Ring & Pinions for 915 box

[chris_seven]

I have been looking to buy a couple of low geared R & P's for a 915 box and the cost seems quite high.

I can buy a new 7:31 for around $2300 not from Porsche and I am not sure where they are made or I can buy an 8:35 made in Germany but at a cost of $2900.

Both of these R & Ps are Klingelnberg Palloid tooth forms and have therfore been lapped after manufacture.

I have spoken to a company that have a Gleason and would make the 8:35 with a face milled technique and then precision grind. The price for these would be less than $1800 which is nearly 40% cheaper.

I have found some technical articles that compare the two methods and tend to say that there is little significant difference in noise, power loss or reliability.

I realise it may be a bit if a step in the dark but I seem to remember that although production 911s have always used the Klingelnberg system that some of the race cars including the 917 may have used a Gleason cut in which case it may be worth the saving.

Any ideas?

[KobaltBlau]

The '89 tech brief on the 928 GT says that the new G28/55 2 switched to the Klingelnberg Palloid type. I would guess that means that porsche was using the Gleason type before on the 928, but I can't prove that.

I couldn't find any information on 911 usage. What engine configuration (torque output) do you have in mind? This may influence whether you choose 8:35 or 7:31.

Also, you may have already checked into other sources, but I found some information that Powerhaus II had done a Klingelnberg type (at least for a G50 box), you might check with them. Also Guard Transmission would be a good contact, and http://www.albinsgear.com.au/ sells a 930 Klingelnberg type and will do custom ratios, so I bet they have done or could do a 915. Worth a call anyway.

[chris_seven]

Albins do make KL type 915 diffs and have 7:31 currently in stock but by the time I have shipped them from Australia they do end up at $2300, better than the German price but still quite expensive.

Albins will also have 8:35 in the next few weeks and it will be about the same price.

We are looking at using the R & P with 3.0 litre Twin Plug motors with relatively high torque and I am not absolutely sure about the 7:31 in this application.

Until now we have used an 8:31 and a CR gear set we make that uses a stock 1 st and then evenly spaced to 5th which will pull around 120mph at 7500 rpm in 5th with 195 x 70 x 15 wheels/tyres. Cars are used mostly on gravel.

[KobaltBlau]

Yes, you are probably on the borderline for 7:31. Gravel might help, but the transition from gravel to pavement not so much! I wish I knew more about which types had been used in porsches. I can think of a couple of potential downsides of a different manufacturing method: 1. Noise and 2. the mechanics of the ring/pinion teeth contact causing a weakness. 3. Differing axial load on pinion bearing Perhaps heat generated could also be different but i doubt it would be substantial.

I do not know which method is better in these respects, but my guess is that higher noise would not be a big issue in your application, and if you went with an 8:35 you would certainly gain some margin of safety in strength even if the tooth contact was different. Axial load on the pinion bearing is harder to assess. The man to talk to about this stuff would be Hayden from Windrush Evolutions (WEVO). He is really the 915 guru. I would give him a call if I were in your position.