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pinion gear assembly (how to shim)

17K views 39 replies 8 participants last post by  bugget_jr 
#1 ·
Hi, I got a pontiac 8,2" 10-bolt b-o-p axle in my firebird-67, and I bought a differential, ring gear and pinion gear. The ring and pinion gear have not the original ratio so I have to "re-shim" those when assembling the axle.

But I kind of got stuck at the beginning thus I don�t know the proper way to shim out the pinion gear. The inner bearing of the pinion gear is really hard to assemble, It�s requires tapping on the bearing, but if I do this it will be really hard to assemble more shims if it�s required.

So the question is: How do I assemble shims and bearings in a proper way (Observe that I gonna have to assemble more shims later, so it�s not the final assemble)?

Grateful for all help I can get :)
 
#2 ·
Use a differential case spreader, you can probably borrow or rent one from NAPA, Advance Auto, and other parts stores. You can also make your own if you have a small welder. Google it. Look here and here to see what they look like, not cheap to buy...
 
#4 · (Edited)
thanks. I also wonder about backlash. Mostly about the differential side gear backlash that I´ve seen people do on video (on non-BOP axles). I think I know how to measure it but not how much backlash I should have, and how to correct it. I have a new differential but the old gears, so do I have to check this? I´ve googled it with no success.

Also anyone know what backlash I should have on ring gear to pinion gear? I´ve read on internet and found that it should be 0.005" to 0.009" but I also found on other sites that it should be .006" to .010". But either way it just a guide-line for a proper pattern check, right?
 
#5 ·
You will have to check and adjust backlash by doing the following:

Take the diff without the ring gear mounted and install in housing with bearings.

Find the total shim height that makes the carrier bearing preload about zero, ie you can pull the carrier in and out with the shims installed but it takes some effort.

Add .008" to the shim height you determined to achieve carrier bearing preload.

Divide the total shim height into two about equal shims and mock up total assembly with pinion and ring gear installed.

Check that the pattern on the coast side of the ring gear is basically centered on the tooth and that the ring gear backlash is .008-.012".
 
#6 ·
Your inner Pinion brg should be BCA#HM89449. Buy a Extra brg and put a sanding wheel on a die grinder and hone just enough off the ID that the Brg will slide on and off.

During your initial set up leave your Seal and crush sleeve out and just set the pinion preload with the nut. Now you can play with your pinion depth and backlash without going thru crush sleeves.

You can start with your original pinion and carrier shims to get in the ball park and adjust from there.

When you get a good pattern pull it apart 1 more time and install the seal and crush sleeve. Remember to keep your preloads and backlash the same during the setup so your final result stays the same.
 
#9 · (Edited)
I was to begin assembling the rear end to day but was really worried. Because I´m a beginner I´ve got a really hard time to figure out what specifications I should follow. Is this specifications something I could follow http://www.cardomain.com/ride/2043632/1970-pontiac-lemans/page-9#20436320232 (both on pinion preload, backlash, ring gear torque and cap torque)?

I´m currently stuck at the preload drag of the pinion nut. According to the link above it should be a drag between 12-15 lbs (that´s the same as lb-ft, right?). Can that be right? And if it is, should I use this preload drag on both the measuring stage and the final stage?

If the specifications above isn´t reliable is there someone out there knowing where to get some reliable specifications, or maybe can tell me?
 
#10 ·
bugget_jr said:
I was to begin assembling the rear end to day but was really worried. Because I´m a beginner I´ve got a really hard time to figure out what specifications I should follow. Is this specifications something I could follow http://www.cardomain.com/ride/2043632/1970-pontiac-lemans/page-9#20436320232 (both on pinion preload, backlash, ring gear torque and cap torque)?

I´m currently stuck at the preload drag of the pinion nut. According to the link above it should be a drag between 12-15 lbs (that´s the same as lb-ft, right?). Can that be right? And if it is, should I use this preload drag on both the measuring stage and the final stage?

If the specifications above isn´t reliable is there someone out there knowing where to get some reliable specifications, or maybe can tell me?
NOT THE SAME.. it needs to be INCH pounds of rotating preload.

So tighten the pinion nut till it take's 12/15 inch pounds to rotate the pinion.
 
#12 ·
bugget_jr said:
should I use this preload drag on both the measuring stage and the final stage?

If the specifications above isn´t reliable is there someone out there knowing where to get some reliable specifications, or maybe can tell me?
Keep all your preloads the same during initial set up and final assy. This will help with your pattern staying the same when you get to final assy.
 
#13 ·
thanks again. How about the side-bearings preload? Should I adjust it after the gear pattern check, is that possible? How do I know when I got the correct side-bearings preload?

As I understand it from other internet sources: if I have a pinion preload of 15 lb-in then I should set the side-bearing preload such that the preload drag on the pinion is 53 lb-in (with a gear ratio of 3.55 (15 times 3.55 = 53)).

and again, thank you for all help. Really appreciate it. :)
 
#14 ·
bugget_jr said:
thanks again. How about the side-bearings preload? Should I adjust it after the gear pattern check, is that possible? How do I know when I got the correct side-bearings preload?

As I understand it from other internet sources: if I have a pinion preload of 15 lb-in then I should set the side-bearing preload such that the preload drag on the pinion is 53 lb-in (with a gear ratio of 3.55 (15 times 3.55 = 53)).

and again, thank you for all help. Really appreciate it. :)
Do you have the pinion in the housing and have you tried setting the carrier in the housing yet? If so.. how tight does the carrier fit in the housing?
 
#15 ·
I´ve assembled the pinion and tried to assemble the differential with the orginal shims but it wouldn´t fit. Then I re-shimed it so the shims was about 0.04 inch less than original. With those shims it would fit if I tap them in place but it would also fit so well that it´s kind of impossible do take the differential out.
 
#16 ·
bugget_jr said:
I´ve assembled the pinion and tried to assemble the differential with the orginal shims but it wouldn´t fit. Then I re-shimed it so the shims was about 0.04 inch less than original. With those shims it would fit if I tap them in place but it would also fit so well that it´s kind of impossible do take the differential out.
When the Carrier Brg preload is correct.. You will have to pry the carrier out of the housing. If it's to loose the carrier Brg race's will spin in the housing and you will have problems.
 
#17 ·
Ok, so I have tried out all steps now and I think the shim thickness behind the pinion head bearing is correct because it has a equal lenght to the toe on both the drive and coast side. The problem now is that it´s not centered, because both the drive and coast side have to come closer to the heel. And the sources I could find says that for a face-milled gear (that´s what I have) I have to adjust this with increasing the backlash, but I have now increased the backlash from 0.007 to 0.013 and it hasn´t changed. Have I misunderstood this? What´s the problem?
 
#21 · (Edited)
Here is pictures, but I have a very bad camera as you may see so I don´t know if you can get something out of it. But if I describe these pictures which is as the gears is set up now: At the coast side the tooth starts at the edge of toe and travels up, at the drive side the tooth starts about 0.2 inch from toe (quite centered but a bit close to toe). The BL is now 0.011 inch and the recomended org. BL is from 0.005-0.009 for firebird -67.
this is the coast side.


this is the drive side.
 
#25 ·
Pinion depth is way too deep. Take about .010 out of the pinion shim and try again. Keep the backlash at about .008 at all times until you get the pinion depth right. Then you can fine tune the backlash. Also, try to get the pictures in focus a little better. It's hard to see details about the pattern when the picture isn't clear.
 
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