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.
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 ...

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.

Thanks for chiming in guys, glad to see people with several years experience contributing to this discussion

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 $$?

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.

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

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.

Yup, a rebuilt unit will serve you better. A used unit will make a ticking sound up until it explodes

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

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!

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.

Longer lever = more force = more stress=

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

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

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!

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

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.

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.

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.

-Steve

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.

Regarding the "through bolting" mentioned earlier. I currently don't think that helps anything. I have had at least one transmission pass through me that was setup with through bolts and was supposedly done by a professional shop. It was a total hack job. I don't think the weak links in this transmission is solved by higher clamping force on the intermediate plate and I don't see loose studs as a common problem (they occasionally back out due to rusted on nuts however).

I am on the fence regarding billet intermediate plates. I see intermediate plates that have worn bearing bores from what I expect are stock engine situations. I can image that the billet plates would be less prone to that problem. When the supply of spare (used, but good) factory intermediate plates runs out, billet replacements will be the only option. There supply of core transmissions to harvest parts from will not last forever.

As mentioned above, I think your driving style is going to have a much much larger impact on the longevity than any particular upgrades. And somethings (like the cantilevered first gear) just can't really be solved other than locking it out. Being able to put more power through "reliably" and given a wide range of potential driver abuse, you need a beefier transmission. Hence Porsche moving to the the 915 and eventually the G50.

Richard

Short answer for locking out first is...

You install a sleeve (copper or steel tube) of appropriate length over the first/reverse shift rod. It goes between the shift fork and the intermediate plate. It allows the rod to select reverse, but not 1st. You can optionally remove 1st gear off the pinion shaft (leaving the spacer/bearing race for that gear in place). You must leave 1st gear on the input shaft as power for reverse flows through that into the reverse idler gear.

If you have a nice condition 1st/Reverse slider, you could even sell that and use a worn one instead as the part that usually wears on that slider is the 1st gear dog teeth (which would no longer be used).

Richard

Thanks, Richard. I think I'll leave it for now. My 3-2 downshifts (really 4-3) are slow and methodical, and that gate feels pretty well defined. I'm hoping my driving style (not into burnouts or anything that really shocks the driveline) will give some longevity, but I realize that even smoothly applied torque of V-8 magnitude can schrapnelize a gearbox.

Currently my setup only allows for 3/4 throttle (914 linkage throw versus Camaro TB), but it's so bloody fast I don't expect to change it. So maybe a little more breathing room for the 901...

Here is the Scruffy Doctors thread on first gear lock out...
Dr Evil First Gear Lock Out

Thanks, Bulitt. That does look pretty straightforward. I think my next course of action is to get a second transaxle, a copy of Dr. Evil's 901 rebuild DVD and put together a second 'box with H gears, etc. My quiet exhaust makes 3500 rpm on the freeway tolerable, but 2500 would be so much better and easier on fuel consumption.

I took the 915 route on my 3.6 914/6 right from the beginning. I read a lot of earlier threads about the pros & cons, and that swayed my decision.

I wanted to drive my car as hard as I desired. So, that being said, the cost of the 915 is not for the faint of heart.
Figure 1. 1000-1500 for a used box.
2. Mine has a Vellios unit but since they are NLA figure 3000.00 for a side shift conversion. Wevo or Bugspeeds kit
3. I also put in a billet bearing plate. 300.00
4. I installed a Guard GT LSD diffierential. 1500.00
5. I did a 7:31 R&P 700.00
6. 800-1000 in rebuild pieces.
7. I did a spray bar, pump & cooler. 300.00
Add it all up, and it is not hard to see 8-10k in a really good setup..
I don't regret my decision a bit. I am driving my car any way I feel inclined to do. It just comes down to how much you're willing to lighten your wallet in the pursuit of fun.
To me, there just isn't anything comparable to putting the hammer down on a 3.6L 914/6 hard!! , and feeling those G's pim you to the back of the seat until you're ready to let off the accelerator.

Good luck on your decision...

400+lbs of tq and quite a bit of drifting on 285 tires and the trani seems to be still strong. Shifting is getting worse, but thats linkage...

....but remember, race tires (even 12 inch slicks?) won't break loose to relieve the stress....bla, bla, bla

Let me introduce you to the 901 that could.........FIRST GEAR REMOVED..ALL STOCK PARTS. ( cept for the LSD)

http://www.youtube.com/watch?v=pB0fTcTHkg4...eature=youtu.be

I have lots of sideshifters.Maybe I will beat on my current one a bit.Britians car is likely harder on a trans than mine.Bigger rubber/racing etc.An LSD and different gearing is in my future tho.Some fellas are also doing a Boxter S tranny..

The irony is that I have a late mag-case 915 with 8:31 and optional ZF LSD lying around, but I figured I would sell it to help offset the cost of this build. If 1st gear on the 901 is unusable no matter what, then I may have to reconsider

A cable-shifted 915 is looking like an increasingly appealing option. The question is, would you rather flip the R&P or run the entire tranny inverted?

If 1st gear is avoided the 901 is not the weak point in the 914 drive train......BTDT.
CVs will go long before in a car that is driven hard. There is no "work-around" there .....except for replacement with something stouter.....but it's your money to spend as you see fit.

My CVs (the original ones) actually held up for a long time till spilling their guts on the starting line.

Another viewpoint - we have a 3 liter in a track car. Two drivers around 20 days each a year. We toast a R&P a year for two years straight. Well built boxes with billet intermediate plates and stock gears.

I'm still running a 901 since 1994 and have had very few problems... two in fact, a worn spider/slider pair and more recently, a broken pinion. The worn spider was my fault and it showed me I wasn't pushing the clutch all the way in during shifts from 4th to 5th over a very long time. I have no idea about the pinion but it was the original R&P from '74 and I think it just got tired of the horsepower.

I also have three 915's. Two are mag-case 7:31's and an '84 which is 8:31. I still haven't committed to the 915 project because the 901 is useable to this day. My thinking on 915 pro's and cons is something like this.

1. The LSD for the 914 fits the early 915 (dimensionally) so I can transfer it to the 915 box. I ran an open diff for many years but now won't go back.

2. The 915 is heavier whether it's a mag-case or not

3. I'm have to modify the flywheel/clutch and shift system if/when I convert

4. If I don't invert it, I still have to remove the gear cluster to get the pinion out of the way if I want to make changes or do maintenance (i.e. clutches) to the LSD.

5. If I invert it, the diff maintenance is easier but I will have a non-optimal axle deflection... creates a "some amount" more heat and the associated hp loss. Don't know how much that is but it's there. Realistically not a deal breaker though.

6. The lubrication and venting will have to be changed but that's not tough.

7. When I do this I'll invert the 915.

Conclusion: The 915 is a VERY cool (fun) project and I'll get to it because it'll be a lot of fun. But if the 901 continues to be a solid choice that's all it is. Fun

Hmmm... another tub?

Flipped

I already have the rebuild 915 with the flipped R&P. All i need now is a LSD and for McMark to build me a cable shifter setup.

I've been putting this off for way too long anyways ...

This subject comes up pretty frequently and gets pretty much the same replies. I'll add my perspective though.

If you are tight on money, run the 901 and be easy on first. Personally, I wouldn't delete it since it's a nice crawl along in traffic gear. However, if you stand on it in first you might walk home.

I made the decision to run a 915 for one main reason. I refused to have the power of a 3.6 with a gearbox totally inappropriately geared for the engine. That means re-gearing and I certainly wasn't going to spend the money to rebuild and re-gear a 901 tranny that was not up to the task of running all 5 gears or the power of a 3.6. Personally, I'd rather pour the money in a better tranny. I would feel differently if I wasn't going to re-gear.

I re-geared my 915. 1-4 is close ratio with first starting higher than a 901 first but lower than a 901 second. First is good for 53 mph.

For 5th I took a 915 7:31 5th gear and installed it in my 8:31 tranny. WEVO said it would not fit in their rear case but my grinder fixed that issue.

What I have now is a really fun gearbox that takes me long past 100mph and a 5th gear that cruises at 80mph at 3000 rpm. It is NOT race gearing but you can easily chat with your passenger on the freeway at speed.

I also added a Guard TB posi

Installing billet side covers is a waste of money since the torque is pushing on the case side and NOT on the cover side.

To say the least, this conversion is not for the financially strapped car builder so beware. I ended up with about $7500 total to do mine including the WEVO conversion.

Here is the gearing I am running....disregard the note that says 901 gearing as installed
Click to view attachment