The Stovebolt Site Forums The Shop Area Driveline Measuring flywheel

For purposes of ordering clutch parts, is there a way to measure flywheel DIAMETER whilst under the truck?

If it's on a 216 or 235, I can tell you what the flywheel overall diameter will be (they're the same.)

But if you're getting a replacement clutch, just count the bolts holding the pressure plate on. If it has 6 bolts, it'll be a 9-inch clutch. If it has 9 bolts it'll be an 11-inch clutch. But you're not likely to find one of the 11-inch clutches on a 3100. They were used on big bolts mainly and are unobtanium now. If you can find one, plan on taking out a big loan to buy it.

Late 235 in an early truck is why I’m uncertain. Is there not a 10 inch clutch?

Clutch size is a measurement of the pressure plate diameter. You can measure the flywheel, but that’s probably not too accurate if you can’t see where the clutch has shined up the flywheel. If the flywheel has a shine on it from the clutch disk, measure the shine. Pressure plate is usually just slightly larger than the clutch disk.

NAPA does list a 10-inch clutch (found using a 1958 3100 as a vehicle.) LINK

It doesn't say how many pressure plate bolts it has, which is critical if it's going to fit on your flywheel. As Rusted nut says measure the worn area on the flywheel, or alternatively, from the outside diameter of the flywheel to the outside diameter of the pressure plate (the part that actually contacts the disk.)

Attached are pics of a 139 tooth (6 volt flywheel) showing the 13-1/2 inch diameter (not including the ring gear teeth), and the diameter of the polished area where the disk runs. This is an 11-inch clutch flywheel with 9 pressure plate bolts. So if you measure from the edge of this flywheel to the pressure plate, you'd find that dimension as 1-1/4 inch.

There is an 11 inch flywheel, clutch plate and pressure plate for sale down in the Swap Meet right now. I think it is a 6 bolt if I recall correctly. I have an 11 inch that is probably the best flywheel I've ever used.

An 11-inch flywheel/clutch would have 9 pressure plate bolts. I have one in my garage that I got from a 235 that was going to go in a 1937 truck. It's the flywheel I pictured above.

I bought the wrong clutch kit. Turns out my 1954 truck has a 1953 clutch. Both clutches had 6 bolt pressure plate housings, but the bolt circle was different. So, before buying the clutch kit, check the number of bolts and the spacing (chord length) between them. This can be done under the truck.

This calculator can help determine the bolt circle. https://a2zcalculators.com/science-and-engineering-calculators/bolt-hole-spacing-calculator

Wow thanks for calculator link. I didn’t need it now but it’s another tool I’ll have to.

Mine has 6 bolts and so does the 11 inch that is for sale in the Swap Meet section. Here's an image of mine before I resurfaced it and also an image of a 10 inch flywheel for the 235 after I resurfaced that one. The 10 inch shows up first in the lineup as I recall.

What I’m learning here….

Might be tough to order a clutch until I have things torn apart. A few different variables to consider.

Yeah, remove the clutch first before ordering replacement parts. Safest bet.

Buy local in case you need to return it. Cost me nearly 1/2 the cost of the kit to send it back to Rock Auto.

Clutch kits are listed as “diaphragm” and “flat diaphragm.” Will either one work and is one better than the other?

I've had the best luck with the plain Jane diaphragm type. When you start out, they both seem okay but I've had a couple of flat diaphragm type that over time (10 or so years) just seemed to go all weak and start slipping. Especially if you haul stuff with your truck.

yeah, I think the flat is used for cars

If it will help, the clutch kit I purchased and installed on my original 1954 3604 Truck with 235 engine, 139 tooth flywheel (6V starting system) , was a Power Torque , K1874-06 Clutch kit. It is a 10" clutch and the pressure plate has 6 mounting holes. It came with a throwout bearing, pilot bearing,and clutch alignment tool. It works just fine. Current cost at Orielly's is $146.99.

A diaphragm clutch is a clutch that uses a diaphragm or Belleville spring, as opposed to a finger and coil spring design. The end of the fingers of a flat diaphragm have a flat spot. A flat diaphragm clutch will have slightly less travel and slightly more foot pressure. If you go with a flat, you’ll need a taller throw out bearing to maintain total stack height. Unless you’re trying to build a drag racer, personally I’d stick with same style clutch as you have now; whatever that is.