One tends to forget how much experimentation was done by those early automotive pioneers; for example, take the clutch. Although most of the industry eventually settled on the single-disc “dry” clutch that so many of us have replaced in the driveway, Hudson used a system of corks bathed in “Hudsonite” oil and pressed into a thin metal clutch disc to drive the car.
Those early pioneers quickly figured out that a driver needed to disengage the car’s engine from its transmission; otherwise, they would have to turn off the engine and restart it every time they needed to come to a stop, which was impractical and potentially deadly. Additionally, as transmissions became more complex, drivers needed to be able to shift between gears without fighting the engine’s load; the clutch handled both tasks. The clutch started out as a simple twisted leather belt, as seen here on a replica of Karl Benz’s 1886 Patent Motorwagen. It had no gears to shift, but a hand lever forced the belt to act somewhat like a modern CVT, powering a differential and drive chains to the rear wheels. It was simple but effective for the job it was doing.
However, as engines became more powerful and there were more gears to shift, the leather belt just wasn’t going to cut it. Eventually, most of the industry settled on the modern “dry” clutch, whose components are seen here. The flywheel is bolted to the engine’s crankshaft and spins with the engine. The pressure plate is bolted to the flywheel itself, and sandwiched between the two is the clutch disc, which is splined to the input shaft of the transmission. When the transmission is installed, the input shaft passes through the clutch fork, throwout bearing, pressure plate, clutch disc, and flywheel, and is supported on the front end by a pilot bearing or bushing, which is driven into a void in the crankshaft itself.
When you push the clutch pedal down, the clutch fork pushes the throwout bearing into the pressure plate, which uses a series of springs and levers to disengage the clutch disc. Remember, the clutch disc is the only part of this system that is splined to the transmission’s input shaft. Once the driver’s foot is on the clutch, the crankshaft and flywheel are spinning independently of the stationary input shaft; therefore, without the pilot bushing, the fairly long input shaft would tend to “whip” around.
After some evolutionary dead ends, most of the industry eventually adapted a dry disc clutch as seen above. The friction facings themselves were long made of asbestos, although other materials are now used. The splines in the center of the clutch hub are connected to the transmission’s input shaft, which is what drives the car. The reason that a friction face is needed is for smooth clutch engagement; if the clutch were like an on/off switch, the engine would stall trying to take off or parts would break, and certainly, nobody would want to ride in your car. Therefore, the clutch lining acts almost like a brake lining in reverse; instead of gently stopping the car, the clutch starts the car off.
Being that the early days of the automobile were filled with innovation, not everybody handled declutching in the same way. For most of its existence as a going concern, Hudson Motor Car Company used a wet clutch, which consisted of a thin metal clutch disc with around a hundred corks pressed into it.
The system is sealed and filled with one-third of a pint of “Hudsonite” clutch compound, which is changed every 5,000 miles. An empty gallon container of Hudsonite was my motivation to explore these clutches, as a friend of mine found one in the attic of an old house he bought. These days, Wildrick Restorations sells clutch fluid, but some owners use their own concoctions, including Dexron-Mercon II or III transmission fluid.
As I mentioned, to contain the Hudsonite, the clutch has to be sealed. Generally, this means using sealer on the crankshaft flange and the bolt threads for the pressure plate and flywheel, a gasket where the pressure plate bolts to the flywheel, and a seal where the throwout bearing enters the pressure plate. Otherwise, the system’s concept is the same as it is for a dry clutch.
What are the pros and cons of using a corked clutch? One downside is the maintenance, but even that’s not a big deal. Considering how little collector cars are driven, you’d end up draining and refilling the clutch housing once every few years; back when Hudsons were daily drivers, it was probably done once every oil change or two (or never, considering how many people take care of their cars). Also, cork clutches tend to anecdotally “stick” to the flywheel and pressure plate when a car is not driven for a length of time, and longtime Hudson owners recommend wedging a broomstick against the clutch pedal when the car isn’t going to be driven for more than a week. The problem was common enough even back in 1948 that the service manual above suggested a method for flushing the clutch housing.
The upside? When the clutch is working as it should, the engagement is about as smooth as it gets, as the cork readily absorbs the Hudsonite Clutch Compound and is naturally compressible. The clutch itself is also durable.
In the forums, some have asked if they can substitute a dry clutch for the sake of simplicity and parts availability, and the general consensus is that it’s a bad idea. The flywheel itself is apparently much thinner than that used with a traditional dry clutch, and therefore has a hard time standing up to the heat of that friction surface. Plus, there’s really no need to upgrade, as Hudson clutch parts are readily available (if not a little expensive), and some enterprising souls even reline their clutches themselves. This picture is a Hudson clutch disc that is temporarily devoid of its corks.
Here is the same clutch “relined”; as you might expect, it is a labor-intensive operation that is easy to screw up. Here’s a detailed writeup on how one Hudson enthusiast does the job.
Wildrick Restoration in Shelbyville, Indiana, sells a lot of the parts Hudson enthusiasts need, and they posted this fascinating video of an impromptu clutch replacement at a Hudson gathering. Those Hudson engineers really made the job a little easier on the mechanic; most of a clutch job can be done from up top by removing the front seat and a portion of the floorpan, which bolts in. The sound on the video is quiet, but the technician makes a point of reminding viewers how crucial it is to line up the transmission using special dowels; a misaligned transmission can cause problems with starter engagement and clutch chatter.
Maybe the most important thing about the Hudson’s wet clutch is that it’s unique. Sure, some British cars used a similar system, but in America at least, Hudson is known for it. It’s one of those features that makes an independent so independent. Aside from the Hudson Jet, all manual-transmission Hudsons used their cork clutches until the end of the Step-Down line in 1954; the last three model years (1955-57, when Hudson became a rebadged Nash) used a traditional dry clutch, which is too bad. Only a few people will care, but when you’re working on your Hornet, Wasp, or Commodore, filling the clutch housing with Hudsonite every few years, you’ll be doing something that few other people in the world will be doing at that moment. And there’s always a certain amount of pride in that.
Related Reading
1953 Hudson Hornet – Hubba Hubba! (by Daniel Stern)
A great website for Hudson owners who maintain their own clutches
Wet clutches are common in motorcycles, where the clutch friction plates sit in the same gear oil lubricant used in the transmission. The critical difference between motorcycle clutches and the Hudson wet clutch is that motorcycles use multi-plate clutches, while the Hudson example is a single-plate clutch. The additional friction plates allow for a more durable clutch in a smaller space, which is important for a powerful motorcycle engine, where space is at a premium. A multi-plate clutch also offers potentially lower engagement forces, important for the hand-operated clutch on a motorcycle, with the clutch lever on the left handgrip, with the throttle on the right handgrip, with the lever for the front brake. The rear brake is operated with a foot pedal under the right foot, while the shifter is controlled with the left foot.
Motorcycle clutches are wet ones also, consisting of multiple driving and recipient discs. The problem with fluid clutches is the inherent friction caused by the oil being dragged by the plates’ surfaces, causing the clutch to never fully disengage, while the engine is running.
Nowadays, sheet cork is readilly available in various thicknesses, rendering hoarded bottle corks redundant
Courtesy of: https://www.rrd-preparation.com/en/transmission-clutch-and-spare-parts-for-vespa-50cc/29422-complete-reinforced-clutch-kit-polini-evolution-for-scooter-vespa-and-ape-50-125-.html
As more wineries switch to screw caps it is good that sheet cork can be used.
That is why, if you place your motorcycle on its center stand while it is idling in neutral, the rear wheel continues to turn slightly.
Thanks, Aaron. I’ve never seen such a detailed look at this interesting system.
You’re welcome!
As mentioned above, most motorcycles use wet clutches. Two famous holdouts that continued to use dry clutches until recently, Ducati (multi-plate) and BMW (single-plate automotive style), have now switched to wet clutches. The Ducati multi-plate clutch was famous for rattling (some would say clattering) at idle with the clutch disengaged. This prompted a meme “Loud Clutches Save Lives”, a takeoff of the “Loud Pipes Save Lives” mantra espoused by some bikers.
Most motorcycle wet clutches just use the motor oil shared with the engine, and modern synthetic or low friction oils don’t always play well with older clutches. Thanks for this article; I never considered that some otherwise conventional cars might have used wet clutches, with unique fluid no less. Even the Honda N360/N600 cars with their motorcycle-like engines, used a normal single plate dry clutch.
I’d quite forgotten that Hudson still used a wet clutch this late. Without looking it up, I believe that wet clutches were not uncommon back in the earlier decades of the car. I seem to remember encountering references to them, and that they were well regarded for their smoother engagement than dry clutches.
The direct link to the disc recorking doesn’t work, but you can find it navigating the website using cork in the search.
Very interesting stuff, the cork really is cork! I love the mixture of something so cutting edge yet so basic (to the point that one resourceful enough can DIY reline it using raw material as shown). That plus the removable floor, oh how I appreciate and long for a manufacturer that actually puts thought into making their products service friendly! I thought step down Hudson’s cool before but they just moved up a few notches on my list!
A side note in that the 1948-54 Hudson Step Down site does not allow direct linking as I found out when trying to head over to see the write up on replacement.
Yeah, that’s too bad. It seemed to work when I was proofreading, but it’s worth searching their website like Matt says above. Recorking a Hudson clutch is something I’d probably just pay to have done; it’s pretty labor intensive.
In an age when cars needed more frequent lubrication than today, say every 1000 miles, a 5000 mile service interval wouldn’t have seemed so bad, but I wonder how many neighborhood filling stations knew to do it (would it have been in a lubrication chart, if they looked?) and if so, did they had a can of Hudsonite compound sitting around? Or did they use to 10W oil that was “just as good?” Unanswerable questions at this point I guess.
Yeah, when these cars got to be 5-10 years old, I’m guessing the gas station mechanics used whatever they thought was best, and I’m guessing those clutches didn’t get drained and refilled that often.
I wouldn’t be surprised if 5000 miles, back then, was every six months to a year for many car owners.
I remember an old pal telling me about an old guy he came across in an alley in Washington DC back in the early ’60s, who occupied himself by re-lining Hudson clutch disks with wine corks, which were abundant there.
Aaron, thank you for taking the time to write about wet clutches in Hudson cars. I didn’t know wet clutches existed outside of motorcycles.
Hudsons sold in Canada, but were very rare. I can recall only ever seeing one, which was for sale on the side of the Trans-Canada Highway where I grew up. It was like a space ship when compared to its more conventional competitors.
You’re welcome! Honestly, I’ve never worked on motorcycles at all, so beyond a general knowledge of how they work and a vague desire to own something old and British, I’m out of my element.
I agree they were rare, but my father’s first two cars were Hudsons. He had a 40s-vintage convertible initially, but by the time I was born he drove a 1950 Pacemaker 4-door sedan, which was the car of my youth. In about 1961, when the Pacemaker succumbed to rust, he bought a 1958 Rambler Ambassador with the 327 V8 and 3-speed + overdrive. All of these, AFAIK, were bought from a Toronto garage called Newell & Ruddell, whose premises at 79 King St. W. disappeared to make room for the TD Centre.
Aaron, this is an excellent article on a very interesting subject. Interesting because it is an important mechanical part that Hudson solved with smoothness of operation. Hudson should have advertised, “Hudson, the car of fine wine connoisseurs!” “Darling, be sure to not throw out the bottle corks.”
Can we look forward to your article on the Lanchester Disc Brake of 1902? Again, many, many thanks. Tom
Thanks Tom…you know, I’m always interested in looking up something new (or old, in this case).
We’re out of “Hudsonite”!
I’ve been looking forward to reading about these clutches, Aaron. When I was a teenager a friend had several Hudsons, and I remember him proudly showing me his can of Hudsonite – not that I understood what it was, though I expect he tried to explain. Hudson certainly believed in doing things their own way. And it doesn’t take as much fluid as I thought it might.
Regarding the amount of fluid, I thought the same thing as you did. Also, I wonder how much of that 1/3 pint actually drains out after soaking into the corks (to some extent).
That’s why soaking the plates beforehand’s recommended, before installing them
Long before I moved here, the guy in the house behind mine bought a new Hudson and insisted on “burning in” the clutch by driving the car up against a tree and slipping the clutch. The dealer told him that wasn’t necessary, but he did it anyway and promptly ruined the clutch and had to get it replaced.
You’d need a mechanic who liked a drink of red, I reckon.
Very interesting article. I’d imagine a wet clutch runs cooler than a dry one, helping longevity.
Wasn’t it the refusal of ZF to use wet clutches in its small-engines dual-clutch that became the ruination of (possibly) millions of Ford Fiesta (and other’s) auto transmissions? I have some memory of them being told they simply would not be able to keep the temperature of the clutches stable without it.
You are correct – the early Double-Trouble-Transmissions used wet clutches and I seem to remember VAG’s Hudsonite was stupidly expensive for the regular changes required.
Again it permitted relatively smooth changes (something about you can’t play a pass by computer design…) but parking on a slope could be hilarious to watch.
Of course, the cheapskates at Ford thought that SDP clutches would do and they didn’t. Plus of course, solenoids and those awful bellows-type concentric slave cylinders ‘made’ by LuK caused endless trouble. Not just at Ford, either; Honda had a big recall over it too. But that was in Japan, as they were sensible enough to use the locals as guinea pigs.
Slushboxes may be heavier and more expensive, but they’re a known quantity. And they have a wet lock-up clutch, too.
I love these heroic inventions – well done, Hudson!
Thanks Aaron, learnt something new!
My father drove a 1940 Hudson coupe 185,,000 miles and it had the original unrebuilt engine, three speed trans and original clutch disc.
He later owned a 1953 Hudson Hornet with the 308 cu in 6 w/Twin H carb setup and Alcoa aluminun head. It had the 4 speed Hydramatic My first car at 17 was a 1951 Hornet. Hydramatic .
Does anyone know why Hudson used a dry clutch in the Jet?
The photo accompanying “Clutch removal from car” in the service manual reminds me that I take suspended pedals for granted. If I were a bit older, I wouldn’t.
I see that Wildrick Restorations just calls the fluid “Clutch Fluid for Hudsons.” I assume that since Hudson was absorbed into American Motors, which was absorbed into Chrysler, which was absorbed into Stellantis, Stellantis probably owns the Hudsonite trademark. But I haven’t heard anything to the effect that they plan to start making it again. 😊
I don’t suppose Hudson direction indicators required…. blinker fluid?
You’re reminding me of those jokes about how a car’s electrical system works on smoke. When your starter gave up the ghost, didn’t the smoke come out?
I am late getting here, but enjoyed this a lot. As stated above, I love that a car manufacturer was still allowing you to remove much of the front floor for working on things below it.
Next up – antique cone clutches? 🙂
Actually, maybe not a cone clutch, but I do have some pictures of something from the 1910s that’s on my to-do list for someday.
Fantastic detailed explanation about these wet clutches .
-Nate
I had a very nice 1948 Hudson. The year was 1957. (I’m now 87), a low mileage dark blue Commodore sold to me by my grandfather for $90.00. I learned everything about that car and found that it had a liquid clutch which needed fluid changing now and then. My method of fluid changing was to run the right side of the car up onto the curb which allowed crawl space underneath. The starter had to be hit a few times to position the drain out port at the bottom. When empty, a few more starter nudges positioned the port at the top for the addition of one small can of Hudsonite fluid. Job done. Smoothest clutch ever.