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Discussion Starter · #1 ·
went for a cruise a few weeks ago, and my parking brake somehow was engaged while I was driving. ( I didn’t apply it) but the drums all locked up. It nearly overheated and blew out the tires, it was PIPING hot.

I’m guessing either the proportioning valve is causing it to lock up, or somehow it’s being engaged by applying the brakes normally. The valve was on there when I bought it, but I’ve replaced it since it blew apart one day.

this is an original 64 with a 283, and the master cylinder has been upgraded to a two bay. The front two drums were recently rebuilt. how do I disengage this parking brake, or prevent it from engaging without my knowledge?
 

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Discussion Starter · #4 · (Edited)
what upgrade kit was installed? got a pic? what size proportioning valve?
what upgrade kit was installed? got a pic? what size proportioning valve?
Im not sure which kit was used, a local mechanic picked out the best match for me. Everything was replaced except the drums. He came highly recommended, so I assume he’s used the proper kit- fingers crossed, haven’t had any. Issue other than the parking brake incident.


31172

The proportioning valve (shown circled in red) is (I think) a front/rear bias valve Style, with one “in” connection from master cylinder and one outgoing line which I assume splits between the front and rear, depending on how much pressure you displace in the system by twisting the knob Further toward, or a away from the firewall, for instance.

I can add a photo in a few days, she’s getting some body work done and everything under the hood is covered up. Cheers thanks again
 

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Discussion Starter · #5 ·
Maybe a dumb question but I did have it happen on my car... Is there enough slack in the parking brake cables? They need to be adjusted with the suspension loaded.
This is something I should look into. Need to get it on jack stands as my driveway is on a slant. Last owner had brrake and fuel lines redone, and I haven’t confirmed or denied that yet.
 

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Discussion Starter · #6 ·
Im not sure which kit was used, a local mechanic picked out the best match for me. Everything was replaced except the drums. He came highly recommended, so I assume he’s used the proper kit- fingers crossed, haven’t had any. Issue other than the parking brake incident.


View attachment 31172
The proportioning valve (shown circled in red) is (I think) a front/rear bias valve Style, with one “in” connection from master cylinder and one outgoing line which I assume splits between the front and rear, depending on how much pressure you displace in the system by twisting the knob Further toward, or a away from the firewall, for instance.In this photo, the knob had been blown out, but I replaced the valve with the same model pictured here.

I can add a photo in a few days, she’s getting some body work done and everything under the hood is covered up. Cheers thanks again
 

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Im not sure which kit was used, a local mechanic picked out the best match for me. Everything was replaced except the drums. He came highly recommended, so I assume he’s used the proper kit- fingers crossed, haven’t had any. Issue other than the parking brake incident.


View attachment 31172
The proportioning valve (shown circled in red) is (I think) a front/rear bias valve Style, with one “in” connection from master cylinder and one outgoing line which I assume splits between the front and rear, depending on how much pressure you displace in the system by twisting the knob Further toward, or a away from the firewall, for instance.

I can add a photo in a few days, she’s getting some body work done and everything under the hood is covered up. Cheers thanks again
can't tell , but is that an adjustable proportioning valve?
 

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Discussion Starter · #8 ·
can't tell , but is that an adjustable proportioning valve?
Yes it is. In this photo, the dial had been backed out too far by the previous owner. When I parked it after he dropped it off at my place, I hit the brakes and the knob popped right out, including the springs and the rest of the inside of the valve. I did replace it with an identical model.

I’ve heard that people install these to the rear brake line, to prevent it from locking up, by adjusting the pressure using the valve. I’m not certain it’s installed in the proper point in the line- it’s installed before the line splits. One mechanic made a comment that I could “just eliminate that entirely”, although I didn’t dig for an answer as to why. I’m guessing if it’s installed before the T where it splits its Less effective? Idk. I’ve done disc brakes before, but this drum brakes thing is a whole new world for me! Haha
 

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1961 Impala 2 Door Sedan
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So the kit I put on my '61 is a disc/drum master cylinder and the front reservoir is for the disc while the rear is for the rear drums. This looks like it is installed opposite to me. The front reservoir is a lot larger because the discs need a larger volume of fluid as the brakes wear to fill the caliper while the brake cylinder on drums is low volume.

I just sorted out an issue where my brakes were free and I could push the car while cold and it would lock up where it wouldn't roll down a hill in N. There is a pushrod between the booster and master cylinder that is adjustable and on mine that turned out to be the issue. Half a turn in and no issues. This is assuming that the pushrod between the pedal and booster have been adjusted properly.

These are my starting points based on my experience.
 

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Yes it is. In this photo, the dial had been backed out too far by the previous owner. When I parked it after he dropped it off at my place, I hit the brakes and the knob popped right out, including the springs and the rest of the inside of the valve. I did replace it with an identical model.

I’ve heard that people install these to the rear brake line, to prevent it from locking up, by adjusting the pressure using the valve. I’m not certain it’s installed in the proper point in the line- it’s installed before the line splits. One mechanic made a comment that I could “just eliminate that entirely”, although I didn’t dig for an answer as to why. I’m guessing if it’s installed before the T where it splits its Less effective? Idk. I’ve done disc brakes before, but this drum brakes thing is a whole new world for me! Haha
correct, these are used to balance the system. you normally find the adjustable version only in vehicles with modified brake systems, as (obviously) the original brake system would have been balanced by the factory engineers.

I also have an '86 El Camino and there is a way to swap out the rear drums for Blazer rear disc brakes, but in order to make sure the system is balanced you have to use an adjustable proportioning valve
 
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