I am breaking into some new teritory by trying to rebuild my 12 posi rearend partially by myself. I have a retired mechanic that is going to setup the rearend for me for free, well maybe a 12 pack. Anyhow I told him that I would do as much as I could by myself so that when he came over it should not take as long. My question is about the center section. I bought a new GM clutch pack, pin, carrier bearings, rounded bushing that sits behind the spider gears. I soaked the clutches before installing. I reinstalled 2 shims behind each shaft gear. The spider gears look new, maybe from a previous persons rebuild. Is there any measurements to anything inside the center section? Should there be shims behind the shaft gears? I am having trouble getting the spider gears in. Are these shims making it too tight? I bought this rearend from someone that raced it with a 6:?? gear, so did they have the shims in for a "Tight" setup. Thanks for any info, pionters etc.
68 12 bolt rebuild ????
68Zgarage
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I am breaking into some new teritory by trying to rebuild my 12 posi rearend partially by myself. I have a retired mechanic that is going to setup the rearend for me for free, well maybe a 12 pack. Anyhow I told him that I would do as much as I could by myself so that when he came over it should not take as long. My question is about the center section. I bought a new GM clutch pack, pin, carrier bearings, rounded bushing that sits behind the spider gears. I soaked the clutches before installing. I reinstalled 2 shims behind each shaft gear. The spider gears look new, maybe from a previous persons rebuild. Is there any measurements to anything inside the center section? Should there be shims behind the shaft gears? I am having trouble getting the spider gears in. Are these shims making it too tight? I bought this rearend from someone that raced it with a 6:?? gear, so did they have the shims in for a "Tight" setup. Thanks for any info, pionters etc.
Yes, there is a procedure in setting the differential gear backlash.
One adjusts the backlash of each axle gear individually with both differential pinion gears, their thrust washers, pinion shaft, one axle gear, one set of clutches behind the associated axle gear, axle, and C-clip.
Install all items, pull out on axle shaft to remove the clutch pack slack, measure backlash from the pinion gear tooth. Add shims to clutch pack to adjust backlash for ? (.006-.012 inches?), I don't remember.
Disassemble the adjusted axle, reassemble other axle set and adjust for the same backlash figure of previous axle.
After backlash adjustment is done, assemble spring plates and springs (two plates and four springs), squeeze ( Good Luck, lots of kinetic energy waiting to be released!) and insert assembly into carrier using a rubber hammer.
You can use the 75 lb (yellow) springs (larger wire diameter vs. green, approx 6 coils) from the dealer. OE is 40 lb. (green) spring, small wire diameter, approx 8-9 coils. At least this was the case several years ago.
Maybe others here, i.e., bgh, might know the differential pinion/axle gear backlash spec.
One adjusts the backlash of each axle gear individually with both differential pinion gears, their thrust washers, pinion shaft, one axle gear, one set of clutches behind the associated axle gear, axle, and C-clip.
Install all items, pull out on axle shaft to remove the clutch pack slack, measure backlash from the pinion gear tooth. Add shims to clutch pack to adjust backlash for ? (.006-.012 inches?), I don't remember.
Disassemble the adjusted axle, reassemble other axle set and adjust for the same backlash figure of previous axle.
After backlash adjustment is done, assemble spring plates and springs (two plates and four springs), squeeze ( Good Luck, lots of kinetic energy waiting to be released!) and insert assembly into carrier using a rubber hammer.
You can use the 75 lb (yellow) springs (larger wire diameter vs. green, approx 6 coils) from the dealer. OE is 40 lb. (green) spring, small wire diameter, approx 8-9 coils. At least this was the case several years ago.
Maybe others here, i.e., bgh, might know the differential pinion/axle gear backlash spec.
Joined
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6,096 Posts
The 2 large gears on the sides are the axle gears. The 2 smaller gears are the pinion gears. Those are thrust washers that go behind the pinion gears, not shims. They are very important and you only use 1 washer behind each gear. The shims go between the clutch pack and the differential case. The shims should be the very first thing that goes into the case. Start with the shims that were originally in the case and make adjustments from there. You have probably figured out how to assemble the clutch plates on the axle gears with the wear pads on the ears of the clutches. Install them and then put the pinion gears in one at a time and rotate them into position. After you get the pinion gears in place, slide the thrust washers in behind them. You will probably have to turn the gears a little to get them in. If they go in easily then it is too loose. If they are hard to get in then you may be all right. When you get them in look through the hole and see of the gears are lined up with the holes in the case. If the gears look like they are offset to one end of the case then you need to add more shim to that side and take some out of the other side to line up the holes. When you get them set correctly, slide the pinion shaft in place. Use an axle in one side to hold the unit. Try to turn the case while holding the axle still. If it is easy to turn then the clutches are not tight enough. If you can not turn it then it is probably tight enough. When you get it set tight then you can install the preload plates and springs. You will have to remove the shaft to get the plates and springs in.
Be sure you get the bearings seated completely when you press them on.
Be sure you get the bearings seated completely when you press them on.
Thanks for the info guys, that's what I needed. I got the springs from GM and they gave me the green ones. It is going behind a 302, M22 setup with 4:56 gears. I don't think I'll ever put slicks on it but maybe some sticky street tires. I did get the carrier bearings pressed on until they seated. I read the directions from Richmond and they said to set the pinion shaft so much distance from the center line of the ring gear and shim accordingly. My friend is going to be doing that part, but while we are on the subject, what is the best way to get this measurement?
Pinion depth is measured with a pinion depth gauge, a special tooling setup for this purpose and for a specific brand of housing, or an universal fit kit for all brands. Most major tool companies have them.
Another method to find the acceptable pinion depth is to re-use the original shim between the pinion gear and its bearing. Install this original shim, and the old bearing with the ID honed out for a slip-fit on the pinion gear, and the new pinion gear into the housimg. Assemble the carrier, set it into place inside the housing, adjust for ring gear backlash, then coat the teeth for a pattern in both drive and coast directions. View the coating as to placement of the pinion, and adjust the pinion shim thickness for proper tooth pattern.
When pattern looks good, then remove the honed bearing, replace it with the new bearing, and final assemble the rear axle.
CRS ( Can't Remember Squat) has taken over with me, there is a ton of info on this topic in this section, do a search. Carrier bearing preload, pinion preload, backlash, whether to adjust preload and backlash with or without oil, break-in procedures, etc., etc.
It definately will be a full afternoon's worth of work. Suck up all the info given it'll prove invaluable later.
Another method to find the acceptable pinion depth is to re-use the original shim between the pinion gear and its bearing. Install this original shim, and the old bearing with the ID honed out for a slip-fit on the pinion gear, and the new pinion gear into the housimg. Assemble the carrier, set it into place inside the housing, adjust for ring gear backlash, then coat the teeth for a pattern in both drive and coast directions. View the coating as to placement of the pinion, and adjust the pinion shim thickness for proper tooth pattern.
When pattern looks good, then remove the honed bearing, replace it with the new bearing, and final assemble the rear axle.
CRS ( Can't Remember Squat) has taken over with me, there is a ton of info on this topic in this section, do a search. Carrier bearing preload, pinion preload, backlash, whether to adjust preload and backlash with or without oil, break-in procedures, etc., etc.
It definately will be a full afternoon's worth of work. Suck up all the info given it'll prove invaluable later.
Joined
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6,096 Posts
I don't like the pinion depth tools. They are only accurate to about +/- .003, which is not close enough. You could use one to get you close and then adjust from there, but I just go by the contact pattern and forget the tool.
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