts has worn, stretched and distorted to the point that you have to start over with baselining all of the tolerances.

Just advice

I wish I had followed the advice myself earlier

On our 901 we would loose the intermediate plate bearing every other year
And have to rebuild it

My builder says the cost ratio for reliability and horse power is around 210 hp to switch to a 915 tranny

We are close to that but just shy off 200hp

So the third or 4th time we had to rebuild we added a trans cooler and the billet intermediate plate

We also put a temp sensor and gauge on it

We were hitting really high temps. 240 plus on the track
With cooling it went to 200

I’m sure the billet plate helped me too
But I give the majority of credit to the cooling

I think I’m on the 4th year of this box with cooling and have had no problems yet

So I would recommend cooling for any one close to 200 hp on a track car

Good advice - especially if enduros are in the mix (they are).
What cooling system did you go with?
My engine is right at or just below 200hp - or at least that's my guess.

We didn’t go with a kit
We found a good cooler and had it cleaned
Made up our own SSI lines and fittings

There is a farm pum sold at the farm and ranch stores that is all the same specs (housing and even dimensions) as the Tipton pump

Farmers use them to pump weed treat and fluid transfer on big commercial sprayers. It might be the same pump manufacturer

But it’s half the price of the Tilton. Just no Tiilton sticker

We had our guy drill holes in the case over the stack/diff/etc

He didn’t even put in a spray bar

And he has used the same set up on nearly a dozen 901’s

The AN fittings screw into the holes he drilled and tapped

I don’t remember the AN size. Probably -8

The cooler should be sized for the same

Great ideas. Thanks. I imagine a significant benefit is simply having more oil capacity and it being cooled is a plus.

You can even use the oil fill and oil drain plugs as inlet and outlet for the oil. For modest hp applications, you can get away without a spray bar. Just cooling the oil is good enough. I ran my car for a number of years without a cooler. The trans seemed to hold up OK, but shifting would get a little notchy by the end of 25 minutes sessions. The cooler helped that.

Wow! Carnage~

Yeah, it was chewed. Sorted now.