Phill Posted November 10, 2020 Share Posted November 10, 2020 My gearbox swap/repair has been very problematic to say the least Quick back ground - my existing box was put in the car 20 years ago as a conversion from Sportomatic. It would appear that the builder used the Sporto gearbox output flanges in the 915 with the Sporto diff. The existing flanges and driveshafts are 4 bolt 2 roll pin 108mm configuration. The "new" box comes with a 6 bolt 100mm configuration. In short, the simplest way to remedy this ( @PorscheApostle will disagree with this but there are other factors at play here) is to change the drive shaft and output flange to 6 bolt 100mm configuration. Ideally the drive shaft and output flange on the SC are separate items. However, Type911 list an 84-89 item which is all one piece (I discussed this with Matt so he knows I am asking here because he couldn't determine the answer for sure) but can I use this on my car? https://type911shop.co.uk/epages/de867ca1-377e-432e-84fd-bdccf2206766.sf/en_GB/?ObjectPath=/Shops/de867ca1-377e-432e-84fd-bdccf2206766/Products/2025 as opposed to this and separate flanges? https://type911shop.co.uk/epages/de867ca1-377e-432e-84fd-bdccf2206766.sf/en_GB/?ObjectPath=/Shops/de867ca1-377e-432e-84fd-bdccf2206766/Products/2023 Help me please before I completely lose my sanity.................... Link to comment Share on other sites More sharing options...
Nige Posted November 10, 2020 Share Posted November 10, 2020 Should you be looking on the back of your hub flanges as well to determine which type you need to install. Isn't the top one piece item for 3.2 915/G50 applications? Link to comment Share on other sites More sharing options...
Phill Posted November 10, 2020 Author Share Posted November 10, 2020 16 minutes ago, Nige said: Should you be looking on the back of your hub flanges as well to determine which type you need to install. Isn't the top one piece item for 3.2 915/G50 applications? Exactly the question I am asking can I use the top item in place of the separate drive shaft and hub flange? Is it the same length? Is the stub axle part the same as the separate stub axle part. Matt says there is no difference in the hubs themselves so in theory it should fit. The back of the hub flanges are 4 bolt pattern which is what ! am needing to lose. (CV joints are not interchangeable on the shaft due to different spline pattern). @SilverWT @jevvy @proporsche Link to comment Share on other sites More sharing options...
Phill Posted November 10, 2020 Author Share Posted November 10, 2020 I may have figured it out. Are the bolts on the 85-89 M10 as opposed to M8 on the other type? Link to comment Share on other sites More sharing options...
Type911 Posted November 10, 2020 Share Posted November 10, 2020 Yes! Spot on! What is the gearbox type, can you find out? Link to comment Share on other sites More sharing options...
Phill Posted November 10, 2020 Author Share Posted November 10, 2020 1 minute ago, Type911 said: Yes! Spot on! Bugger! So next question. Are they still 100mm diameter and is the hole spacing the same? Would it be possible to open out the threads on the gearbox flange to accept M10 without hurting the integrity of the flange? Link to comment Share on other sites More sharing options...
Type911 Posted November 10, 2020 Share Posted November 10, 2020 Link to comment Share on other sites More sharing options...
PorscheApostle Posted November 10, 2020 Share Posted November 10, 2020 48 minutes ago, Type911 said: Yes! Spot on! What is the gearbox type, can you find out? They are both 915/61 transmissions Broken box serial number late 719 8010 Which is a 79 on SC transmission Second hand box early 717 2376 77 on 911,911s, Carrera Just checked the v pages correct me if I'm wrong Matt. Gear ratios are the same but slight differences to the internal recess of the flanges. My suggestion to Phil was to swap the crown wheel to the usable diff and flanges as the housings are identical and share the same part number and dimensions. This personal would be the cheapest option also the correct option in my opinion. There is no requirement to set the the deviation of the r measurement when changing differentials. The backlash and or diff bearing preload would be necessary but the final.drive is set for variances in case dimensions . Phil's builder thinks differently . Ask yourself if you need to strip your gearbox to fit a LSD. There's your answer. D Link to comment Share on other sites More sharing options...
Type911 Posted November 10, 2020 Share Posted November 10, 2020 There is more than one way to skin a cat....................... Of course the best action would be to get a complete new cat................complete with legs Link to comment Share on other sites More sharing options...
PorscheApostle Posted November 10, 2020 Share Posted November 10, 2020 14 minutes ago, Type911 said: There is more than one way to skin a cat....................... Of course the best action would be to get a complete new cat................complete with legs Right answer. You see Phil Matt knows 😂 get your wallet out. Your frustration can be eased with the correct application of cash money. Link to comment Share on other sites More sharing options...
Phill Posted November 10, 2020 Author Share Posted November 10, 2020 I think I'm going to have to insist on my old diff going into the new box. This is not going to be an easy discussion. But it is my car. Link to comment Share on other sites More sharing options...
Type911 Posted November 10, 2020 Share Posted November 10, 2020 Keep hunting for a box with shafts, from an SC Link to comment Share on other sites More sharing options...
Type911 Posted November 10, 2020 Share Posted November 10, 2020 https://www.ebay.co.uk/itm/Porsche-911-Transmission-Differential-915/153294329570?hash=item23b10dd6e2:g:Zo0AAOxyqUpQ7jtE https://www.ebay.co.uk/itm/Porsche-911-915-Transmission-Differential-Housing-911-332-212-0R-15/164247686809?epid=1017807513&hash=item263decce99:g:MmkAAOSw57xcjT0J Link to comment Share on other sites More sharing options...
SilverWT Posted November 11, 2020 Share Posted November 11, 2020 13 hours ago, Phill said: Bugger! So next question. Are they still 100mm diameter and is the hole spacing the same? Would it be possible to open out the threads on the gearbox flange to accept M10 without hurting the integrity of the flange? G50 driveshafts are 108mm (from rusty memory, I can check later). Most SC/3.2 use 100mm 6 x M8. All G50 3.2s use 108mm 6 x M10. But, some late '85 915 3.2s also use 108mm 6 x M10 gearbox flanges. These are super rare and enable you to use G50 driveshafts on a 915 box. From memory, someone on Pelican was machining 915 flanges to use G50 driveshafts. Link to comment Share on other sites More sharing options...
SilverWT Posted November 11, 2020 Share Posted November 11, 2020 Not wishing to tease you Phil (these are destined for my 3.2 and are not for sale), but these are the mythical 108mm 6 x M10 915 drive flanges that let you use G50 style driveshafts on a 915 box. Link to comment Share on other sites More sharing options...
SilverWT Posted November 11, 2020 Share Posted November 11, 2020 Here is the Pelican link I was thinking of... http://forums.pelicanparts.com/porsche-911-technical-forum/854164-915-flanges-930-turbo-spec-car-100-108-mm-help.html You can evidently also modify G50 driveshafts to work in a 915, or use Turbo ones. Mark Link to comment Share on other sites More sharing options...
Phill Posted November 11, 2020 Author Share Posted November 11, 2020 37 minutes ago, SilverWT said: Not wishing to tease you Phil (these are destined for my 3.2 and are not for sale), but these are the mythical 108mm 6 x M10 915 drive flanges that let you use G50 style driveshafts on a 915 box. No good to me as they are fine splined. That pelican thread confuses things a lot and most solutions are based around fine splines and machining. Link to comment Share on other sites More sharing options...
Lund Posted November 12, 2020 Share Posted November 12, 2020 (edited) 108mm flanges, 6xM10 (G50 shaft) fine spline on left, Right is 4xM10 with 2 dowels and is coarse splined. You'll have interference with the end cap if you try to mate the G50 axles on the 4xM10 flange. I have one of the unicorn *beep* 85,5 915 G50 gearboxes and had the same problem with coarse vs fine spline stub axles on my 77, ended up buying some G50 driveshafts from Shirish that I refurbished. Not sure that I'm understanding the problem though, wouldn't just replacing your driveshafts with a set of ø100 6xM8 (p/n 92333203302) sort you out? This thread over on the bird seems to have the same issue which he fixed by replacing the drive shafts. http://forums.pelicanparts.com/porsche-911-technical-forum/684045-sportomatic-conversion.html This is a reference table that I found useful. http://forums.pelicanparts.com/porsche-911-technical-forum/596183-cv-axle-cross-reference-3.html Chris Edited November 12, 2020 by Lund Link to comment Share on other sites More sharing options...
Phill Posted November 12, 2020 Author Share Posted November 12, 2020 45 minutes ago, Lund said: 108mm flanges, 6xM10 (G50 shaft) fine spline on left, Right is 4xM10 with 2 dowels and is coarse splined. You'll have interference with the end cap if you try to mate the G50 axles on the 4xM10 flange. I have one of the unicorn *beep* 85,5 915 G50 gearboxes and had the same problem with coarse vs fine spline stub axles on my 77, ended up buying some G50 driveshafts from Shirish that I refurbished. Not sure that I'm understanding the problem though, wouldn't just replacing your driveshafts with a set of ø100 6xM8 (p/n 92333203302) sort you out? This thread over on the bird seems to have the same issue which he fixed by replacing the drive shafts. http://forums.pelicanparts.com/porsche-911-technical-forum/684045-sportomatic-conversion.html This is a reference table that I found useful. http://forums.pelicanparts.com/porsche-911-technical-forum/596183-cv-axle-cross-reference-3.html Chris Thanks Chris, that's helpful. I am going with the new driveshafts and stub axles. I was trying to avoid this due to the extra cost but it has been too difficult to figure out the right gearbox/diff/flange combo especially with the scarcity of parts. There are so many differences. Porsche really embrace the parts bin philosophy. Link to comment Share on other sites More sharing options...
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