915 differences?

[Matt Monson]

Yes, it all swaps over, even the mainshaft. Just update to the later beating at the same time.

[Porsche84]

Here is some info I've collected

[YankeeFlyGuy]

I don't mean to hijack the thread, but my COA says my car came with a 915/61 and the car currently has a 915/63. Besides the fact that it isn't "numbers matching" is there any reason a 915/63 is less or more desirable than the 61?

[mikedsilva]

Originally Posted by Matt Monson

Yes, it all swaps over, even the mainshaft. Just update to the later beating at the same time.

Thanks Matt.

[Porsche84]

The /61 early was a Magnesium case (early 77), the later /61 and all /63 were aluminum. It looks like second gear might have been different and the /63 was the first to have a fine spline on the drive hub. I could be wrong on this but that's what I had in my notes.

[YankeeFlyGuy]

Originally Posted by Porsche84

The /61 early was a Magnesium case (early 77), the later /61 and all /63 were aluminum. It looks like second gear might have been different and the /63 was the first to have a fine spline on the drive hub. I could be wrong on this but that's what I had in my notes.

Thanks, my car was built in Aug 77 (78 MY) so it sounds like besides that small 2nd gear difference they are pretty similar.

[Solamar]

Originally Posted by Porsche84

The /61 early was a Magnesium case (early 77), the later /61 and all /63 were aluminum. It looks like second gear might have been different and the /63 was the first to have a fine spline on the drive hub. I could be wrong on this but that's what I had in my notes.

I have a late 915/61 (made in '79) that has the fine spline drive hubs. Like most Porsche changes, there must have been some 'fuzzy' cut offs on what parts to use...

[YankeeFlyGuy]

Originally Posted by Solamar

Like most Porsche changes, there must have been some 'fuzzy' cut offs on what parts to use...

I agree 100%

My early SC has lots of factory 1977 911S parts. I have to be careful when mail ordering parts.

[kent olsen]

Bill Verburg

If I understand your chart the 72 915 in my car has 4th gear just short of 1:1 and 5th (0.76) just a little over, interesting. I'm putting a TREMEC 5spd in my 65 Corvette and it is 1:1 in 4th and 0.68 in 5th.

[Matt Monson]

Originally Posted by Porsche84

The /61 early was a Magnesium case (early 77), the later /61 and all /63 were aluminum. It looks like second gear might have been different and the /63 was the first to have a fine spline on the drive hub. I could be wrong on this but that's what I had in my notes.

The AL /61 was used for several years in the SC and were fine spline. Only the 77 mag case version was coarse.

[Trackrash]

Originally Posted by Solamar

I have a late 915/61 (made in '79) that has the fine spline drive hubs. Like most Porsche changes, there must have been some 'fuzzy' cut offs on what parts to use...

I would have guessed that the fine spline drive flanges corresponded with the change from the 7:31 to the 8:31. Porsche changed form the 4 bolt 108mm drive flanges in 75 1/2 which corresponds to the change to the 8:31 FD?

Maybe the experts can confirm. I don't think there were any course flange 100mm CVs?

EDIT: Thanks Matt, you beat me to it.

[Jon B]

Originally Posted by Matt Monson

The AL /61 was used for several years in the SC and were fine spline. Only the 77 mag case version was coarse.

Originally Posted by Trackrash

I would have guessed that the fine spline drive flanges corresponded with the change from the 7:31 to the 8:31. Porsche changed form the 4 bolt 108mm drive flanges in 75 1/2 which corresponds to the change to the 8:31 FD?
Maybe the experts can confirm. I don't think there were any course flange 100mm CVs?
EDIT: Thanks Matt, you beat me to it.

According to PET, the coarse-splined 923 flanges were used in 915 transmissions up through 1979.
The transition occurred either during or after the 79 model year.

See Pete Z's timeline in post 12 here...
http://forums.pelicanparts.com/porsche-911-technical-forum/548265-83-3-0l-engine-trans-swap-85-3-2l-engine-trans-axle-options.html

[Trackrash]

Good to know. I was told that the 8:31 915s were all fine spline.

So if I ever want to put a 8:31 915 in my '71, I only need to find one '79 or older, and my axles will work.

[Bill Verburg]

Originally Posted by kent olsen

Bill Verburg

If I understand your chart the 72 915 in my car has 4th gear just short of 1:1 and 5th (0.76) just a little over, interesting. I'm putting a TREMEC 5spd in my 65 Corvette and it is 1:1 in 4th and 0.68 in 5th.

IN '72 there were 5 different 5 speed 915s, counting the special order as 1 and 2 different 4 speed 915s

All 5spds except the S/O had 29:22 5th

There were numerous detail improvements/changes over the years
here are a few
1972 - Start of production; magnesium case; 7:31 ring and pinion; mechanical speedometer; early style clutch throw out bearing tube.
1973 - Change to input shaft seal design to address service issue flaw.
1974 - Change (final) to input shaft seal design to address service issue flaw. Transmission disassembly no longer required.
1975 - Midyear change from 7:31 to 8:31 ring and pinion
1976 - Change from mechanical to electronic speedometer.
1977 – Start of transition from magnesium to aluminum case. 915/60/61 aux spring on the trans exterior, - Change to 1st and 2nd synchros, split lock before, double lock after, asymmetrically pointed teeth for 1st, smaller syncro ring for 1st stronger guide sleeve 1 & 2
1978 - Reinforced differential side cover (addition of extra ribs), nodular cast iron p/p, cast iron clutch, rubber ctr clutch, All models 5 speed now
1984 - Reduction in diameter of input shaft bearing in differential case.* This significantly helped in the reduction of problems with bearing bore ovaling.
1984 - Addition of oil pump and cooler for 915/67 & 69(RoW), 915/69 uses 930 output flanges
1985 - Improved bearing assembly, input shafts uses cylindrical roller bearing from 930(smaller OD) this was actually introduced 12/16/83 on 915/67 from trans # 915/67 02340 w/ small(100mm) cv flanges, 915/68 02192 small(100mm) joint flanges, 915/69 10081 lrg((108mm) joint flanges, 915/70 10217 large(108mm) joint flanges,
double lock gear syncros for 1 & 2, 3-5 syncros have smoothed and round end syncros(R2.5), lsd modified graphite cast iron case w/ larger holes for fluid flow and fewer disk count, only 1 ea outer and inner (also far less effective than previous lsd versions(sometimes called a 'snow belt' lsd)
all have the large 105mm joint flange
1986 - End of production

[Matt Monson]

Originally Posted by Jon B

According to PET, the coarse-splined 923 flanges were used in 915 transmissions up through 1979.
The transition occurred either during or after the 79 model year.

See Pete Z's timeline in post 12 here...
http://forums.pelicanparts.com/porsche-911-technical-forum/548265-83-3-0l-engine-trans-swap-85-3-2l-engine-trans-axle-options.html

In all these years, I have never once had a customer call me up and tell me I sold them the wrong LSD, and I've sold a lot of LSDs for 78-79 SCs.

[ADDvanced]

There's a 30lb difference between mag and al cases, so from what I read, the late 76/early 77 magnesium 915s are kind of desirable. You get all the updates but with a 30lb advantage.

[Trackrash]

Originally Posted by ADDvanced

There's a 30lb difference between mag and al cases, so from what I read, the late 76/early 77 magnesium 915s are kind of desirable. You get all the updates but with a 30lb advantage.

Depends if you want an 8:31 or a 7:31 final drive.....

[ADDvanced]

Nope. All transmissions from mid 75 onwards were 8:31.

[Trackrash]

Originally Posted by ADDvanced

Nope. All transmissions from mid 75 onwards were 8:31.

Yes. But some of us want a 7:31 FD. Just sayn' a '72-'74 may be what some, me included, wanted.

[edjrbashian]

Does anyone know when the changeover was on the input shaft?

I have an early mag case '77 trans in my car, would that have the strengthened input shaft and improvements to the 1st and 2nd gear sliders ?