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Full Version: So what’s the thinking on 915 gearbox kits for a/6 build these days
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Tdskip
I’ve had a chance to go through some very useful past discussions, but as always win a couple years has gone by it’s worthwhile to revisit this topic The latest thinking and experiences. Looks like there’s a trade off between buying a pre-packaged kit versus trying to roll it all yourself, while expensive having someone else have done the brain damage does have a certain appeal to it.

Any thoughts or coaching out there on this?

I’m assuming if you go the route of a kit do you want to have the kit in hand when the gearbox servicing and flip is done, yes?

Thanks!

Click to view attachment

Tdskip
Is the Bug@5-Speed still the go to?
mepstein
QUOTE(Tdskip @ Oct 10 2021, 09:49 AM) *

Is the Bug@5-Speed still the go to?

They are the only one making a kit to convert a 915 to mid engine use.
I do still have my wevo converted 915 for sale.
rgalla9146
I'm in the process.
I have a Martin Bott (Bug@5speed) 916 set-up in hand for years now. I'm using an early mag case
and mechanical speedo drive
I refreshed the shafts, flipped the diff. and assembled it temporarily years ago.
I don't have the factory tools for drag and backlash on the pinion.
Rather than take any chances I recently sent that work to a friend who has the tools
and experience. I should have it back by the end of the month.
THEN .....I can finally install it behind the long anticipated 3.0 in my GT project.
By the time this is over it'll be a very expensive item. That is with me buying the
trans, doing the cleaning, buying all the parts, drilling and tapping for an internal
shaft support, assembling it and fabricating shift linkage.
Try finding a '72 911 shift tower. Or OEM shift knob. Not easy.
My goal is for it to look and work as close to original as I can make it.
Next spring.
mepstein
QUOTE(rgalla9146 @ Oct 10 2021, 11:42 AM) *

I'm in the process.
I have a Martin Bott (Bug@5speed) 916 set-up in hand for years now. I'm using an early mag case
and mechanical speedo drive
I refreshed the shafts, flipped the diff. and assembled it temporarily years ago.
I don't have the factory tools for drag and backlash on the pinion.
Rather than take any chances I recently sent that work to a friend who has the tools
and experience. I should have it back by the end of the month.
THEN .....I can finally install it behind the long anticipated 3.0 in my GT project.
By the time this is over it'll be a very expensive item. That is with me buying the
trans, doing the cleaning, buying all the parts, drilling and tapping for an internal
shaft support, assembling it and fabricating shift linkage.
Try finding a '72 911 shift tower. Or OEM shift knob. Not easy.
My goal is for it to look and work as close to original as I can make it.
Next spring.

We just purchased the factory R&P tools.
Tdskip
First of all I hope everybody’s having a good weekend. Thank you for the responses.

I thought that I had seen Patrick motorsports offering these, but I think that cost was similar to the vendor in Germany, and it seems like the vendor in Germany is well regarded and has stood by their work.

I’m expecting us to run about $10,000 all in, it seems like that’s close to where you’re going to be.
Steve
I’ve been running the Martin Bott kit for years. Unless a shop has built one before, I wouldn’t trust them. Two well known shops in so cal, couldn’t figure it out. I ended up driving my car to PMS and flew back, so they could work on it. The trans now shifts like it’s supposed too. I’m also running PMS shift linkage and a 911 rennshift. If your going to the WCR, I will be there with my car and you can go for a ride.
Steve
PMS also sells the kit. I don’t know if it’s any cheaper buying it direct from Martin. Personally I would ship the trans and kit to PMS and let them build it or buy the kit from PMS. As mentioned wevo stopped selling there kit, so the 916 kit is the only option out there and Martins is the cheapest.
Luke M
I have a 84 815 trans with the Bott kit installed. I also had a Wavetrac diff installed while at it. I went back n forth with Steve on his Bott 915 trans. I then went with his recommendation to use PMS. PMS did all of the trans work and I also got all of their shift linkage. Not cheap by any means.

http://www.914world.com/bbs2/index.php?sho...67624&st=40
930cabman
Has anyone tried a G50?
mepstein
QUOTE(930cabman @ Oct 10 2021, 07:39 PM) *

Has anyone tried a G50?

They can’t easily be reversed for mid engine use.
sixnotfour
Just had CMS do a 915 ring and pinion setup..plus parts...and diff case...8K
Tdskip
You guys are great, really appreciate the coaching here. Looks like I’m going to road trip to PMS soon, at least I know where to find great pizza in Phoenix.
9146BRUCE
Hi Guys who is PMS and where are they located.
Thanks Bruce
SO.O.C914er
Patrick motor sports in Arizona top shelf work.
Cairo94507
Yeah- James Patrick is the guy when it comes to 914s for sure. His shop is well known for custom hi-horsepower Porsches. I would love to take my 6 to him and have him do the 915 conversion. beerchug.gif
Beach914
My setup waiting for me to get to it.
Click to view attachment
speed metal army
I have a flipped r&p 915.. no side shift conversion bits though.
For a smaller displacement engine say 2.7 and under is a 915 even necessary?
sixnotfour
QUOTE(speed metal army @ Oct 17 2021, 05:23 PM) *

I have a flipped r&p 915.. no side shift conversion bits though.
For a smaller displacement engine say 2.7 and under is a 915 even necessary?

Is it Mag case 7:31 ??
Steve
QUOTE(speed metal army @ Oct 17 2021, 04:23 PM) *

I have a flipped r&p 915.. no side shift conversion bits though.
For a smaller displacement engine say 2.7 and under is a 915 even necessary?

IMHO, I don’t think a 2.7 or stock 3.0 needs a 915, but don’t go crazy off the line with first gear. The 2.7 came out in 74 and in 74 the 915 gearbox was 7:31 r&p same as a 914-4. Compare the gear charts, it’s not much of a difference. My first six was a 2.7 with webers and headers. I thought the trans felt right. As soon as I upgraded to the 3.2 the gearing felt all wrong and I felt like I was shifting all the time and that 1st was worthless. So I switched to a 3.2 1986 915 gear box. Expensive, but it matches the motor and the driving experience on the street and freeway is night and day better.
Dr Evil
QUOTE(speed metal army @ Oct 17 2021, 07:23 PM) *

I have a flipped r&p 915.. no side shift conversion bits though.
For a smaller displacement engine say 2.7 and under is a 915 even necessary?

No. The 901 is perfect for a 2.7, maybe unless you twin turbo it.

I second the Martin Bott kit over the Wevo. I have done the Wevo before, its tedious and it leaves somethings to be desired during set up. Still better than the external fixation methods, though. If going big power, a rebuilt 915, maybe LSD, and a Bott kit is perfect for most applications and worth the money. I do them at EvilWerks, BTW wink.gif
Tdskip
Thanks for the discussion, this 915 will go with a 3.2L engine.

Steve
QUOTE(Tdskip @ Oct 26 2021, 06:22 AM) *

Thanks for the discussion, this 915 will go with a 3.2L engine.

I’m also running a later pedal set with clutch return spring and omega spring on the trans. More complicated, but more positive clutch response.
mepstein
Just saw this - https://m.facebook.com/RetroSportRacingGara...al&mt_nav=0
speed metal army
QUOTE(sixnotfour @ Oct 17 2021, 04:42 PM) *

QUOTE(speed metal army @ Oct 17 2021, 05:23 PM) *

I have a flipped r&p 915.. no side shift conversion bits though.
For a smaller displacement engine say 2.7 and under is a 915 even necessary?

Is it Mag case 7:31 ??

Aluminum case, elec speedo
old914dog
I am with Dr. Evil.
I purchased his video and built a 901 behind a 3.2, 20.3 compression, Web 20/21 cam, headers, Chipped and never had a problem. It was not babied....but no Dairy Queen burnouts either. You can have 2 backups for the cost of a 915!!
But...I am a csob.
old914dog
Fat fingers....10.3 compression
Justinp71
QUOTE(old914dog @ Oct 26 2021, 08:07 AM) *

I am with Dr. Evil.
I purchased his video and built a 901 behind a 3.2, 20.3 compression, Web 20/21 cam, headers, Chipped and never had a problem. It was not babied....but no Dairy Queen burnouts either. You can have 2 backups for the cost of a 915!!
But...I am a csob.


Yes I have a similar setup. You just use 1st as a parking lot crawler, on the highway you scream at about 3500 but that's typical 914. I was reading on the track cars that the 901's only last so long, but if you upgrade the cooling you can get them to last longer. Heck the early 350 SBC guys used them with 1st removed.

A later model 915 probably suits a 3.2 better for general street driving gearing though.

I think a common late 70's 911 mod is to go back to the early R&P for more acceleration. But I think 1st gear in the 915 can take a better beating.

I have a mid-engine 915 sitting on the shelf waiting for a future install... Haven't decided what direction I want to go with it yet.
Steve
QUOTE(Justinp71 @ Oct 26 2021, 08:35 AM) *

QUOTE(old914dog @ Oct 26 2021, 08:07 AM) *

I am with Dr. Evil.
I purchased his video and built a 901 behind a 3.2, 20.3 compression, Web 20/21 cam, headers, Chipped and never had a problem. It was not babied....but no Dairy Queen burnouts either. You can have 2 backups for the cost of a 915!!
But...I am a csob.


Yes I have a similar setup. You just use 1st as a parking lot crawler, on the highway you scream at about 3500 but that's typical 914. I was reading on the track cars that the 901's only last so long, but if you upgrade the cooling you can get them to last longer. Heck the early 350 SBC guys used them with 1st removed.

A later 915 probably suits a 3.2 better for general street driving gearing though.

I think a common late 70's 911 mod is to go back to the early R&P for more acceleration. But I think 1st gear in the 915 can take a better beating.

I have a mid-engine 915 sitting on the shelf waiting for a future install... Haven't decided what direction I want to go with it yet.

agree.gif A 901/914 trans is quicker than a 8:31 915. A 901 is weaker than a 915, but the 901 is quicker on the track or autocross due to the 7:31 RP. It's also nice having 2nd and 3rd in the same plane. But for street, freeway and road trips, the 8:31 915 is nice. You have 5 usable gears, your not shifting as much and with stock gears you are cruising at 80mph at 3200 RPM's. If I was younger and still liked to hot rod around, I would of kept the 914 gear box and maybe put a taller 5th in it.
slivel
I never had significant problems with my 914 transmission in my 3.4l 290 rwhp (open exhaust) track car. Over 23 years of racing had only two failures and they were early on - one R&P and one gear-4 failure. Later, I did pull and freshen every 3 or 4 seasons and had no more failures. As I recall the pinion bearing and bearing race usually showed the most wear when we had the box apart for freshen. Because of this I would drain and replace the gear oil every season and look closely for gold flecks indicating a bearing cage was starting to deteriorate. Also had a magnet in the flow path to the oil cooler which can provide an early warning of problems.

Now the car is just a street hotrod and the gearing (AFNSY) is OK for the street. Hp is probably down 30-40 with mufflers. As has been said several times, take it easy when in first gear. 2-5 handled the rigors of racing very well. The gear box was well built with billet intermediate plate and trans cooler with oil squirters over the R&P and gears 3-4.

Lastly as my transmission tech said, you can rebuild a 914 box a bunch of times for the cost of a 915 conversion.
rgalla9146

I recently had my 915 / 916 set up by a very qualified retired shop owner.
He has the factory tools and experience to properly adjust drag and backlash.
Of course he can do the entire transaxle too.
He is in North Carolina and is open do this work at a reasonable cost.
I've known him for thirty five years.
If interested contact me via PM
Rory
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