thad
02-11-2009, 11:28 PM
This may be of use If you have an aftermarket differential or if you are just swapping an OEM unit to another carrier.
This Is not a write up on removal and installation of a complete Rear differential and Carrier. Be Warned this can be somewhat involved.
There are two ways to select shims for a new diff /carrier combo, the first uses a formula that can be found in the FSM and the numbers printed or stamped on the factory components, the second method requires measurement and a bit of trial and error. In this write up I will be assuming that the new unit is being installed into a carrier with the pinion height and pre-load previously set.
What you need:
-Hand tools, wrenches, etc.
-impact gun and impact sockets, 17mm and 27mm
-well calibrated torque wrench that will read as low as 1in-lb.
-socket adapter to put the 27mm on the torque wrench
-dial gauge and or calipers
-paper and pen
-extra shims
First get your parts all together, choose which bearings you're going to use on the differential, or use new bearings, If you are reusing bearings, match them to their retainers. NOTE: if you have bearings that have not yet been installed on the diff, now is the best time to measure them. You'll also want to match the Crown (ring) Gear to the pinion, so take the one that came with the pinion you are going to use and install it on the new case, an impact gun should make short work of the 17mm bolts holding it all together, then put a towel around the diff case and mount it in a bench vice, torque the bolts down to 76ft-lbs.
You may not use them, but you will want to have an assortment of extra shims on hand, if you have the retainers from a donor diff, this should be enough, if you don't have access to any junkers, new shims can be had from Subaru for around $.87 ea. they come in .20mm .25mm .30mm .40mm and .50mm though .25 and .30 seem to be the most common.
So now that you've got all those shims, let's figure out how many you need and where they go.
http://img.photobucket.com/albums/v731/thadrobeck/IMG_3894.jpg
Method 1: Calculation.
This method came from the service manual for the 00-01 2.5 RS w/ R160 LSD but does apply to other models, this method is however specific to carriers using shimmed side retainers, NOT FOR threaded style retainers.
I don't consider this method to be all that reliable and after shims are chosen, the rotating resistance, backlash and run-out should still be confirmed.
There are two reasons I don't regard this method as totally reliable. the first is that, it assumes all parts are new and have no wear, second is that, in my albeit limited experience with Subaru diffs, I've yet to see one with ALL the reference numbers there.
with that said the method goes as follows.
T1 is the total thickness of the shims on the left side (Ring gear side)
T2 is the total thickness of the shims on the right side (not ring gear side)
A and B are the reference numbers on the right and left side of the diff Carrier
http://img.photobucket.com/albums/v731/thadrobeck/IMG_3870.jpg
you can see in this picture where they probably ought to be.
C and D are reference numbers stamped on the diff case. again, they may or may not be there, here's what they should look like
http://img.photobucket.com/albums/v731/thadrobeck/IMG_3876.jpg
G1 and G2 are reference numbers stamped on the side retainers, I can't find info on which is left and which is right, but all the retainers I've seen have had the same number left and right, the number is stamped next to the raised "G" , here's the tricky part, some years use only a "6", or is it a "9", it depends on which direction it was stamped in relation to the "G" I've been unable to find consistent examples to confirm which way is "up"
if there is no number, use 0
It should look like this
http://img.photobucket.com/albums/v731/thadrobeck/IMG_3881.jpg
For E and F, you will need to measure the width of the differential side bearing and find the difference between the actual measurement and the standard width of 20.0mm.
http://img.photobucket.com/albums/v731/thadrobeck/IMG_3885.jpg
E is left and F is right.
Example: if you measure the right bearing and it is 19.81mm then you subtract that from the std. of 20.0mm to get F=19
Now then, for the formula.
T1=(A+C+G1-D)x 0.01+0.76-E
and
T2=(B+D+G2)x0.01+0.76-F
Crunch that and you'll get the desired shim thickness.
With the Appropriate shim thickness and placement, pre-load, backlash and run-out should all be within spec, but lets not assume.
Method 2: Measure and test.
You can get a pretty good Idea of where you want to be just by looking at the total shim thickness and shim placement of the diff case that you are replacing. You may even want to keep everything as it was for your initial measurements.
First thing you want to know is your total shim thickness including right and left retainer shims.
to figure this out, take the diff case out of the carrier. now put the 27mm socket on your inch pounds torque wrench and set the socket on the pinion nut at the front end of the diff carrier
http://img.photobucket.com/albums/v731/thadrobeck/IMG_3889.jpg
spin it a few times with consistent speed and pressure till you can get a somewhat reliable reading of the torque required to spin the pinion, now reinstall the diff with the shims as they were previously arranged.
spin it again. you are looking for an increase in resistance greater than .84 in-lbs. but not exceeding 5.16 in-lbs. Note, you may be within spec on pre-load, but still loose on run-out so you may have to reset it after measuring backlash and run-out. add or remove shims till you get the right reading.
once you are happy with the rotating resistance numbers, you have your total shim thickness.
Next up is run-out, you'll measure this with a dial gauge or caliper set stationary on the carrier perpendicular to the ring gear. you will be measuring the distance between the carrier and the ring gear on both the right and left sides. With your measuring instrument in place, push on the diff case and ring gear left and right, it should have little to no lateral play. the max spec is .05mm. If you have too much play, step up the shim thickness in small increments.
Now you will need to get the appropriate shims to the side where they can do the most good.
you will check this by measuring backlash and looking at the footprint.
the manual calls for "red lead" to be applied to three or four teeth on the crown gear, I use All purpose Grease to similar effect.
file:///C:/DOCUME%7E1/Thad/LOCALS%7E1/Temp/moz-screenshot.jpgfile:///C:/DOCUME%7E1/Thad/LOCALS%7E1/Temp/moz-screenshot-1.jpgfile:///C:/DOCUME%7E1/Thad/LOCALS%7E1/Temp/moz-screenshot-2.jpghttp://img.photobucket.com/albums/v731/thadrobeck/IMG_3888.jpg
with the retainers torqued, rotate the pinion till the teeth with grease have meshed once, then examine the footprint, and refer to this chart for the appropriate action. Make sure to clean the ring and pinion of all residue before installing the diff on a vehicle.
http://img.photobucket.com/albums/v731/thadrobeck/difffootprint.jpg
since the pinion will be pre-adjusted for this procedure, only pay attention to which way the ring gear needs to move.
Once you have the foot print you are looking for, check the backlash.
This test is similar to run-out, but instead of lateral play, you are looking for play between the ring and pinion. This is done by placing your measuring instrument inline with the ring gear against a tooth. with the pinion held stationary, wiggle the ring gear up and down and measure how far it moves. minimum is .1mm and max is .2mm. Excessive backlash is easily identified by a loud clacking between the ring and pinion when you turn the pinion quickly one way and then the other. A diff with the proper backlash setting will have very little operating noise.
That's all there is to it, with pre-load, lash and run-out within spec, you are ready to close the carrier and put it on the car.
happy motoring.
-Thad-
This Is not a write up on removal and installation of a complete Rear differential and Carrier. Be Warned this can be somewhat involved.
There are two ways to select shims for a new diff /carrier combo, the first uses a formula that can be found in the FSM and the numbers printed or stamped on the factory components, the second method requires measurement and a bit of trial and error. In this write up I will be assuming that the new unit is being installed into a carrier with the pinion height and pre-load previously set.
What you need:
-Hand tools, wrenches, etc.
-impact gun and impact sockets, 17mm and 27mm
-well calibrated torque wrench that will read as low as 1in-lb.
-socket adapter to put the 27mm on the torque wrench
-dial gauge and or calipers
-paper and pen
-extra shims
First get your parts all together, choose which bearings you're going to use on the differential, or use new bearings, If you are reusing bearings, match them to their retainers. NOTE: if you have bearings that have not yet been installed on the diff, now is the best time to measure them. You'll also want to match the Crown (ring) Gear to the pinion, so take the one that came with the pinion you are going to use and install it on the new case, an impact gun should make short work of the 17mm bolts holding it all together, then put a towel around the diff case and mount it in a bench vice, torque the bolts down to 76ft-lbs.
You may not use them, but you will want to have an assortment of extra shims on hand, if you have the retainers from a donor diff, this should be enough, if you don't have access to any junkers, new shims can be had from Subaru for around $.87 ea. they come in .20mm .25mm .30mm .40mm and .50mm though .25 and .30 seem to be the most common.
So now that you've got all those shims, let's figure out how many you need and where they go.
http://img.photobucket.com/albums/v731/thadrobeck/IMG_3894.jpg
Method 1: Calculation.
This method came from the service manual for the 00-01 2.5 RS w/ R160 LSD but does apply to other models, this method is however specific to carriers using shimmed side retainers, NOT FOR threaded style retainers.
I don't consider this method to be all that reliable and after shims are chosen, the rotating resistance, backlash and run-out should still be confirmed.
There are two reasons I don't regard this method as totally reliable. the first is that, it assumes all parts are new and have no wear, second is that, in my albeit limited experience with Subaru diffs, I've yet to see one with ALL the reference numbers there.
with that said the method goes as follows.
T1 is the total thickness of the shims on the left side (Ring gear side)
T2 is the total thickness of the shims on the right side (not ring gear side)
A and B are the reference numbers on the right and left side of the diff Carrier
http://img.photobucket.com/albums/v731/thadrobeck/IMG_3870.jpg
you can see in this picture where they probably ought to be.
C and D are reference numbers stamped on the diff case. again, they may or may not be there, here's what they should look like
http://img.photobucket.com/albums/v731/thadrobeck/IMG_3876.jpg
G1 and G2 are reference numbers stamped on the side retainers, I can't find info on which is left and which is right, but all the retainers I've seen have had the same number left and right, the number is stamped next to the raised "G" , here's the tricky part, some years use only a "6", or is it a "9", it depends on which direction it was stamped in relation to the "G" I've been unable to find consistent examples to confirm which way is "up"
if there is no number, use 0
It should look like this
http://img.photobucket.com/albums/v731/thadrobeck/IMG_3881.jpg
For E and F, you will need to measure the width of the differential side bearing and find the difference between the actual measurement and the standard width of 20.0mm.
http://img.photobucket.com/albums/v731/thadrobeck/IMG_3885.jpg
E is left and F is right.
Example: if you measure the right bearing and it is 19.81mm then you subtract that from the std. of 20.0mm to get F=19
Now then, for the formula.
T1=(A+C+G1-D)x 0.01+0.76-E
and
T2=(B+D+G2)x0.01+0.76-F
Crunch that and you'll get the desired shim thickness.
With the Appropriate shim thickness and placement, pre-load, backlash and run-out should all be within spec, but lets not assume.
Method 2: Measure and test.
You can get a pretty good Idea of where you want to be just by looking at the total shim thickness and shim placement of the diff case that you are replacing. You may even want to keep everything as it was for your initial measurements.
First thing you want to know is your total shim thickness including right and left retainer shims.
to figure this out, take the diff case out of the carrier. now put the 27mm socket on your inch pounds torque wrench and set the socket on the pinion nut at the front end of the diff carrier
http://img.photobucket.com/albums/v731/thadrobeck/IMG_3889.jpg
spin it a few times with consistent speed and pressure till you can get a somewhat reliable reading of the torque required to spin the pinion, now reinstall the diff with the shims as they were previously arranged.
spin it again. you are looking for an increase in resistance greater than .84 in-lbs. but not exceeding 5.16 in-lbs. Note, you may be within spec on pre-load, but still loose on run-out so you may have to reset it after measuring backlash and run-out. add or remove shims till you get the right reading.
once you are happy with the rotating resistance numbers, you have your total shim thickness.
Next up is run-out, you'll measure this with a dial gauge or caliper set stationary on the carrier perpendicular to the ring gear. you will be measuring the distance between the carrier and the ring gear on both the right and left sides. With your measuring instrument in place, push on the diff case and ring gear left and right, it should have little to no lateral play. the max spec is .05mm. If you have too much play, step up the shim thickness in small increments.
Now you will need to get the appropriate shims to the side where they can do the most good.
you will check this by measuring backlash and looking at the footprint.
the manual calls for "red lead" to be applied to three or four teeth on the crown gear, I use All purpose Grease to similar effect.
file:///C:/DOCUME%7E1/Thad/LOCALS%7E1/Temp/moz-screenshot.jpgfile:///C:/DOCUME%7E1/Thad/LOCALS%7E1/Temp/moz-screenshot-1.jpgfile:///C:/DOCUME%7E1/Thad/LOCALS%7E1/Temp/moz-screenshot-2.jpghttp://img.photobucket.com/albums/v731/thadrobeck/IMG_3888.jpg
with the retainers torqued, rotate the pinion till the teeth with grease have meshed once, then examine the footprint, and refer to this chart for the appropriate action. Make sure to clean the ring and pinion of all residue before installing the diff on a vehicle.
http://img.photobucket.com/albums/v731/thadrobeck/difffootprint.jpg
since the pinion will be pre-adjusted for this procedure, only pay attention to which way the ring gear needs to move.
Once you have the foot print you are looking for, check the backlash.
This test is similar to run-out, but instead of lateral play, you are looking for play between the ring and pinion. This is done by placing your measuring instrument inline with the ring gear against a tooth. with the pinion held stationary, wiggle the ring gear up and down and measure how far it moves. minimum is .1mm and max is .2mm. Excessive backlash is easily identified by a loud clacking between the ring and pinion when you turn the pinion quickly one way and then the other. A diff with the proper backlash setting will have very little operating noise.
That's all there is to it, with pre-load, lash and run-out within spec, you are ready to close the carrier and put it on the car.
happy motoring.
-Thad-