K type 3.88 R&P

[Bruce2]

I just pulled apart a Karmann Ghia gearbox, expecting to find a G type 3.88 in it. I was surprised to find it marked K831 instead. K, meaning it has the Klingelnberg Palloid tooth form.
The common G type (Gleason) tooth has a root depth that increases as you move from the end of the pinion towards the bearing. The K type tooth has a constant root depth along its length.

I know of trans builders who covet a K type 4.12 as being better than a G type. But the consensus on 3.88s is that the G type is king. If the K type tooth form is superior on a 4.12, why wouldn't it be superior on a 3.88?

With this new one, I'm wondering what everyone might think about the K vs. G R&Ps?

[Casting Timmy]

I think it's the 4.12 O that's regarded as stronger than the 3.88G for Type 1's.

The best I could find on the K cuts for Type 1 was someone talking about drawing back the temper on them and they had to chase the backlash to keep it alive. My best thought is that maybe they messed up the heat treatment on the K's for the Type 1's and that's why they don't have the strength of the G's which is a weaker cut.

I think it's good that you pointed out the differences with the cuts as I know I've opened one 3.88 "k" that was a K in marking only and the tooth pattern was definitely a G. So there are some mis-marked ring and pinions out there as well.

[Bruce2]

Eric at ERCO told me that the O type 4.12 was "almost" as strong as the G 3.88. Where did you hear that claim?

I've never thought about miss-marked gearsets. I didn't check the gear to see if it was a K. I will do that.

[Casting Timmy]

Probably typing too fast, I think the benefit of the 4.12O would come with the overall transaxle with having a better first gear ratio. So I would rate it a little better in an overall perspective, but soon I think the 4.12O and 3.88G are going to become rare birds.

I do know the 3.88K's are real from talking to other builders, but also know the one I had was luckily a G as I preferred that instead.

[Bruce2]

I checked the pinion gear on the K831 I have and it's constant depth on the teeth.

I'm wondering if the strength reputation is made up. The K831 is so rare that drag racers that know the limits of a G831 might have never had one to test out.

[Bruce2]

The K831 is so rare that drag racers that know the limits of a G831 might have never had one to test out.

This got me thinking about a local friend who's been drag racing the same car for over 30 years. When he first built the tube frame car, it used a Type 1 trans. The car runs mid 10s at 130mph using a 2332 and carbs.
I sent him a message asking if he ever tried a K831:

"Never used a K. The life of a R/P depends on the clutch set up. I got as little as 4 passes but usually over 30. You could hear the teeth turning over on the tow backs. That was the re & re time"

[dangerous]

From the gear manufacturers, the K(and O) is considered the better tooth form,
probably because the heel is a little thicker,
and where the contact patch moves under load.(but I'm just guessing).

It is possible the VW version had different heat treatment,
but I think the G3.875 being better is actually, simply, the tooth is a larger module than the K.