Will a Wheel Horse 5-0621 Deck Fit a 300 Series Tractor?

No – not without major work. The 5-0621 is a 36″ rear-discharge deck from early 1970s Wheel Horse tractors (the old B/C series), while the 300 Series (mid-1970s “Attachomatic” models) uses a completely different mounting system. In other words, you can’t just bolt the 5-0621 onto a 300 as-is – the frames and hookups won’t line up. To make it fit, you’d essentially have to rebuild the deck’s front frame (swapping in a 300-series upper frame or welding on custom brackets) and even then double-check belts and pulleys. For most owners, it’s far easier (and safer) to use a mower deck made for the 300/400/500 Series.

Why a 5-0621 Deck Won’t Bolt Directly to a 300 Series

The main issue is different attachment systems. The 300 Series tractors use Toro’s built-in “Attachomatic” quick-connect system, where the tractor’s frame has a slot and lift arms that hook into the deck’s upper frame. The older 5-0621 deck was made for the older pin-style hitch kit (“Attach‑a‑Matic”) that older Wheel Horses used. In practice, this means the front hitch pin, lift brackets and holes on the 5-0621 simply won’t line up with a 300 Series tractor’s mounts.

• Mount and frame differences: Even though both decks are 36″ wide, the deck frame geometry is different. The 5-0621’s front support and lift pivot were built for the older medium/long-frame tractors. A 300 Series is a “long-frame” model with a longer wheelbase, but its deck frame is designed around the new attach method. As one forum expert noted, the deck “shell and spindles” might match, but “the rest is different”. In short, the 5-0621’s front brackets and hitch won’t accept the 300’s lift arms.

• Attach-o-Matic vs Attach-a-Matic: Wheel Horse terminology can be confusing. The 300 series ‘Attachomatic’ design has the deck slide into a built-in slot on the tractor. Older tractors (B/C series) used an “Attach-a-Matic” kit with separate pins and brackets. Converting the 5-0621 means replacing its entire front hangers with a 300-style frame (or fabricating adapters) – a heavy job. Experts say it’s “more work than it’s worth” to try adapting the old deck (you’d essentially be making a custom mounting kit).

• Even if dimensions seem right: You might notice the 5-0621 is listed as “fits medium frame and long frame tractors”, and a 300 Series is indeed long-frame. However, that listing refers to older long-frame models – the attach points are still different. In fact, official parts manuals do not list the 5-0621 under any 300-series tractor. In practice, nearly every Wheel Horse owner will tell you the same thing: short answer, it’s not compatible as-is.

What It Would Take to Make a 5-0621 Fit

Because of these mismatched brackets and frames, using a 5-0621 on a 300 Series requires major fabrication or parts swaps. For example:

• Swap the deck frame: You’d need the correct 300-series front deck frame (with the right hangers, lift eyes and hitch pins). In practice, that means finding a wrecked 36″ deck from a 300/400/500 Series and transplanting its upper frame onto the 5-0621 shell. The deck housing and spindles could stay the same, but the entire front “hanger” and pin assembly must be replaced. Owners sometimes “find a rotted deck with usable mounts” and swap them in.

• Custom welding: Alternatively, you could cut and weld an adapter. This involves adding new brackets or holes to the 5-0621 frame so that a 300-series tractor’s lift arms could latch on. That’s precise, heavy welding – not a simple DIY tweak. As one expert noted, it would take “custom fabrication” to make the 5-0621’s front end match a 300-series deck.

• Belts and pulleys: Even if you sort the frame, you’d then have to check the belt routing and lengths. The 5-0621 used certain belts (for example 102741 or 102607) that were sized for older engine/deck spacing. The 300 Series often has a higher PTO position or different pulley centers, so the original belts might not be correct. You might need different belts or idler adjustments. All of this means tinkering with lift linkages, belt path and possibly getting custom belts.

In summary, adapting the 5-0621 is effectively a big custom build. You’re changing the front frame geometry, the attachment points, and possibly belts and linkages. As one guide bluntly puts it: “the 5-0621 deck was not designed for a 300-series tractor. The mounting geometry, belt alignment, and lift systems are different.”. Only a dedicated hobbyist would undertake this – most say “if you expect a plug-and-play fit, you’ll be disappointed”.

The Right Deck to Use on a 300 Series

Given all the trouble, the easier solution is to use a deck made for your 300 Series tractor. Wheel Horse (Toro) sold 36″ decks specifically for the 300, 400, and 500 Series that come with the proper Attachomatic hardware out of the box. Here’s what to look for:

• 300/400/500 Series decks: These share parts and frames. A 36″ deck labeled for a 300 Series (or even 400/500 Series) will drop right onto a 300 tractor. Check parts listings or seller descriptions for “36″ 300 series deck”. The manuals list the correct model numbers for those decks.

• Correct frame and brackets: Make sure the deck comes with the front support frame and hitch pins for the Attachomatic system. A painted deck shell by itself won’t latch onto your tractor unless it has the matching frame and mount hardware. Without that upper frame, the deck is useless on a 300 Series.

• Width and clearance: Match the deck width to your tractor’s wheelbase. The 5-0621 was 36″ wide, so if your 300 Series originally used a 36″ deck, get a 36″ replacement. (If your tractor had a 42″ or 48″ deck, note that too.) Also, check that the deck’s height clears your tractor’s engine pulley – 300-series tractors often have a slightly higher PTO, so some decks sit higher.

• Used or NOS deals: Many owners find a deck on classifieds, eBay or tractor forums. You might see “NOS” (new old stock) decks or salvage decks. In practice, it’s often easiest to buy a complete 300-series deck assembly (deck+frame+wheels+belts) from a junk tractor. This way all the right parts are together. For example, salvage yards and Wheel Horse collectors sometimes sell “deck complete” setups specifically for 300/400 series. That approach “saves you the headache of mixing and matching parts,” as one guide notes.

By contrast, forcing the 5-0621 to fit means mixing an old deck with a new tractor – and that mismatch is what causes all the work. Using the correct deck (even if it’s used or NOS) guarantees the mounts, lift pins and belts were designed to work with a 300 Series.

Summary

In plain terms: a Wheel Horse 5-0621 deck will not just bolt onto a 300 Series tractor. It was made for a different era of Wheel Horse machines, with a different attach system. The 300 Series introduced the Attachomatic mounting, so the 5-0621’s front frame and brackets do not align with it. To use a 5-0621 on a 300 series, you’d basically have to rebuild the deck’s front end to match a 300-series deck frame – a large custom project.

Experienced owners therefore recommend skipping the retrofit. Instead, find a mower deck made for the 300/400/500 series with the correct upper frame and pins. A 36″ 300-series deck (new or used) will fit your tractor without the headaches of mismatched brackets and belts. In short: don’t force the old 5-0621 onto a newer tractor. Use the right deck and you’ll save time, money and frustration in the long run.