Front brake pulsation - steel vs cast (??)

1953M100

1953M100

Member
Bought my 1st Model A couple weeks ago. Previous owner replaced the drums with new cast iron about 400 miles ago. I have put about about 20 miles on the car, began to notice a pulsating brake pedal and significant "surging" when coming to a gradual stop. Raised the front axle, and I can definitely feel an obvious oscillating "free-drag-free-drag..." rotational difference when I spin the front wheels. Took the drums to O'reilly's for re-machining. The guys there are saying they are steel drums. Based on photos and searching here on the forum, to me the look like cast... (??)
 

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They sure look like cast drums to me.

The steel ones had a 'lip' around the outer circumference that slightly curved back outwards, if that makes any sense!

I'd take a picture of the steel drums on our Roadster but I'm not too sharp on posting pictures on here... haven't taken the time to learn:p

Also an older Model A guy told me once you can tap it with a wrench, the cast makes a different sound than steel. Steel sounds more of a higher pitched ring. Never tried it might be an old wive's Model A tale. But the visual difference is pretty easy to spot.

Not the old Model A wife. The drums;)
 
Given the "bead" at the edge (rather than rolled "outturning") I would put these as cast.

I'm not aware that anyone is producing pressed steel drums today.

Your pulsation MAY be from other factors related to the wheel bearing. Like not tight enough?

It is unlikely that in 400 miles a cast drum would "season" much to create out of round - although the quality on cast drums is frequently not to expectation. (i.e. offshore produced.)

Joe K
 
Another thing that can cause pulsation is that the brake shoes are not "centered" The rear shoes are self-centering because the cam can slide in its carrier to compensate. The wedge that operates the front shoes is fixed and cannot self-center the shoes.
 
Find someone who does brakes that has a brake lathe ! A good way to ruin drums or rotors is someone who doesn’t have the skills ! Steel drums ring like a bell, cast drums sound more like a thud ! X-2 on the rolled edge
 
Cast iron is more rigid than steel but the thing that affects model A drum size is the wheels. If the drums were thicker, they would have less tendency to warp. Other problems that folks have had is not truing the drums after installing the hubs and lug studs. Most folks in the model A realm know this but not all do. The old steel drums warp quickly after they get hot but less so on cast iron. The model A drums are smoothed out for fit and for a comparative looks to stamped steel. Most cast drums are rough as cast and tend to cool better that way but it is what it is.

Lining types can have an effect. It's good to use linings with known good qualities on cast iron. The condition of the front end is also important. Looseness in any of the movable joints can be problematic. A loose radius joint can cause movement and rebound movement with flexing. Make sure the spring perches and the king pins are relatively tight as well. Remember that the brake rods are attached through all this stuff in one way or another.

Tires can also have an effect if the rubber is getting hard or there are flat spots in the tread carcass.
 
Send them to Randy Gross. Quick turnaround and fair prices. The expert.
 

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1953M100 said:
Bought my 1st Model A couple weeks ago. Previous owner replaced the drums with new cast iron about 400 miles ago. I have put about about 20 miles on the car, began to notice a pulsating brake pedal and significant "surging" when coming to a gradual stop. Raised the front axle, and I can definitely feel an obvious oscillating "free-drag-free-drag..." rotational difference when I spin the front wheels. Took the drums to O'reilly's for re-machining. The guys there are saying they are steel drums. Based on photos and searching here on the forum, to me the look like cast... (??)
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Those are Cast drums. I am surprised your local Auto Parts store had the ability to even mount them on his machine. Maybe that is why they were unable to machine them.


With regard to the pulsating, this is/was caused by improper installation. Machining the drum at this time will now change the pulsing to a harmonic imbalance due to the drum not centered on the hub. To do this correctly, the hub needs to be trued PRIOR to riveting (swaging) the new drum during installation. Remove the drums, true the hubs, and then reinstall.
 
i have put on a few cast replacement drums, after swaging the lug bolts you need to have the drums turned on a brake lathe to true them up.
 
Your drums appear to be made of wrought steel. The presence of rust indicates this whereas cast iron would not. If they have not been properly heat treated this could cause them to distort or ovalize which affects runout. Runout can also occur if the machining setup used to turn the ID's was incorrect. There is also the possibility they were never turned. I recommend taking them to a shop that is capable turning them to run true.
 
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