Contact Patterns on Ring Gears

[Pablo2]

The photo thing is rather perplexing. I understand that photos won't embed (or download) unless beneath the minimum of 800 pixels each direction .. but why some embed for all to see, while others require signing in to see is baffling to me. I note that photos must be added in reverse order of how you wish them to be seen in the post.

Anyhow, as a preliminary bluing check, I first roll bluing on just the pinion, to get a positive print on a few ring gear teeth.

[Steve Arndt]

Pics hosted at shoptalk require login to view.
Pics hosted at other sites do not require login.

[Pablo2]

Thanks, Steve .. that makes sense. Unfortunately, we rarely have such tiny photos hosted elsewhere. It's often easier to just provide links.

[Bruce2]

Here's the stuff to use:

[Bruce2]

I use the VW 385 bar for setting specified pinion depth,

Next time it's in use, can you post a pic of it?

[Pablo2]

This photo will make you drool ..
http://images.thesamba.com/vw/gallery/pix/1237498.jpg

On page 5 of this thread, you'll get the full tutorial of using one on a late Type II ..
http://www.thesamba.com/vw/forum/viewtopic.php?t=568039

Edit note:
I was recently supplied with a number of factory NOS Syncro transaxles to rebuild with altered internals. I like to take notes during disassembly, and was shocked when I came across one transaxle which had been improperly set to 0.02mm backlash. All the others had correct 0.15mm settings. Goes to show that even the factory makes some errors.

[Bruce2]

I once found an 091 ZF disc inside a Type 1 ZF diff. ZF makes mistakes too.

Swing axle this time. Still working with a G type 3.88:



I started with what I think is the most common shim for this R&P, 0.6mm. I looked at patterns of 0.3 and 0.1mm. They were on opposite sides of center, so here's where it is at 0.2mm of BL. I think I will try to reduce the BL a tiny amount to see if I can get it right in the middle on the drive side.

[Bruce2]

Here are some diagrams showing the way contact pattern moves with shim changes:


FACE MILLED:


FACE HOBBED:

[Bruce2]

Well, things didn't change as I expected. Here's .18mm of BL.

[raygreenwood]

Awesome pics and information. Thank you!
Ray

[dangerous]

Thank you for sharing your findings.
Probably the biggest hindrance I find, is the wear on the pinion.
Case wear can be a problem with pattern too, but usually less of a problem provided the bearing sits square.

If you factor in the increased backlash that would exist, you can approximate a better pattern.
But generally you will struggle to change the pattern to improve, once wear is to a certain point.
You will see the wear as a more shiny patch, and some times a very small step.

For used parts, in stock applications, I always set the backlash in the higher range,
because I have found a little more noise if it is set tighter than where it had been running for years.

The method I use on pattern setting, is to coat only 6 the teeth on the crown wheel,
three teeth for drive and 3 for coast.
I use bearing blue.

I then drive the pinion with a drill in coast first, then on drive,
trying to load the crown wheel up while it is running.
Trying to halt the rotation with the coated teeth away from the pinion!

Often the pattern is a compromise,
but generally I like a bias toward the nose on drive,
and centred, or slightly heel biased on coast.
More nose bias on race applications, or higher weight and torque.

Ultimately you will want it as centred as possible on the height of the tooth.

You can then look at the pinion pattern and decide which way you might like to improve things.

Often once I am happy with the crown wheel,
I will make a change to improve the pinion situation.
This can be at the compromise of what the crown wheel wants,
and how much wear exists.
..but this is a judgement I make based on the application.

For example, a road car that wants to be quiet on deceleration
would be different to a race application that is trying to achieve a better tooth thickness point
when the crown wheel is forced out of mesh.

[Bruce2]

I tried printing the charts I previously posted and they are unreadable. Originally I had taken a photo of the page, so this time I scanned the pages. Then using photoshop, I moved things around to make these charts.

G type:
http://images.thesamba.com/vw/gallery/pix/1264555.jpg

K and O type:
http://images.thesamba.com/vw/gallery/pix/1264567.jpg

[Bruce2]

Here's the contact pattern of a G type 3.88 as I opened up the gearbox. This gearbox had been rebuilt before.

[madman4]

Hope this help.

[Bruce2]

I can report the previous gearset runs quiet.