Player0

Hi guys,

Now that I have a 3.0L turbo motor completed and ready to go in the car, I got to thinking about the transmission. I have an 86 951 trans, freshly rebuilt, with the guard's LSD.

I really don't know what to expect HP wise out of this motor, but I do suspect it's more than the drive train is going to be happy with.

What generally fails in these transmissions? Should I have certain things hardened or improved in my transmission? Or am I better off picking up an S2 transmission and putting the investment in there?

Or do I just keep the boost turned down so I don't spray gear teeth out the tailpipe?

Anecdotally, how many of you 3.0L turbo owners have had any issues with the transmissions? I've done some searching and I've not come up with much other than a few V8 owners having issues. Maybe instatorque is the issue, not so much with turbo spool torque?

Tom M'Guinn

I blew my 2nd gear shortly after turning the boost up on my 3 liter. Read about it and a few other experiences here:

https://rennlist.com/forums/944-turb...ing-power.html

I ended up having Kevin Gross rebuild a transaxle, using the stronger 1st and 2nd gears from the Turbo S cars, and it's been fine for about 30k miles. Would definitely recommend the hardened gears.

I've also broken CV joints, so this thread might be worth reading too...

https://rennlist.com/forums/944-turb...servation.html

Would also suggest skipping trial and error with the clutch and just going straight to a KEP1 pressure plate and cup disk -- unless it's a pure track car and/or you don't mind clutch shudder/chatter.

Player0

Thanks Tom,

Good info. I think it was Kevin Gross who did the rebuild on my 951 transmission in the first place. It was sent to catellus from my mechanic. Gotta be the same guy. I have an email out to him to see what he can do.

I have aftermarket CVs, the ones Lindsey sells which I think come from the driveshaft shop. Beefy units, though I had one fail due to a boot issue already. Hope it was just a fluke.

I have the spec twin disc clutch which I'm hoping is a decent unit and will hold up to whatever.

So I'm thinking it's just the transmission which could be the weak link.

How much power do you reckon you were pushing to the wheels when it popped, Tom?

333pg333

Biggest issues would come from dumping the clutch. If you don't do that then you'll be fine under most circumstances imho. I would check which version of the LR axle/CV combo you have. Show a pic and we can identify.
EDIT: If you have the one with the black boot then they've sold you the old one that wasn't fit for purpose.

gruhsy

I have a 3.0L with stock transaxle. I have not had any issue and also don't run the high HP axles.

I do have Hankook Ventus V12 285/30/18 rears though. They do not stick well to the pavement.

Someone joked about my tires as being axle savers They loose traction before the axles or transaxle take damage.

So far it's worked well with 444ft/lbs of torque at 15 psi

Player0

Thanks Patrick, I've got the lower one in the picture. Boot kind of tucks inwards. I'm concerned about the design because my boot ripped at the center of where it turns inwards.

Got a hold of Kevin Gross today and it sounds like I can put the AOR input shaft with the hardened 1/2 gears. Guess I'm dropping the transmission again.

Oh well, needed to do some fuel tank things anyway.

Auto_Werks 3.6

Dropping the transmission is just a warmup activity! My Co driver and I have been talking about whether we think we could swap transmissions on Saturday evenings of two day events if we want different gear ratios! Grand scheme of things super easy, bordering on relaxing.

Tom M'Guinn

When mine popped, it was right in the middle of a 2nd gear pull, getting on the highway at WOT. It was pulling strong, then just blew apart with a seriously cringe-worthy screech. It was 18psi, so based on subsequent dynos I'd guestimate I had about 425-450 ft lbs of torque to the wheels at the moment it popped.

Player0

On the registry, it looks like your numbers are closer to 500 these days Tom. So I'm guessing the transmission can hold that much safely with the upgrades?

I think near 500 is in the realm of feasibility for my build. The turbo can push it, the engine can hold it, the head can support the CFM, and the fuel system with the 044 and big lines can just about do it.

Tom M'Guinn

Right, when the tranny blew I was still exploring the limits. Since then I've seen as much as 500rwhp on a dynojet... It's a street car though, so doesn't see the kind of wear it would get on a track.

V2Rocket

Quoted for posterity....

refresh951

I am running an AOT S2 tranny (hardened 1st and 2nd just like AOR) with a urethane filled tranny mount. No issues at all.

Humboldtgrin

My AOR before it was rebuilt with the correct turbo ring and pinion.

Dimi 944

Has the input shaft been replaced?....the AOT does not come from the factory with hardened 1st and 2nd gears.

Player0

I've heard that the S2 transmission has a stronger ring and pinion.

Should I be upgrading that as well?