1974 FJ40 disc brake drag with front FJ60 conversion (1 Viewer)

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I have an 11/1974 FJ40 with an FJ60 disc brake conversion up front and I’m experiencing some intermittent brake drag on the front discs. The booster is a city racer for a 40 with a 40 series disc/drum master. Master is an O’reilly I believe. I didn’t do the conversion so I don’t know it as well. It’s also got a proportioning valve on it. The last time I was experiencing drag I opened the bleeder and the caliper released and you could spin the wheel freely. Drag occurs on both driver and pass sides so I’m thinking it’s something master related. No drag on the rear drums. Any ideas what could be causing the calipers to not be releasing? This is a sporadic deal and happens only sometimes so I’m looking for some outside help.

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Folks more knowledgeable than me will chime in but isn't that a residual valve and not a proportioning valve? Is it on the front circuit or rear?
 
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There may be a 2lb residual valve in the master cyl. , under the large fitting the brake line screws into., remove if it's there. FWIW I have had calipers get sticky, the piston gets gummed up and they drag, however letting off the bleeder does not solve that so I am leaning toward residual valve.
 
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Folks more knowledgeable than me will chime in but isn't that a residual valve and not a proportioning valve? Is it on the front circuit or rear?
The proportioning valve is for the rear.
There may be a 2lb residual valve in the master cyl. , under the large fitting the brake line screws into., remove if it's there. FWIW I have had calipers get sticky, the piston gets gummed up and they drag, however letting off the bleeder does not solve that so I am leaning toward residual valve.
@peesalot Any idea what the residual valve looks like? Will I need to fish it out with needle nose?
 

wngrog

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Skreddy

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The booster to master rod has gotten many a 40 owner.
 

Dynosoar

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That looks like a Drum / Drum Master.
Try a FJ60 master
 
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Wngrog, are you saying that a drum/drum MC does not have a residual valve in the front circuit ? Please elaborate.
 
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Residual valves (by design) are for drums, not disks, so they will not be in the front brake circuit. The manufacturer puts them in drum circuits to reduce the latency of the brakes and make them respond more quickly to pedal input (someone correct me if this is wrong).

The booster to master rod has gotten many a 40 owner.

Agreed. I would start there.
 
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Taking y’all’s advice and eliminating one thing at a time. I checked for the residual valve and there is none in the front. No brake fluid came out when I opened it up but there was fluid down in there. Re-bled the brakes and initial shakedown run it’s performing fine. Keep in mind the problem is sporadic though. When my tool comes in next week I’ll verify the clearance on the booster rod.

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Dynosoar

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The thing the arrow is pointing to and circled is the residual valve.
Dyno

RV.PNG
 

Skreddy

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You can check the booster rod if you have normal calipers, just math. But the tool makes it much easier.
 

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