12 bolt ring and pinion question

[mrobvious34]

I have a question for anyone good with setting up a ring and pinion. I have a 67 C10 and I swapped out the worn out 3.07s and open diff for a Yukon limited slip and 3.73s. When setting up my pinion, the gear was engraved with a depth of 2.751. I got it dead on and my backlash set at .006. When checking the mesh with gear marking compound it indicated that the pinion was too far from the ring and need more shims between the pinion and bearing. I added more shims and got the gear pattern looking good and backlash set at .007. My question is, is it ok that my pinion depth isn’t what the manufacturer says it should be as long as my gear pattern looks good? I ended up with a pinion depth of 2.730 instead of 2.751. Second question, when did gm switch to the wider rear end? I got moser axles for a 67 but they are too short. I’m guessing the rear has been swapped at some point but I can’t find any ID numbers on the axle

[mrobvious34]

These are pictures of the initial check, before I added more shims

[americanmusc1e]

Originally Posted by mrobvious34

These are pictures of the initial check, before I added more shims

You usually can't go wrong following what the pattern tells you. What brand ring and pinion?

I think the rear end width was a mid 1970 change. They look identical. you really have to measure them.

[Ironangel]

The pattern is not bad but could be better. You probably have a later model wider axle, measure your existing axles. Pinon bearing thicknesses were right around .030" and no it's not unusual to have to add .010". Unmolested later model carriers used one piece cast iron shims that were faced to fit, usually about .250" thick. Using the Yukon Supershim packs you can move the carrier towards the pinion to center the pattern on the ring. You didn't indicate the amount of shim you have under the pinion? Did you record the thickness of the existing shim(s) under the original pinion when you dismantled the axle? Pinion depth is a good reference but will vary depending on the pattern and pinion shim thickness. You have it very close, close enough to run but I'd try .050" less pinion shim which is .050" more pinion depth and shim the carrier away or to the left of the pinion and check pattern and backlash. Read the bottom of page 7... https://www.randysworldwide.com/web_...l_Complete.pdf

[pjmoreland]

I may be wrong about this, but I believe the wider rear ends had GM54 cast into the center housing, whereas the narrower design was GM51. That's how it was on a wide 1970 housing I sold recently vs. a 1968 housing I purchased to replace it. Measuring the width of the rear end would be the conclusive way to tell.

https://www.67-72chevytrucks.com/vbo...d.php?t=578793

Copied from the thread below:

axle width is 55.5 wide with 30.5 long axles on the narrow rear end. earlier rear end
axle width is 57 wide with 31 5/16 long axles on the wider rear end. later rear end

http://67-72chevytrucks.com/vboard/s...d.php?t=640514

[mrobvious34]

Originally Posted by Ironangel

The pattern is not bad but could be better. You probably have a later model wider axle, measure your existing axles. Pinon bearing thicknesses were right around .030" and no it's not unusual to have to add .010". Unmolested later model carriers used one piece cast iron shims that were faced to fit, usually about .250" thick. Using the Yukon Supershim packs you can move the carrier towards the pinion to center the pattern on the ring. You didn't indicate the amount of shim you have under the pinion? Did you record the thickness of the existing shim(s) under the original pinion when you dismantled the axle? Pinion depth is a good reference but will vary depending on the pattern and pinion shim thickness. You have it very close, close enough to run but I'd try .050" less pinion shim which is .050" more pinion depth and shim the carrier away or to the left of the pinion and check pattern and backlash. Read the bottom of page 7... https://www.randysworldwide.com/web_...l_Complete.pdf

The original pinion shim was .026, and this rear did have a single cast shim on each side of the carrier, one was .236 and the other was .242. When the pinion depth showed correct, I had .018 shim behind the pinion gear. I changed it to .030 shim and the pattern looks much better. I do not have a picture of the new pattern, but it is centered on both the coast and drive side.

[mrobvious34]

Originally Posted by americanmusc1e

You usually can't go wrong following what the pattern tells you. What brand ring and pinion?

I think the rear end width was a mid 1970 change. They look identical. you really have to measure them.

Im not sure what brand the ring and pinion are. I ordered a kit from quickperformance.com and it came with the yukon lsd, and gears in a red box with no labels or brand. Maybe their own in house brand?

[mrobvious34]

Originally Posted by pjmoreland

I may be wrong about this, but I believe the wider rear ends had GM54 cast into the center housing, whereas the narrower design was GM51. That's how it was on a wide 1970 housing I sold recently vs. a 1968 housing I purchased to replace it. Measuring the width of the rear end would be the conclusive way to tell.

https://www.67-72chevytrucks.com/vbo...d.php?t=578793

Copied from the thread below:

axle width is 55.5 wide with 30.5 long axles on the narrow rear end. earlier rear end
axle width is 57 wide with 31 5/16 long axles on the wider rear end. later rear end

http://67-72chevytrucks.com/vboard/s...d.php?t=640514

The cast number on the center housing on mine says GM66. And now that i think about it, the axles appear to be original and they are 5 lug, a 67 should have been 6 lug. Another indication that it is indeed a later one

[Ironangel]

Originally Posted by mrobvious34

The cast number on the center housing on mine says GM66. And now that i think about it, the axles appear to be original and they are 5 lug, a 67 should have been 6 lug. Another indication that it is indeed a later one

If your pattern looks good, set the pinion preload
and then the backlash. Setting the pinion preload can be tricky, you need a dial inch pound torque wrench. Holding the yoke while you make slight increases in tightening the pinion nut until you reach 13-15 inch pounds of preload which is resistance. It's very easy to go to far so once that nut gets tight you still have to crush the sleeve about 3/32" more to achieve the correct preload. Then set the backlash...Did you get your initial backlash of .006" using the cast iron shims? It would be surprising and a stroke of luck if you did, thats why I suggested the Super Shim packs, they allow any thickness sandwiched between two thick protective outer layer shims allowing you to tap the shims in place with a nylon or hard plastic drift. Getting the carrier tight minimizes deflection under load. I actually take a preload measurement of the carrier by adding 10 -15 inch pounds to the pinion preload to read anywhere between 20 - 30 total inch pounds on the 12-bolts. Hope I didnt overwhelm or confuse you, sounds like you have a good handle on the situation, good luck. Axle width is 55.5 wide with 30.5 long axles on the narrow rear end. And
axle width is 57 wide with 31 5/16 long axles on the wider rear end. later rear ends...

[mrobvious34]

Originally Posted by Ironangel

If your pattern looks good, set the pinion preload
and then the backlash. Setting the pinion preload can be tricky, you need a dial inch pound torque wrench. Holding the yoke while you make slight increases in tightening the pinion nut until you reach 13-15 inch pounds of preload which is resistance. It's very easy to go to far so once that nut gets tight you still have to crush the sleeve about 3/32" more to achieve the correct preload. Then set the backlash...Did you get your initial backlash of .006" using the cast iron shims? It would be surprising and a stroke of luck if you did, thats why I suggested the Super Shim packs, they allow any thickness sandwiched between two thick protective outer layer shims allowing you to tap the shims in place with a nylon or hard plastic drift. Getting the carrier tight minimizes deflection under load. I actually take a preload measurement of the carrier by adding 10 -15 inch pounds to the pinion preload to read anywhere between 20 - 30 total inch pounds on the 12-bolts. Hope I didnt overwhelm or confuse you, sounds like you have a good handle on the situation, good luck. Axle width is 55.5 wide with 30.5 long axles on the narrow rear end. And
axle width is 57 wide with 31 5/16 long axles on the wider rear end. later rear ends...

That makes perfect sense, I appreciate your help. I did get an install kit with new bearing, races, seals, pinion nut, and a boat load of shims. I did not reuse the cast iron shims. I used the thick protective shims with the small shims sandwiched inside. I got it tight enough that i had to use a soft hammer to tap them in, but ramrod them in. My pinion bearing preload i got to 15 in/lbs rotational force. I bought a special tool that holds the yoke so that I could tighten the nut. You are right, that is very easy to go to far. I used a crush sleeve and I think next time I do it I would like to try a solid spacer instead. I am satisfied with how everything turned out, I was just more concerned about that fact that I had to set my pinion depth different that the manufactures reading in order to get a good pattern on the teeth. I guess theres only one way to really know, button it up and drive it. Im not hard on my stuff so im not worried about breaking anything, I just dont want to hear a howl. Which is the main reason i did this in the first place

[Ironangel]

Good job! Go easy on it and follow the break in procedure and it will give you many years of trouble free use. Make sure you use the "posi-additive" and change the lube out after the first 500 miles, with the additive. The phosphate coating on new gears actually aids in the breaking in period by helping the gears wear in. Gear howling is often attributed to loose backlash and or the pinion developing end play. You did good!