New Idea 5408 Disc Mower Parts Diagram

Working With the New Idea 5408 Disc Mower Parts Diagram

I spent about three hours last month trying to trace where a specific bearing housing belonged on my 5408 without the diagram, and let me tell you that was a waste. Having the right parts diagram saved me from ordering the wrong components twice. These machines are everywhere in hay operations, and the diagrams themselves can be frustrating to work with if you don't know what you're looking at. The New Idea 5408 Disc Mower Parts Diagram breaks down the mower head assembly, disc stack, gearbox, belts, and the linkage system that connects everything to the tractor. What most people don't realize is that there are actually several variations depending on the year your machine was built. The early models from the mid-1980s have a different spindle arrangement than the late-model versions from the early 1990s, and New Idea didn't always update their diagrams to reflect every minor change. I learned this the hard way after ordering a spindle kit that fit physically but had the wrong thread pattern for my year. Took about a week for the part to arrive and another three days to realize the mismatch. You need to match the diagram to your serial number range, not just assume one diagram covers the entire production run.

New Idea 5408 Disc Mower Parts Diagram

Here's a practical breakdown of what you'll find in the diagram and why each section matters when you're doing actual repairs. The disc stack section shows the cutting discs, spacers, and the arbors they slide onto. This is where most failures happen. The discs themselves are hardened steel and typically last tens of thousands of acres before needing replacement, but the spacers between them are a different story. They wear down from debris buildup and constant vibration. In the diagram, you'll see them listed with part numbers, but what the diagram doesn't tell you is that replacing spacers without inspecting the arbors is a common mistake. I've seen operators put new spacers on worn arbors and wonder why the disc wobbles after an hour of cutting. The arbors develop a ridge where the spacer rides, and that ridge will chew through any new spacer within a season. Measure the arbor diameter at multiple points before ordering replacement spacers. If you're more than two thousandths out of round, replace the arbor instead of just the spacer. It costs about forty dollars more upfront but saves you a teardown next summer. The gearbox section of the New Idea 5408 Disc Mower Parts Diagram shows the main drive reduction box and the individual disc gearboxes. The main drive gearbox takes the input from the PTO and reduces the speed before sending power to each disc through the belt system. One thing nobody warns you about is the input seal. It fails more often than people expect because it's exposed to moisture and debris from the tractor PTO shield. When it leaks, you lose gear oil and eventually the whole gearbox seizes. The diagram shows the seal part number, but it won't tell you that many mechanics recommend replacing it preemptively every other season rather than waiting for a leak. A input seal runs about fifteen dollars. A replacement gearbox is over four hundred dollars plus your time to pull it out of the frame.

The belt routing and tensioning system is another area where the diagram can be misleading. New Idea used a spring-loaded idler system on most 5408 models, and the diagram shows the belts in their relaxed position. When you're actually installing belts, you need to relieve that tension properly. I've watched people force belts on and damage the idler pulley bearings in the process. There's a relief bolt near the tensioner arm that backs off the spring load. Once that's loose, the belt slides on without any drama. Takes about thirty seconds and prevents a $60 bearing replacement down the line. The cutter bar and deflector assembly is straightforward in the diagram but tricky in practice. The deflector plates control where the cut material blows out, and they're adjustable. The diagram shows the adjustment points but not the optimal settings. If you're cutting wet alfalfa, you want the deflector angled slightly more downward to prevent material from throwing back against the discs. Dry grass is lighter and throws differently, so the setting changes. Start with the deflector halfway up and work from there based on what you see coming out the side. I usually set it so the material lands in a neat windrow about two feet from the mower. That's your baseline, then you fine-tune from there. One edge case that trips people up involves the slip clutch on the disc arbors. The diagram shows it as part of the disc assembly, but some aftermarket replacements don't match the original friction characteristics. If you swap to a cheaper slip clutch and it starts slipping during normal operation, you're not cutting consistently and you're damaging the disc edges. I ran into this on a neighbor's mower last fall. He'd replaced the original clutches with budget units from an online catalog. The machine would cut fine until the stalks got thick, then the clutch would slip and the disc would stop spinning. I swapped back to the OEM clutches and the problem disappeared immediately. Don't skimp on the slip clutch. It's doing critical work protecting the gearbox from overload.

Where to Find the Diagram

The most reliable source is a New Idea dealership parts department. They can pull the diagram specific to your serial number and print it out or email it to you. This usually takes one business day. Some independent implement shops also carry these diagrams and may sell copies for around twenty dollars if the dealer is being difficult. Online marketplaces like eBay sometimes have scanned copies of the full manual with the diagram included, though the quality varies depending on whoever digitized it. If you're trying to order parts online and the seller won't show you the diagram first, that's a yellow flag. Any reputable parts supplier should be able to match your serial number to the correct diagram before taking an order. If they can't, send them elsewhere.

Using the Diagram Effectively

Print it at full size. The small thumbnail versions online are useless for identifying part numbers because the text gets too small. A proper 11 by 17 printout lets you read the callouts clearly and reference the part numbers without squinting. I keep mine in a plastic sleeve in the cab so I can mark up notes directly on it with a dry-erase marker. Over a season, these annotations become useful. I write down which parts I've replaced and when, what symptoms led to each replacement, and any deviations from the standard assembly. The diagram alone won't tell you how tight to torque anything. For that, you need the service manual, which often accompanies the parts diagram in the same publication from New Idea. If you only have the parts diagram and you're rebuilding a gearbox, you'll be guessing on bearing preload and seal installation direction. The service manual covers all of that. Buy them together if you can. Another practical note: the New Idea 5408 Disc Mower Parts Diagram uses a parts list format with exploded views. The exploded view shows how components fit together, and the parts list gives you the part numbers in a table. Cross-reference them. Sometimes the part number in the legend doesn't match the number callout on the drawing, and having both tables side by side catches those discrepancies. I found a mismatch like this once where the bearing shown in the exploded view was listed under a different part number in the table. Ordering from the table number would have given me the wrong bearing. Checking both prevented that mistake.

If you're working on a 5408 that's had previous repairs, the diagram shows the original configuration, not whatever modifications someone made years ago. I've pulled apart mowers where someone had fabricated custom brackets or used substitute bearings from a different application. The diagram won't reflect those changes, so you need to physically verify each component rather than assuming it matches the drawing. This is especially common on older machines that have changed hands multiple times. Assume nothing until you've confirmed it with your own eyes.