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Rebuilding A GM 8.25 IFS Differential **56K Beware! Pic Heavy**


This is a discussion on Rebuilding A GM 8.25 IFS Differential **56K Beware! Pic Heavy** within the Gear Central forums, part of the High Performance Mods category!
I am going to try to cover the basics on rebuilding the front differential in a GM truck with the ...

Rear Gears| Front Diffs| Transmissions

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Old 01-01-2011, 10:21 PM
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Rebuilding A GM 8.25 IFS Differential **56K Beware! Pic Heavy**

I am going to try to cover the basics on rebuilding the front differential in a GM truck with the 8.25" IFS differential. I am doing a gear change but also a full rebuild while I have it apart.

Parts you'll need: Ring & Pinion Gear set, Master Install Kit, lock tabs (2)- (GM PN - 15588312)

Make sure to download the pdf attachment at the bottom of this post, it contains all torque specs you'll need and a few notes that I have found while doing this myself.

Tools needed: General hand tools, bearing pullers, slide hammer, shop press, dial indicator with magnetic base, inch pound bar type torque wrench, special spanner wrench: http://www.yukongear.com/ProductDeta...px?ProdID=5227

To start off place your diff over a 5 gallon bucket and drain the gear oil from it.

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Now place the diff up on a work bench, or the floor if it won't fit on your bench. Stand the diff up with the short shaft down and remove the bolts around the case.

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Remove the electric motor actuator by unscrewing then set aside.

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Now lay the diff over on it's side and place a slide hammer on the axle flange. Give it a few good wraps and the casing should split apart.

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With the case split in two, flip the section over with the short shaft pointing up. Lift the case up and the carrier may fall out. If not, which was my case, use your slide hammer on the axle flange and give it a few tugs up. This should lift the case free of the carrier.

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Flip the case over and using the handle of a ball pein hammer tap the stub axle out of the housing.

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The stub axle was held into the carrier by a small circlip, look down in the spline area of the carrier and you should see it in a groove.

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Using a long punch knock the stub axle seal out.

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This will give you access to the stub axle bearing, lock tab, adjuster and carrier bearing. Using a screwdriver or chisel pry the lock tab up enough to be free.

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Flip the case over and drive out the axle bearing with a punch.

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Now this is where my experience ( or lack of it) will help you. The adjusters should be driven out, towards the inside of the case. Using a brass drift hammer them out evenly. This will also allow you to replace the lock tabs. If the carrier bearing races have fallen out before you drive out the adjusters, take a measurement and write it down. This will help for setup down the road.

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How not to do it, but it won't hurt to do it this way. Just a few unnecessary steps is all.

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**I should have left the two pieces screwed together before driving them out. Learn from my mistakes**

Remove the pinion nut and drive the pinion out. Leave the nut screwed on a few threads until the yoke turns loose of the splines, then remove the nut and yoke. Finish driving the pinion out.

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Remove the pinion seal and outer bearing. For ease of removal, using a chisel fold over a portion of the lip of the seal. Then stick a pry bar in and roll the seal out, catching the bearing as the seal comes out.

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Using a long punch from the outside, drive the inner pinion bearing race out.

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Flip the case over and drive out the outer pinion bearing race.

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Remove the old ring gear from the carrier and remember these are left handed bolts.

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Using a gear puller remove the carrier bearings.

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I pulled the inner pinion bearing off to measure the factory shim, this gave me a starting point for the new gear set.

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Attached Files
File Type: pdf Front diff stuff.pdf (177.7 KB, 323 views)
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Old 01-03-2011, 08:20 PM
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Now you still need to strip down the long axle tube. Place it up on a bench and remove the 5 bolts holding the two cases together.

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Set it aside and remove the spring, shift fork and gears. Remember the order that you took them apart and don't lose the spring.



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Remove the stub shaft from the case and pull the small roller bearing out using a small internal bearing puller.

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Now flip the case over with the small end down, drive the bearing out of the adjuster. Then flip the case back over and drive out the adjuster assembly.

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Place the axle tube on the bench with the axle flange down. Remove the circlip, thrust washer and tabbed locating washer.

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Flip the housing back over and remove the axle completely.

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Using a pry bar, roll the axle seal out and then drive out the axle bearing.

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You now have a ton of parts to clean. Clean everything up spotless for re-assembly.

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Old 01-03-2011, 10:06 PM
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So now with all of the parts clean let's start re-assembling the differential. Take the long shaft housing and install the axle bearing and axle seal. Smear a little bearing grease on the lip of the seal after it's installed.

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Insert the axle shaft into the housing and flip it over, resting on the axle flange.

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Place your tabbed locating washer, thrust washer and circlip onto the axle. Make sure the circlip is properly seated in the groove of the axle splines.

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Prep your carrier by installing the ring gear and carrier bearings. Ring gear and bearings will probably need to be pressed on using a shop press or a block of wood and a hammer. Use Lock tite on the ring gear bolts and tighten to spec.

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Take your carrier bearing adjusters and install the roller bearings in both. Install new lock tabs, using a dab of grease to hold them in place, then drive the adjusters into place in both case halves. Set your distance on the adjusters back to about what they where when you removed them, this will just give you a starting point for setup.

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Install both carrier bearing races, also called cups, into the cases.

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Install the inner and outer pinion bearing cups.

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Old 01-03-2011, 10:44 PM
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If you are doing the front on your own you probably did the rear on your own. Using the inner pinion setup bearing, from your rear diff install/setup, and the factory thickness of shims on the pinion. Put the pinion into the case without a crush sleeve. Using the old outer pinion bearing, with the ID ground out for setup, install the bearing and yoke, washer and old pinion nut. Tighten up snug until you get about one revolution of spin out of the yoke when spun by hand.

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Place the assembled carrier into the case and snug up the bolts drawing the two halves together. Do not get too carried away tightening and put anything in a bind. If you need to loosen the adjusters as the case comes together do so.

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Once your case is together, remove the large plastic plug on the side of the case. This will give you access to the ring gear for setup checking.

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Setting back lash is a little different with the front diff. Place the diff on a good solid workbench, with a dial indicator reading the yoke. Yes I said reading from the yoke.

This takes some getting used to the feel to get right. Check back lash by taking the yoke reading and dividing by 2, this will give you the proper backlash. It's best to either have a buddy weigh the diff down or place a heavy dumb bell on the case to keep unnecessary movement from skewing your backlash reading. Like I said this takes some time to get the hang of.

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Make backlash adjustment at the adjuster, using the special spanner. I didn't have the special spanner and will not do another front diff without one again. It was a major PITA without it and I managed to rip a finger nail almost completely off when my home made tool slipped. Get the tool.

If your backlash is too large: move the carrier closer to the pinion with the adjusters.
If your backlash is too close: move the carrier away from the pinion with the adjusters.

Once backlash is set it's time to run the mesh pattern. Paint gear marking paste on about 4~5 teeth, front and back.

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Rotate the marked teeth through several cycles, forward and reverse then check your pattern. Adjust pinion depth to attain the proper pattern. This can take some serious time getting the correct pattern. I had the case apart about 7 or 8 times in this process, so be patient.

A helpful tip that I read AFTER I did this, was to use a 1/2 drill motor to spin the yoke. The guy used an extension that was ground down to fit the drill chuck along with a socket on the yoke nut. Then spin the hell out of the pinion, stop and check your pattern. It sure would have been helpful if I had seen that before doing this one.


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Old 01-03-2011, 11:23 PM
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Now we'll assume you have achieved the proper mesh pattern and backlash is set. It's time to take it all apart one last time. Remove the carrier and clean off the gear paste. Remove the pinon and setup bearings.

Install the new inner pinion bearing into the case and install the pinion seal. Install the new inner pinion bearing by pressing it on with a shop press. Slip the crush sleeve onto the pinion and insert it into the housing.

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Clean the seal surface of the yoke and install it over the splines of the pinion. Install the washer and nut and draw the yoke onto the pinion, being careful to not over tighten. Just tight enough to seat the bearings in the races and still be able to spin freely.

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Once the yoke is snugged up begin checking pinion bearing pre-load using an inch pound bar type torque wrench.

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Set pinion bearing preload to spec.

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Install carrier and use some sealer on case sealing surfaces. Put case halves together and torque bolts to spec.

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Place diff back on a bench and double check backlash. To adjust carrier bearing preload, use the torque wrench on the yoke nut and tighten up the adjuster that is farthest away from the ring gear until proper preload is achieved. Check backlash one last time, if satisfactory using a punch knock over the adjuster lock tabs into place.

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Put all remaining items back as removed. The stub shaft will require a slap with a mallet to get it seated. Double check engagement of the circlip by pulling the shaft out, if it comes out by hand the circlip didn't seat.

Put the long axle housing along with shift fork, gears and spring back together using some sealer on the mating surfaces. Use a little pipe dope on the electric shift motor threads and a little grease on the oring of the large plastic plug. Paint the diff if you want and re-install.

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Old 01-09-2011, 12:49 AM
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Extra Parts

Some of your parts seem to be from a 9.25" differential instead of the 8.25". The 8.25" doesn't have a thrust washer between the circlip and tabbed locating washer. The small gears are also different. Take a look at these two parts diagrams.

This is the 8.25"
Click the image to open in full size.

This is the 9.25"
Click the image to open in full size.

Weird thing is, your ring gear bolt count matches the 8.25".

Here is a picture of the small gear from the 8.25" I am rebuilding right now. Notice how it is clear all the way through (no step).
Click the image to open in full size.

Any idea why the differences?

What got me interested was I have over an 1/8" of end play on the longer axle. I'm thinking about adding one of those thrust washers from the 9.25" and see if it tightens it up....

Tom
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Old 04-23-2011, 09:47 PM
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My son just removed the front differential assembly from his 2003 Escalade this afternoon. Tommorrow we will begin rebuild, using this post as a guide. Therefore, some questions to J-Rod about the procedure.

J-Rod

1) You state driving the adjusters into the case for removal. Maybe this will become obvious as we actually do it, but if the adjusters are threaded, why would they be driven into the case? Or, is the adjuster some type of assembly which has a stationary O.D. that is driven into the case?

2) The backlash measured off the flange is suppose to be divided by 2, but in the PDF file attachement, it is stated to multiply by 0.7. Dividing by 2 is the same thing as multiplying by 0.5, so which is more up to date, .5 or .7?

3) The adjuster nuts you advise buying the tool. Have you subsequently found a source for the tool?

4) In setting backlash during the trial assembly, I assume the adjusters do not move around too much, so final assembly gives the same (or relatively close) backlash readings. Yes?

5)Setting the differential bearing preload after setting back lash, do you tighten the adjuster that would normally push the ring gear into the pinion, or the opposite one?

6) We weren't planning on changing the ring & pinion, just the bearings. Any comment on this?

Lots of questions, I hope you pick up on the post & have an opportuninty to answer.

Thanks in advance, FJK12
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Old 04-23-2011, 10:10 PM
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Quote:
Originally Posted by FJK12 View Post
My son just removed the front differential assembly from his 2003 Escalade this afternoon. Tommorrow we will begin rebuild, using this post as a guide. Therefore, some questions to J-Rod about the procedure.

J-Rod

1) You state driving the adjusters into the case for removal. Maybe this will become obvious as we actually do it, but if the adjusters are threaded, why would they be driven into the case? Or, is the adjuster some type of assembly which has a stationary O.D. that is driven into the case?

Adjusters are an assembly, you'll see when you get it opened up. This is a pic of the assembly. The splines on the upper edge actually hold the assembly from spinning in the case.

Click the image to open in full size.

2) The backlash measured off the flange is suppose to be divided by 2, but in the PDF file attachement, it is stated to multiply by 0.7. Dividing by 2 is the same thing as multiplying by 0.5, so which is more up to date, .5 or .7?

That was a point of great debate, a rep from Randy's Ring & Pinion stated the .7 route and the GM manual stated the .5. I went the .5 route but seriously doubt either would be wrong enough to cause any issues.

3) The adjuster nuts you advise buying the tool. Have you subsequently found a source for the tool?

Saw the tool at most local parts stores, just haven't picked one up yet. Take one of the adjusters with you to the store so you get the right one.

4) In setting backlash during the trial assembly, I assume the adjusters do not move around too much, so final assembly gives the same (or relatively close) backlash readings. Yes?

Correct, they won't move much if at all.

5)Setting the differential bearing preload after setting back lash, do you tighten the adjuster that would normally push the ring gear into the pinion, or the opposite one?

Tighten the opposite one.

6) We weren't planning on changing the ring & pinion, just the bearings. Any comment on this?

As long as you are showing even wear you should be alright.

Lots of questions, I hope you pick up on the post & have an opportuninty to answer.

Thanks in advance, FJK12
Should be a real fun project for a father and son, take your time there are a ton of pieces in these things.
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Old 04-23-2011, 11:03 PM
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J-Rod
Thank you for the quick reply. I might have more questions as we go along. My experience is with Ford 9" & 8.8 gear sets. Only a few over the years, but I enjoyed doing them & they always worked fine. My kid is a super wrench, but I really have to slow him up when it comes to doing precision work. In this case, I will have to tell him, "no Mr. Impact" here. As removed, the diff is showing ~5 in-lbs to rotate. Looks like all the bearings lost alot of preload.
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Old 05-01-2011, 02:39 PM
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J-rod

Per your notes in the pdf file, it is stated that 1 notch adjustment on the adjuster is approximately .003" change in backlash. Is that .003" change for actual ring gear backlash or backlash measured off the flange?

Right now, I'm having trouble convincing myself of what I am measuring on the flange. I can see & feel the backlash on the ring gear. I am 3 notches in from zero backlash on the ring gear.

My backlash measurement set up is virtually identical to yours. It is not the setup, but the "feel" I'm getting on the flange.

Please advise on my question & any other comments you may have.

Thanks, FJK
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4wd, 4x4, front diff, gear change, gm 8.25, ring and pinion, silverado, truck mod, z71

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