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disc brake problem


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I recently purchased a 1974 Datsun 1600 pu with disc brakes. My problem is the front keep locking up and i was told it was because I had the original 1 line master cylinder for drum brakes on it. Is there a direct replacement for the disc brake set up, I know I would have to rebuild my brake lines to fit if there is.

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Interesting. I believe you have a poorly made custom brake setup. The 1974 Datsun 620 should have a brake booster with two hydralic lines and it would also have four wheel drum brakes.


We would love some pictures of the brake master, the front suspension, and brakes. Perhaps some of it was welded on from a later datsun truck that had discs in front.

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Drum brakes have a higher pressure (10lb vs 2lb?) residual valve, so it could be that. The valve is in the master cylinder where the brake line connects. Also, check that you have some amount of free play between the brake pedal rod and the master cylinder. At rest, the rod should be loose enough that it's not holding the master cylinder "in" at all.

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Original poster made just the one post, never came back.


Disc brakes only require a 2 PSI residual valve so the pads just barely ride against the rotors. If it's a drum brake master cylinder the residual pressure is about 5-6 time more than needed. This wouldn't cause lock up.


Insufficient pedal play as mentioned would. The master cylinder isn't returning all the way an pressure isn't all being released back into the reservoir. Each time the brakes are applied the pressure builds till it can't move.



On 8/4/2022 at 1:21 PM, Rick69 said:

I recently purchased a 1974 Datsun 1600 pu with disc brakes.


Only the '73 was a 1600 (L16) and yes, they did not have disc brakes.

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