915 for 1970 911

[panzer]

Can anyone give me an overview about installing a 915 transmission into a 1970 911; what's involved and which 915 box I should be looking for?

Thanking your support.

[TRE Cup]

sent u an e mail

i forgot to include the shift tower and shift rod in my notes

[Grady Clay]

Dave,

Post all that here so everyone can benefit.

My recollection is the two evaporative emissions hoses need repositioning and the welded-in bracket holding them needs removal.

This conversion is for ’69-‘71, not earlier.
To convert a SWB to a 915 is a much bigger deal.

Best,
Grady

[TRE Cup]

The parts menu:
1972 thru 1974 trans is best as the actuation arm works in a standard pull manner, the ring and pinion ratio (7:31) is the same as the oe box, and you can use the existing speedo cable connection

Transmission mount plate, the aluminum spacer, and the two mounts (same as the engine mounts)

72-77 flywheel and clutch pack. You can re use the ring gear from your 70-71

72-75 clutch cable, actuation "wedge", 7 mm nuts, and get a new yoke and clip for the pedal end while you are at it

Clutch pedal shaft for a 72-77. Get some new bushings for the pedal assembly while you are in there

73-86 shift tower- so much nicer than mop in the bucket 72 and earlier shifters

Shift rod in the tunnel (don't forget the bushings) for 72-86 or get an over all measurement of one and shorten the earlier shaft (requires welding)

Check axle output flanges on the trans to make sure they match the axles you currently have (another argument for 72-74 as they have the right 4 bolt flange type)

oil and filter, new trans lube (Kendall or Swepco)

Operation:
The r and r is fairly straightforward. The mods beside the hoses and bracket mentioned by Grady, also include using a mallet to pound out the hump (between the seats) from the underside to make clearance for the larger 915 housing.
The shift rod cannot be changed while the motor/trans are in the car.
While you are in there, check out fuel lines, electrical, e brake cables, heater parts as you have maximum access with the motor/trans out.
Make sure you follow the factory torque specs and double check the axle bolts again after driving the car a bit (30-50 miles)

Rather than use the paper/cardboard gaskets between the axle cv and the trans output flange, we clean both surfaces well, then put a thin layer of silicone on them. The excess squeezes out while torquing down and we turn the axle wiping the silicone smoothly on the joint. Big plus as no grease has ever escaped the joint this way and its easy to clean when you have to service the cv / remove the trans again

Before disconnecting the existing trans from the coupler in the tunnel, carefully note the relationship of fore/aft and side to side movement. This will aid you in initial set up for adjusting the 915 once installed. You do your other adjustment with the trans in reverse. The shifter should be located smoothly in its reverse position. The rest of the gears should readily fall in place, with only slight fore aft positioning of the coupler within the tunnel shift shaft

[911pcars]

I could have used Dave's menu when I did this some years ago (915 into '69).

I might add that in order to enlarge the tunnel area with said BFH, I temporarily removed the nose housing from the gearbox, then used it with the trans. mount to pinpoint the specific areas in the tunnel area to bash for the needed clearance.

Updating to aluminum trailing arms makes it relatively easy to also use standard, MY axles/CV joints, part of the inevitable slippery-slope conundrum.

Sherwood

[RD911T]

The parts menu:

1972 thru 1974 trans is best as the actuation arm works in a standard pull manner, the ring and pinion ratio (7:31) is the same as the oe box, and you can use the existing speedo cable connection



Transmission mount plate, the aluminum spacer, and the two mounts (same as the engine mounts)



72-77 flywheel and clutch pack. You can re use the ring gear from your 70-71



72-75 clutch cable, actuation "wedge", 7 mm nuts, and get a new yoke and clip for the pedal end while you are at it



Clutch pedal shaft for a 72-77. Get some new bushings for the pedal assembly while you are in there



73-86 shift tower- so much nicer than mop in the bucket 72 and earlier shifters



Shift rod in the tunnel (don't forget the bushings) for 72-86 or get an over all measurement of one and shorten the earlier shaft (requires welding)



Check axle output flanges on the trans to make sure they match the axles you currently have (another argument for 72-74 as they have the right 4 bolt flange type)



oil and filter, new trans lube (Kendall or Swepco)



Operation:

The r and r is fairly straightforward. The mods beside the hoses and bracket mentioned by Grady, also include using a mallet to pound out the hump (between the seats) from the underside to make clearance for the larger 915 housing.

The shift rod cannot be changed while the motor/trans are in the car.

While you are in there, check out fuel lines, electrical, e brake cables, heater parts as you have maximum access with the motor/trans out.

Make sure you follow the factory torque specs and double check the axle bolts again after driving the car a bit (30-50 miles)



Rather than use the paper/cardboard gaskets between the axle cv and the trans output flange, we clean both surfaces well, then put a thin layer of silicone on them. The excess squeezes out while torquing down and we turn the axle wiping the silicone smoothly on the joint. Big plus as no grease has ever escaped the joint this way and its easy to clean when you have to service the cv / remove the trans again



Before disconnecting the existing trans from the coupler in the tunnel, carefully note the relationship of fore/aft and side to side movement. This will aid you in initial set up for adjusting the 915 once installed. You do your other adjustment with the trans in reverse. The shifter should be located smoothly in its reverse position. The rest of the gears should readily fall in place, with only slight fore aft positioning of the coupler within the tunnel shift shaft

Dave, great write up, I found an 915 for my 71 coupe, but the owner thinks it's a 75. Serial # 764 341. Is there a way to tell what it is from the serial number!

[newms]

I don't know the answer to your question (likely yes from the serial number) but there are a couple of ways to tell what you have. First is the transmission type number which is 915/xx stamped into the trans case. That will give you all you need, if it is still visible or legible. It often is not.

Or, if you remove the large round side cover plate and remove the differential you can easily count the number of splines on the pinion shaft. 7 splines 7:31; 8 is of course then an 8:31. You can also count the number of splines on the ring gear which is, naturally, then 31 on both. This does not tell you what year, but if its a 915 with 7:31 then its 72-73-74 only. To complicate a bit the gearing was slighlty different by year, for example I believe the 74 915 has a taller 5th gear which would make it desirable for highway travel, less so for track use. Likely done for gas mileage improvement during the then 1973-74 fuel crisis, etc.

[PCA7GGR]

"mop in the bucket"

Dave, that's the best description I've heard of the old style shifter.

I've got an early 915 in my '70 based RSR plus a WEVO shifter - shifts like buddah.

[RD911T]

Originally Posted by newms

I don't know the answer to your question (likely yes from the serial number) but there are a couple of ways to tell what you have. First is the transmission type number which is 915/xx stamped into the trans case. That will give you all you need, if it is still visible or legible. It often is not.

So if it's the 72-74 tranny, what will the the type number be?

[RD911T]

The number on the case 915.301.301.OR in one spot and 915.301.102.OR. Is this the one with the 7:31 R&P? The seller has never taken a tranny apart and doesn't know what to do to open it and check the number of splines. Tia!

[mpetry]

+1 on what was said above about replacing your old 901 shifter with a 915 in an early car - you can modify a 915 shifter to work with the "dog leg" 901 transmission, using a kit from Seine Systems. I had a setup like this and it worked great.

[Walt Fricke]

The numbers on the case which count are the ones stamped on a cross rib casting on the bottom of the case, where part of the clutch release system attaches. Casting numbers are usually lots tougher to line up with model years.

[RD911T]

Thanks Walt, it took me a while but I figure that out. Sadly they were worn off of that low spot. I got the seller to pull the R&P and confirm the 7:31