How to replace gears/rebuild a 12 bolt rear end.

[Winston Wolf]

Well, since I blew out my rear end last weekend, I need to rebuild the rear end. I thought I would show people who don't know how to do it that it's not that hard.

 

Part 1: Dissasembly

The first step is to get the car up in the air and remove the wheels. Remove the rear cover to expose the differential.

Here we can see the problem. The ring gear is missing some teeth. I wasn’t using any additional bearing supports for the carrier bearings, so with enough power and a bit of deflection and we have broken teeth.

 

On a stock type rear end, the axles are held into the carrier with a c shaped washer. To get at the washers, we have to remove a pin. The pin is held in by this bolt.

Remove pin bolt

Now we can slide out the pin in the middle of the carrier.

Now push the 2 axles in towards the center of the car as far as they will go (remove brake drums first) This will expose the c clips that hold the axles in. Use a magnet to grab them and take them out.

Now you can remove the axles, they will pull right out.

Once the axles are out, the carrier can be removed. It is held in by a bearing cap on each side. Be sure to mark the caps so you get them back on the correct side they came off of.

Loosen these bolts.

 

Now the carrier can come out. They are usually in there pretty good, so you probably won’t be able to just pull it out. I usually loosen the pinion nut at this time and give the pinion a few taps with a deadblow to pop the carrier loose. If you do it alone, keep the bolts in a couple threads so it doesn’t fall out of the rear end. There are shims on each side of the carrier bearings too, keep them separated by drivers and passengers side as a start point for the install.

Now remove the pinion yoke. I use an impact.

 

[Winston Wolf]

Pinion will come out the back.

Remove the pinion seal, and then the front bearing will fall out.

Next is removing the front and rear pinion races. There are notches in the housing that allow you to use a punch and pound them out.

Here we have an empty housing

On to the the carrier bearings. The easiest and best way to remove and install them is a press. I don’t have a press, (like most people) so we are going to take them off the old fashioned way. Use a chisel to break the bearing cage and remove it with the rollers.

If you’re lucky, and I’m not, you can get the bearings off with a 3 jaw puller, or even 2 jaw if the carrier has notches in it to get under the bearing. I needed to cut the bearings first with a dremel. Cut them almost all the way through, then a couple hits with a chisel will crack them. Should come off easy with any puller then.

Now you can remove the ring gear. It’s a tight fit, so you will probably have to hammer it off. I just remove all the bolts but 2, leave them half threaded and hit the heads to free the ring gear.

 

I am not replacing my axle seals or bearings, as I just did it last week, but now is when you would do that. You simply pull the seals out and use a inside bearing puller to hammer them out.

 

Now clean everything with solvent before assembly.

 

[Winston Wolf]

Now that the carrier is clean (or maybe you are adding a posi or a stronger carrier) We have to put the new bearings on it. Again, I don't have a press, so we have to do things the "other" way.

 

Debur the ends where the bearings will go and hit them with a quick brush of emery cloth or sandpaper to make sure they are smooth. Then stick it in the freezer. We are going to shrink it. Once the carrier has been in the freezer an hour or so go ahead and put the 2 new carrier bearings in oven at 200 deg. We will bake them for an hour.

 

While our parts are baking and freezing, get your stuff set up, cause you need to work quick once we go. I put a piece of wood on the floor to set the carrier on. Get one of the old bearing remnants you took off, as we will need to use this to pound on the new bearings. I also use a piece of steel and of course a hammer, and an oil can. Get everything set up and close together.

 

Once the dif has cooled for a couple hours and you have baked the bearings for an hour, take the carrier and set it up on the wood. Quick put some oil where the bearing will slide on. Now get the bearing and set it on the housing. Using the old bearing pound on the new one, being careful not to hit the rollers or cage. Just a few good hits and it should be on. Work fast and don't give up. As soon as it's set, flip it over and run get the 2nd bearing. Repeat.

 

If you have never done it before, it's a good idea to set everything up ahead of time so you have an idea what to do.

 

 

Here is the carrier with new bearings on it. You can see this Moroso Brute Strengh has recesses to allow you to pull off the bearings....

 

 

 

We will do the same heat/freeze method to get the pinion bearing on, but not quite yet. Here is a rear pinion bearing. I have taken and ground off some of the inside so it fits easy onto the pinion. It's a spare cheapo bearing I got a Napa. This will be used to set our pinion depth. Since I don't have a press, we only get one shot at installing the pinion bearing with the correct shims under it. We will get into that when I put things back together in the next couple days.....

 

[201fireman]

I look forward to reading it. This is very interesting to those of us who haven't dug into differentials...yet! I have a 12 bolt but it is an open 12 bolt with 2:73's. I would love to find some 3:55's for it.

[Canuck]

I love these tech posts.

[72-CLASSIC_RIDE]

IMPORTANT NOTE:

 

As stated! Mark Bearing Caps before removal so that each Cap goes back on in same location exactly as removed. (The Bearing caps are not interchangeable from side to side, reversable or to another Housing). They are fit only for that Housing at their specific location!! I would use a punch and put a impression on one cap at one end and another nearby on Housing at same end. Two impressions on opposing Bearing cap using same methodology. This way you will always know exactly where each one goes. You get the idea.....

Just wanted to make that clear for everyone so they realize just how important this procedure is!!

Great Post. It will provide a excellent reference for the Do-It yourselfers.

 

Doug

[DRDIRT11]

just did this but mine wasnt this easy. the bolt that holds the pin in center was sheered off. some drove it this way and pretty well ruined the spool. i had to beatthe pin out2 inches cut it off, beat it out cut it off, you get the point. was alot easier than i thought putting back together. this was the rearend in a truck project i got and not my monte so i figured that would be a good experiment. seams fine and no whining or noises.

[wallaby]

So far, so good!

I have thought about taking pictures as I go like you have done, but let's face it...it takes a lot longer to do the job if you keep stopping and getting good photos at every step. I start out with a picture, and before I know it I have a pile of parts and relaize I didn't get pictures of the process. LOL

 

I'm looking forward to the next installment.

 

[Heckeng]

Nice job Winston, I'm with Wallaby here. You always start out with good intentions of getting pics, then it is too much of a pain in the @#$ so you just get it done!

[TommyP]

Thanks for the great posts. I'm getting ready to change my axles and have never done any work like this before so the timing couldn't be any better.

[Vaughn]

Thanks for taking the time to share this. Very informative.

Looking forward the next steps.

[Phil]

Great, very interesting.

[Mo's70MCs]

Great write-up. For those of you that may encounter the "old broken lock bolt" in the future I have used this tool twice, it is god sent. Well worth the price, specially if you ever need one. Used carefully it will render great results.. just passing along some info.

 

 

the bolt that holds the pin in center was sheered off.

 

 

 

 

Product Description: Differential Pinion Shaft Lock Bolt Extractor Kit link

 

 

Removal of broken differential pinion shaft lock bolts in GM and Ford integral (WER) type rear ends can be time consuming and frustrating! Often the differential pinion shaft lock bolt is found in a broken state when servicing this type of rear end. Removal of this bolt is required to perform any type of service. From axle seals to complete overhaul this bolt must be removed. The removal of this lock bolt is essential in performing rear axle replacement, rear axle bearing replacement, rear axle seal replacement, most differential repairs, as well as all differential overhauls and rebuilding Although many believe this lock bolt is broken at the time of attempted removal, this is not the case. What causes this breakage is the back and forth rotation of the smaller spider gears, which causes a back and forth motion of the pinion shaft. This in turn flexes or, in effect, bends this lock bolt back and forth causing it to fatigue and break. When found in a broken state much damage and expense is incurred in the removal process. Current removal procedures include the use of hammer and punches along with torches and impact chisels (not to mention the swearing and throwing of tools!) The price of these methods range from the cost of a pinion shaft to the expense of an entire carrier plus the labor. This kit provides drill bit, drill guides, and extractors so the lock bolt may be removed in a five minute extraction procedure! The instructions are easy to follow and very thorough. All components come in a re-sealable tube for safe and convenient storage.

[Winston Wolf]

Part 2, Assembly:

 

Here are the parts needed to overhaul a rear end. This includes the gearset and an installation kit. The kit has all the bearings for the carrier and pinion, but not the axle bearings or seals. There are shims included and a pinion seal, along with marking grease.

I also bought a new fancy cover.

Once you have the carrier bearings installed, you can clean and bolt on the ring gear. It’s a semi-tight fit, but you should be able to get it on without the heating/cooling method.

Install the front and rear pinion bearing cups into the housing. Use the old cups to hammer them in. I have this plate that I use to get good hits on them and pound them in straight. Make sure they are seated all the way. You will know they are when the sound of the hammer strikes changes pitch.

Ring and pinion gears are a match set. They are test run at the factory and a backlash and pinion depth setting are determined. They etch the pinion depth in the end of the pinion and etch the backlash on the ring gear. If you are setting up the rear end and have a pinion depth gauge, you will use that number to set how deep the pinion is in the housing (how far from the carrier bearing centerline to the pinion face). I don’t have one, so we will set it by looking at the gear pattern.

If you are reusing your gears, use the same size of spacers that came under the original pinion bearing. If you have a new set of gears, you should start with the same thickness of spacers also, if you can get the bearing off to measure.

If you have no idea what the thickness of the shims is, start at .035, this will be very close and often time right on for a 12 bolt. We will start with 35 thousands here.

Put the shims on the pinion and slide on our checking bearing. This is the cheapo bearing I bought and gound out just enough material to let it slide on the pinion without having to press or hammer it on.

Here you can see the shims under the bearing.

Now’s where the fun part starts. It is really a trial and error procedure. Don’t get discouraged if it doesn’t work right the first time. Take your time and make sure to do it right.

 

Put the pinion in the housing. Install only the front bearing on the pinion, do not use the crush sleeve at this point. It goes between the front and rear bearings, but not yet at this step. Install the pinion yoke, washer and nut. You should use the old nut if you still have it.

Now we have to set the bearing preload. Tighten the nut until it takes 20 inch lbs to spin the pinion . This will be tight, but you will still be able to rotate it with one hand. I use and impact to bump it, checking by hand, then put my inch lb torque wrench on it when it feels close. I like the old school torque wrench for this, as the breakaway torque is always more that the actual turning torque.

 

[Winston Wolf]

Next, install the carrier. Use the same thickness of shims on each side as you took out. This will be a good starting point. The total shim thickness is usually around .485”

The carrier will go in tight, so you will need to tap the shims in with a brass punch. Use a deadblow hammer to help you pound in the carrier.

Once it is in, reinstall the bearing caps on the correct side you removed them from and torque them down, 60-65 ftlbs.

Next we need to check for backlash. The backlash is determined by the thickness of the shims on each side of the carrier. I use my dial indicator out of my cam degree kit, or use a magnetic base indicator. Set it up like the picture below. You want it to be as close to perpendicular (90 deg) to the surface of the gear tooth as possible or you will not get an accurate measurement.

To check the backlash, simply rock the carrier back and forth while watching the indicator. This gearset calls for a .010 backlash. (etched into the ring gear) Richmond says the backlash can have a tolerance of +.004” That means the measurement must be between .010-.014 You can see here I had .020” Too much.

 

 

Since we have too much backlash, we need to bring the ring gear closer to the pinion. If the backlash was too tight, we would move the ring gear away from the pinion.

Take the carrier out and measure the shims. In this example we will need to move some thickness from the passenger side and add some to the drivers side. Let’s just say it was .240 on the left and .245 on the right. We would increase to .245 on the left (drivers) and decrease to .240 on the right. This will move the ring gear .005 closer the the pinion and decrease the backlash.

Reinstall the carrier with the new shim measurements and recheck the backlash. Always check the backlash in at least 3 spots on the ring gear. I have found they often vary by one or two thousands around the gear.

Once we get the correct backlash, we will check the gear mesh pattern. Use the marking grease with the kit and paint a section of the gear teeth.

 

Now you need to turn the carrier a few revolutions both ways so we can get some marks. Either just grab ahold of the ring gear, or slide one of the axles in and use that to spin it. Don’t use the pinion to turn it, or you will not get a good pattern.

Here is the pattern. Pretty good for the first try. The installation instructions in the Richmond kit have some pictures of correct patterns. You could probably live just fine with this pattern, but I want to move the contact area just a bit closer to the center.

The way to move the contact area from the inside to the outside is to reduce the thickness of the shims under the pinion bearing. That will bring the pinion closer the the carrier. Just a couple thousandths on the pinion shim will make a difference.

If you need to make adjustments to the pattern, remove the carrier again, remove the pinion nut, yoke and pinion. Adjust the thickness of the shims, put it all back together again. Make sure to set the preload and backlash again before you repaint the gears and check the marking again.

Once you have a pattern that you are happy with, take everything apart again. We now need to put the new bearing on the pinion. This is the setup I am going to use to tap the bearing on.

Freeze the pinion and heat the bearing. Make sure they get enough time in the freezer/oven, and they should almost fall together. DO NOT FORGET THE SHIMS when you put the bearing on.

Once you have the new bearing on, go ahead and put the pinion back in the housing and place the crush sleeve on the shaft, then the front bearing on the pinion. Next install the new pinion seal.

If you don’t want to use a crush sleeve, they now have adjustable spacers that can be used to set the preload. You simply install the spacer with the proper thickness shim, tighten it down and check the preload. Adjust the thickness of the shims until you get the correct preload. (must be done before you put in the pinion seal) I tried to use one of these, but it didn’t work for me. If was either too tight (60”lbs) or too loose (5”lbs). I needed a .003 or .005 thickness shim, and the smallest one in the kit was a .008”

Install the yoke, washer and nut. You will now need to crush the sleeve. It takes a couple hundred pounds of torque to crush them, so an impact wrench is almost a necessity. Tighten it in small increments, checking the preload. Be careful not to over tighten it, or your bearings can fail prematurely.

Install the carrier again. Double check the backlash with your dial indicator one more time, then double check the wear pattern again.

 

Here you can see how moving the pinon depth only .002” changes the wear pattern significantly. Below that, my backlash settings. .013, good to go.

[Winston Wolf]

Now, slide the axles back in as far as they go. Reinstall the c-clips and push the axles back out.

 

Now you can reinstall the pin and the bolt that holds the pin in. Torque the bolt to spec.

Now install the differential cover.

The cover I have as 2 bolts that run though it. The bolts press on the carrier caps and put a preload on them. This helps in a high horsepower application. Since the gears are cut at an angle, under torque the pinion gear tries to “push” the carrier/ring gear out the back of the car. If you throw enough torque at it, the drivers side cap can deflect and allow too much gap between the teeth. When this happens, teeth break off; as mine did. Putting this cover on loads the caps by pushing on them and helps combat this.

Install the cover and fill with fluid. There is a fill hole with a square plug on the passenger side, just above the axle tube. Use this to fill the rear end with a stock type cover. Once oil starts to run out the hole, it’s full. They take just over 2 qts of gear lube. If you have a posi, be sure to add limited slip additive or purchase gear lube with additive already in it.

 

 

Install the wheels and go for the test drive. Richmond says to drive 10 miles, cool for 30 min, repeat. This will heat the gears and set them in.

When set up properly you shouldn’t have any rear end noise under power, cruise or decel. If you do, chances are you didn’t have the backlash or depth right. Time to start over.

 

If you had a bad failure like I did, it’s a good idea to change the fluid right away after the test drive. There are lots of cracks and crevices inside the case, and you don’t want any junk in there.

 

Good luck!!

The Wolf.

 

[Heckeng]

Nice write up Winston, and great pictures.

[TommyP]

Thanks for all the great pictures and the write-up!!!!

[Sam (Bones)]

nice write up

[Mo's70MCs]

Nice write up Winston, and great pictures. This for sure "Tech Archive" material. Especially for all the DIY'ers in here... Thanks for sharing. Rebuilding on car! "Priceless"

[7tonemonte]

Great write up!!

We might need to add a section in the forums just for you to put your pics and instructions in

Detailed instructions are even better with pictures, not like that last giant chinese dollhouse I put together for my daughter

[72MC]

Winston and for all you guys that like homemade tools. This is a tool that I made after seeing it in action when I was taught to do rear ends. My teacher/friend, like me, was not a big fan of pre loaded carriers and this tool aids in the turning process while loading the steels clutches, spider gears, and side gears into a carrier. All it is is an axle, cut to length, welded on length of pipe for a "T", and a welded bead mid way up the axle shaft so it does not enter the carrier all the way. It is a great tool for carrier builds.

 

Nice write up Winston. Like some have stated, I have started to do the same thing in the past and the job just becomes more important than the pics. I'm sure you have helped alot guys with questions they may of had about rears. Gotta say though, your final pattern on the gear mesh looks a tad shallow. It may be the pics but that's the way it looks to me. Good luck with the tranny build. I would recommend Gear Star out of Akron, OH but it looks as if you have already got the process started. - Dave

[footballubet]

Good write-up! Everybody knows we like pictures. Just one tip..when installing the side bearings, don't use oil on them. They are a pressed fit and oil takes up space, makes it harder to install than when dry. But that's just my .02 cents.

[MCfan]

Many thanks, Winston! The open sharing of technical knowledge and practical applications makes this club and forum extremely valuable to less experienced members like myself.

 

I have been anticipating replacing my 3.31 stock gears with either 3.55 or 3.73 gears this winter after I install taller 275/60-15s on the rear in case I lose too much "zip" with my M20 around town. Your excellent photo documentary of how it's done certainly takes the mystery out of it and also reduces much of my former apprehension.

 

Nearly 40 years ago, I allowed a local Phillips 66 station owner to replace a leaking pinion seal on my first '70 Monte. I headed east from Kansas City the next day and by the time I got to St. Louis the rear end was howling like a Banshee. After several hundred dollars and a day at the local Chevy dealer, I was back on the road. Later, the station owner admitted that he "forgot to properly torque" the pinion shaft nut so he reimbursed me for the labor and I paid for the new parts. I've never allowed a "service station" to do major mechanical work since.