915 transaxle into 914-6 questions Options

[Steve]

I have Martin Bott 916 conversion kit in my GT project on a
magnesium case 1972 915 trans.
I had a friend flip the differential and rebuild the ZF limited slip.
I rebuilt the rest of the trans and located and mounted a bracket inside that is a
necessary part of of the conversion
It as now in my car and working.
I have two issues.
I'm using a 1972 911 shifter which is a 'one year only 'item, it looks the
same as a 914 rear shifter but is quite different in detail to suit the 915 shift pattern.
The linkage between the shifter and trans is similar to a 914 rear shift
and is adjusted in the same way. Adjustment is difficult and is still not perfect.
I supplied the 915 shifter parts Bott needed to modify for the kit.
I also provided the stock 911 speedo drive parts.
My cable driven speedo indicates 50 percent too high. At 50 mph (gps) it indicates
~ 100 mph I've tried different speedos. Same result.
No solution yet, but haven't chased it too much either. Ideas ?

Hi Rory,

When PMS did my Bott 915/916 conversion they also installed a sensor for an electric speedo. I'd have to dig through some paperwork to find out what they ended up using. The bracket and sensor mount right on the trans/cv output shaft. Then you'd have to run wires to and from the speedo/sensor. I'll see if I have pics of the bracket and sensor.

If the trans is an electronic speedo trans then it should of been part of the flipped differential required for the 914. Wevo makes the side cover for the electronic speedo sensor. https://www.wevo.com/Products/TransmissionP...nSideCovers.htm
I don't miss the bouncy cable speedometer. Easy to wire up to a stock 911 Electronic speedo. I also just used a straight bracket connected to one of the side bolts to prevent the sensor from popping out. I will look for a picture.

[mepstein]

Rory’s is a 72. First year use of 915 trans. Mechanical speedo. I’m curious since I’m also building one mechanical, one electronic

[rgalla9146]

[quote name='Luke M' date='Oct 29 2026, 06:48 AM' post='3276756']
[quote name='rgalla9146' post='3276716' date='Oct 28 2026, 01:48 PM']
I have Martin Bott 916 conversion kit in my GT project on a
magnesium case 1972 915 trans.
I had a friend flip the differential and rebuild the ZF limited slip.
I rebuilt the rest of the trans and located and mounted a bracket inside that is a
necessary part of of the conversion
It as now in my car and working.
I have two issues.
I'm using a 1972 911 shifter which is a 'one year only 'item, it looks the
same as a 914 rear shifter but is quite different in detail to suit the 915 shift pattern.
The linkage between the shifter and trans is similar to a 914 rear shift
and is adjusted in the same way. Adjustment is difficult and is still not perfect.
I supplied the 915 shifter parts Bott needed to modify for the kit.
I also provided the stock 911 speedo drive parts.
My cable driven speedo indicates 50 percent too high. At 50 mph (gps) it indicates
~ 100 mph I've tried different speedos. Same result.
No solution yet, but haven't chased it too much either. Ideas ?
[/quote]


Hi Rory,

When PMS did my Bott 915/916 conversion they also installed a sensor for an electric speedo. I'd have to dig through some paperwork to find out what they ended up using. The bracket and sensor mount right on the trans/cv output shaft. Then you'd have to run wires to and from the speedo/sensor. I'll see if I have pics of the bracket and sensor.
[/quote

Hey Steve
Thank you for the offer.
Part of me wants to stick with OEM parts and solve this problem as I've always
done.
I don't know my differential ratio or if the speedo drive parts are correct and
compatable. I didn't think these unknowns would becone an issue.
I'm not too keen on disassembling the trans only to find nothing is wrong and the
problem still exists.
Your solution might be the most sensible way forward.
Any information is appreciated.
Thanks again
Rory

[Luke M]

Here's what my sensor looks like. The sensor bracket gets mounted to the side cover then wires run from sensor to electric speedo. The wheel gets mounted on the cv.
PMS did not send me any installation instructions so if anyone has some out there that may help too.

[scallyk9]

[quote name='rgalla9146' date='Oct 29 2026, 03:06 PM' post='3276816']
[quote name='Luke M' date='Oct 29 2026, 06:48 AM' post='3276756']
[quote name='rgalla9146' post='3276716' date='Oct 28 2026, 01:48 PM']
I have Martin Bott 916 conversion kit in my GT project on a
magnesium case 1972 915 trans.
I had a friend flip the differential and rebuild the ZF limited slip.
I rebuilt the rest of the trans and located and mounted a bracket inside that is a
necessary part of of the conversion
It as now in my car and working.
I have two issues.
I'm using a 1972 911 shifter which is a 'one year only 'item, it looks the
same as a 914 rear shifter but is quite different in detail to suit the 915 shift pattern.
The linkage between the shifter and trans is similar to a 914 rear shift
and is adjusted in the same way. Adjustment is difficult and is still not perfect.
I supplied the 915 shifter parts Bott needed to modify for the kit.
I also provided the stock 911 speedo drive parts.
My cable driven speedo indicates 50 percent too high. At 50 mph (gps) it indicates
~ 100 mph I've tried different speedos. Same result.
No solution yet, but haven't chased it too much either. Ideas ?
[/quote]


Hi Rory,

When PMS did my Bott 915/916 conversion they also installed a sensor for an electric speedo. I'd have to dig through some paperwork to find out what they ended up using. The bracket and sensor mount right on the trans/cv output shaft. Then you'd have to run wires to and from the speedo/sensor. I'll see if I have pics of the bracket and sensor.
[/quote

Hey Steve
Thank you for the offer.
Part of me wants to stick with OEM parts and solve this problem as I've always
done.
I don't know my differential ratio or if the speedo drive parts are correct and
compatable. I didn't think these unknowns would becone an issue.
I'm not too keen on disassembling the trans only to find nothing is wrong and the
problem still exists.
Your solution might be the most sensible way forward.
Any information is appreciated.
Thanks again
Rory
[/quote]

Something to check is the final drive ration on your 915 because the early 915 FDRs were different from the later versions.

I have a 1979 915 transaxle (aluminum case) in my 3.2L conversion using the Martin Bott kit. I have a CPS side plate with a standard electronic sensor wired to a 1987 Carrera speedometer and it is very accurate except for a change in tire size.

[rgalla9146]

[quote name='scallyk9' date='Oct 29 2026, 06:32 PM' post='3276819']
[quote name='rgalla9146' date='Oct 29 2026, 03:06 PM' post='3276816']
[quote name='Luke M' date='Oct 29 2026, 06:48 AM' post='3276756']
[quote name='rgalla9146' post='3276716' date='Oct 28 2026, 01:48 PM']
I have Martin Bott 916 conversion kit in my GT project on a
magnesium case 1972 915 trans.
I had a friend flip the differential and rebuild the ZF limited slip.
I rebuilt the rest of the trans and located and mounted a bracket inside that is a
necessary part of of the conversion
It as now in my car and working.
I have two issues.
I'm using a 1972 911 shifter which is a 'one year only 'item, it looks the
same as a 914 rear shifter but is quite different in detail to suit the 915 shift pattern.
The linkage between the shifter and trans is similar to a 914 rear shift
and is adjusted in the same way. Adjustment is difficult and is still not perfect.
I supplied the 915 shifter parts Bott needed to modify for the kit.
I also provided the stock 911 speedo drive parts.
My cable driven speedo indicates 50 percent too high. At 50 mph (gps) it indicates
~ 100 mph I've tried different speedos. Same result.
No solution yet, but haven't chased it too much either. Ideas ?
[/quote]


Hi Rory,

When PMS did my Bott 915/916 conversion they also installed a sensor for an electric speedo. I'd have to dig through some paperwork to find out what they ended up using. The bracket and sensor mount right on the trans/cv output shaft. Then you'd have to run wires to and from the speedo/sensor. I'll see if I have pics of the bracket and sensor.
[/quote

Hey Steve
Thank you for the offer.
Part of me wants to stick with OEM parts and solve this problem as I've always
done.
I don't know my differential ratio or if the speedo drive parts are correct and
compatable. I didn't think these unknowns would becone an issue.
I'm not too keen on disassembling the trans only to find nothing is wrong and the
problem still exists.
Your solution might be the most sensible way forward.
Any information is appreciated.
Thanks again
Rory
[/quote]

Something to check is the final drive ration on your 915 because the early 915 FDRs were different from the later versions.

I have a 1979 915 transaxle (aluminum case) in my 3.2L conversion using the Martin Bott kit. I have a CPS side plate with a standard electronic sensor wired to a 1987 Carrera speedometer and it is very accurate except for a change in tire size.
[/quote]

Hi Scally
What is a CPS side cover ?
By 'standard' electronic sensor do you mean a 911 part ? or an aftermarket sensor
getting a signal from a wheel attached to a CV ?
TIA
Rory

[mepstein]

Probably CMS - California Motorsports

https://californiamotorsports.net/products/...llet-side-plate

[Steve]

I have Martin Bott 916 conversion kit in my GT project on a
magnesium case 1972 915 trans.
I had a friend flip the differential and rebuild the ZF limited slip.
I rebuilt the rest of the trans and located and mounted a bracket inside that is a
necessary part of of the conversion
It as now in my car and working.
I have two issues.
I'm using a 1972 911 shifter which is a 'one year only 'item, it looks the
same as a 914 rear shifter but is quite different in detail to suit the 915 shift pattern.
The linkage between the shifter and trans is similar to a 914 rear shift
and is adjusted in the same way. Adjustment is difficult and is still not perfect.
I supplied the 915 shifter parts Bott needed to modify for the kit.
I also provided the stock 911 speedo drive parts.
My cable driven speedo indicates 50 percent too high. At 50 mph (gps) it indicates
~ 100 mph I've tried different speedos. Same result.
No solution yet, but haven't chased it too much either. Ideas ?

(IMG:style_emoticons/default/hijacked.gif)
@rgalla9146
Rory,
Curious what motor are you running? Most of the time people switch to the 915 for 3.2 or bigger motors, even though the factory 916's also used the early 7:31 ring & pinion 915 trans with up to 2.9 liter motors (Brutus and the Recaro fire engine 914-6GT), but that's all that was available at the time. The 914/901 trans is also 7:31, so what is the advantage of a 7:31 915? More reliable 1st gear? Better stock gearing? Period correct? Just curious. I know that some 911 owners switch to the earlier 7:31 915 trans because it was better for the track. Lower gears and close ratio shifting.

For me, I went with a 1986 915 8:31 ring & pinion trans for gearing that matched my 3.2. The 914 trans with the 3.2 drove me up the wall, since all the gears were too short for the street and I felt like I was shifting all the time. The later 915 trans also has an electronic speedometer and omega spring. The stock 8:31 Ring & Pinion 915 is awesome with the 3.6. The gears feel a little short compared to the 3.2, but it makes the car very quick. I still plan on changing 5th gear to the tallest 5th which is a TL 29:21 gear. This gear is the same as the stock G50 five speed 5th in a 964. It's also easy to change, since its in the nose cone. You don't have to remove the trans.
(IMG:style_emoticons/default/beerchug.gif)

[sixnotfour]

Rory Said...
My cable driven speedo indicates 50 percent too high. At 50 mph (gps) it indicates
~ 100 mph I've tried different speedos. Same result.
No solution yet, but haven't chased it too much either. Ideas ?

Martins website says...

In case of mechanical speedo drive we need the OEM speedo drive parts out of your 915 gear cover.

Modifications to gearbox and kit have to be made. Speedometer has to be adjusted.

I have a mech. speedo, mag case.. Kit Too..
and an sc 915 with factory eletronic speedo..

[rgalla9146]

I have Martin Bott 916 conversion kit in my GT project on a
magnesium case 1972 915 trans.
I had a friend flip the differential and rebuild the ZF limited slip.
I rebuilt the rest of the trans and located and mounted a bracket inside that is a
necessary part of of the conversion
It as now in my car and working.
I have two issues.
I'm using a 1972 911 shifter which is a 'one year only 'item, it looks the
same as a 914 rear shifter but is quite different in detail to suit the 915 shift pattern.
The linkage between the shifter and trans is similar to a 914 rear shift
and is adjusted in the same way. Adjustment is difficult and is still not perfect.
I supplied the 915 shifter parts Bott needed to modify for the kit.
I also provided the stock 911 speedo drive parts.
My cable driven speedo indicates 50 percent too high. At 50 mph (gps) it indicates
~ 100 mph I've tried different speedos. Same result.
No solution yet, but haven't chased it too much either. Ideas ?

(IMG:style_emoticons/default/hijacked.gif)
@rgalla9146
Rory,
Curious what motor are you running? Most of the time people switch to the 915 for 3.2 or bigger motors, even though the factory 916's also used the early 7:31 ring & pinion 915 trans with up to 2.9 liter motors (Brutus and the Recaro fire engine 914-6GT), but that's all that was available at the time. The 914/901 trans is also 7:31, so what is the advantage of a 7:31 915? More reliable 1st gear? Better stock gearing? Period correct? Just curious. I know that some 911 owners switch to the earlier 7:31 915 trans because it was better for the track. Lower gears and close ratio shifting.

For me, I went with a 1986 915 8:31 ring & pinion trans for gearing that matched my 3.2. The 914 trans with the 3.2 drove me up the wall, since all the gears were too short for the street and I felt like I was shifting all the time. The later 915 trans also has an electronic speedometer and omega spring. The stock 8:31 Ring & Pinion 915 is awesome with the 3.6. The gears feel a little short compared to the 3.2, but it makes the car very quick. I still plan on changing 5th gear to the tallest 5th which is a TL 29:21 gear. This gear is the same as the stock G50 five speed 5th in a 964. It's also easy to change, since its in the nose cone. You don't have to remove the trans.
(IMG:style_emoticons/default/beerchug.gif)

Hey Steve
I went with the 915/916 because I intended to install a bigger 911 engine.
I've been delayed (big time) with what is now a 3.2 short stroke.
To keep the car mobil in the meantime a stock '68 911 2.0 is installed in front of
the 916 !
The 3.2 is almost ready.
My '72 915 most likely has the stock 7:31 ...I never thought to count the teeth
when it was apart .
Based on my experience driving the current combo I know a longer 5th gear is in
my future . 3800 rpm at 70 mph. Maybe other ratios as well.
When I first drove the car with the 916 the speed was obviously way off. I wrote to
Martin Bott but received no reply.
Did Bott say to someone here that a 'speedo adjustment' will be necessary ?
Do you know of anyone with a 916 and an operating mechanical speedo ?
I was told by an instrument specialist thay my speedo error is too great to be
corrected in the instrument.
TIA Rory
Any info from anyone is appreciated. A mechanical solution would be my first choice.

[Steve]

Rory,
Did you try reaching out to the guys in this thread with the mechanical speedo option?
http://www.914world.com/bbs2/index.php?showtopic=102988
Otherwise my electronic speedo is pretty accurate but I am also running stock 25” height tires.

[mepstein]

I have Martin Bott 916 conversion kit in my GT project on a
magnesium case 1972 915 trans.
I had a friend flip the differential and rebuild the ZF limited slip.
I rebuilt the rest of the trans and located and mounted a bracket inside that is a
necessary part of of the conversion
It as now in my car and working.
I have two issues.
I'm using a 1972 911 shifter which is a 'one year only 'item, it looks the
same as a 914 rear shifter but is quite different in detail to suit the 915 shift pattern.
The linkage between the shifter and trans is similar to a 914 rear shift
and is adjusted in the same way. Adjustment is difficult and is still not perfect.
I supplied the 915 shifter parts Bott needed to modify for the kit.
I also provided the stock 911 speedo drive parts.
My cable driven speedo indicates 50 percent too high. At 50 mph (gps) it indicates
~ 100 mph I've tried different speedos. Same result.
No solution yet, but haven't chased it too much either. Ideas ?

(IMG:style_emoticons/default/hijacked.gif)
@rgalla9146
Rory,
Curious what motor are you running? Most of the time people switch to the 915 for 3.2 or bigger motors, even though the factory 916's also used the early 7:31 ring & pinion 915 trans with up to 2.9 liter motors (Brutus and the Recaro fire engine 914-6GT), but that's all that was available at the time. The 914/901 trans is also 7:31, so what is the advantage of a 7:31 915? More reliable 1st gear? Better stock gearing? Period correct? Just curious. I know that some 911 owners switch to the earlier 7:31 915 trans because it was better for the track. Lower gears and close ratio shifting.

For me, I went with a 1986 915 8:31 ring & pinion trans for gearing that matched my 3.2. The 914 trans with the 3.2 drove me up the wall, since all the gears were too short for the street and I felt like I was shifting all the time. The later 915 trans also has an electronic speedometer and omega spring. The stock 8:31 Ring & Pinion 915 is awesome with the 3.6. The gears feel a little short compared to the 3.2, but it makes the car very quick. I still plan on changing 5th gear to the tallest 5th which is a TL 29:21 gear. This gear is the same as the stock G50 five speed 5th in a 964. It's also easy to change, since its in the nose cone. You don't have to remove the trans.
(IMG:style_emoticons/default/beerchug.gif)

Hey Steve
I went with the 915/916 because I intended to install a bigger 911 engine.
I've been delayed (big time) with what is now a 3.2 short stroke.
To keep the car mobil in the meantime a stock '68 911 2.0 is installed in front of
the 916 !
The 3.2 is almost ready.
My '72 915 most likely has the stock 7:31 ...I never thought to count the teeth
when it was apart .
Based on my experience driving the current combo I know a longer 5th gear is in
my future . 3800 rpm at 70 mph. Maybe other ratios as well.
When I first drove the car with the 916 the speed was obviously way off. I wrote to
Martin Bott but received no reply.
Did Bott say to someone here that a 'speedo adjustment' will be necessary ?
Do you know of anyone with a 916 and an operating mechanical speedo ?
I was told by an instrument specialist thay my speedo error is too great to be
corrected in the instrument.
TIA Rory
Any info from anyone is appreciated. A mechanical solution would be my first choice.

Rory - when you originally purchased the kit, did you send the speedo gear and other exchange pieces to the place in NJ. That was a requirement for my mechanical kit before Martin shipped from Germany.

[rgalla9146]

I have Martin Bott 916 conversion kit in my GT project on a
magnesium case 1972 915 trans.
I had a friend flip the differential and rebuild the ZF limited slip.
I rebuilt the rest of the trans and located and mounted a bracket inside that is a
necessary part of of the conversion
It as now in my car and working.
I have two issues.
I'm using a 1972 911 shifter which is a 'one year only 'item, it looks the
same as a 914 rear shifter but is quite different in detail to suit the 915 shift pattern.
The linkage between the shifter and trans is similar to a 914 rear shift
and is adjusted in the same way. Adjustment is difficult and is still not perfect.
I supplied the 915 shifter parts Bott needed to modify for the kit.
I also provided the stock 911 speedo drive parts.
My cable driven speedo indicates 50 percent too high. At 50 mph (gps) it indicates
~ 100 mph I've tried different speedos. Same result.
No solution yet, but haven't chased it too much either. Ideas ?

(IMG:style_emoticons/default/hijacked.gif)
@rgalla9146
Rory,
Curious what motor are you running? Most of the time people switch to the 915 for 3.2 or bigger motors, even though the factory 916's also used the early 7:31 ring & pinion 915 trans with up to 2.9 liter motors (Brutus and the Recaro fire engine 914-6GT), but that's all that was available at the time. The 914/901 trans is also 7:31, so what is the advantage of a 7:31 915? More reliable 1st gear? Better stock gearing? Period correct? Just curious. I know that some 911 owners switch to the earlier 7:31 915 trans because it was better for the track. Lower gears and close ratio shifting.

For me, I went with a 1986 915 8:31 ring & pinion trans for gearing that matched my 3.2. The 914 trans with the 3.2 drove me up the wall, since all the gears were too short for the street and I felt like I was shifting all the time. The later 915 trans also has an electronic speedometer and omega spring. The stock 8:31 Ring & Pinion 915 is awesome with the 3.6. The gears feel a little short compared to the 3.2, but it makes the car very quick. I still plan on changing 5th gear to the tallest 5th which is a TL 29:21 gear. This gear is the same as the stock G50 five speed 5th in a 964. It's also easy to change, since its in the nose cone. You don't have to remove the trans.
(IMG:style_emoticons/default/beerchug.gif)

Hey Steve
I went with the 915/916 because I intended to install a bigger 911 engine.
I've been delayed (big time) with what is now a 3.2 short stroke.
To keep the car mobil in the meantime a stock '68 911 2.0 is installed in front of
the 916 !
The 3.2 is almost ready.
My '72 915 most likely has the stock 7:31 ...I never thought to count the teeth
when it was apart .
Based on my experience driving the current combo I know a longer 5th gear is in
my future . 3800 rpm at 70 mph. Maybe other ratios as well.
When I first drove the car with the 916 the speed was obviously way off. I wrote to
Martin Bott but received no reply.
Did Bott say to someone here that a 'speedo adjustment' will be necessary ?
Do you know of anyone with a 916 and an operating mechanical speedo ?
I was told by an instrument specialist thay my speedo error is too great to be
corrected in the instrument.
TIA Rory
Any info from anyone is appreciated. A mechanical solution would be my first choice.

Rory - when you originally purchased the kit, did you send the speedo gear and other exchange pieces to the place in NJ. That was a requirement for my mechanical kit before Martin shipped from Germany.

Hey Mark
Yes, I sent the speedo gears and shifter parts that would be modified to suit
the relocated selector mechanism.
Martin Bott has an assaciate here in New Jersey... Oliveri ?

[mepstein]

I have Martin Bott 916 conversion kit in my GT project on a
magnesium case 1972 915 trans.
I had a friend flip the differential and rebuild the ZF limited slip.
I rebuilt the rest of the trans and located and mounted a bracket inside that is a
necessary part of of the conversion
It as now in my car and working.
I have two issues.
I'm using a 1972 911 shifter which is a 'one year only 'item, it looks the
same as a 914 rear shifter but is quite different in detail to suit the 915 shift pattern.
The linkage between the shifter and trans is similar to a 914 rear shift
and is adjusted in the same way. Adjustment is difficult and is still not perfect.
I supplied the 915 shifter parts Bott needed to modify for the kit.
I also provided the stock 911 speedo drive parts.
My cable driven speedo indicates 50 percent too high. At 50 mph (gps) it indicates
~ 100 mph I've tried different speedos. Same result.
No solution yet, but haven't chased it too much either. Ideas ?

(IMG:style_emoticons/default/hijacked.gif)
@rgalla9146
Rory,
Curious what motor are you running? Most of the time people switch to the 915 for 3.2 or bigger motors, even though the factory 916's also used the early 7:31 ring & pinion 915 trans with up to 2.9 liter motors (Brutus and the Recaro fire engine 914-6GT), but that's all that was available at the time. The 914/901 trans is also 7:31, so what is the advantage of a 7:31 915? More reliable 1st gear? Better stock gearing? Period correct? Just curious. I know that some 911 owners switch to the earlier 7:31 915 trans because it was better for the track. Lower gears and close ratio shifting.

For me, I went with a 1986 915 8:31 ring & pinion trans for gearing that matched my 3.2. The 914 trans with the 3.2 drove me up the wall, since all the gears were too short for the street and I felt like I was shifting all the time. The later 915 trans also has an electronic speedometer and omega spring. The stock 8:31 Ring & Pinion 915 is awesome with the 3.6. The gears feel a little short compared to the 3.2, but it makes the car very quick. I still plan on changing 5th gear to the tallest 5th which is a TL 29:21 gear. This gear is the same as the stock G50 five speed 5th in a 964. It's also easy to change, since its in the nose cone. You don't have to remove the trans.
(IMG:style_emoticons/default/beerchug.gif)

Hey Steve
I went with the 915/916 because I intended to install a bigger 911 engine.
I've been delayed (big time) with what is now a 3.2 short stroke.
To keep the car mobil in the meantime a stock '68 911 2.0 is installed in front of
the 916 !
The 3.2 is almost ready.
My '72 915 most likely has the stock 7:31 ...I never thought to count the teeth
when it was apart .
Based on my experience driving the current combo I know a longer 5th gear is in
my future . 3800 rpm at 70 mph. Maybe other ratios as well.
When I first drove the car with the 916 the speed was obviously way off. I wrote to
Martin Bott but received no reply.
Did Bott say to someone here that a 'speedo adjustment' will be necessary ?
Do you know of anyone with a 916 and an operating mechanical speedo ?
I was told by an instrument specialist thay my speedo error is too great to be
corrected in the instrument.
TIA Rory
Any info from anyone is appreciated. A mechanical solution would be my first choice.

Rory - when you originally purchased the kit, did you send the speedo gear and other exchange pieces to the place in NJ. That was a requirement for my mechanical kit before Martin shipped from Germany.

Hey Mark
Yes, I sent the speedo gears and shifter parts that would be modified to suit
the relocated selector mechanism.
Martin Bott has an assaciate here in New Jersey... Oliveri ?

Yes - Alex Olaverri in Belleville NJ.

[rgalla9146]

I have Martin Bott 916 conversion kit in my GT project on a
magnesium case 1972 915 trans.
I had a friend flip the differential and rebuild the ZF limited slip.
I rebuilt the rest of the trans and located and mounted a bracket inside that is a
necessary part of of the conversion
It as now in my car and working.
I have two issues.
I'm using a 1972 911 shifter which is a 'one year only 'item, it looks the
same as a 914 rear shifter but is quite different in detail to suit the 915 shift pattern.
The linkage between the shifter and trans is similar to a 914 rear shift
and is adjusted in the same way. Adjustment is difficult and is still not perfect.
I supplied the 915 shifter parts Bott needed to modify for the kit.
I also provided the stock 911 speedo drive parts.
My cable driven speedo indicates 50 percent too high. At 50 mph (gps) it indicates
~ 100 mph I've tried different speedos. Same result.
No solution yet, but haven't chased it too much either. Ideas ?

(IMG:style_emoticons/default/hijacked.gif)
@rgalla9146
Rory,
Curious what motor are you running? Most of the time people switch to the 915 for 3.2 or bigger motors, even though the factory 916's also used the early 7:31 ring & pinion 915 trans with up to 2.9 liter motors (Brutus and the Recaro fire engine 914-6GT), but that's all that was available at the time. The 914/901 trans is also 7:31, so what is the advantage of a 7:31 915? More reliable 1st gear? Better stock gearing? Period correct? Just curious. I know that some 911 owners switch to the earlier 7:31 915 trans because it was better for the track. Lower gears and close ratio shifting.

For me, I went with a 1986 915 8:31 ring & pinion trans for gearing that matched my 3.2. The 914 trans with the 3.2 drove me up the wall, since all the gears were too short for the street and I felt like I was shifting all the time. The later 915 trans also has an electronic speedometer and omega spring. The stock 8:31 Ring & Pinion 915 is awesome with the 3.6. The gears feel a little short compared to the 3.2, but it makes the car very quick. I still plan on changing 5th gear to the tallest 5th which is a TL 29:21 gear. This gear is the same as the stock G50 five speed 5th in a 964. It's also easy to change, since its in the nose cone. You don't have to remove the trans.
(IMG:style_emoticons/default/beerchug.gif)

Hey Steve
I went with the 915/916 because I intended to install a bigger 911 engine.
I've been delayed (big time) with what is now a 3.2 short stroke.
To keep the car mobil in the meantime a stock '68 911 2.0 is installed in front of
the 916 !
The 3.2 is almost ready.
My '72 915 most likely has the stock 7:31 ...I never thought to count the teeth
when it was apart .
Based on my experience driving the current combo I know a longer 5th gear is in
my future . 3800 rpm at 70 mph. Maybe other ratios as well.
When I first drove the car with the 916 the speed was obviously way off. I wrote to
Martin Bott but received no reply.
Did Bott say to someone here that a 'speedo adjustment' will be necessary ?
Do you know of anyone with a 916 and an operating mechanical speedo ?
I was told by an instrument specialist thay my speedo error is too great to be
corrected in the instrument.
TIA Rory
Any info from anyone is appreciated. A mechanical solution would be my first choice.

Rory - when you originally purchased the kit, did you send the speedo gear and other exchange pieces to the place in NJ. That was a requirement for my mechanical kit before Martin shipped from Germany.

Hey Mark
Yes, I sent the speedo gears and shifter parts that would be modified to suit
the relocated selector mechanism.
Martin Bott has an assaciate here in New Jersey... Oliveri ?

My history with the 916 has been long and sporatic...ten plus years.
Distractions were frequent and important.
The trans is currently in my GT project driving and shifting better than ever.
I'm a stickler for period correct parts and appearance whenever possible.
I'll be installing the long delayed 3.2 in the near future.
My take on the speedo issue.
The cable drive is reaching the instrument. Could stock 911 speedo drive gears
inside the trans be so far off as to spin the cable 50 percent too fast ?
AFAIK my R&P is 7:31 same as every 914
My rear tires are not so short that they could be at fault. 225vr50/16"
My angle drive is 1:1 911s don't have an angle drive... so same result.
Maybe the answer is already known.
Send the instrument and the GPS info to a specialist and get it 'adjusted'
My take on the electronic solution.
AFAIK the original speedo sender for a 911 can not be used with a flipped
differential making an aftermarket sender/wheel necessary.
I don't have an electronic speedo and don't love the idea of buying one and then
having to get it backdated to match my other instruments.
A bracket /sender near a CV with wiring extending to the instrument panel ?
Not a fan.
Does anyone have or know of a working mechanical speedo on a 916 ?
TIA
Rory

[mepstein]

I’m hoping the one I’m currently building will work properly but if not…
Have you tried contacting Martin about it.

I’m using an electronic speedo on mine. GPS sender.