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Disc o Tech red flag! Why does it do this?
#1211540
04/07/12 10:45 AM
04/07/12 10:45 AM
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Joined: Apr 2008
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Mid Michigan
Coronet-R/T-Rag
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Just completed a front disc brake swap on my 67 b body. Went from power drums to manual discs. 15/16 master cylinder. Wilwood / mp adjustable proportioning valve. It's all bleed and everything works great! Except - The back brakes lock up first no matter what i do! What am I doing wrong? I guess I'm wondering if my factory proportioning valve is sticking? I thought the drum / drum valve was more like a splitter that a proportioning valve? Help.
Last edited by Coronet-R/T-Rag; 04/07/12 01:15 PM.
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Re: Disc o Tech red flag! Why does it do this?
[Re: 70_FY1_N96_BEEP]
#1211543
04/07/12 12:58 PM
04/07/12 12:58 PM
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Quote:
Sticking parking brake? What wheel cylinders you have back there?
Rock Auto/Raybestos Wheel Cylinders WC37236
will help the biasing.
Parking brake works freely. Wheel cylinders are stock / unchanged. I thought I could adjust the bias with the wilwood proportioning valve but not so much.
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Re: Disc o Tech red flag! Why does it do this?
[Re: Grizzly]
#1211544
04/07/12 01:07 PM
04/07/12 01:07 PM
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Do the rear drum adjusters need to be backed off? Someone correct me if I'm wrong. 
I was wondering about that. I did adjust them tight then back them off till there was no drag. Backing them off farther might help but does that fix the problem?
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Re: Disc o Tech red flag! Why does it do this?
[Re: Coronet-R/T-Rag]
#1211545
04/07/12 01:52 PM
04/07/12 01:52 PM
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Joined: Jul 2011
Posts: 817
Eugene, Oregon
Secret Chimp
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Eugene, Oregon
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No, it shouldn't. You refer to an adjustable valve and then wonder about your factory valve, which one are you using? Why haven't you just adjusted the bias forwards (maybe you put it on backwards?)
1967 Dodge Coronet Deluxe station wagon
1.03" T-bars, QA1 arms/rods, Cordoba/GM Metric/Volare brake & knuckle, XHDs, Hellwig rear sway, 318 Magnum w/ air gap, 727, 3.23s
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Re: Disc o Tech red flag! Why does it do this?
[Re: Secret Chimp]
#1211546
04/07/12 02:02 PM
04/07/12 02:02 PM
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No, it shouldn't. You refer to an adjustable valve and then wonder about your factory valve, which one are you using? Why haven't you just adjusted the bias forwards (maybe you put it on backwards?)
I used the Mopar Action / Disc o Tech as a guideline and it said to leave the factory proportioning valve in place and just add an adjustable valve in the rear line to control bias. So I am running both valves. The Wilwood valve is marked in / out and is installed correctly. I have rotated the knob all the way in both directions and when it is "closed" I have mostly back brakes. When it is "open" I have better front brakes but the backs still lock first. It is close though.
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Re: Disc o Tech red flag! Why does it do this?
[Re: Coronet-R/T-Rag]
#1211551
04/07/12 02:58 PM
04/07/12 02:58 PM
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Joined: Sep 2003
Posts: 1,688
Marlboro, NY, USA
Rick_Ehrenberg
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Quote:
I used the Mopar Action / Disc o Tech as a guideline and it said to leave the factory proportioning valve in place and just add an adjustable valve in the rear line to control bias. So I am running both valves. The Wilwood valve is marked in / out and is installed correctly. I have rotated the knob all the way in both directions and when it is "closed" I have mostly back brakes. When it is "open" I have better front brakes but the backs still lock first. It is close though.
I NEVER WROTE THAT. if you are using an adjustable valve, which is what I always recommend, THERE SHOULD BE NO OTHER VALVE. Just leave the OEM drum-car distribution block and splice in the adjustable valve downstream from there.
Rick E.
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Re: Disc o Tech red flag! Why does it do this?
[Re: Rick_Ehrenberg]
#1211554
04/07/12 04:15 PM
04/07/12 04:15 PM
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Quote:
Quote:
I used the Mopar Action / Disc o Tech as a guideline and it said to leave the factory proportioning valve in place and just add an adjustable valve in the rear line to control bias. So I am running both valves. The Wilwood valve is marked in / out and is installed correctly. I have rotated the knob all the way in both directions and when it is "closed" I have mostly back brakes. When it is "open" I have better front brakes but the backs still lock first. It is close though.
I NEVER WROTE THAT. if you are using an adjustable valve, which is what I always recommend, THERE SHOULD BE NO OTHER VALVE. Just leave the OEM drum-car distribution block and splice in the adjustable valve downstream from there.
Rick E.
Sorry Rick, I mixed up proportioning valve with Distribution block. I am running the OEM drum-car distribution block with the adjustable valve downstream. No other valve.
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Re: Disc o Tech red flag! Why does it do this?
[Re: Rick_Ehrenberg]
#1211555
04/07/12 04:19 PM
04/07/12 04:19 PM
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Incidentally, using the 11.75" rotors typically improved proportioning a bunch.
Getting the "native" proportioning as close as possible (by juggling caliper and rear wheel cyl bores) and then using the adj. valve will improve light-pressure stops (rain, etc.) a whole bunch -- the valve doesn't kick in until a few hundred PSI.
Rick
I am running the 11.75 rotors with Cordoba caliper brackets. I will change up the rear cyl bore size and see if that helps.
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Re: Disc o Tech red flag! Why does it do this?
[Re: pro451bee]
#1211556
04/07/12 04:22 PM
04/07/12 04:22 PM
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Maybe the rear shoes are contaminated with oil ? You got master routed corectly and dont have circuits reversed?Rear port should go to front brakes . 
Oil makes the shoes "grabby"? I'll double check. I do have the master cylinder circuits correct.
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Re: Disc o Tech red flag! Why does it do this?
[Re: AndyF]
#1211558
04/07/12 05:04 PM
04/07/12 05:04 PM
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How hard are you braking when the rears lock up? The brakes shouldn't lock up unless you're really standing on them. If they are locking up under normal braking force then you have different problem. The brakes could be put together wrong, or be contaminated, or the drums are machined wrong, something like that.
If the rears are locking up before the fronts during a full on panic stop then you have a bias issue.
(I covered this topic in more detail in my B-body book.)
I've read your new book, it's very good. So good in fact that a friend has already "borrowed" it. The backs are locking first under a maximum "panic" stop. Under normal driving the brakes work great. Much better than before. I took advice from your new book and got the stainless brake hoses from Dr. Diff for my rear mounted calipers. They are a perfect fit and I would suggest them to anyone doing a swap.
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