Okay, see if you can follow this. When I first built my ’53 DJ-3A I used low-pinion Ford 9-inch axles with 5.83s and stock 2.46:1 gears in a Spicer 18 T-case. With the junkyard Warn Overdrive engaged, I could turn 2,850 rpm at 65 mph on the street, and the SM420’s 7.05:1 First gear gave a 101:1 crawl ratio, which was just about perfect for my relatively low-torque 3.5L Shortstar DOHC V-6. Then the hardcore bug bit and I replaced the Spicer 18 with a built Dana 300 running stock 2.62:1 gears and 32-spline front and rear output shafts. The Dana 300 has a much higher rear output location than the Spicer 18, so to get a rear driveshaft in the thing I had to build a new centered rear axle with a high-pinion True Hi9 centersection. The axle build required a gear change to 5.38s since that’s the lowest ratio offered for the True Hi9. But even with the high-pinion rear diff, to prevent U-joint binding at full droop I had to run offset-trunion U-joints in the Tom Wood’s 1350 rear driveshaft. The crawl ratio of the new setup was nearly identical at 99:1, but without an overdrive, my engine speed was a whopping 3,500 rpm at 65 mph. Not that I could ever reach that speed since the crazy rear driveshaft U-joints caused the Jeep to feel like you were riding a paint shaker even at modest road speeds.
If you read my Trail Head editorial this month, you know all about why I want to go back to an Overdrive-equipped Spicer 18 to make my ’53 DJ-3A highway-capable once again. It turns out that I had it right the first time. But unfortunately I’d sold off my genie Warn Overdrive and Spicer 18 to help pay for the Dana 300 swap. However, companies like ATV Manufacturing and TeraFlex are still supporting these 70-year-old T-cases. And that’s where I found the solution to my dilemma of how to add the lower rear output location and overdrive ability of the Spicer 18 without killing my crawl ratio.
If I used stock 2.46:1 Spicer 18 gears with my 5.38 axle gears, my new crawl would be around 93:1. That’s not terrible. In fact, it’s just about ideal for most normal V-6 and V-8 powered Jeeps. But my little Shortstar needs all the torque multiplication it can get. By using 3.15:1 Low18 T-case gears from TeraFlex, I’d have a 119:1 crawl ratio, which will make the Shortstar much happier and help its resistance to stalling when idling over obstacles. The 3.15:1 gears are also a great solution for a good crawl ratio if you’re not running a granny-gear T-case or deep axle gears. Plus, I could engage the Overdrive for a more-modest 89:1 crawl when the obstacles aren’t as gnarly. Done! A quick call to ATV Manufacturing in Brush Prairie, Washington was all it took to line up the ultimate Spicer 18 build using a Dana 20 case, Low18 gears, and ATV’s own ATV Mfg. Overdrive. I hopped a plane and stood over the shoulder of vintage Jeep parts guru and ATV’s owner Herm Tillford as he assembled my new T-case and ran through some of the finer points of successfully rebuilding and running Spicer 18s. Tune in next time for a more in-depth look at ATV’s Overdrive and the T-case installation into the Jeep using an adapter from Novak Conversions. Then, how about a good old-fashioned vintage Jeep road trip?
ATV Manufacturing buys huge...
ATV Manufacturing buys huge volumes of rebuildable transmissions, T-cases, knuckles, winches, many other vintage Jeep goodies and maintains an impressive inventory. After disassembly, each component is thoroughly cleaned, inspected, and refurbished. On left is a stock 11⁄4-inch, large-hole Spicer 18 and on right is a Dana 20 case ground for clearance of the larger 3.15:1 Low18 intermediate gear (arrow).
On the right is the 3.15:1...
On the right is the 3.15:1 Low18 gearset from TeraFlex compared with a stock 2.46:1 gearset. The Low18 gears require a 11⁄4-inch Spicer 18 or Dana 20 case and are manufactured with factory-spec heat treating and exacting tolerances. For about $140 less than the full four-gear set, you can buy the Low18 gearset without the input gear (shown upper left) if you’re planning on running an overdrive.
In years past, aftermarket...
In years past, aftermarket intermediate shaft quality was hit-or-miss, with galling and shafts spinning in the case often the result. Only certain companies like Novak paid much attention to proper heat treating practices. From gears to shafts, Tillford checks each batch he receives on his Rockwell hardness tester. As our benchmark, we measured the Novak shaft at HRC 551⁄2 (’bout the same as a quality knife blade). Then we measured an Omix shaft at HRC 53 and two recently improved Crown Automotive shafts identical to those that come with the Low18 gearsets at HRC 571⁄2 and HRC 601⁄2.
Tillford only charges $110...
Tillford only charges $110 labor for a normal T-case rebuild, plus parts. He begins by assembling the output shaft gear and sliding gear on the front and rear output shaft assemblies and drives the rear output bearing onto the shaft. Next, the shift rods are hooked up, the front bearing and retainer are installed, and the shift extension housing installed on the front of the case. Tillford even tests his bearings for Rockwell hardness and uses only the best CE-grade Nakagima bearings.
Cleaned and inspected for...
Cleaned and inspected for cracks, factory Spicer shims are used to set the output shaft endplay after the rear bearing is driven on the output shaft. Tillford reports good luck avoiding leaks using no sealant; only factory-type paper gaskets and dry shim packs. He reports the secret is making sure everything is completely clean during assembly and hitting gasket surfaces with a light sanding disc to knock down burrs.
The shim pack is placed over...
The shim pack is placed over the back of the case, the speedo gear drive installed, and the rear cover bolted down. Going by the dial indicator, you want to set the shaft end play at about 0.004-inch, but going by hand, push and pull the output shaft feeling for any play. Pull shims until you get no perceivable play, but make sure the shafts spin feely. If not, add thinner shims.
During assembly, Tillford...
During assembly, Tillford uses white lithium grease to prelube all the bearings and contact points. The lithium grease will dissolve into the gear oil once the T-case comes up to operating temperature. Never use heavy grease, as it may not dissolve and can actually block oil flow though the case. Tillford uses liberal amounts of grease to hold the roller bearings in place inside the intermediate gear before assembly.
Lay the brass thrust washers...
Lay the brass thrust washers over the intermediate shaft bores and hold in place with grease. The intermediate shaft is installed from the rear of the case. Lay the intermediate gear in the case and carefully drive the shaft through. Periodically make sure the needle bearings and thrust washers don’t drop down as the shaft is inserted.
Insert the locking tab on...
Insert the locking tab on the intermediate gear and check for smooth gear mesh by spinning the output shafts. Tillford now installs the pan with a dry gasket and drives on the front and rear output and shift rod seals. The input gear (or overdrive in our case) isn’t installed until the T-case is positioned behind the transmission.
Tillford goes the extra mile...
Tillford goes the extra mile in his rebuilds to do everything he can to deliver a leak-free unit for his customers down to inspecting the output yokes for excess wear and pitting. Yokes with too much wear aren’t used, while usable units are chucked up on ATV’s lathe and polished to ensure a smooth seal surface.
Here’s a little tidbit we...
Here’s a little tidbit we never realized. If you have a Spicer T-case and the output shaft has a hole in it for a cotter pin, the yoke nut threads are 3⁄4-18. If there’s no hole, the threads are a 3⁄4-16. You can readily buy 3⁄4-16 nuts, but the 3⁄4-18 nuts are only available through special-order vendors. Tillford reuses the stock 3⁄4-18 nuts and indexes for the cotter pin.
Spicer 18 Through the Years
1- The standardized ’41-‘45 WWII-era flatfender and very early ’45 CJs used the T-84 transmission with shift rails that protruded through the rear of the tranny case, requiring corresponding holes in the mounting face of the Spicer 18. These holes can be a source of leaks when not used with a T-84. These first Spicer 18s ran a small 3⁄4-inch intermediate shaft with bronze bushings and only had 1.97:1 low range with a special 27-tooth x 6-spline input gear and are considered to be somewhat weak. All Spicer 18s with the exception of the late V-6 models have a 3.150-inch input bore diameter and are referred to as “small hole” cases.
2- Early ’46 models increased the intermediate shaft to 11⁄8-inch with caged needle bearings on the intermediate gear. The low range was upped to 2.43:1 and the input gear was 26-tooth x 6-spline. Note, early 11⁄8-inch cases still have vestigial T-84 shift rail holes, so Tillford speculates Spicer merely bored leftover 3⁄4-inch hole MB cases.
3- The later ’46-’55 models were essentially the same as the early ’46 models, but the T-84 shift holes were gone and a solid T-case to transmission mounting face helped prevent leaks when bolted to a T-90 or other transmission.
4- The late ’55-’71 models received a larger 11⁄4-inch intermediate shaft that utilized free roller bearings inside the intermediate gear for more strength and longer service life. The input bore diameter remained at 3.150-inch and input gear was 29-tooth, 6-spline, although pickups and many later four-cylinder CJs received the “large hole” 4-inch bore case. Low range for the 29-tooth cases is 2.46:1.
5- All ’66-’71 V-6 models got the “large hole” 4-inch input bore cases with slightly heavier construction more akin to a Dana 20 case and a 11⁄4-inch intermediate shaft. The input gear is a 29-tooth, 6-spline with the T-86 and 29-tooth, 10-spline unit with the T-14 transmissions.