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

[Matt Romanowski]

For the folks who are rebuilding their own transmissions, what are you using for a backlash measurement? The manual says around .007, but that seems a little tight. We're trying to get some temperature out of the transmission and were thinking about running a little looser. Anyone tried that?

[Mark Henry]

I wouldn't try that, maybe it's time for a pump and cooler set-up

[Matt Romanowski]

I wouldn't try that, maybe it's time for a pump and cooler set-up

Have a cooler and pump. The 901 is set very tight compared to most other transmissions, so we thought it's worth a try. What do you set yours at?

[Mark Henry]

I don't race so mine is just stock.
But, I'd would worry that the loading/unloading would cause excessive wear. I'd keep a close eye on the wear pattern, if it gets to close to the root or edge of the tooth it will begin to break things.

[pcar916]

(IMG:style_emoticons/default/agree.gif) The backlash and contact pattern go work together to make the (sliding) contact area large enough and in the right place. It doesn't have to be dead center but that's ideal.

Years ago I broke a pinion tooth by setting the proper backlash and the wrong contact pattern. Bad juju that.

[Matt Romanowski]

You can have good settings and contact and still break stuff.

[Dr Evil]

I use the factory tool, or at least a clone of it. The factory states that .012-.018 (edit:McMark 0.12-0.18mm or 0.005-0.007") is tolerance. The way that the back lash is set at the factory is that the pinion is mated to the ring at a set design measurement "N" and then the unit is run on a machine and slowly adjusted out from the center line of the ring gear until the quietest operation is attained. This number is then scribed onto the pinion head, i.e. n=18 would mean that you need to set the pinion back from N +.018.

To do this correctly, you need the special tool. Varying in or out will not give you much in the form of performance and I do not think it will effect cooling all that much either. One can surmise that the quieter running factory setting is the least amount of friction one can get from the R/P.

[Jon B]

The factory states that .012-.018 is tolerance... scribed onto the pinion head, i.e. n=18 would mean that you need to set the pinion back from N +.018.

These dimensions are incorrect.

New to forum, reviewing old topics and came across this. Numbers above are noted as 1/1000 of something, but incorrect whether mm or inch. Factory dimensions should be noted as 1/100mm:

Backlash range: 0.12mm to 0.18mm
Pinion dimension: N18 = +0.18mm

In inches, equivalent backlash range would be 0.005" to 0.007".
Hope the good doctor wasn't using those dimensions himself, nor anyone else.

Jon B.
Vista, CA

[Dr Evil]

Not using inches, why would you assume so? Decimal was out of place, sure.

[Jon B]

Not using inches, why would you assume so?

I didn't assume numbers were in inches, I said "1/1000 of something" because it wasn't noted, just .012-.018 of something. But in US when people see .018 they do assume inches. Matt began thread with .007, an inch dimension although also not noted as such.

Just felt it should be corrected in case future forum members search "backlash".

No?

Jon B.

[Dr Evil]

Sure, whatever

[Matt Romanowski]

Jon - Good call.

As an update, we're going to pull the transmission this winter and still plan on loosening the R+P some.

We also have a clone of the factory tool that we made.

[76-914]

Jon - Good call.

As an update, we're going to pull the transmission this winter and still plan on loosening the R+P some.

We also have a clone of the factory tool that we made.

I'd like to see a video or write up when you do that, Matt. (IMG:style_emoticons/default/popcorn[1].gif)

[0396]

Not using inches, why would you assume so?

Hi, I didn't assume numbers were in inchs, I said "1/1000 of something" because it wasn't noted, just .012-.018 of something. But in US when people see .018 they do assume inches. Matt began thread with .007, an inch dimension although also not noted as such.

Just felt it should be corrected in case future forum members search "backlash".

No?

Jon B.

Some might not know Jon B. But as an FYI, he's one of the premiere 901/915/G50 trans experts on the west coast. Jon, good catch on the decimal thing. Only an expert would have caught that. (IMG:style_emoticons/default/piratenanner.gif)

[r_towle]

Matt, what kind of differential do you use?

Rich

[zambezi]

Not using inches, why would you assume so?

Hi, I didn't assume numbers were in inchs, I said "1/1000 of something" because it wasn't noted, just .012-.018 of something. But in US when people see .018 they do assume inches. Matt began thread with .007, an inch dimension although also not noted as such.

Just felt it should be corrected in case future forum members search "backlash".

No?

Jon B.

Some might not know Jon B. But as an FYI, he's one of the premiere 901/915/G50 trans experts on the west coast. Jon, good catch on the decimal thing. Only an expert would have caught that. (IMG:style_emoticons/default/piratenanner.gif)

If thats Jon Bunin, then add 356 trans guru as well.

[Jon B]

As an update, we're going to pull the transmission this winter and still plan on loosening the R+P some.

Matt,

It's best to stay within factory specs when adjusting a ring & pinion, even for racing. Porsche manuals note "...the pinion shaft and ring gear is matched as a pair during production. They are checked on testing machines for correct contact pattern and low noise level in both directions of rotation". Gear noises are the result of excessive vibrations. These vibrations can be annoying but also destructive, as they contribute to material fatigue. It's best to take advantage of their tests and stay within factory specs.

Jon B.
Vista, CA

[Jon B]

I use the factory tool, or at least a clone of it.

Photo below of factory tool, P258, with all accessories.
This tool will only measure pinion depth; other tools are needed to determine ring gear backlash and differential bearing preloads.

I'm curious to see the clones being made.



Jon B.
Vista, CA

[Matt Romanowski]

Matt, what kind of differential do you use?

Rich

Just have an open diff in it right now.

[Dr Evil]

I use the factory tool, or at least a clone of it.

Photo below of factory tool, P258, with all accessories.
This tool will only measure pinion depth; other tools are needed to determine ring gear backlash and differential bearing preloads.

I'm curious to see the clones being made.



Jon B.
Vista, CA

Mine was made by a machinist and has the same dimensions as the factory tool. I only have to use it when replacing R/P for failure of inspection or traumatic failure. Most of the time, and I have covered this extensively here and in my DVD, I instruct people to measure gaskets and maintain factory set specs. The vib issues is not much of a concern in the small increments we deal with. It is mainly a nuisance. Many other manufacturers do not do the finite test in leu of just matching patters with dykem or other indicator to a visual pattern.

In a race box, though, I would keep as much friction and vibe out of your setup as fatigue will be highly magnified. Bearings wear and tolerances are quickly lost.