I have the Olds with the '51 Ford truck 3 sp installed. I installed a correct Ford clutch release cross shaft for a '51 Ford trans. and a clutch pedal. After installing the complete assembly I press on the pedal and the throw out bearing engages the PP, but under foot pressure on the pedal the PP won't budge. The pressure plate is a modern version and designed to work with a '51 Merc 10" clutch.
It looks like the clutch fingers lay awfully low in the clutch cover. Did the original clutch have fingers that stood out further from the cover? Does the clutch pedal look like it might be running out of travel. Could you possibly have too short of a T.O. bearing? Some more pics of the cross shaft, bell housing and other clutch linkage might be helpful.
I agree with Clay, those fingers look very low to me. Stupid question, no offense intended, but is the disc in backwards?
If in fact your pressure plate is a 51, it's wrong ! The fingers are too long & are clashing with the bearing retainer. Either grind the fingers shorter or get a '49 of '50 Mercury pressure plate with the proper shorter fingers.
It looks big for a 10" PP, does it have 3 sets of 4 springs? That might be a truck-truck clutch not a pickup which would be an 11" with 3 sets of 3 springs.
Its possible that you have the disc in backwards as they only go one way. That could be jamming things. If the clutch is correctly installed, then it pretty much has to be either the wrong length throwout bearing or your linkage is wrong leveragewise. You should be able to smack each finger individually on the clutch with a hammer and see it move and release. If the fingers move properly, then look at your linkage.
Your Merc pp has a Borg & Beck bolt pattern, six equally spaced holes and the Ford pp will have three pairs of 2 bolt holes. Is your flywheel drilled for B&B and Long bolt pattern?
JFYI, Mercury started using the Borg&Beck evenly spaced pressure plate in '49. The '49, '50 (and some early '51) Merc transmissions use the old style 1 3/8" input and large OD throw out bearings. The regular production '51 Mercs used the new 4-bolt narrow pattern B/W transmissions that had a smaller 1" input and smaller T/O bearing requiring a different B&B pressure plate, like the one you have. You need the early Mercury B&B pressure plate to work with the large 1 3/8" '51 truck input and large T/O bearing. The Fords all used a Long style pressure plate with three groups of two bolts, so switching to a Long would require flywheel mods, unless your wheel is multi-drilled. Longs also come with fingers designed for early large and latter small T/O bearings. The '51 Ford car Long p-plate requires a small T/O bearing, like the '51 Merc.
Last year a friend with a stock 40 had same issue, new repro clutch assembly all completely installed and could not depress clutch pedal, turned out fingers were too long and hit the bearing retainer, got a different pressure plate and all was good.
I was only commenting that a Long pattern pp will not bolt to his ‘wheel unless it has both bolt patterns.
1st thing that comes to my brain is the disc is in ass backwards . Very hard to decide for sure by the image but it looks for sure to be reversed . Any way to get a closer look ?
Unfortunately 6 spaced but I have made reservations to drill the flywheel if I need to. I've got everything out so I will be working to solve the problem one way or another.