MTFCA Forum

I have what looks to be a good narrow T transmission brake drum. What’s the best way to check for cracks besides having it magna fluxed. I heard you can use lacquer thinner on a cleaned up drum and it can cause a crack to show up. Thoughts?

If you are looking for cracks, magnaflux is usually best but liquid penetrant testing can also detect cracks. Basically, you get your part squeaky clean, then spray a dye (usually dark red) and let it dwell for a specified time, then wipe it off. Then spray a "developer" which will draw dye out of any cracks through capillary action. You can usually buy liquid penetrant test kits from a welding supply house. Or, I imagine, you can buy it somewhere on line.....

Hi John,
Yes lacquer thinner, brake clean, carb clean will show cracks in clean parts ( bead blasted is best ) but may not show very small ones.
Magna-flux & zyglow as well as dye penetrant are better. Using light distillates it helps to tap on the part to help bring out the crack.
Craig.

Bead blast it perfectly clean. Obvious cracks will show. Then wash with paint thinner. Smaller cracks will show up as wet lines.
Brake drums dont typically have cracks, unless dropped. The lugs, however get notched from the large steel clutch disks & will need smoothing if not to bad.

The cracks are not always in the surface where the lining rides. a hint to check for damage is blue color of the drum caused by band dragging caused by either trying to feather the shifts. Another problem is when the cam and pedal notch are worn out and the band has to tightened excessively in order to get it to be tight above the floorboard. This happens most often with the low cam and notch which are inside the hogs head. Sometimes there will also be cracks in the web inside the transmission and can only be detected by disassembling the transmission.
Norm

Thanks for the crack check tips. I’ve got some brake cleaner and will try it. I may try some carb cleaner that may work. Might get some lacquer thinner too. The drum is one that came out of a 15 engine years ago. It was in a pile of farm junk and I saved the engine. The engine was to far gone and badly locked up. But I did save the transmission for the drums.
The earlier drums were in use until 1918 if I remember. It’s one of those T parts you get to the point of saving or not to save. I’ve always wanted to save good usable T parts but my parts boxes are getting to full!

Certainly check the webs of the drums as well as the band surface. Brake drums also often crack from the threaded bolt holes down the side of the clutch plate lugs. Some of thee are inconsequential, but if one cracks to the band surface, it might be better to find another drum. Also, there can be small cracks between the rivets holding the drums on their shafts. These may well have been there all along, having been made when the shafts were installed.

I always have the drums magnafluxed for certainty.

Allan from down under.

Im going through the Transmission in my model t with a fellow club member.
Hold the drum loosely and tap on it if it rings nice like a bell its a rough way to test it and is probably ok. If it thunks more than rings, theres a crack somewhere.

Austin, the ring test is often advised to "test" for crankshaft bends. These forgings do give some indication in their ring, but still it is not reliable. I doubt it is reliable at all with a casting. Others may have different opinions.

Allan from down under.