996 C2 vs C4 gearbox

[lgliam94]

Hi all,

I have a '99 C2 and the 2nd gear syncro has failed, the is still driveable but I have to double clutch going down the gears. A rebuild isn't really an option as I can't have the car off the road for that long so I'll be putting a used gearbox in it. My question is would a C4 gearbox be useable in my C2?

I know I'll be sacrificing my LSD, and I know the output shaft going to the front of the gearbox will just spin away in use but does anyone know of anyone that has done the above? It's a slim chance I know but the 4WD gearbox is much cheaper and more plentiful around me.

Many thanks,
Liam.

[IREvans]

lgliam94 said:

Hi all,

I have a '99 C2 and the 2nd gear syncro has failed, the is still driveable but I have to double clutch going down the gears. A rebuild isn't really an option as I can't have the car off the road for that long so I'll be putting a used gearbox in it. My question is would a C4 gearbox be useable in my C2?

I know I'll be sacrificing my LSD, and I know the output shaft going to the front of the gearbox will just spin away in use but does anyone know of anyone that has done the above? It's a slim chance I know but the 4WD gearbox is much cheaper and more plentiful around me.

Many thanks,
Liam.

There are many reasons why it won’t work, but centred largely on the way that front and rear torque is split using a clutch pack.

Just get your C2 gearbox rebuilt, you may just get away with a synchro hub and a few other parts. It shouldn’t take long at a decent specialists.

[lgliam94]

IREvans said:

There are many reasons why it won’t work, but centred largely on the way that front and rear torque is split using a clutch pack.

Just get your C2 gearbox rebuilt, you may just get away with a synchro hub and a few other parts. It shouldn’t take long at a decent specialists.

Thanks for that, I've had a google and seen rebuild prices "from £2400 onwards" which is a fair old chunk of cash, do you know of any specialists that you would recommend?

My reasoning for asking about the C4 gearbox is that I've heard stories of C4's and Turbos being converted the RWD.

Cheers,
Liam.

[C4ME]

Worth doing a search online. Rennlist has a few threads about it, here is one

https://rennlist.com/forums/996-forum/762585-how-t...

Might also be worth signing up on there and asking as there may well be differences to your car and the thread above is for converting a 4WD car and I don't know if the 4WD cars have additional electronics, etc.

PS I am not a 996 expert at all but use Rennlist myself and can be quite useful for modification details.

Edited by C4ME on Saturday 31st August 19:19

[lgliam94]

C4ME said:

Worth doing a search online. Rennlist has a few threads about it, here is one

https://rennlist.com/forums/996-forum/762585-how-t...

Might also be worth signing up on there and asking as there may well be differences to your car and the thread above is for converting a 4WD car and I don't know if the 4WD cars have additional electronics, etc.

PS I am not a 996 expert at all but use Rennlist myself and can be quite useful for modification details.

Edited by C4ME on Saturday 31st August 19:19

I've got a thread on rennlist already asking the same as I frequent rennlist a lot also, thanks for that link though, it inspires a bit of confidence in the idea!

Cheers.

[IREvans]

lgliam94 said:

Thanks for that, I've had a google and seen rebuild prices "from £2400 onwards" which is a fair old chunk of cash, do you know of any specialists that you would recommend?

My reasoning for asking about the C4 gearbox is that I've heard stories of C4's and Turbos being converted the RWD.

Cheers,
Liam.

You don’t need to replace the whole gearbox if the only symptom is a worn 2nd gear synchro hub. Stripping down the gearbox and rebuilding it can be an unknown task. You could be lucky and it’s just 2nd gear that needs replacing, however, it’s reasonably likely that there’ll be some other worn parts, or that the wear from the synchro has caused increased wear on various other parts.

The other issue is that you’re looking at 3-6 hours labour to remove the gearbox, assuming of course that everything comes apart easily, and that isn’t always the case.....

Sorry to be so vague, but there isn’t a definitive answer on this until you strip everything down....

Regarding the C4 gearbox - bear in mind that even if you could make it work, you’ll really limit your market when you come to sell the car, as I’d imagine nobody really wants a C2 with a C4 gearbox....

[Pope]

IREvans said:

lgliam94 said:

Hi all,

I have a '99 C2 and the 2nd gear syncro has failed, the is still driveable but I have to double clutch going down the gears. A rebuild isn't really an option as I can't have the car off the road for that long so I'll be putting a used gearbox in it. My question is would a C4 gearbox be useable in my C2?

I know I'll be sacrificing my LSD, and I know the output shaft going to the front of the gearbox will just spin away in use but does anyone know of anyone that has done the above? It's a slim chance I know but the 4WD gearbox is much cheaper and more plentiful around me.

Many thanks,
Liam.

There are many reasons why it won’t work, but centred largely on the way that front and rear torque is split using a clutch pack.

Just get your C2 gearbox rebuilt, you may just get away with a synchro hub and a few other parts. It shouldn’t take long at a decent specialists.

[Pope]

IREvans said:

lgliam94 said:

Hi all,

I have a '99 C2 and the 2nd gear syncro has failed, the is still driveable but I have to double clutch going down the gears. A rebuild isn't really an option as I can't have the car off the road for that long so I'll be putting a used gearbox in it. My question is would a C4 gearbox be useable in my C2?

I know I'll be sacrificing my LSD, and I know the output shaft going to the front of the gearbox will just spin away in use but does anyone know of anyone that has done the above? It's a slim chance I know but the 4WD gearbox is much cheaper and more plentiful around me.

Many thanks,
Liam.

There are many reasons why it won’t work, but centred largely on the way that front and rear torque is split using a clutch pack.

Just get your C2 gearbox rebuilt, you may just get away with a synchro hub and a few other parts. It shouldn’t take long at a decent specialists.

Pretty sure it will go in without an issue; the C2 castings are the same - just not finished to accept the C4 output shaft. The drive apportioning is (unlike 993 and prior, the 964) all done outside the main transmission with a clutch pack housed in the front axle final drive. The FA output on the C4 transmission will be spinning in fresh air with no detrimental effects.

You could fit the C4 transmission in a few hours and get the C2 box repaired 'at your leisure' so to speak then sell the C4 box again afterwards once back to standard.

[url|https://thumbsnap.com/m2pv8llI[/url]

Edited by Pope on Saturday 31st August 21:39

[lgliam94]

Pope said:

Pretty sure it will go in without an issue; the C2 castings are the same - just not finished to accept the C4 output shaft. The drive apportioning is (unlike 993 and prior, the 964) all done outside the main transmission with a clutch pack housed in the front axle final drive. The FA output on the C4 transmission will be spinning in fresh air with no detrimental effects.

You could fit the C4 transmission in a few hours and get the C2 box repaired 'at your leisure' so to speak then sell the C4 box again afterwards once back to standard.

[url|https://thumbsnap.com/m2pv8llI[/url]

Edited by Pope on Saturday 31st August 21:39

Thats a decent idea actually! Now I'm toying with the idea of trying to rebuild the gearbox myself, I've built engines before but never touched a gearbox, and considering this is the second time this has happened to me (first in my Boxster) I may as well learn!

[IREvans]

If you’ve got the space, and the correct tooling, rebuilding a gearbox is relatively straightforward, and it’s also hugely rewarding

[mmcd87]

What companies in UK deal with these gearboxes. I know S&C do, but do any other independents? Who is most cost effective?

[ATM]

Funnily enough I was just asking about this detent product in another thread as I'd never heard of it but consider my Porsche beardage to be mightier than most. Its clearly not. Anyway I'm led to believe it can help with crunchy 2nd gear or 2nd gear pop out. That's just hear say though so don't quote me. The company also rebuild gearboxes.

http://www.gboxweb.com/detent.html

[Onetrackmind]

Think the decent prevents 2nd gear pop out rather than stopping it. Could be worth a go though. Don’t think it’d cure 2nd gear synchro crunch though as thatas a mechanical issue. 2nd synchro is weak on my turbo and the box needs to be fully warm before any change downs. I’m planning a rebuild but I can drive around it for the time being as it’s early stages.

[Bullet-Proof_Biscuit]

I somewhere have a PDF of a 986/996 gearbox rebuild procedure for second gear synchro replacement by some American, plz send me a PM if you need it and i'll dig it out after work,

Cheers,

[ATM]

I think setting up as a small independent rebuilding these gearboxes could be a good money earner. A basic engine rebuild costs 4 grand and we know they are potentially not too great. I paid £2500 for a used gearbox and thats before fitting. Ok mine might not have been a cheap repair as I had broke some chunky innards but surely they are simpler inside than an engine which deals with petrol, water, electricity and oil. Its just cogs right and bearings and clips and stuff. I think I saw a vid on youtube where the carrera light weight guy had his gearbox apart. He was just doing it is his garage. It cant be that hard.

[nebpor]

That's exactly what Sports and Classics do (I was in today talking to Mike), they repair and rebuild the boxes. It's not cheap, but then quality never is - especially when talking gearboxes - the parts and the machinery required to do it properly cost money, plus the skills and experience to do a quality job.

I think their prices are not unreasonable at all, plus Mike his team are all lovely - I walked away with a real sense of comfort.

[poppopbangbang]

IREvans said:

There are many reasons why it won’t work, but centred largely on the way that front and rear torque is split using a clutch pack.

Just get your C2 gearbox rebuilt, you may just get away with a synchro hub and a few other parts. It shouldn’t take long at a decent specialists.

Why even comment, especially with such authority, when you genuinely don't know?


OP it'll bolt straight in, your LSD will also be a straight swap from the C2 box if you wanted to swap them over just keep the CWP the same. The casing is identical (bar the front driveshaft output is un-machined on the C2 box) as are 99% of the internals.

If you do want to rebuild the C2 box yourself keep in mind there are some bearings that require specialist tooling and methods to remove from the casing. However if these bearings are in good order you can just swap the whole C4 cluster into the C2 box or pick and choose between the best condition synchros/ratios etc. as appropriate.