gear swap demystified

[photo_van]

At the risk of posting concurrently with Lifted (whom I owe great appreciation too), this is for those that have never had a diff apart, but for various reasons (worn bearings, gear swap, etc) think they would like too. I don't suggest that I'm an expert by any means as this is only the second gear swap I've done, but this is how I did it and what I found.

If you are on this site, then chances are you don't like, or can't afford to have someone else work on your van.

Differentials have always held this mystery of the un-touchable, or taboo, that for some reason if we go in there, we're never coming out. But really, it's just a few gears and bearings that have to be assembled with in some set guide line tolerances, a Swiss watch it is not! I say this all now, but I only have a few hundred miles on my swap, so time will tell.

After swapping 4.10s in the front end viewtopic.php?f=60&t=8579 a month ago, with road trip season upon me, I needed to get the rear to match.

First myth to debunk: you need a nice clean shop, with lots of special tools:

welcome to my shop (note the wheel chocks on the wrong side)

As far ar special tools, I did the front end with three: dial indicator, a torque wrench and a small fish scale.

This time, because I thought I was going to reuse all the bearings, and I had recently visited my Dad's old shop with cool tools, and to make it easier, I did use some additional tools: feeler gauge. micrometer, calipers, bearing separator and puller. On both the front and rear I used an air impact to loosen the pinion nut, but that may not be necessary.

This job was to replace the broken G30 limited slip with an Eaton Truetrac ($388 Amazon) and install a set of used OEM 4.10 gears ($110 ebay).

[photo_van]

It's nice to jack up van high enough so you can sit under it while you fiddle with the carrier, removing the spare will be a lot of help here. Remove the wheels and drums and the 10 bolts holding the diff cover. It will look something like this inside

Next remove the 8mm axle retainer pin bolt. Be careful not to round it off: I couldn't get a straight shot with a socket and extension until I removed the right carrier bearing cap (the thing with the two bolts on the right in the above photo). ***be sure to mark the right or the left carrier cap before you remove them both so they are identifiable from on another***

This is the 8mm retainer bolt

Once removed, slide out the axle retainer pin. Go around to the R & L sides of the van (not at the same time) and push in on the axles. The c clips on the ends of the axles inside the diff will either fall out or you will need to work them around with a screw driver until they do (fall out).

You can now pull out the axles (be careful of the wheel bearing seals if your not replacing them). Now is a good time to check the wheel bearings and clean up the seals.

Now, after the carrier bearing caps are marked L&R (I used a center punch), remove the four bolts and caps: at this point I had a can for left parts and one for right. If you still have carrier pre-load the whole carrier won't immediately end up in your lap. But if your bearings are shot it may, so be careful. If it doesn't fall out, you are going to have to pry the entire assembly with a 2x4 or pry bar being careful not to mare the rear cover gasket surface. As you do this be aware of the bearing cups and production shims (actually thick washers, one on each side) that are going to fall out on the left and right, you'll want to keep those all separate as to L&R. Sorry no pictures here as it took all hands.

[photo_van]

If your working in a sandy, wind blown environment, you might want to run the carrier into a clean working environment such as a tool shed. You might also want to put the rear cover in place with a couple of bolts and stuff rags in the axle tubes.

So now to remove the pinion. Take the drive shaft off and tie it up out of the way (or remove it all together). At this point you may want to take note of the existing pinion preload with either the fish scale or an inch/lb torque wrench.

this is where you might want to start making some notes.

To remove the pinion nut I put a pipe wrench on the yoke and cheater wedged against the passenger leaf spring. With a 32mm socket on the impact wrench the nut came right off.

If you are planing on re-using the pinion bearings, you may want to make yourself up a little puller (or use another puller) and pull off the yoke rather than try and beat the pinion thru it with a hammer, my yoke was pretty stuck.

Put the pinion nut back on and tap the pinion thru with a soft hammer if you have one. Remove the pinion seal and shove a rag in the hole.

[photo_van]

here's some trout from my last backpacking trip

[LiftedAWDAstro]

No problem posting the same time as me. I don't mind at all. Nice pics by the way. The trout looks yummy!

[photo_van]

Hey, someone is out there!

So now we're in a nice clean environment in the tool shed and the wind can blow sand all it wants. So lets start with the pinion because it's the easiest. If your putting in used OEM gears, chances are that the inner pinion bearing is still on. This is a good thing as it will have the OEM shim behind it for reference. I'm going to remove the inner bearing from both pinions to see what shim they both have and because I want to reuse the bearing from my original (only 100,000 miles and look good). Because of this and because I wrongly assumed I'd need a bearing separator to remove the carrier bearings, I purchased a separator $20 HF.

The tapper was to thick to fit under the bearing so I ground them down a little

I'm not sure of the correct way to use this tool, but I tightened the clamp down good and tight and then started beating on the pinion nut with a brass hammer. As it broke loose, I would tighten the clamps some more and hammer some more and continue until it came loose. If you do it this way, put something soft under the pinion gear so when it comes flying out it dosen't smack the vise. There are also holes in the separator so that you can use it in a more civil manner with a puller, or a press if you have one. If you are planning on reusing the bearing, be careful not to "pull" on the bearing cage

Both pinions had .0038 shims (stamped with a 38). In fact that's the same shim that was under the front pinion as well. I'm kinda thinking that that thickness is the standard for OEM gear sets. So I went with one of the OEM shims and pressed the existing bearing onto the "new' 4.11 pinion with an 1 1/2 id pipe and a big hammer.

The pinion is now ready for setup install using the same install nut (without the staked head) that I created for the front (same size and threads, an unusual and pleasant occurrence in the automotive world)

[photo_van]

If the sand has quit blowing around, you can go out and install the pinion without the crush sleeve or seal: put a little oil on the bearings and tighten it up so it has a little bit of drag (preload).

Now, back in the shed we get to start playing with the new carrier (Truetrac) and ring gear. I should have mentioned before, you are going to need an install kit, either a "master" if you're going to replace the bearings, or a "mini" if you're not. This time I got a G2 mini install kit ($39 mudflaps.com) rather than a Yukon, about 2/3 the price and included a new gasket and new ring gear bolts. The bolts alone run about $2 a piece.

If you have never ordered an install kit from Yukon, I highly recommend it as it comes with a very useful installation guide and list of tolerances for new and more importantly, used gears and bearings.

The first thing I'm going to do with the old carrier is pull off the bearings so I can press them onto the Truetrac. This is when I discovered that the carrier bearings can't be removed with a separator, but need a bearing or pulley "puller". Fortunately I had found this great old school puller in my Dad's shop that did the trick.

Upon close inspection of one of the races though, I found a small gaul or imperfection, that suggested new bearings

So it was off to the parts store for new bearings. First I called NAPA (15 miles north) "sure we have those". So after a 20 min drive, "oh, uh, the computer says we have them, but there not on the shelf" Great... Next try is O'Rielly, 25 miles south. I give them a call; "what's a carrier bearing?" "No, we don't have a listing for no carrier bearings". The only other parts stores are 150 miles away. Fortunately O'Reilly has a pretty good website and after a bit of digging I found a part # for "inner axle bearings" and to my luck, the local store had two. Made in Mexico rather than China.

I put the Truetrac in the freezer to shrink the metal and went for the bearings. I used the same 1.5" pipe to drive the new bearings on to the new carrier

be sure the bearings are seated all the way to the inner shoulder; it took a lot of force.

While the carrier is still cold, grab the "new" 4.10 ring gear that has been getting nice and hot on the dashboard in the sun, and attach it to the carrier. As you first get it started, make sure you get it lined up with a couple of bolts as you won't be able to turn it once it's in place. While some internet sites strongly suggest NOT pulling the ring gear into place with the bolts, it IS the recommended method in the OEM manual. In any case, mine slid right on with a few light taps of the copper hammer.

Next you need to torque the bolts to 65 ft/lbs. These are LEFT HAND or REVERSED threads. The Truetrac is pretty smooth unlike the OEM carrier and is tough to hold in a vice. I used a piece of flat stock to keep it from turning.

the carrier is now ready to install

[Stroverlander]

Another great write-up, can't wait to see the rest of the install.

[photo_van]

Alright, that was the nuts and bolts, now we have to pay attention. Turn off the ipod and grab a pencil and paper. There are four measurements in the differential that we need to pay attention to: Pinion pre-load, pinion depth, ring gear back lash and carrier preload.

Pinion Preload is the load applied to the bearings and is measured by the amount of force it takes to turn them, it is actually pretty stiff. Because used bearings are already "seated" the preload for used is less than new (or at least I think that is the reason). Preload is measured in in/lbs.

Pinion depth is adjusted by the shim we placed under the inner pinion bearing. It appears that this depth is pretty set in stone for OEM gear sets.

Back lash is the play between the ring gear and the pinion mesh. It is measured with the dial indicator.

Carrier preload is adjusted by pressing in extra shims on both sides of the carrier and isn't actually measured as such.

Here are the set up specs for a GM 7.5/7.6" 10 bolt according to the Yukon instructions:

pinion PL in/lbs - new 12-15 used 6-7
backlash .006-.010
ring gear bolt torque 65 ft/lb
carrier bearing cap 60 ft/lb

According to the OEM manual

Pinion PL new 24-32 used 8-12
BL .005-.009
the ring gear torque is 90
the caps are 55.

I had a hard enough time getting the ring gear bolts to 65. I did so and used loctite blue.

Ideally you would have an in/lb torque wrench to measure the pinion preload. I don't, so I use a fish scale on one of the yoke bolts. The bolts are somewhere around 1.5 inches from center (don't recall exactly), so the force applied there can be multiplied by 1.5. i.e. 6 lbs on the fish scale will be ~10 in/lbs.

So go ahead and crawl back under the rig and set the pinion preload to whatever specs you decide.

Now on to the carrier. The shims, or big thick washers that came out with the OEM carrier are called production shims. They are machined to the proper thickness required during set up at the factory. They look like this.

I thought I would go ahead and measure these just because I wanted to play with the micrometer.

The install kit will come with service spacers and service shims. These are used in place of the production shims when we calculate the new shimming necessary. Here are, from L to R, the production shim, service spacer and service shim(s).

The service shims will end up being sandwiched between the service spacers: seen to the right below (production shim on left)

There will be two sets of these, one for left and one for right.

[photo_van]

OK? Let's figure out what shim packs we need on the carrier. Put a thin film of sticky grease on the outer bearing races so they stay in place on the bearings. Make sure the outer surfaces of the races are wiped clean, as are their mating surfaces inside the differential housing. Grab one of the production shims and two service washers (make sure all surfaces are clean). Now, using all four hands, put the carrier in the diff housing and "slam it" all the way to the LEFT ( once in place, I used the left bearing cap and one bolt to hold it in place). Now, slip the production shim and two service washers in between the RIGHT bearing race and diff. housing. You need to make sure that the bearing races on both sides are seated and square. Below is a pick of where the shim pack will go (the carrier is out)

Now, with that old feeler gauge set that you used to set the points in your VW with back in the day, measure the clearance between the production shim and the bearing race. Due this while applying some force leftward on the carrier.

Work the gauge in to the back and around top to bottom to get a good "feel" (ie feeler gauge). The right gauge will be snug but not tight. This isn't overly critical as we will see, in that the shims only allow for adjustments to +/- 5 thousandths.

The sum of the spacers plus the feeler gauge equals the ENTIRE shimming (L+R) that will required before pre-load. Do the math and write that down.

Now, with the spacers removed, slid the carrier all the way RIGHT. At this point the ring gear will come into contact with the pinion so the right carrier bearing is not going to come up tight to the diff. housing. Wiggle the ring gear back and forth a bit to make sure it is meshed with the pinion gear. Now, repeat what we did on the right but this time on the LEFT bearing. Apply some light pressure on the carrier to the right find a pack of spacers/shims that fit and measure with the feeler gauge. Add the sum of the spacers and feeler gauge for the left and write that down.

To get the sum of the spacers/shims, measure them individually. Don't have a micrometer? Use the dial indicator and stand on a nice flat steel surface and slide the shim in

[photo_van]

The left side shims are what will be used to adjust the ring gear backlash. The pack we measured on the left is with the ring and pinion tight. For every .002 removed from the left shim pack will increase the backlash by .001.

My overall shim pack was .456. Left was .241. .456-.241=.215 which is the base pack for the right. Now, we'll remove .015 from the left and add it to the right (all shim adjustments must mirror each side) which should give us a back lash of .007.

So, we are now at .226 LEFT and .230 RIGHT. Now, we're supposed to add .010 to each side for pre-load. I didn't want to have to deal with prying the carrier out again, so I left the preload until later.

OK, now time to put the carrier in with the shims, it should fit quite snug. Be sure to oil up the bearings well. Bolt up the caps good and tight. Now time to set up the dial indicator and measure the backlash. The dial indicator should be set up perpendicular to the top outside of the tooth. I forgot to photo this so stole these images from Lifted.

I got lucky and nailed .007 backlash on the first try.

Now apply gear marking compound on 4 teeth in three places on the ring gear. Apply some load to the pinion and rotate the ring gear a number of times to get a good pattern. Here is where the interpretation comes in. According to Yukon used gear patterns are suspect at best. They say to only pay attention to the coast side and that the only critical aspect is that the contact is not to deep in the root or to high. With that in mind, here was my pattern.

In the bottom of the photo is the coast side, the top is the drive side. The coast to me looks dead on with full contact on the tooth and proper depth. The drive side is way to and off the toe. On a new set this may suggest the pinion is too close. Given the fact that the pinion is set at OEM specs, and according to Yukon, trying to get contact patterns perfect on used sets "will lead to noisy gears", I accepted the pattern. At this point too, it may be interesting to quote the OEM manual: "contact pattern... is NOT a substitute for pinion depth and backlash adjustment".

[photo_van]

All right, now take it all apart, including the pinion. Put the new crush sleeve on, install the pinion seal. I used the same pipe wrench cheater set up, but needed to tie it up below the leaf spring now. There is some special goop that looks like plumbers putty that is suposed to go on the pinion yoke under the washer; I used RTV. Blue thread lock and a new nut. Using a 24" braker on the 32mm socket, I could do leg presses through the drivers side wheel well. Take your time here, once the whole pinion assembly comes up tight, the pre-load comes on fast. I turned the nut about 1/8th turn at a time then crawled under to see how in felt. I found this sleeve much easier to crush then the front differential. If you go to far, you have to take it all apart and get a new crush sleeve.

Once the pinion is tight and the preload is set to whatever spec you need, you can put in the carrier. You can now add the .010 shim on each side for the pre-load. I put in the left pack first, the right pack will then need to be tapped in with a soft hammer. Don't forget to oil the bearings, as without it, the carrier will be surprisingly hard to turn under the preload. (Ask me how I know ). Put the caps on, torque them to spec. Check the backlash and pattern again to be sure nothing has changed.

Grease the wheel bearing seals, slip the axles in, put in the c clips, inner axle spacer and retainer.

Gasket, cover, fluid, take for a spin. It is recommended to only drive 20-30 min at a time for a couple of times with plenty of cool down time. There will be a lot of heat generated by (I think) the new preloads. The fluid should be changed after 200-300 miles.

If this sounds complicated, it's really not. I'm pretty sure it took more time to write this up then it did to do the job which was only a Saturday.

So there you have it- mine is quiet as new and now pulls the grade coming back home, loaded with groceries and gas, from town without dropping into 2nd gear

[LiftedAWDAstro]

AWESOME! Better write-up than I ever have done. Great job and it's not as bad as it seems is it?

[photo_van]

Thanks Lifted. It really isn't hard at all. I think most anyone that does any wrenching at all could probably pull it off. You just have to pay attention, stay organized and follow the manual. I think the trickiest thing is that darn crush sleeve and pinion pre-load. I got mine a little tighter then I wanted to.

[MountainManJoe]

If this topic had a "thumbs up", I would click it. Thanks!