I would have suggested that you're low on Hudsonite -- and that you might even have lost it, through a leaky gasket. This would explain why the problem gets worse as you drive the car. (Without Hudsonite the clutch disc and corks heat up, expand, and pretty soon you can't disengage the clutch disc from the plate, so you can't shift out of gear.)

But you say you've changed the clutch and Hudsonite. Since changing it, you haven't noticed any leakage on your garage floor, under the clutch....have you?

How much freeboard does your pedal have? It should be at least an inch. If the pedal is limiting on the floor the clutch may not be engaging fully hence slipping slightly, thus overheating and swelling up.
Geoff

Thanks, Jon and Geoff, for your input. I had a mechanic replace the clutch so I'm not very familiar with the Hudsonite issue as this is my first Hudson. He said he did add a bottle of Hudsonite (which I provided) and I have no reason to doubt him but apparently there is no way to check the fluid level, right? So I would have to go thru the drain/refill procedure to make sure.

I read both the shop manual and owner's manual and I'm still confused. Apparently the drain/fill hex plug is visible if you crank over the starter until the plug appears in the little opening in the flywheel cover which is supposed to be sort of behind and to the left of the starter solenoid - according to the illustration. On my car there is a engine block drain plug obstructing the view and access to the hole. Is this normal? I can't believe I'd have to remove the drain cock to do this procedure. And what happens if the hex plug falls into the flywheel cover when removing it? And if I do drain the Hudsonite, where does it go? I guess I need further advice.

Thanks
Denny

First, I assume your mechanic adjusted the free play (freeboard as Geoff says) so that you have to push the pedal down maybe 1-1/2" before you feel it engage the clutch. Is that correct? If there is NO freeplay....or if you have to push the pedal WAY down before you feel resistance, then adjustment may be your problem, as he says.

Second, as to the Hudsonite. Correct, there is no dipstick, so to speak. You simply drain the old Hudsonite, put in a bottle of new Hudsonite, screw the plug on, and you're good to go. However...

1. If your mechanic didn't drain the old Hudsonite before adding the new, he's over-filled the clutch. If so, drain it and fill again.
2. If there is a leak in the gasket and the new Hudsonite drained out, THAT too would be a problem.

So, first thing would be to phone the mechanic to ask if he drained the old before adding the new. Second thing would be to check the garage floor under the flywheel to see if it's wet with leaked Hudsonite. This is usually not the problem, though.

Changing Hudsonite is a ten minute job once you get the hang of it. And frankly, I haven't done it in several years on my car. The opening for draining / filling, is where you would look for the timing marks in the flywheel. Visible from engine compartment on the driver's side, next to the starter. Just rotate the engine until one of the two hex plugs appear in the opening. Then stuff a rag into the opening in the space between the steel support plate and the flywheel -- so the plug won't fall down if you drop it. (If you do, it's no big deal; just remove two bolts from the flywheel guard under the car, and it comes off. With the missing plug in it.)

Rotating the engine is easy if you have the starter solenoid with the remote control button on the back. It's hiding under a screw cap. I don't know whether they still had that feature with your car.

Anyway, you unscrew and remove the cap, take out the rag, and rotate the flywheel until a "star" appears in the opening. That means the fill hole has now rotate to the 6:00 position and the Hudsonite is draining out onto your garage floor, unless you remembered to put a pan there to catch it.

When drained, rotate the engine 'til the fill hole reappears in the opening. Stuff the rag back in, and insert the Hudsonite. Replace the fill cap, pull out the rag, and you're ready to go.

As Geoff has mentioned here, Check the free-travel. Free-travel tight or too loose can be the culprit. If there is TOO MUCH free-travel, the clutch does not dis-engage completely, and as it warms up, does swell some, thus making the shifting problem much worst. Then when you try to shift, you are forcing it into gear. One of the easiest ways to check for this is-- once the engine is warmed up, and shifting concerns are evident, shut the engine off, then try shifting through all of the gears. If it is easy or much easier to shift, then this tells you the clutch was dragging and wasn't adjusted enough to remove the free-travel and/or enough to dis-engage the disc from the flywheel.
Something that is usually the culprit when this occurs is there is too much movement in all the linkage and clutch pivots. It has been mentioned many times here before about the pivot cross linkage-where it bolts to the frame - will have noticeable wear in the end bracket. You can usually see the hole is worn egg-shaped. the linkage cushions are worn out, and then something that always get over-looked is the actual cross-shaft in the bell-housing. I would say we see the cross-shaft bushings are completely worn out 95% of the time. When the bushings are worn out completely, you will also find the shaft is completely worn out! . If these bushings and shaft are not replaced, the chances are you will have a clutch chatter and/or excessive free travel, that you can't really adjust out. If you need to over-adjust the free-travel, and make it tighter or I should say, less than spelled out in the shop manual of 1.250-1.500 , the cross-shaft bushings are usually the reason. With all this said above, I am assuming the pressure plate, clutch disc, engine and trans.mounts are good. Saying something is good because you don't want to deal with it, or don't know how too is only cheating yourself of the benefits the Hudson Wet clutch provides!!!! Hudson clutches were a very good design, yes different, but very good design, that should give long, smooth service if done correctly. Because they are a wet clutch and different than everything else, most people immediately decide they need to change it to a dry type. THIS IS NOT REQUIRED! The Hudson wet clutch is not really a weak link at all ! I have torn up many a transmission input shafts, axles, center driveshaft cushions and broken bell-housings! I could take a broken drivetrain apart to find the clutch still work and was still in good shape! Changing to a dry clutch, Geoff can tell you, is like re-inventing the wheel. You will need a much thicker flywheel, which will be a custom design, then with a thicker flywheel, you will need to engineer a new P/pl. and disc set-up, in turn this pushes the transmission back further, requiring more re-engineering, then all the standard linkage needs to be modified, then the driveshaft is too long, the starter doesn't work proper, and requires re-engineering,..... the list goes on and on. I'm sorry to keep rambling, but again, NO REASON to re-invent the wheel. Just fix all the pieces that are worn out, make it new again, and enjoy one of the smoothest clutches ever designed.

Remember, most fork lifts have wet clutches. They are wet because they are ALWAYS some kind of abused but keep working day after day, month after month, and then years!,......