transmission 901 vs 915?

[flash951]

I need a new transmission, as I think it would be to much work and to expensive to rebuild my old 901.

What is the difference when using 901 in opposite to the newer 915?
Given that both transmissions is rebuild and in good condition?
Faster gear change with 915?

Note: I already have the Rennshift shifter, new bushings and new shift coupler for the 901, and also an over halt mechanical speedometer and new speedometer cable and new clutch cable.

[pwd72s]

I'd say it depends on your horsepower. The 901 isn't as strong as the 915, but the 915 will need some mods (hammer work ) to your car in order for it to fit.

Neither is what I would call a "smooth shifting" gearbox...they are NOT meant to be speed shifted.

[RWebb]

the 915 has a much worse shift pattern & worse "feel"

rebuild your 901 or pay someone else to do so

[1971 911T]

i am a 901 fan. to me it has more of a vintage "look" amd shift pattern is great. the 915 is a much stronger box, but operating it is like driving any european sedan from the 80s onwards.

[Walt Fricke]

901s have a cult following, I see. But they are fine for T (which does not stand for turbo) motors.

I have a friend who runs a 2.8 race motor's torque through his. But I think he is living on borrowed time.

[sc_rufctr]

Originally Posted by RWebb

the 915 has a much worse shift pattern & worse "feel"

rebuild your 901 or pay someone else to do so

The 73 RS came with a 915. And that car is considered one of the best drivers cars ever made.
A good 901 is a sweet shifter. Often described as a better shifter than a 915.
That's because the input and output shafts are closer together and therefore the shift seem "easier" than a 915.

However... I believe a good 915 is very underrated. Just take a look at this. This car is a 74 with a 915 gearbox.
These GBs have a bad rep because instead of a proper rebuild most folks seem to hobble them back together and hope for the best.

(from the Targa Tasmania thread)

[Walt Fricke]

Well, I couldn't tell when there was shifting going on.

What fun.

Very professional navigator there - telling his driver not to race the other car, never missing a beat.

In the Carrera Panamericana I ran in 1991 our intercom went out. The navigator (who had never done a rally type event before) used hand signals. But it was a VW Beetle cab and couldn't do over 100 mph on a straight anyway, which made things easy for the Mark 1 eyeball.

[PCA7GGR]

If your 911 has the original tranny, its a "Type911" 901. It has a "pull" instead of the usual "push" type clutch fork. This means that the clutch fork rides on a "fork pivot bolt" that id mounted on the tranny and cannot (or is extremely difficult) to get at once the engine and tranny are mated.

These pivot bolts have a tendency to break at the most inopportune times - like three stop from home. When they do, the clutch pedal drops to the floor. Fortunately, when it happen to me, traffic was light and I was able to do "California Rolls" at the last two stops in 2nd gear and nursed the car home. That's when I decided to replace the 901 with the 915 I had sitting in the garage (on my "to-do" list).

Having driving both a 901 and 915, when both have properly bushed/adjusted shift linkage, I prefer the 915.

[Grady Clay]

Remi,

I have both 901/911 (3) and 915 (2) and I far prefer driving the 901/911.
No question, the 901/911 operates better than the 915.
The limiting factor is the size (torque) of the engine.

Your type 911 will handle your 2.7 just fine.
Yes, a 915 will be stressed much less and it is heavier.

To convert to a 915 will involve some minor clearance issues with the metal between the rear seats.
You will need 915-compatible shifter and shift rod in the tunnel.
Depending on the year 915, there can be an axle-compatibility issue.
You will also need to have one compatible with a mechanical speedometer or convert the car to electronic speedometer.


In either case, it is difficult to find a ‘good’ used transmission.
You will need to build yourself or commission one from a pro that is close to ‘new’.

Just like engines, every transmission has a ‘service life’.
This ‘life’ is very use and operator dependent.
Keep in mind your ’71 is now 40 years old.
In general, they can be rebuilt forever – just after a century or so there won’t be any original parts.

While the ’70-’71 ‘pull-type’ clutch operating parts were designed by Rube Goldberg, it can function just fine.
With good pieces and some ‘fine tuning’, you can’t tell it isn’t a ’69 and earlier.
The failure Sergio notes above is common from mal-adjustment and worn parts.

Best,
Grady (cult follower, living on borrowed time since 1968 )

PS: For racing, all of these transmissions should have an oil pump, filter, magnets, oil cooler and very regular maintenance.

[Flieger]

Another vote for the type 911.

[Matt Monson]

901/911 all the way.

[pwd72s]

IF he hasn't retired by now...as far as I'm concerned, the best gearbox rebuilder of this area, and possibly the country, is Gordon Ledbetter, Portland, OR.

[RWebb]

I spoke to Gordon a year or so ago, and he was still doing some transmissions. You can also contact Steve W. and AFAIK, the trans. may wind up being done by Gordon. He is not very interested in doing modification work.

[Grady Clay]

Remi,

I have known Gordon for 35 years and Matt for a while. Good guys and very professional.
From Norway to the PNW or here in Colorado is a bit of shipping.


With everything you found you can do yourself on your Targa, the type 911 transmission should be easy.
Buy the basic tools from our host.
Make some of the others.

Read this thread:
1970 (911/01) transmission refurb issues
There are several others also.

If you find you need to replace or reset your ring and pinion gears, have a local pro or someone in the UK or Germany do that (with you watching).
The three operations take very special (read expensive if you can find them) tools and the skill and experience to use them.

You should note what Mike Caterino (link above) eventually decided about my original suggestion about buying some ‘good’ salvage transmissions.

These are easy transmissions to rebuild yourself.

Best,
Grady

[J P Stein]

I too am a 901 fan
My old 901 (914) was living behind a 215ft/lb 2.7L for going on 11 years. For the past 7-8 years this was along with 10 wide R35 Hoosier slicks. The tires were hazed at will for AX starts in first gear(B).

Things changed somewhat by the elimination of first gear a couple years back. One has to work at quick (F second) starts by reving to about 4K , side stepping the clutch, & burying the throttle This results in 2 satisfying black streaks.

Recently the 901 is living behind a 330hp
315 ft/lb, 2.0L Subie (the motor Porsche should have built). The jury is still out on it's longevity.

Gordon Ledbetter built the box initially and went thru it for a look see last year...it needed no parts replaced, if I understood it correctly.

In it's latest configuration. .....

[calling911]

Originally Posted by sc_rufctr

The 73 RS came with a 915. And that car is considered one of the best drivers cars ever made.
A good 901 is a sweet shifter. Often described as a better shifter than a 915.
That's because the input and output shafts are closer together and therefore the shift seem "easier" than a 915.

However... I believe a good 915 is very underrated. Just take a look at this. This car is a 74 with a 915 gearbox.
These GBs have a bad rep because instead of a proper rebuild most folks seem to hobble them back together and hope for the best.

(from the Targa Tasmania thread)

Nice.. "Dont try to race him Rick" (ie. please dont kill me ok?).. "Im just havin fun".. what a jack ass..

Rule #3.. run your own race or pay the price.

I noticed long pauses between shifts.. it aint no honda.

[H-viken]

Can you use the 915 carrier when installing a 915 in a LWB or do you have to use the carrier from the 901?

[Matt Monson]

901 carrier. I have a couple of you need one.

[Long Nose]

Hello, thanks for the feedback. I just had my 901 rebuilt from my 70 2.2T, and it cost roughly the same if not more than it would have to buy a rebuilt 915 transmission. However, there were a couple of reasons I stuck with the 901. First, I love the 'dog leg' 1st gear, and the typical H pattern being 2 thru 5, its a joy to drive. Secondly, having seen a 901 transmission on the bench next to a 915 transmission, the 915 is a lot bigger and heavier than the 901. The 901 is a light, compact transmission, one person can lift it and move it around. The 915 is a beast by comparison, it really surprised me that it would even fit in the early 911s after 1972.

Third, the synchros and dog teeth and gear clusters that went into the 901 all had 915 part numbers, as all the 901 internal parts have been 'superceded' by 915 part numbers, so assume they are all 915 internals. So, I assume that there is not much difference in the gearing and shifting mechanism, although the shift pattern is different.

The 915 case seems to be larger and stronger and offers more reinforcement for cornering and hard starts. However, you can now get and aluminum center plate and diff cover on our host that will add reinforcement and strength to the 901 case. You can also retrofit a 901 with the LSD.

So, with a LSD, case reinforcement, it was not cheap, but I think I will have a strong gearbox but one that is also very light weight and compact.

[kevingross]

Originally Posted by Long Nose

Secondly, having seen a 901 transmission on the bench next to a 915 transmission, the 915 is a lot bigger and heavier than the 901. The 901 is a light, compact transmission, one person can lift it and move it around. The 915 is a beast by comparison, it really surprised me that it would even fit in the early 911s after 1972.

You're right, but I have to chuckle a bit at this, comparing the size and weight of the 915 to later transmissions which just kept getting heavier and heavier! I have a 901 and an early G28 (from a 928) on the bench at the moment... and I think the G28 weighs twice what the 901 does!

With respect to strength, I'd caveat that the mag case 915s are not that impressive in terms of their strength and mechanical integrity. For example, I serviced one a few years ago that took over 2 mm more shimming than original to preload the differential carrier bearings, which is a huge amount. Fatigue. They are frequent candidates for repair to the bores for the input and pinion shaft bearings in the diff carrier and gear housing.

The stronger aftermarket bits for the 901 are good things, and I use the intermediate plate (gear carrier), diff cover plate, and bearing retainer that CMS makes. Cheers,