4 speed 901 transmission questions.

[Acox914]

Hello guys,

i picked up a 4 speed 901 trans from a fellow pelicanite.
it is currently in transit to me.

but i have the following questions:
ive been told that early 901's had aluminum cases AND intermediate plates- is this true? assumed to be stronger than the Magnesium cases from what im told.

Also-
Can a 4spd case be used as the basis for a 5 speed 901? (different rear housing etc)- but can 5 speed gear stacks be installed in this housing? just install them into the 4sp's intermediate plate?

the number on the housing says:
901 301 101 0R

im assuming that the gears inside this box are:
A (11:34) HB (19:31) S (25:26) and Z (29:23)
is this a reasonable guess as to what gears are inside?
here is a picture of the transmission in its current state:


thanks guys, im sure ill have more questions for you experts.

Aaron Cox

[YTNUKLR]

Yes, aluminum all the way through, and yes, you can get a 5-speed stack in there.

[Acox914]

ytnuklr-

thanks for your reply.
Am i wrong to assume that an AL case is stronger than an MG case?

Also- are my gear assumptions correct?

Thanks again for the speedy reply
AA

[YTNUKLR]

Al is stronger than Mg. Where it counts is the intermediate plate.

Your gear assumptions sound very plausible, but you don't say the type number on the transmission.

Best, Scott

[Grady Clay]

That appears to be an aluminum casting ’69 901/06. Wait until you get the transmission in hand and post the type number and serial number on this thread.

The castings are the same aluminum parts as the earlier 901 transmissions.

Before you post, disassemble the transmission and show us images of the inside. Some gears and parts may be reusable.

What is your purpose? What use do you anticipate? What donor 5-speeds do you have? What distress do they have?

I would be interested in your doing some simple measurements on that transmission for me.

Best,
Grady
gradyclay@hotmail.com

[Joe Bob]

He wants a custom geared five speed for a 914 mid engine application....he wants to use SOME of the 4 speed gears but with the R/P form the 914 box....

[Acox914]

yep. thanks mike.

planning on going
A F (flipped ZD) S ZD (or something slightly taller for 5th (flipped HA maybe) on small AX rubber

close(r) ratio 1-2-3-4 with stock 5th for cruising....

have 2 914/4 boxes to harvest gears out of and now this 901 4 speed

[Acox914]

and in all the spec books, i could only find the above for gear ratios for a 901 4 speed box.
A HB S Z or ZD

[Grady Clay]

Aaron,

Yes, this is very doable. Exchange the studs and the 2.0 nose piece will fit. The ’72 and later shift linkage will all fit. I assume you want to continue using a 215 mm clutch so all that stuff will fit. Since you are using your 914 ring & pinion you have to reset the differential bearing preload any way so setting the pinion and ring position is not much additional when you flip the ring gear.

If you use flipped gears you will want to replace the pinion ball bearing with new (read expensive.) You are significantly adding to its axial load. You will also want to replace the input shaft ball bearing as it is a weak link. Keep all your bearings matched with their races.

What is the rolling radius (or diameter) of your tires?

Now that you have a late 4-speed you can find a 904 E 2nd gear and weld it onto the shaft. Search for my post within the past few weeks.

I am not a fan of asymmetrical gear ratios for normal use. You can have several different transmissions for the many uses. A 914 should have a zipper for gear box attachment.

Tell me more about your car.

Best,
Grady

[Acox914]

Clay
well currently a weekend warrior and short distance driver. Falken Azenis AX stickies which are about ~23 inches tall.

been playing around with the ratios, and talked with people who say flipping 5th in the third slot does wonders on an AX course. but then the gap between your new third and stock 4th is too large, thus the S gear. currently, on such small tires, 80 mph (~indicated 90) is about 4000 rpms, just a tad excessive, yet always in the power band

here is a break down of what i hope to do. (gearchart.xls)





let me know what you think. pulls like a freight train...and a useable freeway gear.

BTW - went conservative withe 5000 rpm number

[Acox914]

BTW- not planning on using the tail shifter linkage. so i guess i will have to use a MG 914 side shifter case, and the 901 AL intermediate plate

[jluetjen]

What sort of engine are you using? Where's the peak torque RPM and the peak HP RPM?

[JWest]

Originally posted by Acox914
BTW- not planning on using the tail shifter linkage. so i guess i will have to use a MG 914 side shifter case, and the 901 AL intermediate plate

Nope, I am almost positive that the Al intermediate plate is thinner than the Mg (The aluminum case extends out a little further). The tail cone can be interchanged as the parting line at that interface is in the same location.

[Joe Bob]

Originally posted by jluetjen
What sort of engine are you using? Where's the peak torque RPM and the peak HP RPM?

Most likely a 2.0 Type IV with a whopping 100+/- HP....

[Acox914]

Basic big cammed and carbed 2L. powerband starts at 3000 - and pulls to 6000.