Doing the brakes on a '52 chevy pickup and the drums are not marked with a max. diameter - isnt there a rule of thumb as to how much is the max. that is safe to take off when it doesnt specify on the drums??
Usually the rule on unmarked drums is .060 over the standard dia. you can probably get away with going up to .100. Anything over .040 and you should get the shoes re-arched to fit the drums properly.
Why weren't these drums embossed (or stamped) with a maximum allowed size? I believe there is a Brake Czar...
i took a drum with no marking recently to get turned. They guy told me he usually looks at the beveled edge as a marker, If there is still an edge left it should be ok. pic i found online as an example, to big to post http://www.kcfrome.net/Drum2.jpg
I had the drums for my 50 turned the minumum amount to smooth them out. I have had no trouble with them.
I know a guy who wanted to shave the friction material 50% to save weight. He was serious. I slowly backed away without eye contact, then ran. Go with the bevel. Thats what its there for.
The factory turned the diameter of the iron brake drums of the 1962-1963 Pontiac 421 Super Duty A/FX drag cars .125" to save weight...and backed off the shoes reduce rolling resistance. The brake pedal went to within 1-1/2" of the floor after a run but at most NHRA sanctioned drag strips there was plenty of room to slow down except at Temple Raceway in Texas. That drag strip opened in 1957 as Little River Dragway and Temple Academy Dragway and was NHRA sanctioned. "The Best Little Drag Strip in Texas." Little River Dragway is now called Temple Raceway and is IHRA sanctioned for 1/8 mile drags with 1/4 mile for street cars on Friday and Saturday night. In 1963, my associate's new 1963 409/409 Impala S/S was put in NHRA D/Gas just because he removed his front shocks.
The factory turned the diameter of the iron brake drums of the 1962-1963 Pontiac 421 Super Duty A/FX drag cars .125" to save weight...and backed off the shoes reduce rolling resistance. The brake pedal went to within 1-1/2" of the floor after a run but at most NHRA sanctioned drag strips there was plenty of room to slow down except at Temple Raceway in Texas. That drag strip opened in 1957 as Little River Dragway and Temple Academy Dragway and was NHRA sanctioned. "The Best Little Drag Strip in Texas." Little River Dragway is now called Temple Raceway and is IHRA sanctioned for 1/8 mile drags with 1/4 mile for street cars on Friday and Saturday night. In 1963, my associate's new 1963 409/409 Impala S/S was put in NHRA D/Gas just because he removed his front shocks.
GM said no more than .060" in 48-51 manual. Don't know that 52 would be different. Problem is they don't give a max. measurement-how do you know if they have been previously turned in the last 50+ years? http://chevy.oldcarmanualproject.com/1948_51truckshop/51ctsm0527.htm Might try autozone's website? I plugged in my 51 3/4 ton ad got specs for max. diameter 11" drums 11.060 & 12" drums 12.060 http://www.autozone.com
I hate to ask the question but I have wondered this for a long time, so here goes. Why are brake drums turned down in the first place? I'm thinking that if they are a little "wavey" the shoes will wear into the shape of the drum. Naturally that will wear the shoes more quickly at first but will it cause any long term brake performance problems? An enquiring mind wants to know.
hmm ... obviously I dindn't meet him, but surely his cousin ... back on ... drums grow , or better: diminish to an elipse-form, meaning the brake-shoes touch-don't-touch-don't, or better brake-don't-brake-don't, simply translated as a kind of "knock". Turning down means making "round", so you get permanent contact, no knocking, no fading, and better performance M
Well!! From personal experance and about 40 years in the automotive trades they tend to pull one side or the other. Grooving increases the effective surface area of the brake face. If one side has more surface area than the other it will cause a pull to that side. This is much more noticeable with drum brakes compaired to disks do to the self engerising effect of Bendix style brakes. Although it will also so happen with early Ford Lockhead brakes.
I had some 51 drums turned and had the same question. the guy who turned them had some book with specs for old stuff. so take them to an old crusty guy with lots of books, not some new "technician" with a computer.
Some replacement brake shoe manufacturers used a thicker lining than standard on replacement brake shoes to compensate for wear / turning down of the brake drums, these would be a real tight fit with standard dia drums, max back off on the adjuster, a quick rub with a file on the edge of the lining (chamfer) emery on the drum chamfer even then it would be awkward / tight fit until the shoes wore a little . I don't know if this is in general, but It certainly was the case with the brand stocked by my local accessory shop.
On the third pass is close succession with my 69 Cutlass S in 1969 I went out the gate with faded brakes at Little River. That was with stock four wheel drum brakes. The end of the track got interesting at times if your brakes were suspect.
Model B 32 and John, I didn't know that brake drums wore "out of round" that explains a lot of things. I did suspect that grooving increased the surface area and thus the breaking effect; it just never occured to me that it would be uneven side to side. Thanks, I have now been educated.
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