Description

Dana Spicer 1214, 1420 Service Manual – Factory OEM Print for Heavy-Duty Transmissions

I’ve seen guys tear down a Spicer 1214 or 1420 transmission using an aftermarket guide printed on thin paper. Then they come asking why the shift fork binds on reassembly. Because the aftermarket manual left out the air system line routing. This Dana Spicer 1214, 1420 Service Manual is the original OEM document. 71 pages thick. No guesswork, no third-party cherry-picking. You get the exact same information the factory gives to dealer techs.

If you are a home garage guy with a heavy-duty truck or a shop owner in San Antonio like me, you know that 14‑ and 20‑speed transmissions are not forgiving. One wrong torque spec on the mainshaft nut and you’re pulling the box again. This manual walks you through the entire rebuild sequence from section I to section VIII. Page 2 gives you the specifications and shift instructions for the 1214 model. Page 5 starts the 1420 data. You need the charge pressure? It’s in the general information, not hidden in an appendix. Every section mirrors the order of assembly — no flipping back and forth through random pages.

Let me tell you why the table of contents matters more than the cover. Section II covers maintenance with a dedicated lubrication section that includes towing instructions. If you pull a loaded trailer without proper lube, you will wipe the countershaft bearings. Section III details overhead controls and remote control linkage — something every DIYer gets wrong on first install. Section IV has an exploded drawing of the shifter housing for both forward control and center control. You see the part before you start pulling.

General Information & Shift Instructions

Section I gives you the raw specs: gear ratios, shift pattern, air pressure requirements. For the 1214, the shift sequence is different from the 1420 because of the splitter arrangement. Page 2 lays out the exact shift gates. If you blow through that sequence, you will grind third gear every time. The manual does not assume you know — it tells you. Also includes a tool reference list on page 12. You need a Spicer SST-XX? They tell you. No generic “use standard puller” nonsense.

7 Major Sections Across 71 Pages

The manual is split into eight sections, but seven cover actual disassembly and reassembly. Section V alone covers the rear case sub-assembly and front case sub-assembly with separate exploded drawings for air control parts and gears. That is critical because the air control lines on a 1420 are often mismarked in generic manuals. Here, page 26 shows the front case sub-assembly exploded view — you can trace every air line route before you crack the case. Section VI handles mainshaft disassembly, inspection, and reassembly. Page 33 starts the mainshaft tear-down. Page 36 has inspection procedures — they tell you what wear limits are, not just “replace if worn”.

Disassembly Precautions: Why They Matter

Section II includes a subsection called “Disassembly Precautions” on page 11. If you ever pulled a Spicer transmission without reading that page, you probably dropped a shift fork spring into the bottom of the case. The manual lists specific handling requirements for the air control pistons and the rear case gasket surfaces. Ignore them and you will have an air leak that costs you a full day of troubleshooting. I have seen it happen. This manual treats those precautions as a separate heading, not a footnote.

What Lubrication Data Is Included?

You need the correct viscosity for ambient temperature. The manual specifies SAE 50 or 80W‑90 depending on the ambient range. It also covers towing — if you flat-tow the vehicle with the transmission in neutral, you must disconnect the output shaft or you starve the rear bearings. That is on page 8. No aftermarket guide covers towing because they assume you never move the truck with the box full. This manual does because it was written by engineers who designed the driveline.

Does This Manual Cover Both the Model 1214 and the 1420?

Yes. Section I splits the specification pages — page 2 through 4 are for the 1214, page 5 onward for the 1420. The shift instructions differ, and the air control routing is different for the 1420’s higher splitter count. If you are working on a 1420, you need the dedicated pages. This manual gives you both in one document.

FAQ

Where do I find the torque specs for the mainshaft nut?

Torque values are listed within the reassembly sections for each sub-assembly — mainshaft reassembly begins on page 37. The manual does not consolidate all torques on one page, so you must follow the step-by-step sequence to get the correct value for each fastener.

Can I use this manual for a 5-speed Spicer transmission?

No. This manual is strictly for the 1214 and 1420 14- and 20-speed models.

Does the manual include wiring diagrams for the air control solenoids?

No wiring diagrams. The air system section covers pneumatic line routing and valve identification, not electrical schematics.

Are the exploded drawings in this manual scaled or actual size?

They are not to scale but include part numbers and callouts that match the factory parts catalog. On page 26, the front case sub-assembly drawing labels every bearing and snap ring location. Use it to verify you have the correct parts before reassembly.

You can cross-reference this manual with other Manual Transmission”>manual transmission documentation, but for these specific Spicer models, this is the only factory source you should trust. If you need rebuild data for other Dana units, check out the Dana Spicer 1372-A Service Manual – Factory Specs & Rebuild Guide”>Dana Spicer 1372-A Service Manual – Factory Specs & Rebuild Guide or the Dana Spicer ES60-5, CM59, ES60-5A, ES60-5C, ES60-5D Service Manual”>Dana Spicer ES60-5 series manual. For the ES46-5 family, use the Dana Spicer ES46-5 ES56-5 2002 Service Manual – 40 Pages of Factory Specs”>Dana Spicer ES46-5 ES56-5 2002 Service Manual. And if you are still using aftermarket reprints, stop. This is the real thing. Manual Transmission”>Manual Transmission knowledge starts with factory data. Access the Factory Manual and get to work.