The biggest hassle with setting up rear end gears is setting pinion depth. It's critical to the life of the parts and, until now, has required an expensive pinion setting tools to do the job properly. We know because we bought that T&D pinion depth tool several years ago to help set up the Ford 9-inch, GM 12-bolts, and Dana 60s we've used over the years. But now, Ratech has come up with pinion setting tools that are based on a simple concept. Pinion depth is the location of the pinion-gear teeth relative to the ring-gear teeth. This placement is established when the gears are machined, precisely matching the pinion to that particular ring gear. Aftermarket gear manufacturers assist the setup process by scribing the pinion depth number on the end of the pinion gear. The number is the distance from the machined end of the pinion gear to the ring-gear centerline. In the past, measuring this distance required a dial indicator on a mandrel that rides on adapters in the carrier bearing housings. Measuring the distance from the pinion face with a dial indicator produced a number that, once calculated using some simple subtraction, established the pinion depth. The procedure's only downside is the pinion setting tools cost around $400. For the typical car crafter who may only set up a rear end once every five years, a the pinion depth tool price is difficult to justify.
Most rear axlehousings are designed to use a shim to locate the pinion at the precise distance to the ring gear. In the case of a GM 12-bolt, Ford 8.8, or Dana 60, for example, the shim is placed between the head of the pinion gear and the bearing. The hassle with this method is that you need a hydraulic press to remove and install the bearing when changing shim thickness. A common trick is to create a setup bearing using a flapper wheel on a die grinder to hone the inside diameter of the bearing so it will easily slide over the pinion gear. This makes checking the pinion depth and changing the shim much easier. Of course, you should press on a new pinion bearing once the proper depth has been established.
The Ratech pinion depth tool is unlike the cheaper models you may have seen in the past. One such pinion depth gauge used the carrier bearing cap centerline as a reference point for measuring pinion depth. The problem with that idea is the parting line is usually not the true bearing centerline, introducing major errors into the measurement process. In contrast, the Ratech tool measures from the bottom of the carrier bearing saddle, and with some simple math (dividing the carrier bearing diameter in half to establish true ring gear centerline), it allows you to determine actual pinion depth.
We decided to test this pinion depth gauge to see if it really worked. As you will see, it was within 0.006 inch of the pinion depth we measured using the more expensive T&D tool. And since the ultimate final judgment of pinion depth is based on the gear-tooth pattern, the Ratech tool is certainly accurate enough to get you very close to a final pinion depth at a very reasonable cost. The tool runs $29 and is available for all the popular performance rear-axle assemblies such as the Ford 9-inch and 8.8, the Dana 60, and most of the GM rear ends.
Parts List Description PN Source Price Ratech 12-bolt tool 10005 Ratech $29.00 Ratech 8.2 GM 10002 Ratech 29.00 Ratech 8.5 GM 10003 Ratech 29.00 Ratech 8.8 Ford 10006 Ratech 29.00 Ratech 9-inch Ford 10013 Ratech 29.00 Ratech 8-inch Mopar 10007 Ratech 29.00 Ratech Dana 60 10009 Ratech 29.00 Ratech install kit 315K Ratech 77.00 T&D tool 11001 Internet 387.95 Yukon 3.73 gear YG GM12P-373 Summit Racing 272.57 Eaton Truetrac 913A555 Summit Racing 449.95 Amsoil gear oil SVGQT-EA Amsoil 14.90/each
This is the budget Ratech pinion depth tool for a 12-bolt, but there are similar tools for all the popular rear-axle assemblies like the Ford 9-inch, Ford 8.8, Dana 60, and the other GM rear ends. Each Ratech tool has a different number etched into its face. This makes each pinion depth gauge more accurate. Our tool’s specific reference number is 3.391. We will use that number to help establish the actual pinion depth.
Moore placed the Ratech tool in the housing as shown, using his left hand to hold the tool in place over the pinion while it rested on the carrier bearing saddle. Then, with his right hand, he used a dial caliper to measure from the tool face through to the bottom of the carrier saddle. This requires some finesse because the end of the caliper is flat but placed against a round saddle. Greater accuracy can be obtained by chamfering the square edges of the dial caliper plunger. The depth measured with the dial caliper was 0.596 inch. Using the Ratech reference 3.391 number stamped in the face of the tool, we subtracted the 0.596 from the 3.391 and came up with a pinion depth of 2.795. The T&D tool established the pinion depth at 2.801, which means the Ratech tool was only 0.006 inch off the T&D measurement—close enough to make it a good working number.
Before we assembled our pinion in the housing, we used an abrasive flapper wheel mounted on a die grinder to increase the inside diameter (id) of a used pinion bearing to eliminate the press fit. Once the bearing easily fit over the pinion, we placed a shim over the pinion (arrow) and then slid the bearing in place. Moore then installed the pinion in the housing along with the second bearing and tightened the U-joint flange to zero the endplay.
This is the Yukon 3.73:1 gear set we ordered from Randy’s Ring & Pinion along with an Eaton Truetrac limited-slip differential and a complete installation kit from Ratech.
GM gears are designed to fit a specific carrier for the ratio. For example, all 3-series gears (3.08:1–3.90:1) must be used on a 3-series carrier. Curries can be identified by the thickness of the ring gear flange.
Here’s a final installation of the gears and limited-slip in the housing. If the pattern is good, all that’s required is installing the cover and filling the housing with a couple quarts of Amsoil Severe Gear 75W-90 lube. The gear design of the Truetrac limited-slip does not require a friction-modifier additive.
