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Sorry, 620 brakes questions, just can't figure it out


jwerty1

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So, I have a 74 620, no nlsv as I've read. I made my own front brake conversion with silverado rotors that I machined the center bore on and 12 Altima front calipers. Upgraded to a 7/8 master from a z, just installed a new booster as mine developed a leak. Have bled the brakes several times. My brakes suck, at best. Before the new master they were really bad, then they got a touch better, but I had to stand on the pedal for anything. With the booster I thought my issue would be solved figuring the rock hard pedal was due to no power assist. Well, I can tell the assist is there but the brakes are still pretty marginal. Today after a little ride I felt the front rotors and they were cool to the touch. The rear drums were hot! Yes they are adjusted ok, just checked at work earlier today. Seems weird to me that when bleeding the rear, whether at the master or at the wheel cylinders I get a lot of fluid when I crack the bleeders, for the front the fluid doesn't come out nearly as fast and furious. I was thinking maybe the front and rear were switched on the master, (front should be rear circuit on master, correct?) seems to me it should push more fluid to the front than the rear. Also, the rears definitely aren't dragging, but when I stomp the pedal the rear will lock up pretty easily. Please help

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Not sure on that one, just installed a reman booster yesterday. Not quite the same symptom, the rears will lock up, but I have to stand on the pedal, light braking is pretty bad, but it's tons better than it has been, without the booster

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Something everyone has overlooked..............

 

When you installed the new/remanufactured brake booster, did you adjust the pushrod length so the master cylinder and the brake booster were properly mated? This will DEFINITELY cause the issue you're

having. Basically, in layman's terms, even though you're standing on the brakes you'll have minimal force being applied to the master cylinder due to a too-large of gap between the pushrod and master cyl.

 

Also, I see that you said the rear drums were getting hot..... switched the lines around..... now brakes kind of work.....

 

This would make since if the pushrod is not adjusted correctly. It WAS applying rear brakes only, but nut it's practically applying front brakes only slightly. (I'm fairly certain the brake fluid pressure is first applied to the rear and then the front, but i've been wrong before....)

 

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It's a z reman, no it's not marked

 

Mhub, I did adjust the pushrod as per the service manual. After I drove it and came back, both the discs and drums were hot to touch(I was trying some all out stops) so they were definitely all getting used

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