Contact Patch & Pinion Depth Explained

Thanks, My goal is Short, sweet and too the point with quality video and audio.

I don’t get it!! He change the adjustment and return to 10 and got different backlash!!!!!

I changed the depth adjustment which changed the backlash. I reset the backlash to .010" and retested the contact patch which moved slightly. What don't you get? I'm willing to explain it.

This really applies to all differential designs however the 9" style was much easier to make an adjustable pinion to demonstrate the effects pinion depth has on a contact patch.

Glad I could be of help. Don't hesitate to reach out if you need additional info or help.

The Dial indicator is measuring Ring to Pinion gear backlash (clearance) The gear contact paste, is indicating Pinion gear engagement depth with the ring gear. Two very different measurements... What you are not told is in order to setup a pinion on an 8.8 Ford, it requires the purchase of an extra (setup) bearing, identical in manufacturer to the bearing you will finally use. This bearing must be modified to "slip fit" on to the pinion so pinion depth can be setup. Additionally, you will need a few extra crush sleeves for this process...

Thanks

Should emphasize the fact that contact patch and backlash should be checked with the axles in the differential (loaded) and tires on to offer some resistance in drive and coast.

Thank you for your comment and observation. The axles do not have to be in and in this removable design that is really difficult. It is very important to provide a load or resistance to rotation to obtain a good contact patch pattern. What you can't see so well is I built in a braking mechanism that is applying rotational resistance to the ring gear. This is adding enough load to provide a good pattern. The objective of this video was not to show how to perform a contact patch pattern but instead to explain how the pattern is effected by the change in drive pinion depth.

:)

You are correct.

My factory training taught me to paste every tooth and it can revel some information about the setup however in real life I paste 4 teeth every 90 degrees. This gives me a feel for the setup.

Your Welcome

I try to do this with all my videos.

Thank you stay safe and healthy

I'm glad. My goal is quality training video's.

Your drive side pattern is your most important and the biggest goal is to make sure the pattern is not running off the toe, heel, face or too deep into the flank. It would be great if drive and cost would always both be perfectly centered but that is rare. In fact I prefer the drive side to be slightly towards the toe and coast to be slightly towards the heel. I do this because under heavy load the pinion will thrust slightly towards the front of the vehicle causing the drive and coast side patterns to center. If you are working on a front diff and it's flipped so the pinion centerline is above the axle like front diff's on 4x4's offend are for ground clearance the drive and coast sides of the ring gear are reversed. The drive side is concave and the cost side is convex. I hope this helps.

If you are getting clucking from too much backlash especially when switching from D - R or R to D you most certainly can change the backlash adjusters (Shims or Threaded Adjusters) to correct or reset the backlash. You won't need to mess with pinion depth and you should not have to worry about contact patch. As long as you have the dial indicator and the tools and methods to make the adjustment. Just make sure to check your backlash in at least 6 to 8 different locations around the ring gear and make sure the backlash is never smaller than the minimum specification. If your getting humming or moaning noises that is not a backlash noise and readjusting the Backlash will not fix this type of noise.

@@DrivelineMaster the noise I am getting is a moaning noise from about 30 mph on up. It moans when I am on the gas. If I let off the gas and coast it gets a lot quieter. I changed both rear axle bearings as on side was bad. I didn't see any play in the pinion bearing and it spun freely. There were no visual defects in either gear. What do you think is the cause? Thanks in advance

This is a description of a classic rear drive pinion bearing noise. Sometimes worn gears will do this but it's not as common as a pinion bearing. Normally if it's gear noise you can't see the wear but a contact patch can sometime identify worn gears. The contact patch should be non symmetrical triangular or oval. Normally if the gears a bad the contact patch will be a straight thin line. Place a listening device such as a mechanics stethoscope or you can use a screw driver or extension bar up to your ear while holding the other end against the differential housing in different locations. Once near the rear pinion bearing and once near the front pinion bearing. Do this with the wheels off the ground and someone driving the vehicle accelerating and decelerating as you listen. I put 95% chance your problem is the rear pinion bearing even if rotation feels smooth when turning it by hand.

@@DrivelineMaster Thank you for your detailed advice!!!!!

Most likely.

severely worn ring and pinion sets are normally noticeable by visual inspection however they will often exhibit patterns that look like thin lines as compared to oval or triangular shaped.

DrivelineMaster Thank you for your reply! I will bring this ; and use it. Teach it;also.

Glad this helped

The drive side of the ring gear tooth is always the pattern of most concern. If the coast side is off a bit I don't worry too much as long as the drive side is where I want it. Two other factors effect contact patch. Backlash and worn gears. Although Backlash effects the pattern differently (hey, that give me an idea on a new video) worn gears will create all kinds of weird patterns that won't make any sense.

Thanks

Well......... if your not interested no one is forcing you to watch.

@@DrivelineMaster actually it was a compliment, very relaxing voice!

Sorry for the reaction. I thought I was boring you.

God yes...I've got a Dana 44 I need to do and I'm dreading it.

I believe this is a face milled Five-cut gear set. If you have been doing some research then you most likely found this URL. gearsolutions.com/features/face-off-face-hobbing-vs-face-milling/ also this from Yukon gear www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwif_e-JxbL0AhXloFsKHYN6DQ0QFnoECAIQAQ&url=https%3A%2F%2Fwww.yukongear.com%2Fweb_images%2Fpages%2FBrochures%2F2-Step-vs-5-Step-Gears.pdf&usg=AOvVaw2q8lfMkwNzdKq7Hzfd8FJ-. The pattern is different and moves across the tooth differently depending on how it's cut.

1/8 of an inch is equal to 0.125" and that is excessive. Each differential is different but on an average most differentials will have free play (called backlash) between 0.005" and 0.009". I have see specifications as low as 0.003" and as high as 0.014". Evan at 0.014" that is a large difference to 0.125". It requires a dial indicator like what I used to accurately make this measurement.

Only on an ox cart...

Watch from timestamp 0:26 to 0:31 and 1:16 and 1:22. The pinion moves to the left but I don't like to say to the left because what would happen if the image was flipped 180 degrees or even just 90 degrees. So it's not a good idea so say the pinion moves left, right, up or down but instead talk about in relationship to the centerline of the ring gear.

@@DrivelineMaster I'll try to look again, maybe I can watch the video on a 65 inch TV. Thank you

might be hard to see on a phone with a small screen but any monitor larger than 13 inches should be large enough to see the movement.

Some differentials are more sensitive to pinion depth shim change than others. In other words .006" change on one diff won't make much of a difference when on others it will make a huge change. There is a contact patch sweet spot on the drive side of the ring gear tooth that allows for some flexibility as long as the contact patch is not off the edges of the toe or heel or too high on the face or too deep on the flank the pattern is fine. So yes, it is possible to have multiple depths with the correct contact patch. More than likely those depths are within a few thousands of a inch of each other. This is a really small window.

It does happen but not as often is I would like. Start with a case with zero axial run out. Add a quality gear set with tight tolerances. Have it assembled by someone who takes a lot of care and attention to details. Finally the proper pinion depth. I don't think the perfect pattern is that critical. I personally like the drive side a little towards the toe and the coast side a little towards the heel when I take my pattern.

@@DrivelineMaster Thanks.

Yes, You are correct. The cut away I used had a friction shoe pressing on the ring gear that you could not see as I turned the pinion. When I do this on the workbench or on the car I rotate the ring gear and apply rotational friction to the pinion. One easy way to do this is to enlist an aid. Wrap a shop rag around the pinion just under the flange. Have the assistant pull on the rag to create rotational friction to the pinion. This can make it impossible to turn the ring gear so the assistant needs to give a little on the force just enough to allow you to turn the ring gear. I hope this made sense. The greater the load the better the contact patch you will get.

@@DrivelineMaster That makes total sense to me. I really appreciate your help and video. I'm currently restoring a 1970 Mercedes 6.3. As I'm sure you know the rear end of a Mercedes of this era is a little different, but I'm assuming all the principle's you spelled out apply. I may message you from time to time if that's ok:)? Thanks once again for your video. Cheers John.

Yes you can email for advice. The principles are the same. I don't have much vintage Mercedes experience.

@@DrivelineMaster Thank you very much. I really appreciate that.

You can't. Go with the drive side. How far off is the coast. As long as the pattern is not totally running off the toe or heel or too high on the face you should be OK. I'm assuming your backlash is also within specification. If it is really bad make sure you don't have excessive backlash variation or ring gear run-out. If all is good and the patterns are still really far off there is a problem with the gear set even if it is new. I like to set mine so the drive side is a little towards the toe and the coast is a little towards the heel. that way under load they will move slightly towards the middle of the gear tooth. Hope this helps.

@@DrivelineMaster very helpful info. thanks. it was a hypothetical question. I'm not experiencing the issue, just curious if it was possible to remedy if it occurred. i figured it would be a faulty ring/pinion if it happened though. i'll be assembling mine in the next week or 2.

@@callofgeorge this is what i am experiencing now in trying to resetup a set of gears in a Dana. My coast and drive pattern are no way the same.

The more centered the better and I could have changed the depth a little more in the video to bring it up just a little more however it is very common to not be able to get a perfect pattern when building a differential so there is a bit of a trade off and compromise that sometimes has to be made. As long as there is some paste that is not wiped off on all sides the differential build should be OK. Depending on how hard it is to keep the trial an error method going to get the perfect pattern and if time is a concern such as when you are doing this for a living and not just your own vehicle you may not have the time to play with minor adjustments to get the perfect pattern when the one you have will work just fine without any problem. As I was trying to say, it is kind of rare to be able to get the perfect pattern for every differential build.

Yes there will be a minor change due to heat expansion. The backlash is more likely to change but the depth is not likely to change. I doubt the contact patch would change enough to see or measure it. Of course the higher the heat the more likely the change.

The dial indicator is a standard 1" dial indicator. For in the shop I normally use one that can be setup using vise grip locking pliers similar to this Central tool. store.dealershopusa.com/product_info.php?products_id=77440&gclid=EAIaIQobChMI1sHB_4Gd_gIVkR-tBh0ZUwCtEAQYBiABEgJLgPD_BwE The spanner nut wrench is a Mazda specialty tool that is adjustable making it universal but I don't think it can be purchased anywhere except from a Mazda specialty tool store. To perform the contact patch watch this video. kzhead.info/sun/iK2Cm5dobF-wn4k/bejne.html. To adjust backlash watch this video. kzhead.info/sun/l52cqNtxm1-Zpqs/bejne.html. If you would like to Mazda spanner nut tool number write back and I will look at the tool one day next week and write you back.

@DrivelineMaster I would like to get into differential rebuild. Most people remove the pinion and check. I notice he didn't do that. He was using a tool to adjust the depth and lash. I'm interested in that tool also. Was that the Mazda tool you mentioned? Thanks

The Mazda tool was the spanner wrench that I used to adjust the backlash. I did not use a tool to change the depth. Instead I customized that differential to allow me to change the depth just by turning a threaded rod. For all other applications pinion depth is adjusted by disassembling the differential and changing a shim thickness. I also have a video on how to use a pinion depth measurement tool. You might want to look at these two video's. kzhead.info/sun/ms9vmdGhq5Nmlps/bejne.html and kzhead.info/sun/hLBmlNGgnYWgaaM/bejne.html and these two as well. kzhead.info/sun/ksaOmJ2GfH-il4E/bejne.html and kzhead.info/sun/ldyiZ6mhiKylbH0/bejne.html

Thank you for noticing. That is one of my goals along with; Short, clear, informative, accurate and quality.

One thing that I forgot to show was that I did do that. I formulated a section of brake pad onto a bracket with a pressure adjustment screw so the crown gear or ring gear as we call it was under pressure. I just didn't show that because the focus of the video was on what happens to the pattern as the depth is changed.

The greater the backlash the more the contact makes contact on the heel and high on the face of the tooth. Smaller backlash moves the contact closer to the toe and deeper into the flank of the tooth. I normally don't bother with backlash patterns because I can measure the backlash and adjust it based on the dial indicator measurement. I don't need to make backlash adjustments based upon a contact patch like we often have to do with pinion depth.