Sportomatic Conversion

[Mr. 911 T]

I'm in the process of converting my 1972 Targa 911T from a Sportomatic to a 915/61 five speed. At this point, the issue I'm having is the 72 axles have four bolts and two pin c.v. joints and the 915/61 has a six bolt flange. Do you think changing out the inner c.v. joints to match 915/61 transmission who fix the problem?

Any knowledge in this manner would be greatly appreciated.

Thanks,

[Fishcop]

I've done a similar conversion. I can tell you for sure that you can't mix CV joints on the drive shafts - they have different spline counts... You need to commit to either the early drive shafts and change the gearbox flanges, or (easier) locate later 6 bolt driveshafts and hub inners.

Hope that helps.

[Mr. 911 T]

Fishcop,
Thanks for your reply. When you speak of the 6 bolt driveshafts and hub inners, are you speaking of the two cv joints and the flange on each side?

[Mr. 911 T]

Fishcop,
Thanks for your reply. When you speak of the 6 bolt driveshafts and hub inners, are you speaking of the two cv joints and the flange on each side? Thanks again for your assistnce.

[RWebb]

Glad somebody could answer this - BTW, if you do the conversion, you may need to find a crossbar support for the manual trans.

Also, with this much effort, you should go with a conversion to a the wonderful road racing shift pattern typ 911 trans. used in the 1070/71 cars.

[Mr. 911 T]

RWebb,
Thanks for your information. In doing much research, some of the experts advised drilling out the two pins on the inner cv joint and use the 10mm bolts for strength. The other option is to replace the axles with ones that will fit the 915/61 transmission. What do you think about these idea?

Thanks again for all of your knowledge in the conversion.

[Fishcop]

Originally Posted by Mr. 911 T

Fishcop,
Thanks for your reply. When you speak of the 6 bolt driveshafts and hub inners, are you speaking of the two cv joints and the flange on each side?

Yes that's it. The actual wheel hubs can stay in place, you just need the outboard flange that mates with the 6 bolt CV at one end and with the 30mm axle nut and split pin at the other end.

I don't think the larger 4 bolt flanges will mate accurately with the later gearbox's smaller drive flanges. Even with them drilled for 6 bolts, the diameters are significantly different. I know from experience that getting the correct gearbox drive flanges can be hard as there are "fine spline" and "course spline" varieties which match your differential, so you really need to know what you're chasing. That's why I recommend you locate the later (and cheaper to service/replace) CV/driveshaft combination from the SC series. Your '72T engine will not produce enough torque to worry the smaller CVs... they coped fine up to the '85 234hp Carrera

Oh, and Randy is right; you will need the correct x-member for a 915. You also need to order the correct clutch cable for the 915/61 box and not the '72 year car.

[Mr. 911 T]

Fishcop,
This information is so helpful, thanks. I guess replacing the axles is the best way to go. In investigasting, do you think the axle Part Number 923-332-033-02-M60 is the correct one I need to complete the job? The tranny is a 915/61 which is from a 1978/79 SC. Do you think I will also need a flange? The conversion is almost complete. I'm have a tech do the job for me as I don't have the skills necessary to accomplish this task. He has also had my vehicle for four months and I'm very happy with his work. I would recommend him to anyone. I'm trying to help him and save time because I'm excited to drive my 911.

Once again, thanks again for all your time and knowledge!!

[RWebb]

you know with a '72 motor in there you may want to check on the R:P and see if they changed the numerical ratios by that year 915

[Fishcop]

My car runs a 915/62 which is the ROW (rest of world) SC gearbox. The only difference between the 61 and the 62 is the taller 5th in the 62. I don't think the gearbox will effect MR.911T's car too much, thought the taller (8:31) differential ratio will likely make the car feel a bit sluggish off the mark - but quite economical No matter what, it will feel entirely different to the sportomatic.

In relation to part numbers, I don't have ready access to see - but if the shafts have the smaller (90mm I think) CVs then you should be fine. I'd be inclined to contact a breaker/wrecker and see in they have a pair. Reconditioning is relatively cheap and easy and they have a very long service life if the boots stay intact or are replaced regularly. The flange you need to replace is the one at the rear wheel hubs.

[Mr. 911 T]

Fish Cop & RWebb,

Thanks again for your thoughts!!! I will be sharing this information with my mechanic as soon he is open for business. The last time I spoke with him, he was going to purchase a different cv joint to match it to the 915. This was way before I posted on Pelican. If this didn't work, he was thinking of putting in a 901 he had. Before changing transmissions, I will suggest the new shafts. Do you think putting in a 901 would be easier for the conversion?

[Fishcop]

A 901 box may be incorrect for a '72... I think it's the cross-over year for the 901-915 transition. They are the same amount of "ease" to fit, though the 901 should bolt straight up to your drive shafts if that's the main concern. I would be going with which ever box is in the best condition...

Definitely don't bother trying the two different CV joints at either end of the driveshaft, it just won't work

[Mr. 911 T]

Fishcop,
I read your incredible story about your car today. You are truly talented in what you do. I can't thank you enough for helping me with my endeavor. I bet you are excited about getting your 911 on the road. My 911 has been out since January 5th, and I can't wait to drive it again. I'm in Arizona and this is the best time to drive the 911's. I purchased the driveshafts along with the flanges from a salvage yard today. The salvage yard and Pelican both thought the 923 320 ===02 was the correct shaft. I'm hoping it will work and I'll be driving the 911 soon.

Once again, thanks again!

[RWebb]

the '72 came with the 915 - stronger but a step backwards in terms of the shift pattern

be sure to go thru the CV joints with new grease & inspect carefully before mounting them with new bolts (or old bolts that have good threads & good wrenching fixtures) - use new Schnorr washers always; and make sure the moon plates are not all bunged up

clean the threads with brake cleaner & Q-tips for the internal ones - use no grease or anti-sieze

then torque them & re-check in 100-200 miles

there is a long thread on this, but that is the gist of it

good luck

[Mr. 911 T]

RWebb,
Your expertise is surely appreciated!!! I will share th is information with my tech. I'm hoping the used shaft will work. I know the flange coming from the transmission is 100 m.m. and the shaft i purchased is 100 m.m., my only question is will I have to purchase new hubs? I can't wait to see.

Thanks again,
I will let you know.

[Mr. 911 T]

FishCop & RWebb,

I just wanted to let you know that changing the axles worked perfectly. Thank you so much for sharing your expertise. The car should be on the road very soon.

[RWebb]

great! post some pics

you could also post your parts list for the next person

[Fishcop]

Really pleased to hear! Post some shots of your car when you can.

[Mr. 911 T]

Will do when I get the car back!

Thanks again...you guys save me a lot of time!