I picked up a 12 bolt open diff rearend for my '66 Impala. I installed a new Eaton posi unit and new Summit 3.55 ring gear and pinion. I am at the point of checking the pattern. Can the rear diff experts review the photos and tell me if the pinion needs further adjustment? Originally the pattern was too deep so I adusted the pinion shim from 0.024. to 0.018 in. The photos represent the 0.018 in shim.
The backlash is currently 0.010 (see video). I believe this is the high end tolerance for backlash.
Thanks for any help. BTW, the noise in the video is my propane torpedo heater.
Dave
The pinion is not deep enough. The pattern is too close to the face of the tooth and needs to move toward the root more. Add pinion shim. It also looks like you are using the pinion to turn it. Stick an axle in it and use that to turn everything when checking the pattern. If you have the bearing preload set right on the pinion bearings then this will give more than enough resistance to give a clear pattern on the ring gear teeth. Turn it through the compound several times in both directions to give a clean pattern.
Do you have all of the ring gear bolts in it? One picture shows that several ring gear bolts are missing. If you are trying to check it like this then you need to stop right now and put in all of the bolts and torque them to 45 foot pounds with red Locktite on the threads. If you don't have all of the bolts in it then you will probably have some run out in the ring gear which will cause problmes with the pattern.
Thanks for the response. I checked the runout and it was nearly spot on 0. You're right though I have to put the rest of the bolts in. A correction to the previous post: The original pinion shim was about 0.029 not 0.024 in. I changed it to the aforementioned 0.018 in (pretty drastic). Based on my limited knowledge of "reading" the patterns, I changed the shim to 0.024 and got the following:
I agree with Big Gear Head, more pinion shim, and it still looks like you need more yet in the second set of photos. I have rarely ever found a 12-bolt that needs less than an .030" shim, and usually they need more, in the .032-.035" range. I've only ever had one below .030" and it was .028". The drive side still looks too high towards the tip of the tooth and needs to move closer to the root. The second set of photos does look better than the first.
Wrap an old fan belt around the pinion yoke and have a helper pull down on it while you with a box end wrench on one of the ring gear bolts run the ring gear up and down about 5-10 teeth.
There is a reason that I recommend using an axle to turn it. You need to make several complete revolutions of the ring gear in both directions. The reason that you need to do this is because the pinion gear needs to be able to wipe the compound off of it's self onto clean teeth so that when it goes over the teeth with the compound on them it will remove more compound and make the pattern easier to see. If you just rock it back and forth over the same teeth without making complete revolutions then the teeth don't get wiped off well. Use an axle to turn it in both directions several times and the pattern will be easier to read.
I would say that you are close with .028. Probably somewhere between .028 and .024 will get you what you need. Try it again and turn it with and axle. When you are turning it be carefull not to stop in the middle of the teeth with the compound on them. Be sure that you set the backlash the same each time, and the pinion bearing preload needs to be set the same each time too.
I just paint my pinion gear with the compound and then see what it puts on the ring.....for me, it's much easier to see the pattern it leaves on the ring that way.
To me it looks good at .028"(maybe try .027" and see what it looks like) if you are going to run it hard , say a drag or street/strip car as the pattern will spread out to the outside on the tooth on the drive side when power is applied. I would tighten the backlash down to .006-.008" if you can.
It's a Summit Racing gear set. 3.55:1 for my '66 Impala convertible. It will be strictly street, no racing. It's got a 700 R4 tranny, so I thought that ratio would fine. The backlash is currently at at 0.008" after the pinion adjustment. Thanks to all for the input thus far. BGH I will try the axle test.
I have built many hundreds of rear ends over the last 12 years and I have found that turning everything by the ring gear gives a clearer, easier to read pattern. It doesn't change the pattern, it just makes it clearer. When you turn the pinion gear the pattern will have lines running through it (as seen in the pictures above) and the edges are not as sharp and clear. If you have a 4.10 gear then you have to turn the pinion 4 times to get the ring gear to turn one time. When you use an axle or ring gear bolt to turn everything then the pattern doesn't have lined running through it and the edges are sharper and more clear. You also only have to turn the axle one time to make one full turn of the ring gear, and the gear has more resistance when turnig this way. You can do it by yourself wothout anyone having to add resistance for you. I've tried it every way that there is and for me it is clearly easier to read the pattern when you turn everything with an axle.
It turns out that I had to make an adjustment to the backlash and lowered the pinion shim from 0.028" to 0.025". It's actually the lowest shims I can put in because of the combos that came in my kit.
Here are the drive and coast sides with the adjustments. Some literature says that this is acceptable, others say less shims. BGH what do you think? I did use the axle rotation method.
It looks like the pinion is a little deep to me. Notice how the pattern on the drive side is slightly tapered toward the root of the tooth. I would remove about .002 from the pinion shim and try again.
The status of my last post was I rechecked the backlash and it was 0.013" (too high). As a result I moved the carrier (ring) 0.004 towards the pinion gear. This got my backlash down to 0.009", but changed my pattern, so I lessened the pinion shims down to 0.025", which got the pattern I show in the last post. I have to go to the dealer and get an 0.022 - 0.023 shim as I can't currently get that with the shim pack that came with my bearing kit.
Also to clarify this is a brand new Eaton posi carrier and Summit ring and pinion (3.55:1) if this means anything.
My question now is do I need to be worried that my pinion shim is so thin that it can be easily damaged. Again this car is for street not for racing. This is my first rebuild so the help so far is much appreciated !!
I got sick of trying to read an unclear pattern, so cleaned thoroughly,lightly smeared only 3 teeth. Then put the cordless drill on the input nut and as Orville said to wilbur"Let er fly bro" Hold that on there for ten seconds or so flat out,you'll have something to read :evil:
Funny you say that. I thought I was the only one to figure that out. Works real good for me too. 1/2 Cordless Drill, 1/2 adapter, big socket! Makes good patterns I think. Maybe it doesn;t matter what way you do it as long as its the same way every time.
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