Need help reading 8 3/4 gear tooth pattern

[vdk2010]

It's my first time trying to rebuild a differential and so far it doesn't go that well for my sanity...

Can someone please help me read this tooth pattern?

It looks totally wrong to me. It's not a roundisch spot like in all the pictures in the FSM and the book I bought. I reaches completely from toe to heel...

Thanks for the help!

 

[CBODY67]

Were there any markings on the gears as to shims thicknesses needed for the installation? Or are you doing this from scratch, so to speak? I believe you can also use a dial indicator, too?

Basically, there are "side shims" and "pinion gear shims". The side shims move the ring gear laterally in the case, as the pinion shims move the pinion gear "in and out" in the case. There was also a "crush sleeve" which might have replaced the pinion shims in some cases, but I now seem to suspect the crush sleeve is now measured and replaced by a solid item of that thickness?

What gear ratio is being replaced? Same ratio or different from the orig? Just curious.

Just some thoughts,
CBODY67

 

[vdk2010]

It's just a rebuilt, so it's all stock, but has all new bearings and a crush sleeve eliminator.

I got the preload on the pinion gear right between 20-30 in. lb. with the eliminator!

First I added the same thickness shim than it had stock (.030) but that was not thick enought so I added another .011.

I had no problem setting the .006 - .008 initial backlash.
After that, according to the FSM, I'm supposed to tighten the adjusters equally in the same amount into the same direction to seat the carrier bearings.
My understanding is, that I have to tighten both adjusters an equal amount on both sides until I achieve backlash between .0005 - .0015 to seat the carrier bearings.
Which is not easy because every time I move the adjusters, I have to move them a full notch in, in order to get the locks on later.

After that I'm supposed to keep on tighten the ring gear tooth side adjuster in until I'm back to the correct .006 - .008 backlash. But to do that I had to use a big pipe on the spanner to spin the adjuster and that doesn't feel right...

 

[john-9]

what was the reason for the rebuild on your stock center section was it making noise or ?? . if you did a gear change the pinion depth shim will change ,,,, if this is the stock gear set up from the factory DO NOT change the pinion depth shim from the original one , to set the correct backlash snug the carrier bolts down and loosen off the adjuster/spanners for your carrier bearings ,, now start to tighten the driver side spanner (ring gear side ) as you do this rock the ring gear back and forth till you have NO backlash ( 0 ) between the ring gear and pinion , go slowly , making sure the opposite side spanner is still loose ,, once you reach that point of no backlash tighten the opposite side spanner until you reach the correct backlash . on the 8-3/4 differentials there are NO shims to adjust the carrier as stated above . 489 case factory pinion gear shims range from .028 - .032 . if you can go back to the .030 shim and post a picture of that gear pattern , what you have now is a decent pattern for used gear set ,trying to get the pattern shown in the manuals is for new gear sets.

 

[vdk2010]

what was the reason for the rebuild on your stock center section was it making noise or ?? . if you did a gear change the pinion depth shim will change ,,,, if this is the stock gear set up from the factory DO NOT change the pinion depth shim from the original one , to set the correct backlash snug the carrier bolts down and loosen off the adjuster/spanners for your carrier bearings ,, now start to tighten the driver side spanner (ring gear side ) as you do this rock the ring gear back and forth till you have NO backlash ( 0 ) between the ring gear and pinion , go slowly , making sure the opposite side spanner is still loose ,, once you reach that point of no backlash tighten the opposite side spanner until you reach the correct backlash . on the 8-3/4 differentials there are NO shims to adjust the carrier as stated above . 489 case factory pinion gear shims range from .028 - .032 . if you can go back to the .030 shim and post a picture of that gear pattern , what you have now is a decent pattern for used gear set ,trying to get the pattern shown in the manuals is for new gear sets.

The reason for the rebuild is the full restoration of my 1969 Imperial

The original pinion shim was destroyed during disassembly and in the rebuild kit from Doctor Diff were different Shims.
The original shim sat between the housung and the bearing race, the new ones are supposed to sit between the pinion and its inner bearing.

Initially I replaced the original shim with the exact amount of new shims, but the gear pattern was way off.

So I added anouther .011 shims which resulted in the gear tooth pattern in my first post.

But as mentioned before, the way until I was able to check the gear tooth pattern was horrible... Nothing worked as it should.
I had to use way too much force for my liking. (Don't know if that's normal, using a big pipe on the spanner to turn the adjuster in...)

I will try your procedure and see if it works better for me! Is it normal that the last step will take A LOT of force?

To set the correct backlash

• Snug the carrier bolts down and loosen off the carrier bearing adjusters.
  The FSM stated to just tighten 1 of the carrier bolts on each side?
• Start to tighten the driver side spanner (ring gear side).
  As you do, rock the ring gear back and forth till you have NO backlash ( 0 ) between the ring gear and pinion.
  Go slowly, making sure the opposite side spanner is still loose.
• Once you reach that point of no backlash, tighten the opposite side spanner until you reach the correct backlash.

If interested, you can find all the pictures I made so far from the rebuild of the center section in my Dropbox.

 

[john-9]

here are some photos of used gear rebuild patterns --- last photo is a new gear set pattern

 

[john-9]

snug both bolts down -- yes it will take some force to set the backlash but you have to have preload on those bearings -- been rebuilding differentials since 1975 and have had no issues yet. your pattern with the thicker shim looks very good i would be very tempted to go with it -- but try the .030 again just to make sure with the backlash set correctly. gear pattern is the final say in any gear set up.

 

[vdk2010]

snug both bolts down -- yes it will take some force to set the backlash but you have to have preload on those bearings -- been rebuilding differentials since 1975 and have had no issues yet. your pattern with the thicker shim looks very good i would be very tempted to go with it -- but try the .030 again just to make sure with the backlash set correctly. gear pattern is the final say in any gear set up.

Thanks for your help. I appreciate it!

The backlash was correct on my first try as well!
I'm going to redo everything using your procedure and see what results I will get and post pictures of the pattern here.
If it's not correct then, I will try to use the original .030 shims!

 

[vdk2010]

snug both bolts down -- yes it will take some force to set the backlash but you have to have preload on those bearings -- been rebuilding differentials since 1975 and have had no issues yet. your pattern with the thicker shim looks very good i would be very tempted to go with it -- but try the .030 again just to make sure with the backlash set correctly. gear pattern is the final say in any gear set up.

Ok, here are the gear tooth patterns measured in 4 different locations.

One location was slightly out of the desired .006 - .008 backlash. I don't know how problematic that is, but due to adjuster lock placement, I can't adjust it any more.

Backlash
Position #1 .0070
Position #2 .0055
Position #3 .0070
Position #4 .0080

Position #1

Position #2

Position #3

Position #4

 

[my5thmopar]

I've rebuilt several over the years. The photos @john-9 posted all look acceptable. That's what you're looking for. Pattern looks too deep to me but, maybe you didn't load the ring gear. Normally the coast side is what to look at on used gears.

 

[vdk2010]

I have not loaded the ring gear, no. I didn't know I had to. None of the guidelines I have (The FSM and a rebuild book) mention to do so.
So how do I load the ring gear correctly?

Another problem I had was that when I had the perfect backlash set, both the adjusters were in a position where I couldn't install the locks. Is it better to tighten or loosen the adjusters in this situation?
For the pattern above, I tightened them a bit.

 

[john-9]

to do a proper pattern check best to have the differential locked down in a vice or some type of fixture ,, wear a glove and keep pressure on the ring gear as you turn the pinion ,, loosen off the adjusters/spanners again and reset the ring gear side to just 0 backlash ,, rock the ring gear against the pinion slowly as you turn the spanner ,, do not jam the gears together ,,, when you get to 0 backlash check to see if the the spanner holes line up for the lock clip if not tighten the adjuster a bit more to fit the lock, now adjust the other side to set your preload and backlash .006-.008 see if the lock clip lines up ,, if not ALWAYS tighten to line up the lock . this may change the backlash slightly but nothing to worry about ,,.backlash is always measured at the tightest spot and should not vary by more than .003 between readings so your backlash figures you posted are very good. i always set the backlash to the lowest figure as when everything is run in during use the backlash will open up .

 

[vdk2010]

to do a proper pattern check best to have the differential locked down in a vice or some type of fixture ,, wear a glove and keep pressure on the ring gear as you turn the pinion ,, loosen off the adjusters/spanners again and reset the ring gear side to just 0 backlash ,, rock the ring gear against the pinion slowly as you turn the spanner ,, do not jam the gears together ,,, when you get to 0 backlash check to see if the the spanner holes line up for the lock clip if not tighten the adjuster a bit more to fit the lock, now adjust the other side to set your preload and backlash .006-.008 see if the lock clip lines up ,, if not ALWAYS tighten to line up the lock . this may change the backlash slightly but nothing to worry about ,,.backlash is always measured at the tightest spot and should not vary by more than .003 between readings so your backlash figures you posted are very good. i always set the backlash to the lowest figure as when everything is run in during use the backlash will open up .

This time I pressed a wood block against the ring gear to preload it while someone turned the pinion gear for me.

Backlash was almost identical on all 4 positions this time!

Position #1 .0065
Position #2 .0065
Position #3 .0065
Position #4 .0060


Position #1

Position #2

Position #3

Position #4

 

[vdk2010]

I was not satisfied with the last pattern so I reduced the pinion depth shims another .005" to .0036"

Backlash was pretty close to each other and in spec. on all 4 positions again!

Position #1 .0070
Position #2 .0075
Position #3 .0080
Position #4 .0065

I'm pretty happy with the pattern now. What do you think @john-9 ?

Position #1

Position #2

Position #3

Position #4

 

[john-9]

looks good on the coast side ,, drive side is ok for a used gear ,, what i am having trouble with is , if these gears were run with the .030 shim all those years and look to be in excellent shape you should not have had to make a shim change when you rebuilt it .would still like to see what the .030 shim pattern is now that you have the set up procedure worked out .. i think with the .030 original shim your drive side pattern would widen out a bit and coast should be the same ,but if what you show in the first photos at .030 those gears should have destroyed themselves,-- again you pattern looks to be excellent at .036 and if you are happy with it run it,,, i would.

 

[vdk2010]

Ok, so, I went with the .0036, removed the setup bearings, pressed on the final bearings and of course the pattern changed... Ideally I should install a thinner shim, but then I have to cut off the inner bearing again and buy another one
So the big question is now, is it still fine as is..? @john-9

Backlash was pretty close to each other and in spec. on all 4 positions again!

Position #1 .0070
Position #2 .0070
Position #3 .0075
Position #4 .0065

Position #1

Position #2

Position #3

Position #4

 

[john-9]

your coast pattern still looks excellent , and the drive side pattern will move up under load ,, shim changes on a 8-3/4 too much toe ( pattern towards inside of gear ) remove shim -- too much heel ( pattern towards outside of gear ) add shim ,,, all shim changes in increments of .003 to see a change in the pattern ,,,, only way to know for sure is to install and drive.----still do not understand why the original .030 shim would not work i have never had that issue on any factory original set up for the Chrysler 8-3/4 , 8.8 and 9 inch Ford , GM 10 and 12 bolts etc.

 

[vdk2010]

Thanks!
I have no idea why it was that much off with the original .030 shim thickness. It's always possible that I made some dump mistake in the beginning of this journey..!

I installed everything in the car today anyway just to get the car on it's own feet so she can go back to the paint shop asap. The pattern as is will for sure not hurt anything.
I will change the shims again later if neccessary.

What would be the indication for an improper pattern while driving?

 

[vdk2010]

 

[thethee]

I want to, no, I NEED to see this car in person one day. It is truly a work of art