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| Drum brake question https://slantsix.org/forum/viewtopic.php?t=67479 |
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| Author: | valleyguy [ Thu Oct 26, 2023 6:47 am ] |
| Post subject: | Drum brake question |
63 Valiant; I have installed new drums and shoes all around... new single master cylinder., non-power. Th car is very hard to stop, even with max pressure on the pedal, the brakes just don't grab, wiill stop but it takes some time.., too dangerous to drive on the street. Brake shoes adjusted. Any idea what the problem is?? |
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| Author: | SlantSixDan [ Thu Oct 26, 2023 10:58 am ] |
| Post subject: | Re: Drum brake question |
The brake shoes haven't bedded-in on the drums, so only a small portion of the shoes makes contact. Years ago before the grievous safety hazards of asbestos-laden brake dust were understood, new shoes used to be ground (out in the open air, kerCHOO) to conform to the drum surface, greatly shortening the bed-in period. This isn't done any more on account of the health danger. Depending on the extent of the contour mismatch, you may wind up with small portions of the shoes glazed due to highly local overheating; this calls for removing the drums, wetting down the shoes thoroughly with water, and hand-sanding the affected areas to remove the glaze. Wear a good mask and keep those shoes wet; even though today's shoes don't contain asbestos, silica and other materials they contain are not happily compatible with lungs. Moreover, the new shoes are "green" (haven't been really hot yet) so are still outgassing whenever they do get hot. The gas they let off acts as a cushion between the shoe and the drum, counteracting your attempt to force the two into hard contact with each other. This could have been addressed in advance by heating each brake shoe to 350° for a couple of hours (old toaster oven in a well-ventilated place, because it's gonna stink). Continuing to run a single-pot master cylinder on a vehicle used even semi-regularly in traffic is unwise. |
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| Author: | valleyguy [ Thu Oct 26, 2023 11:59 am ] |
| Post subject: | Re: Drum brake question |
I'll pull the drums tomorrow; assuming there IS no glaze (i've only driven the car out of my driveway and a short distance) how can I bed the drums in? |
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| Author: | Greg Ondayko [ Thu Oct 26, 2023 2:49 pm ] |
| Post subject: | Re: Drum brake question |
Post up a picture of the shoe to drum contact pattern. Dull spots are not touching the drum. I have a similar issue on the '62 valiant but I don't need to correct it immediately. Have you confirmed all brake hydraulics have been bled properly? Does pumping the brake pedal help it to stop better? Greg |
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| Author: | valleyguy [ Thu Oct 26, 2023 4:06 pm ] |
| Post subject: | Re: Drum brake question |
brakes were bled correctly, and I have a firm pedal.... Gonna pull the drums tomorrow to get a look so see if there are dull spots |
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| Author: | wjajr [ Fri Oct 27, 2023 6:36 am ] |
| Post subject: | Re: Drum brake question |
Are the primary and secondary shoes in their correct position? The primary shoe has the shorter lining, and faces to the front of the car when installed. |
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| Author: | Charrlie_S [ Fri Oct 27, 2023 8:44 am ] |
| Post subject: | Re: Drum brake question |
Not likely, since you said they were properly bled. I had a situation, with a high very hard pedal, and poor braking. Rear brake line was crimped shut. So only front brakes were working. Just throwing this out there. The brake pedal should not be "rock" hard and at the very top. If it is, look for a restriction. Could even be a bad master cyl. |
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| Author: | Greg Ondayko [ Fri Oct 27, 2023 9:28 am ] |
| Post subject: | Re: Drum brake question |
The brake hoses can also deform inside causing a restriction or a "magic check valve effect" effect. Unlikely and rare, but it can cause havoc and a misdiagnosis. This happened on my wife's 2011 Ford Escape. The I.D. of the hose got so small that I could not force some 0.025" Mig wire through the hose. Greg |
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| Author: | valleyguy [ Fri Oct 27, 2023 11:00 am ] | |||
| Post subject: | Re: Drum brake question | |||
Well here are two pics of one of my front brakes.. does not look good, not sure what to make of them. I thought I had them properly installed and adjusted, but... you can see the wear, its a wonder they worked at all! Also, the leading shoe seems to me to be a thinner lining.. both drum and shoes are new..... pls help!!
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| Author: | SlantSixDan [ Fri Oct 27, 2023 12:11 pm ] | ||
| Post subject: | Re: Drum brake question | ||
Your first pic appears to show what I was talking about; most of the shoe area has not touched the drum. How can you bed-in the shoes? Well…keep stopping the car, without leaning too hard on the brakes until the shoes match the drums (if you wind up having to stand on the brakes hard enough to glaze the shoes, you'll have to wet-sand them as described above). Here's a pic from a good mid-'70s auto repair manual, of grinding the shoes to match the drum. Lookit that cancer-causing brake dust fly! Aw, that's awright, the machine operator was probably filtering his air through a cigarette. The past is a foreign country, making a '63 Valiant an unusual foreign car in 2023. One must adapt and make do as best one can.
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| Author: | wjajr [ Fri Oct 27, 2023 1:52 pm ] |
| Post subject: | Re: Drum brake question |
I remember seeing those machines being used, one in particular comes to mind was housed in a glass box to contain the dust while operating. I don't recall if it is had an integrated ashtray. LOL Most of the brake shoes from the 60's and older contained asbestos. |
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| Author: | SlantSixDan [ Fri Oct 27, 2023 6:35 pm ] |
| Post subject: | Re: Drum brake question |
Quote: Most of the brake shoes from the 60's and older contained asbestos.
Asbestos-containing brake linings were restricted by US federal law in '99, but there were categorical exemptions, and it was still used as OE into the 2000s, longer in some other countries. The import of asbestos-containing brake linings has only been unlawful in Canada since 1 January 2019!
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| Author: | Killer6 [ Fri Oct 27, 2023 9:19 pm ] |
| Post subject: | Re: Drum brake question |
I have a Barrett Tru-Arc brake shoe grinder, no, I'm not in a hurry to use it..lol.. If I arrange a HEPA filtered 5hp shop vac effectively, or some sort of wet spray/recovery setup, I might give it a whirl. Otherwise I'll just continue to let them break in easy 'til they bed themselves. Brake shoes aren't the only thing You can put radii on, and so it hangs around 
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| Author: | bcschief [ Sat Oct 28, 2023 7:30 pm ] |
| Post subject: | Re: Drum brake question |
Did you have the drums turned? Were they measured to see if they are oversize? |
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| Author: | Reed [ Sat Oct 28, 2023 11:30 pm ] |
| Post subject: | Re: Drum brake question |
Another thing to check is proper initial adjustment of the shoes. The adjuster screw needs to be tightened until the shoes very lightly dragon the drum when the brakes are not applied. |
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