3.6L + 901 transaxle?, Is this a recipe for disaster? Options

[Hydra.]

I'm seriously contemplating going with a 3.6L 964 motor for my 914, but I'd like to keep the existing 901 transaxle. I understand that this doesn't leave much in the way of a safety factor, but what can be done to suitably strengthen the 901? Is it absolutely necessary to lock out 1st gear, or would something like an Albins 2.400 1st gear, along with a billet sideplate help out? I understand the alternative is to go with a 915-based setup, but if a 901 can be made to work satisfactorily then I would rather do that...

[SirAndy]

I'm seriously contemplating going with a 3.6L 964 motor for my 914, but I'd like to keep the existing 901 transaxle. I understand that this doesn't leave much in the way of a safety factor, but what can be done to suitably strengthen the 901? Is it absolutely necessary to lock out 1st gear, or would something like an Albins 2.400 1st gear, along with a billet sideplate help out? I understand the alternative is to go with a 915-based setup, but if a 901 can be made to work satisfactorily then I would rather do that...

I've been running the same (stock) 901 behind my 3.6L for 5 years now. (IMG:style_emoticons/default/driving.gif)
However, i don't use first gear at all, i take off in second, effectively turning it into a 4-speed.

This has worked surprisingly well, but i'm at the point now where i am ready to make the switch to the 915 that has been collecting dust in my shed.

1st in the 901 will always be the weak link ...
(IMG:style_emoticons/default/popcorn[1].gif)

[pcar916]

I've been using the 914 transaxle with my 3.6 since 1999. There are many opinions about this and you probably should spend an hour or so going through the threads on transaxle life with big engines. There are several threads in the Paddock that talk a lot about ways to make it last longer. Here's my short version.

1. If it's a street/now and then track car then you'll be fine if you start with a good transaxle. That means good bearings, synchros, R&P etc. If you intend to race you'll be rebuilding/replacing stuff yearly anyway. Race tires aren't going to break away and relieve the stress on the drivetrain like street tires will.

Again read some of these threads including this one that addresses a lot of this. Remember that as you read this, I didn't cool mine until this year. Frankly, in a pure street car I don't think it's needed.

http://www.914world.com/bbs2/index.php?showtopic=161520 and

http://www.914world.com/bbs2/index.php?showtopic=177277

2. I use 1st gear all the time, but don't overstress it with excessive throttle and/or crappy clutchwork. Smooth is hyper important.

3. Did I say smooth will save your equipment?

4. Controversy alert: I have run synthetic hypoid for the entire life of the box, but most folks will tell you that dino oil is better for the synchros. My thinking is that I'd rather replace a synchro than bearings or the R&P.

I've replaced exactly one synchro in 15 years and that was only because I was installing an LSD diff and had one that was better on the shelf. Your call!

5. The 915 installation is an interesting thing. Expensive as well so make your decision after some reading in the first thread and crunching your cash numbers.

6. I ran the stock CV's/axles for years with no real problems, but they'll wear faster if you're doing a lot of heavy throttlework, so you'll want to keep an eye on them i.e. inspect/repack once every year or two. Then installed 108mm turbo cv's. Now I'm running 100mm 944 CV's because the 108's are so very much heavier.

The 901/914 transaxle is definitely lighter. This was important for me since the 3.6L engine (either 964 or 993) is so much heavier. If I blow up more than three transaxles in a row I'll install a 915 and a cable shifter, eat the weight difference (roughly 35-40 lbs IIRC) and see how that goes. But I think the 914 box will be just fine if I drive smoothly.

If you are one of those folks that shift/clutch fast then none of these boxes will last very long.

Good luck and enjoy the reading.

[Hydra.]

Thanks for chiming in guys, glad to see people with several years experience contributing to this discussion (IMG:style_emoticons/default/smile.gif)

So installing a taller aftermarket 1st gear won't do much for strength? What about the other mods such as the billet intermediate plate and diff cover, are they worth the $$?

[Dr Evil]

No taller first will be worth it because it will still be hanging unsupported on one side off the back of the intermediate plate. The billet stuff is pretty, but not worth it, IMHO. For a 3.6, a 901 will always leave you wanting, but can be adequate as those above have stated. Gonna need an H gear.

[SirAndy]

So installing a taller aftermarket 1st gear won't do much for strength?

No. The gear itself is not the problem. The problem is that it hangs off the end of the shaft and is not supported well.

Too much torque and (IMG:style_emoticons/default/blowup.gif)

[pcar916]

(IMG:style_emoticons/default/agree.gif) Ditto on the billet things and first gear. You can get most of any strength gains by through-bolting that plate wherever possible with the existing piece. I run my car "fairly hard" and never had any of those fasteners loosen up. Just stick to the torque specs and build them as close to utterly clean as you can get.

You really do need to verify that the transaxle is really healthy to start with.

[Dr Evil]

Yup, a rebuilt unit will serve you better. A used unit will make a ticking sound up until it explodes (IMG:style_emoticons/default/smile.gif)

[rick 918-S]

901 behind a 350+ hp 928 V8. I use first gear to get myself rolling but never hammer it.

[Hydra.]

I'm aware that first gear is overhung/cantilevered on the 901, but I figured that maybe going with a taller 1st gear makes it less weak and increases the tranny's torque limit somewhat, much when Ford specified a 2.95 1st gear instead of 3.35 on the Cobra T-5z to increase its torque rating from 300 to 330 lb-ft... Plus it actually makes 1st gear useful!

[mittelmotor]

901 behind a 350+ hp 928 V8. I use first gear to get myself rolling but never hammer it.

Similar situation here...320-bhp stock LS1 V-8 with 901. 2nd gear feels incredibly natural as 1st with all the extra torque, and makes it a standard H-pattern as a bonus (albeit a 4-speed). I tried 3rd away from a stop a few times, and it worked surprisingly well! I never use 1st, and I'm looking into stronger springs for the 1st/reverse detent so I don't go there inadvertently.

But I shift like I'm in a long, lazy endurance race. If I were really going to beat on it, I'd probably go the 915 route, but I'm very pleased with the 901 so far.

[rick 918-S]

Longer lever = more force = more stress= (IMG:style_emoticons/default/blowup.gif)

[shoguneagle]

These are all excellent points and ring of 100% truth. Years and Years Ago (that is ten eons for younger troops) I ran a 901 behind a 350 Chev (300hp; 300 torque) using 1st gear. Still have the transaxle today which recently was replaced with on of Doc Evil "Evil Black Magic Boxes". Never had any trouble but again I did not hammer it. Had plently of hp and torque for the other four gears.

You call based on the mentioned above information but at least have it rebuilt to give you longevity.

Steve

[Dr Evil]

901 behind a 350+ hp 928 V8. I use first gear to get myself rolling but never hammer it.

Similar situation here...320-bhp stock LS1 V-8 with 901. 2nd gear feels incredibly natural as 1st with all the extra torque, and makes it a standard H-pattern as a bonus (albeit a 4-speed). I tried 3rd away from a stop a few times, and it worked surprisingly well! I never use 1st, and I'm looking into stronger springs for the 1st/reverse detent so I don't go there inadvertently.

But I shift like I'm in a long, lazy endurance race. If I were really going to beat on it, I'd probably go the 915 route, but I'm very pleased with the 901 so far.

It is easy to lock out first in the box. Better too.

[pcar916]

... all say to rebuild...

Not necessarily a rebuild, but inspect everything to make sure you have intact bearing cages, smooth bearing races, decent wear patterns on your R&P, good sychro's/dog teeth and sliders, and no leaks. The least it can cost you is a new gasket set. All of this and if the R&P is set up properly you're good.

You're gonna put out the upper limit of what this box will tolerate if you drive in a "spirited" manner.

Good luck and let us see the conversion as it unfolds!

[mittelmotor]

901 behind a 350+ hp 928 V8. I use first gear to get myself rolling but never hammer it.

Similar situation here...320-bhp stock LS1 V-8 with 901. 2nd gear feels incredibly natural as 1st with all the extra torque, and makes it a standard H-pattern as a bonus (albeit a 4-speed). I tried 3rd away from a stop a few times, and it worked surprisingly well! I never use 1st, and I'm looking into stronger springs for the 1st/reverse detent so I don't go there inadvertently.

But I shift like I'm in a long, lazy endurance race. If I were really going to beat on it, I'd probably go the 915 route, but I'm very pleased with the 901 so far.

It is easy to lock out first in the box. Better too.

How, exactly? I'm sure there are multiple threads on it, but what's the short version?

[Bruce Hinds]

Before you lock it out, you may find it usefull if you find yourself in a steep driveway or trying to start on a steep hill. I also use it for stop and go traffic, rather than in and out with the clutch in second constantly. It won't hurt anything to keep it in there, it might come in handy.

I've been running the 901 behind about 330HP SBC for over 20 years and the only problem I've ever had was when I side stepped the clutch in second to do big burnout. It got the ring and pinion.

Second makes a perfect first! Drive it smoothly and once the clutch is out, give it hell. See all the gear threads, I don't know what I have now, but years ago Renegade widened my ratios and it made a big difference.

[iamchappy]

Still working fine in my turbo car, with LSD and short gears. I use 1st all the time but never hammer it, use it only to get rolling.

[siverson]

I blew up 3 901s with my 3.6 until I switched to a 915 (Vellios kit). I try to be gentle, but I can't help myself. And I didn't install a 3.6 to be gentle. (IMG:style_emoticons/default/smile.gif)

-Steve

[computers4kids]

300 + SBC with stock 901 going on three years now and no problems. Added an H gear for freeway cruising. I left first, but never use it--like the others have said, 2nd feels real natural as a first gear. I wouldn't block it off it is handy for loading the car on a trailer or sitting at a red light on an uphill stop...literally will stand still like an automatic with clutch out.