Contact Patterns on Ring Gears

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rstucke
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Location: Wamberal, NSW, land down under

Re: Contact Patterns on Ring Gears

Post by rstucke » Wed Jan 14, 2015 10:48 pm

Hi
I'm new to the forum and am busy reading all I can to catch up. There is a saying that helps work out what to move (when the tooth pattern is out). We used this in our transmission courses. "Toe and heel, move the wheel (crown wheel). Face and flank, move the crank (pinion). but I think you guys already have that under control.

Bruce2
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Re: Contact Patterns on Ring Gears

Post by Bruce2 » Wed Jan 21, 2015 10:09 pm

This is a G type 3.88.
With a proper procedure, the task of setting the contact pattern goes a lot faster now. When I first assembled the pinion and diff, I used a .6mm pinion shim and two diff shims that were way too thin such that there was no preload on the diff. One change gave me lots of preload with lots of backlash. With the measureable preload, you can now calculate the shim change to get the preload right. After that change, the backlash was pretty good, so I greased up the teeth to see where the pattern was. This is the first, and I have to say it's pretty close. Backlash here is .23mm.
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Bruce2
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Re: Contact Patterns on Ring Gears

Post by Bruce2 » Sun Jan 25, 2015 7:53 pm

Here's the most centered pattern I could get on the drive. It took a .4mm shim on the pinion. I don't like the thin pattern so I think I'll allow a more toe biased pattern to give more contact area on the teeth.

What do you guys think?
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Bruce2
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Re: Contact Patterns on Ring Gears

Post by Bruce2 » Wed Mar 18, 2015 6:46 pm

My current gearbox has the R&P from hell! It doesn't matter what I do, the pattern will not move away from the toe.

The first one is the best I can get. It uses a .7mm shim and the backlash is .25mm.
D .7 .25BL.JPG
Here's the coast:
C .7.JPG
This is the only other pic I took at .9mm pinion shim
D .9.JPG
C .9.JPG
I looked at the pattern with pinion shims ranging all the way from 0.15mm to 1.05mm. Every one of them was severely biased to the toe. The pattern at .7mm pinion shim was the only one where the pattern seemed centered in the tooth from root to top.
The strange thing is that this R&P previously ran in another gearbox and it made no noise.

Any advice or comments welcomed.
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dangerous
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Re: Contact Patterns on Ring Gears

Post by dangerous » Fri Mar 20, 2015 3:02 pm

This is typical of teeth with wear.
Under load, material is worn off the heel of the tooth,
and sometimes off the toe on coast.
so even pushing the pinion closer to the crown wheel will rarely fix it.

You may actually see small traces of pattern contact near the heel, usually near the root.
Or, as you may have with your .15 shim, a thin vertical contact strip right at the heel on the unworn section.
When I say vertical I mean at 90 degrees to the pinion axis.

The majority of worn teeth I see are on the heel of the drive side,
so you can try to make the heel-pattern correct (slight heel bias on coast), and you will be close.

Often you have to look at the coast and drive on BOTH, crown wheel, AND the pinion
to get a picture of what is worn, and get a pattern
that represents, and, makes sense of the wear, on the tooth.

Remember also, that tooth wear will mean a little more backlash,
so try a little more if you want, and see if that makes the pattern better.

I never go above .25mm backlash,
but some times if you run them tighter than they were 'running-worn',
you may find them to be noisy.

Bruce2
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Re: Contact Patterns on Ring Gears

Post by Bruce2 » Fri Mar 20, 2015 7:45 pm

I just realized I neglected some info on that R&P.
It is a USA made 3.44 by US Gear. It is said to have about 10k miles on it, driven by about 120hp.

I made sketches of the contact patterns, and most patterns were with that "thin vertical contact strip" you described.

I also don't go above .25mm backlash, and with this customer noise is the #1 concern, so I don't want to risk going with less BL.

Bruce2
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Re: Contact Patterns on Ring Gears

Post by Bruce2 » Mon May 11, 2015 9:07 pm

My customer gave me a 3.44 equipped gearbox that his customer claimed had a strange reverse gear noise. It turns out that one tooth on the slider was damaged and rolled over a bit. I told my customer that this type of damage is driver error, not covered by any warranty anywhere. I was also asked to go through the gearbox so I took a contact pattern as is. I do not know who built this gearbox. I also don't know if it made noise, although looking at the contact patterns, I bet it did.
3.44 coast.JPG
3.44 drive.JPG
Here's a pic for Paul of how the gear marking grease transferred to the pinion.
3.44 pinion.JPG
A pretty bad bit of workmanship, IMO.
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Bruce2
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Re: Contact Patterns on Ring Gears

Post by Bruce2 » Mon May 11, 2015 9:12 pm

I'm also doing a 4.12 in a SSC, and I just happened to have a late Type 3 DC code gearbox. I took it's pattern at the start. Well done Mr VW! If the bearings are good, I have an easy rebuild.
4.12 coast.JPG
4.12 drive.JPG
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Bruce2
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Re: Contact Patterns on Ring Gears

Post by Bruce2 » Sun Jun 07, 2015 11:54 pm

Refer to my post of Mar 18.
This one didn't work! It's in the car now and has only been driven at slow speeds due to poor braking in the car. It makes lots of gear noise on decel.
This trans has other problems too. It makes a squeaking sound when not moving with the main shaft turning. Push in the clutch, it is quiet.
Then, on top of the squeaking sound it also makes a clicking/rattle sound. Definitely got oil in it.

I'm working on supplying a replacement gearbox. This time I start with a new 3.44.
Here are patterns in the gear marking compound and below you can see the original lapping pattern by US Gear. It's clear why there's a Toe bias on the drive and a heel bias on the coast.
Drive y.jpg
coast y.jpg
drive lap.jpg
coast lap.jpg
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Bruce2
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Re: Contact Patterns on Ring Gears

Post by Bruce2 » Fri Jun 12, 2015 1:20 am

This R&P was a lot easier to build than the last one. I got a good pattern very quickly and was able to deliver the gearbox this morning. By the afternoon, they were driving the car and happy with the replacement.

Here's what the contact pattern on delivery looked like:
Drive P.5 bl .26.jpg
Coast P.5 bl .26.jpg
Any drag racers out there wanna buy a low mileage 3.44 R&P that makes a bit of gear noise?
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rayhawk
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Re: Contact Patterns on Ring Gears

Post by rayhawk » Thu Sep 24, 2015 5:51 pm

How does this look:

Image

Image

Image

This is a used 4.12 R&P going back into the original trans with the original (.65mm) shims. I replaced the pinion bearing and installed a super diff.

Bruce2
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Re: Contact Patterns on Ring Gears

Post by Bruce2 » Tue Sep 29, 2015 3:33 am

Is the new pinion bearing the same type as the old? Ie, FAG for FAG?
I would say the drive pattern is a bit too close to the toe. Have you tried a 0.6mm shim? What was your backlash?

Here's a tip for when you are making small changes.
Normally it is not necessary to paint all the teeth on the ring gear. Especially when you are dealing with a genuine VW diff. The first time you set the backlash with an aftermarket diff, check the lash all the way around to see if it is constant. Then when you take a contact pattern, you only need to look at it in one area.

What I do is grease up two groups of three teeth on opposite sides of the diff. Then when you take a pattern, only roll the pinion on one side of the ring gear. Look at the pattern and decide on your shim change. Now take a pattern on the other side of the diff. Sometimes the changes in pattern are slight, and by doing this, you can quickly compare your new pattern to the previous one.

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