Wednesday, October 20, 2010

GM 10 Bolt - How To Switch Gears

Switching Gears

Rebuilding a GM 10-bolt rearend

By Jefferson Bryant / Photography by Jefferson Bryant

If transmissions are shrouded in mystery, then the rear differential follows on its coattails. Unlike transmission building, rebuilding a rearend is basic nuts and bolts stuff, but that comes with a caveat — the setup is the tricky part.

Backlash, pinion depth and wear patterns are science and art mixed together, and you do need a few specialized tools. We set out to rebuild an aging GM 8.5-inch 10-bolt rearend.

Before you start, you need to identify your parts. Some people will trash talk the GM 10-bolt as a “junk” rearend, and if they are talking about the 8.2-inch, then they are not far off. But the 8.5-inch 10-bolt is actually just as strong as a 12-bolt or Ford 9-inch rear, with only a fraction of an inch difference in the ring gear diameter. Since both the 8.2 and 8.5 10-bolt rears have the same cover, you have to look for some key signs as to which unit you have (short of taking it apart and measuring). All 8.5-inch 10-bolt rears have two squared-off ears at the 4- and 6-o’clock positions on the bottom of the pumpkin — that is the No. 1 telltale sign. If you don’t have those, you don’t have an 8.5-inch 10-bolt. Up until 1988, all GM 8.5-inch 10-bolts had 28-spline axles, which are thinner than and not as strong as the upgraded 30-spline axles. Finding 30-spline axles is easy, you just have to take some measurements and order them. You should also check to see if the rear carrier is posi or open-style; the easiest method is to jack up the rear of the car and spin the wheels — if they both spin the same direction, you have a posi; if they spin in opposite directions, you have the classic pegleg rear.

Our 8.5-incher had 28-splines and an open carrier, not to mention some clanking, groaning and general worn-out feel, so we ordered some parts. While we could have stayed with the open carrier and 28-spline axles with no real consequences, posi is so much better. We ordered a new TrueTrac posi unit from Eaton (the makers of the Detroit Locker) so that we would have the excellent noise-free turning and straight-line traction that we need. The TrueTrac comes in both 28- and 30-spline versions and we chose the 30-spline. That meant we needed new axles. We ordered the rest of the goods — 30-spline axles, 3.73:1 gears (an upgrade from the 3.07s) and all the bearings, seals and gaskets.

To get the rear set up properly, you will need some tools — specifically, a dial indicator with a magnetic base and some calipers. These are used to check the backlash of the gears and the thickness of the shims respectively. Backlash is the amount of play the ring gear can move before the pinion moves. Each rear-differential type (as in 12-bolt, 10-bolt Dana 60, etc.) has its own specs, and these are usually included in the gear-set instructions. The 8.5-inch 10-bolt should have between .006 and .010-inch of backlash — we are not talking about much, and the only way to check this is with a dial indicator. We ordered our dial indicator kit; it came with a nice plastic case, too. This is the basis for the rest of the install, so it needs to be checked first and it needs to be right. Next the contact pattern must be checked, which is done with colored grease (included as part of the new gear install kit).

Once you have the basics down, swapping gears is not that difficult, it just takes time to learn and a lot of trial and error. Setting the backlash and pinion depth (dictated by the contact pattern) means installing and removing the carrier and pinion. On this swap, we did this about 15 times, for various reasons. The end result is better traction, more power (though the engine does spin a bit faster at speed because of the lower gears) and all-around better drivability. Whether you want more performance and capability or you just need to replace some worn-out parts, rebuilding your rear differential at home can save you money and be one more thing that you did yourself.

1 Drain away: We raised the car up on our new lift from Quality Lifts. You don’t have to have a lift, but it is really nice for a project like this. With the wheels off, we removed the driveshaft and cracked the seal on the rearend. Surprisingly, the gear oil was not as bad as expected. One note — don’t wear basic shop clothes for this, you want to wear something that you won’t mind throwing away; nothing smells worse than used gear oil.

2 C-note: This is a C-clip rear (most Buicks and some Pontiac 8.5-inch 10-bolts had bolt-in axles), so the drift pin must be removed to gain access to the C-clips. The drift pin is held in place by a small bolt to the side of the carrier, and then the drift will slide out. Don’t let it fall, as these are not easily replaced.

3 Don’t drop: A magnetic tool is the easiest way to get the C-clip out and not drop it. Once you have these out, the axles slide out of the carrier.

4 Mark it: Before pulling the carrier caps, mark them for side and position. You can’t swap these side-to-side or flip them upside down, so make a solid mark on each one. Some caps have arrows pointing towards the outside, which makes it easier.

5 Punch-out: The pinion nut requires a large socket; we used a 3/4-drive set from Gearwrench on an impact gun to remove it. The pinion gear must be hammered out, but use a drift punch, don’t just smack the pinion stud, it will become unusable and could warp enough that is gets stuck permanently.

6 Code cracker: If you are unsure of the original gear ratio, it is stamped into the face of the pinion. The 13-40 represents 13 pinion teeth and 40 ring teeth, which breaks down to 3.07:1.

7 Tough stuff: You can see a big difference in structure when comparing the carriers. The stock open carrier to the left is not as solid as the new TrueTrac from Eaton (right). The TrueTrac is a positive-traction limited-slip unit, meaning both wheels are driven under even loads, but when cornering, the carrier allows the inside wheel to slip a little, which is a good thing. And it lets you do big smoky burnouts with both tires. The TrueTrac requires different bearings from the stocker, which set us back about $50 for the bearings and matching races.

8 Measured analysis: We learned a few things along the way with the axles. There are two ways to measure axles, from the outside wheel surface to the C-clip flange or to the end of the axle. Different companies measure different ways, so you need to have both specs and check with the tech department before ordering axles. Also note the slightly larger diameter of the splined area for the top axle; this is the 30-spline, versus the smaller 28-spline stocker. The 30-spline will handle more torque.

9 Bench-press: The main pinion bearing (as well as the carrier bearings) have to be pressed off, so we took them to the local NAPA machine shop for that. You don’t want to toss the old pinion bearing, you need it for the setup. Using a fine carbide burr, grind out the inside of the bearing until is slips onto the new pinion shaft easily. This is so you can check the fitment of the gears without destroying bearings.

10 Torque stop: The new Yukon ring gear was bolted to the carrier and torqued in a cross-bolt pattern (like you torque a wheel) to 65 lb-ft. No threadlocker needed.

11 Trust but verify: Many times the original pinion shim will get you there in terms of pinion depth, but you can’t trust that – not by a long shot. Always start with the stocker and go from there.

12 Test-tight: The pinion gear is installed with the old bearings, no crush collar and the pinion nut tightened down firm enough to get just a bit (enough to tell it’s there, no slop, but not tight) of drag on the bearings, using the original pinion nut. The new nut has flat spots on it that serve as locks; you don’t want to use the new one for this.

13 Carrier shims: As with the pinion shim, the stock carrier shims often get you closer but, in this case, not even. We used one factory shim and then stacked up a set of the new shims to get us closer. The carrier should be tight, but you don’t want to have to beat it into place either; consider it “hand-tight.”

14 Backlash: The dial indicator was set up to read 90 degrees off the coast (back) side of the ring gear. Once zeroed, the pinion is held tight and the carrier rotated until the pinion is engaged, both forward and reverse. The carrier should move easily — it should not bind, grind or be difficult to move. Here we had .006-inch play, which is spot-on. Adjusting the carrier side to side moves the gear closer or further from the pinion, reducing or increasing the backlash. An adjustment of .010 in shims is worth about .007 of backlash. Be patient. Once the backlash is set, don’t change the shims.

15 Grease trap: Next the grease comes out. Spread a little grease over four to five ring gear teeth, then rotate the carrier (not by the pinion) back and forth over the pinion gear about five times. Then bring this section back to the open side and check the pattern. The instruction booklet has a guide for the acceptable patterns. You are not looking for centered placement, more the relation of the markings to the teeth. The drive side has a flat edge in the deep part of the gear, showing that the pinion is too close to the ring — it needs less shim.

16 Shim it: Using the supplied pinion shims, we measured the stock shim and reduced it by .015. You want to make big changes (.01-.15) at first, then work your way to smaller changes (.03-.04).

17 In the house: Once the pattern came out how we wanted, we had the new bearing pressed on, slipped on a new crush collar and dosed the pinion threads with some threadlocker and put the pinion in the housing. The front (smaller) pinion bearing was installed, along with a new seal before the pinion was installed.

18 Preload: The last step in the pinion install is setting the pinion preload. The specs for this particular unit are 6-8 pounds per inch, which is barely anything. You can’t rent lb-in torque wrenches (at least not in our town) and they cost about $100 to buy one, and that one wasn’t even small enough to hit 6 lb-in. We talked with a few local experts (not shadetree guys, real experts) who told us that they use an impact to get the pinion nut to the shoulder (you need the torque for that job) and start to crush the collar, then carefully tighten the nut until there is just a bit of drag on the bearing. It does not take much, and you get a feel for it during the setup process, so don’t freak out. If you go too far, you need to pull the pinion and get a new crush collar. The kit comes with two for this very reason.

19 Tap dance: Once set, the pinion nut needs to be hit with a pointed punch in two spots. This keeps it from backing off, which will happen if you don’t do this. You don’t have to kill it, just a few taps with the hammer will do.

20 Carrier: Next the carrier is reinstalled with the correct shims and then torqued to 65 lb-ft.

21 Hammer time: The new axles don’t come with wheel studs, which we forgot. We had to put the job off till the next day so we could get the studs. If you have never done this, it’s easy. Just use a brake drum and a 3-lb sledge. Knock the studs flush. When you torque the wheels for the first time, give ’em a little extra and make sure the studs are seated. Recheck them after a few miles.

22 Last look: Changing bearings can tweak the settings, so it’s a good idea to check it one last time before buttoning it all up. This pattern looks good. The TrueTrac carrier uses a different locking system. A hardened steel disc rests between the axles, keeping them from sliding to center; this replaces the drift pin on the older unit.

23 Plug it: The plug is inserted and retained with a large snap ring – much more secure. The previous 10-bolt we built had a broken drift pin that almost destroyed the housing. It managed to kill the stock posi carrier in the process.

24 Cover-up: The rear cover cleaned up a little, was treated to a new gasket and reinstalled.

25 Fill ’er up: We filled the rear with Royal Purple gear oil. The oil needs to be changed after the first 500 miles. Once filled, the driveshaft went back in and the job is done. Take it easy for the first few miles; the gears need some time to heat- cycle to break in.


  1. There some very impressive points in your blog. I must appreciate your excellent work. I find the blog post very interesting and moreover very informative.

  2. It takes immense knowledge to produce this piece of art.
    Johnson outboard gear set

  3. thank you for information

    โปรโมชั่นGclub ของทางทีมงานตอนนี้แจกฟรีโบนัส 50%
    เพียงแค่คุณสมัคร สล็อตออนไลน์ กับทางทีมงานของเราเพียงเท่านั้น
    สมัครสล็อตออนไลน์ >>> Goldenslot
    สนใจร่วมสนุกกับ คาสิโนออนไลน์ คลิ๊กได้เลย
    มีทั้งคาสิโนออนไลน์ หวยออนไลน์ ฟุตบอลออนไลน์ สล็อตออนไลน์ และอื่นๆอีกมากมาย

  4. A beautiful purse or handbag from Coach Outlet Online can last for many years, and represent a great overall value.
    There are Michael Kors Bags Outlet in a large number of shopping malls located throughout the country.
    Cheap Michael Kors Bags is a great way to determine which models best suit your needs.
    Official Coach Factory Outlet Online all strive to provide comfort and convenience for their owners and the seams are double-stitched for maximum durability.
    Michael Kors Factory Store, has one of the most popular handbag and accessory lines on the market today.
    Coach Handbags Wholesale says a lady is classy, elegant and sophisticated.
    Coach Store Near Me trends come and go, but a Coach stands the test of time.
    The official Michael Kors Handbags On Sale Outlet regularly posts various handbags being offered for sale.
    Compare your Coach Bags On Sale Outlet to the logo provided on the website to make sure it is similar.
    All Michael Kors Outlet Online Store have serial numbers.

  5. I was very impressed about it, wish you would have stayed next share
    drawing games

  6. The presence of insects in our homes or other places such as gardens, fields or factories, is embarrassing and disturbing to us and may expose many of us to diseases, because there are many types of insect vectors and harmful bacteria such as flies, mosquitoes, flying insects and crawling insects: Like ants and cockroaches.
    شركة مكافحة النمل الابيض بالدمام
    شركة مكافحة حشرات بالدمام
    شركة رش مبيدات بالدمام
    افضل شركة مكافحة حشرات

  7. Hi Very Nice post you can also watch Philippine tv shows on our website, Pinoy ako, Pinoytv1, Pinoy Teleserye, Pinoy Tambayan, Pinoy Channel and free download here all videos.
    Pinoy Ako Tv, Pinoy Tv ReplayPinoy TambayanPinoy Tv Show, ABS-CBS Tv Show All HD Quality ,GMA Show,Full Episode Watch On PinoyTvShows.Our team at care for our community and bring you daily fresh episodes of your favourite tv shows. You can enjoy your favourite shows, Pinoy Tambayan, Pinoy Teleserye

  8. Hi Very Nice post you can also watch Philippine tv shows on our website, Pinoy ako, Pinoytv1, Pinoy Teleserye, Pinoy Tambayan, Pinoy Channel and free download here all videos.
    Pinoy Ako Tv, Pinoy Tv ReplayPinoy TambayanPinoy Tv Show, ABS-CBS Tv Show All HD Quality ,GMA Show,Full Episode Watch On PinoyTvShows.Our team at care for our community and bring you daily fresh episodes of your favourite tv shows. You can enjoy your favourite shows, Pinoy Tambayan, Pinoy Teleserye

  9. I am Adan. I work at a leading web design company in Los Angeles. I have read this blog and i must say there is some very good information given in this blog. Thanks for that.

  10. Carpet Cleaning quick and easy. Clean your carpet free of spill, spots, stains and allergens with our Carpet Cleaning Near Me experts. Call us 24x7.

  11. Get connected with the experts in an instant by dialling British Airways Phone Number and get to know about flight tickets bookings, status, schedule, booking procedure, offers, deals, services and many more. Travel the world in comfort and in luxury without paying a hefty amount. Save more by booking with us!

  12. Get your booking with American Airlines Phone Number and get the best deals. You can book your fares over a call and as per your specifications without any hassle or paperwork. Read on to know all about us and the services we offer.

  13. To book a ticket at ease, you are just a call away. For booking tickets like economic or business class, you are supposed to call at the toll-free helpline Air China Airlines Phone Number. The travel assistants that are available at the customer support are prompt while serving you. You can have faith in us and leave the whole booking procedure on our hands. Just pack your bags and be ready for your trip.

  14. You can know about the benefits of flying with us as we choose the reliable service provided by Air China Airlines Customer Service. Get your booking done with Air China Airlines Customer Service. We are a third-party service provider that is offering assistance to Air China Airlines. Offering ticket booking and travel support to our customers is our aim.

  15. Call us at our Allegiant Airlines Customer Care Phone Number. We not only serve our customers with an exquisite service for seat reservations with Allegiant Airlines, but provide a service that is cheap and hassle free. Call us at our toll free Allegiant Airlines Customer Care Phone Number and get your tickets done instant and hassle-free.

  16. Thinking to travel at cheap rates? Get the best and reliable assistance for your journey and make your best moments when booking with us. At our platform, you will the best working professionals who are working deliberately in order to offer you the hassle-free services. For your booking, reach to our team and book tickets through Southwest Airlines Customer Care.

  17. Many of the fliers around the world face don’t have enough time to spend hours on the internet to find the right for their itinerary. To solve these problems of fliers, our team of experts provides reliable services and assistance through Hawaiian Airlines Contact Number. So, none of any fliers could face any trouble to reach their destination. Till now from starting of our firm, none of our customers face any issue regarding flight tickets booking.

  18. Well, the answer is simple, we are a third party ticketing agents for Southwest Airlines. That’s why we have a lot of discount offers and deals that no other travel booking site can offer you. Our process of registration is very much simple. Southwest Airlines Phone Number team does not work like big giants of tourism industry who spend most of their profits on advertisements to attract more customers than such agencies end up selling flight tickets with hidden charges. Southwest Airlines Phone Number team believes in fair pricing and serving customers with honesty.

  19. If you are finding deals and offers for American Airlines, dial American Airlines Reservations Number and talk with agents. American Airlines Reservations Number is toll free.

  20. Get flight tickets and instant assistance with Emirates Customer Service number
    which is available round the clock to resolve any problems during your air journey.

  21. Difficulty in bringing your Canon Printer back online? Follow the easy steps in the blog to fix "Canon Printer Offline Window 10" issue.

  22. With so many good reservation facilities, you can get effective deals with American Reservations numbers. The convenient reservation choices make it easy for the travellers to book flight tickets according to their needs.

  23. Your blog is valuable us with significant information flight booking at,your new travel Southwest Airlines Reservations booking associate. Contact our pros. It was the key bearers to show Premium Economy Each and each tip of your post are astonishing. Much refreshing for sharing. Keep blogging.if you any issue you can interface authorities groups master bunch best deals.

  24. I appericiate your comments i want to share that Get all data about of service at Southwest Phone Number,the brisk and proficient helpling large number if you any problem you can call my expert teams.


  25. I appericiate your comments i want to share that Get all data about of Spirit Airlines Phone Number more ect Booking Airlines Tickets the brisk and proficient helpling large number if you any problem you can contact us my expert teams.

  26. Geek Squad tech support have massive experience in managing numerous clients. They come to us with issues for various items and brands. Our trade and IT experts take care of those issues efficiently. Geek Squad tech support whenever you want to remove a technical glitch, you must ask for our support. They are knowledgeable in settling all minor/significant issue your gadget experiences. Jump accessible if the need arises, coming up, online help, Geek Squad chat eye to eye operator support and in-home assistance at whatever point and any place you stall out with your gadgets. Gain admittance to our help and administration according to your benefit. Geek Squad appointment | Geek Squad chat

  27. Your blog is useful us with important data flight booking at Southwest Phone Number,your new travel booking accomplice. Contact our specialists. It was the key carriers to display Premium Economy Each and each tip of your post are amazing. Much appreciated for sharing.

  28. Looking for Local Plumber Near Me services on web Local Plumber Near Me, Our professional plumbers are there to assist the commercial caretakers and residents.

  29. Search Plumbers in san diego and find our plumbers across the United States. We provide best plumbing services, actively responding to query of Plumbers in san diego.

  30. This is also a very good post which un jobs I really enjoyed reading. evden eve nakliyat adana It is not everyday that I have the possibility to see something like this jobs in usa

  31. Get the online programming assignment help and online assignment help from qualified experts at affordable prices. Quality solution, delivery before deadline.
    irish assignment help

  32. Thank you very much for sharing such a useful article.
    Personalized Care For PC

  33. Students from different parts of the world rely on Best homework help UK Service, as we are providing secure payment gateways, confidentiality agreements and financial aid centers for communication.
    Do my essay assignment
    Law case study writing service
    Online physics homework help
    Do my research paper
    Assignment help

  34. NOw watch and enjoy all the latest seriale turcesti subtitrat in hd. We provide provide daily all the seriale turecesti subtitrat in romana which you will be watch on despre seriale turcesti