Porsche 911 Ring & Pinion

[ale911]

Hi

The time has come to rebuild the 5 speed gearbox of my 1972 911 2.4 T-E series (chassis 911 310..). My mechanic says that the gears are good but I need a new pinion&gear, plus obviously: bearings, syncros and all gaskets/seals.

I am looking around for a new or good second hand pinion&gear set, but see there are various solutions out there to choose from and I am a bit confused on what we can use.

The pinion&gear set I have on the original gearbox has 31 and 7 teeth. Can I have the stronger 31- 8 set installed or do I have to stick to the original set?

FYI the engine was been completely rebuilt with high compression pistons, modified E camshafts and S MFI pump shaft. I plan to use the car for amateur hill climbs here in Tuscany.

Does the limited diff improve a lot the drive? Do you suggest any particular limited diff upgrade?

Any other suggestion would be highly appreciated, and remunerated with some good wine if you pass in Tuscany

All the best,
Alain

[ale911]

I add another picture of the head of the pinion. I believe this is for the mechanical speedo. Any help would be appreciated!

[BSMotorsport]

Hi I am just making new Ring and pinion slightly lower ratio @ 5:1 7/35 or I probably have a std 7/31 mech drive set if you get stuck
Neil

[ale911]

Hi BSMotorsport
7/35 sounds perfect. Does it fit in my gearbox without modification?
Do you suggest also the limited diff upgrade?

[ale911]

Can I install 31:8 pinion & ring without modifications?
Originally I have the 31:7 with mech speedo.

[Matt Monson]

There's only a few gearboxes that ran an 8:31 with mechanical speedo. It's a very limited production window. You may be shopping a while.

It's also a tricky setup. The ring gear flange thickness and offset is different, so things get a little funky when shimming it for backlash.

[ale911]

Ok, thanks
Are all 7:31 the same? i.e. if I find another 7:31 is the setup complicated as well?

[ale911]

Will all 31:7 with mech speedo pinion&ring set fit on the 915 gearbox? Or is it tricky?

[Matt Monson]

Sorry. Wasn't around much yesterday. You are still going to need a professional to fit any replacement ring and pinion. However, all 7:31s are the same as each other and don't have the weird shimming of an 8:31 in your box. But without a 385 bar, you cannot properly fit a replacement by yourself. It is not a DIY job.

[ale911]

Thanks!
I see there are around for sale various 31:7 p&r from the 914.
Would these work?

[Matt Monson]

Nope. The 914 gearbox is 901 based.

[ganun]

you mention hillclimbs...then a longer ratio like the 31:8 is the opposite of what you would want.
4.43:1 vs 3.88:1

[ale911]

Thanks Matt, so I have to look for a 31:7 for 915 gearbox.

Ganun, I agree, better off to find a 31:7.
The 35:7 tempts me, but will probably drive me crazy if I ever had to drive on the motorway.

After all, I think I will go for the stock 31:7 but would like to add a nice limited slip diff. Any suggestion on type and make for the 2.4 915 5 speed gearbox?