randys blog
Common Carrier Breaks
As discussed in detail last month, there are many situations where a different height carrier case is needed when making a gear ratio change. Included here is a list of carrier breaks for most popular rearends. Many of these have thick or thin ring & pinion sets available to eliminate the need for changing carriers. Rearends with those options available for some ratios are indicated in the chart below. Now you have the chance to memorize them all and impress your friends. There is really no magic formula the original equipment manufactures uses to decide the actual breaking point for each design. It depends on the placement of the carrier case and the pinion centerline, and those are really arbitrary and up to the whim of a design engineer. As mentioned last month, I do NOT recommend ring gear spacers in any situation. Remember that using a thick or thin gear set has no side effects and will be just as strong and hold up just as well as a gear set that is the factory thickness. AMC M35 3.31 & down / 3.55 & up (a.k.a. Dana 35. Some early models used a thin 3.08 that only fits the 3.55 & up case) M20 2.73 & down / 3.07 & up General Motors Cast Iron Corvette 3.90 & down / 4.10 & up D36 ICA 2.73 & down / 3.07 & up D44 ICA 3.73 & down / 3.92 & up 55-64 Chevy passenger 3.70 & down / 4.10 & up (some came stock with thin or thick gears) 55-62 Chevy 1/2 ton all use same height carrier Early Olds Drop-out 3.23 & down / 3.55 & up 7.2″ IFS 3.08 & down / 3.23 & up 7.5″ 3.08 & down / 3.23 & up 7.75″ 2.77 & down / 3.27 & up 8.2″ Chevy 2.76 & down / 3.07 & up 8.2″ BOP 2.76 & down / 2.94 to 3.23 / 3.31 & up 8.25″ IFS all use same height carrier 8.5″ 2.56 & down / 2.76 & up 9.25″ IFS all use same height carrier 9.5″ 14 Bolt all use same height carrier 12 Bolt Passenger 2.76 & down / 3.07 to 3.90 / 4.10 & up * 12 Bolt Truck 2.73 & down / 2.76 to 3.42 / 3.73 & up 10.5″ 14 Bolt 4.11 & down / 4.56 & up Ford Ford does not use any carrier brakes in any of their “corporate” rearends. Chrysler 7.25″ 2.47 & down / 2.76 & up 8.25″ 2.45 & down / 2.56 & up 8.75″ all use same carrier 9.25″ all use same carrier Dana Spicer D27 3.73 & down / 3.92 & up D28 3.45 & down / 3.73 & up D30 3.54 & down / 3.73 & up D44 3.73 & down / 3.92 & up D50 all use same height carrier D60 4.10 & down / 4.56 & up D61 3.31 & down / 3.54 to 4.10 with thick gear / 3.54 to 4.10 with regular gear D70-1/2″ & 5/8″ offset 4.10 & down / 4.56 & up D70-31/31″ offset 3.42 & down / 3.54 to 4.10 (4.56 & up will NOT fit this housing) D80 3.73 & down / 4.10 & up Toyota 7.5″ all use same height carrier 7.8″ (a.k.a. 8″) 3.73 & down / 3.90 & up The OEM Toyota gears of 4.88 and numerically higher ratio used a different carrier case or a spacer. Virtually all aftermarket gear sets made for this rear end are a thick version that does not require a spacer. V6 all use same height carrier. There is however a housing offset difference in vehicles factory equipped with a 4.88 ratio. Installing aftermarket gears in these vehicles requires changing the drop-out housing to a 4.56 & down design. The carrier case is the same height for both housing and can be interchanged if the appropriate housing is used. * Thin Available ** Thick Available Popular Resources: Ford 9 Inch Differential Information Four Critical Ring & Pinion Settings
Installation: Spartan Locker Walkthrough
Unboxing: Spartan Locker
What Does “Complete” Really Mean?
Have you ever had to call around town on a Friday to find pinion shims or a crush sleeve so you could be on the trail for the weekend? Working on a rear end is hard enough with the right parts, and can be downright impossible with the wrong parts. A good installation kit can make the job a lot easier and save hours of frustration. Every distributor claims to have the best installation kits available. I have seen a number of items labeled “Installation Kit” or “Master Kit” that didn’t deserve to be named as such. Since there is really no established standard, the terms will always be used loosely and it is up to the customer to put the sales person through the drill of explaining what is in each kit, in detail. There are many good questions to ask when ordering. Does the kit include good instructions? Does it include ALL of parts necessary to rebuild or setup the rear end completely? Are both pinion and carrier bearings included in the kit, and are they the highest quality available? Many kits use cheap import bearings and seals. If the salesperson is not certain what kind of parts their kit uses, ask them to open the box and see. Many kits do not include useful carrier and pinion shims. This is due to the cost of making good shims. Are there just enough shims for one adjustment, or does the kit contain enough shims to setup the rear end from scratch? In my opinion, a complete “Installation Kit” includes: both pinion and carrier bearings, a crush sleeve or preload shims, enough pinion depth shims to set the depth without having to reuse any of the original shims. For most applications, a complete set of carrier shims. A high quality pinion seal, an OEM quality pinion nut, a gasket or silicone for the cover, Loctite® or thread locker for the ring gear bolts and pinion nut, an instruction manual with pattern diagrams and details that really help, and real gear marking compound. (If you are looking for gear marking compound in a handy tube, try GM part number 1052351.) It really doesn’t matter which parts a supplier includes in their installation kit, as long as they explain, in detail, what the kit contains. There are many high quality kits out there. Ask a lot of questions and don’t take “I’m not sure” for an answer. Remember, this is your rear end we are talking about.
Myths Regarding Differentials
Over the years I have heard a lot of myths regarding the setup and design of differentials. Anyone with a little experience can fix a diff. I have heard time and time again that the following situations make a person a qualified differential expert: They are an old-timer, a grizzled guy with stained overalls. They are a machinist. They are in a four-wheel drive club. They have built a few rear ends for their buddies. I believe there are only a few people who really know how to setup a rearend correctly, and they have learned from years of experience and collecting facts. The gear ratio in the front of a four wheel drive has to be different from the rear so the front wheels will pull more. There have been many different ratio combinations used in four-wheel drive vehicles, but not so that the front will pull more. Gear manufactures use different ratios for many different reasons. Some of those reasons are: strength, gear life, noise (or lack of it), geometric constraints, or simply because of the tooling they have available. I have seen Ford use a 3.50 ratio in the rear with a 3.54 in the front, or a 4.11 in the rear with a 4.09 in the front. As long as the front and rear ratios are within 1%, the vehicle works just fine on the road, and can even be as different as 2% for off-road use with no side effects. 1 point difference in ratio is equal to 1%. To find the percentage difference in ratios it is necessary to divide, not subtract. In order to find the difference, divide one ratio by the other and look at the numbers to the right of the decimal point to see how far they vary from 1.00. For example: 3.54 ÷ 3.50 = 1.01, or 1%, not 4% different. And likewise 4.11 ÷ 4.09 = 1.005, or only a 1/2% difference. These differences are about the same as a 1/3″ variation in front to rear tire height, which probably happens more often than we realize. A difference in the ratio will damage the transfer case. Any extreme difference in front and rear ratios or front and rear tire height will put undue force on the drive train. However, any difference will put strain on all parts of the drivetrain. The forces generated from the difference have to travel through the axle assemblies and the driveshafts to get to the transfer case. These excessive forces can just as easily break a front u-joint or rear spider gear as well as parts in the transfer case. Positraction is better than limited slip. I have heard many people call a standard open differential a “limited slip” and I have been asked for a limited slip instead of a positraction because they wanted something that was not too aggressive. From my experience positraction and limited slip are just two different names for the same thing. If anyone can find a SAE standard or printed definition please let me know and I will gladly correct myself. Popular Resources: Diagnosing Noise (Part 1) Ford 9 Inch Differential Information Four Critical Ring & Pinion Settings