Ring and Pinion Backlash, What's everyone doing? Options

[Jon B]

Can you replace the ring and pinion with the 8 tooth setup yet still fit inside the 914/901 box and have everything work properly?

Not with a 915 ring & pinion, it will not fit earlier transmissions.

Porsche made an 8:35 ring & pinion for the 901 transmission, but they're fairly rare and expensive, even in used condition. They're still smaller than a 915 R&P, and only a marginal improvement to the standard 901 set...

http://www.ebay.com/itm/300572148895
http://www.ebay.com/itm/300510781903

Jon B.
Vista, CA

[Dr Evil]

Going to more teeth on the pinion of a 901 will actually net you a weaker pinion as the teeth will be smaller/thinner. The 915 is thicker overall in all parts.

[Jon B]

Going to more teeth on the pinion of a 901 will actually net you a weaker pinion as the teeth will be smaller/thinner. The 915 is thicker overall in all parts.

More teeth increase the gear's load bearing surface and help decrease material fatigue. Gear tooth design can be adjusted if the pinion isn't enlarged, for example, the root circle can be increased, shortening the tooth. It's unlikely that Porsche would've offered a weaker design with no specific advantage, such as significant change in ratio.

The 915 8-tooth pinion was increased in size from previous 7-tooth pinion, with ring gear offset 2mm on differential.

Jon B.

[Dr Evil]

I disagree. When it comes to the 901 pinion, more teeth takes away from the overall girth of the pinion base with smaller/thinner teeth. They would definitely put this in a box that was not intended to handle crazy tq. These weaknesses become evident when high tq is passed through a box not built for it. When keeping in with parameters speced for the boxes, the number of teeth is not an issue.

Your mention of the change made to gain an extra tooth on the 915 supports what I am saying. Increased size was mandatory and that box handles more tq/hp than a 901. All parts are thicker in that one.

[Jon B]

More teeth increase the gear's load bearing surface and help decrease material fatigue. That is a fact. Each tooth surface bears less sustained load per cycle, as time spent in contact is briefer. And having a slightly taller ratio, the 8:35 pinion has fewer cycles per mile as well.

We can disagree.

In any case it's really not a viable solution for anyone, as sets are both scarce and expensive.

Jon B.

[Dr Evil]

We can disagree.

In any case it's really not a viable solution for anyone, as sets are both scarce and expensive.

Jon B.

True that.

[Dr Evil]

Late, but none the less relevant.

[Jon B]

It only began in April, so not quite a resurrection of Biblical comparison.
Hopefully prevented some potential grief, contributed new information.
Matt still hasn't done anything since beginning the thread, so still relevant as well.

Jon B.

[Dr Evil]

Yup, relevant, addressed two misplaced decimals, I have no idea what I was doing and in what state of mine I was in when I posted that; work, drunk, sick with bad cold?

I just saw this meme and it made me think of this.

[John]

John,

Those are excellent tools, and Porsche-recommended alternative to P258 for 901/911/914 transmissions. I use my set often. Lower photo from 915 manual, showing tool in use with diff cover removed...





Jon B.
Vista, CA

Your set is certainly more complete than mine. I found that some of these tools including the storage box are still available new. I see that you have several fixed depth setting gauges as well as your master gauge. If you have duplicates that you wouldn't mind parting with, I may be interested.

Thanks,

John

[Jon B]

John,

I have more than one bar, but keep the small items in one case.
If I part with any fixed gauges, the rest will fall over like dominoes.
Baum or Zelenda may still have some.

Photo below of Porsche sizes through 915/930.
The 901/911/914 gauge is VW385/12, Ro=63.50mm.
Smaller gauges are 924/944/944 Turbo and 905/925 Sportomatic sizes...



Jon B.
Vista, CA

[Jon B]

914 Transmission
Measuring differential bearing preload
Measuring ring gear backlash
Adjustments made using differential shims
Factory shim range: 0.25mm shim; 2.4mm to 3.7mm shims
Photos, specs from factory 914 Workshop Manual

Measuring differential bearing preload
Nominal value approx 0.15mm (0.006")



Measuring differential bearing preload (drag), pinion disengaged
SKF Bearings 25-35 cmkp (22-30 lbs. in.)
FAG Bearings 40-65 cmkp (35-57 lbs. in.)



Locking pinion shaft with P259 clamp



Measuring ring gear backlash
Backlash range 0.12mm to 0.18mm (0.005" to 0.007")
Measured 4 times at 90 degree intervals


Jon B.
Vista, CA

[0396]

Thanks for the indepth education. Now we know who has all the trick factory tool.

[Jon B]

914 Transmission
Setting Ring & Pinion

Factory Tools
P258 Pinion Depth Gauge
P258b Bearing Sleeves
P259 Backlash Set
P261 Torsiometer
P357 Locking Disc, Indicator Tip

Suitable tools can be purchased or made as substitutes





Jon B,
Vista, CA