Bulletside_Bomber Posted July 13, 2013 Report Share Posted July 13, 2013 Hey, new to ratsun here as far as posting. Im having brake issues and wondering if anyone could point me in the right direction. I installed Belltech lowering spindles for a hard body on my '79 620. I grabbed some front calipers, hubs and vented discs from a king cab at the junk yard (are those considered hard body?). Everything bolted up nicely so I went ahead and bled the brakes. They seemed squishy after a couple bleeding cycles. I decided to grab new rear wheel cylinders, a new master cylinder, bench bleed it and, after some research, bleed the NLSV with the rest of the system. The brakes started to seem stiff until I turned the truck on. With the help of the brake booster, the pedal goes to the floor. Ive tested the booster's check valve and vacuum tested the booster itself. I can get the truck to stop but brakes are still feeling squishy. There are only two possibilities that I can think of: 1. I may need a different master cylinder to match my front calipers. 2. My drums may need severe adjustment. (Even after reading my truck's manual I don't understand the adjusting procedure) Quote Link to comment
Bulletside_Bomber Posted July 13, 2013 Author Report Share Posted July 13, 2013 For pictures of the truck follow @bulletside_bomber on Instagram Quote Link to comment
flatcat19 Posted July 13, 2013 Report Share Posted July 13, 2013 Go get a master from a Late 70's-1980 Z car. Repeat process. Have drums adjusted tight before bleeding. Not so tight that they can roll, but tight enough that you'll only be pushing air out of the lines when bleeding. Not moving shoes. Quote Link to comment
Bulletside_Bomber Posted July 13, 2013 Author Report Share Posted July 13, 2013 The masters on a Z look identical, if memory serves me right. Is the bore or front-to-rear ratio going to be any different? Quote Link to comment
Eagle_Adam Posted July 13, 2013 Report Share Posted July 13, 2013 Bore is different, 15/16th come on Z cars, I think urs is 3/4 it's stamped on it Quote Link to comment
Eagle_Adam Posted July 13, 2013 Report Share Posted July 13, 2013 And you should post pics here, not every body is on Instagram Quote Link to comment
Bulletside_Bomber Posted July 13, 2013 Author Report Share Posted July 13, 2013 My bore is 13/16 but I think kingcabs, or at lesat 720's have 7/8. I might try that master. Quote Link to comment
datzenmike Posted July 13, 2013 Report Share Posted July 13, 2013 The disc brake '78 and '79 620 had a 13/16" (0.8125") master. Going to D21 or even later 720 front calipers which are much larger, will require a larger master. The 720 uses a 15/16" and D21 use a 15/16" or 1" depending on application, so start looking there. If all the air is out it will work but need to push more volume of fluid and so will travel farther and feel squishy. Quote Link to comment
Bulletside_Bomber Posted July 13, 2013 Author Report Share Posted July 13, 2013 At the junkyard now and pulled a 15/16". There's a small amount of fluid coming from the "cup" where the pushrod goes in. Should that concern me? Quote Link to comment
oldskoolvws Posted July 14, 2013 Report Share Posted July 14, 2013 Also, I thinks its the 78-79 Z (15/16) that is setup with disks up front and drums in the back. This is the master you need as it has the right residual valves. Quote Link to comment
MikeRL411 Posted July 15, 2013 Report Share Posted July 15, 2013 At the junkyard now and pulled a 15/16". There's a small amount of fluid coming from the "cup" where the pushrod goes in. Should that concern me? Yes. It needs a rebuild to correct the leakage unless the shaft is so worn that you need a complete rebuild kit including everything but the main casting. And then you have to hope you can ream/polish the bore without going over bore for the replacement parts. See what a pickle this is? Quote Link to comment
flatcat19 Posted July 15, 2013 Report Share Posted July 15, 2013 Also, I thinks its the 78-79 Z (15/16) that is setup with disks up front and drums in the back. This is the master you need as it has the right residual valves. 79-80 is the 15/16" Everything before that is the 7/8" 15/16" are hard to find new/freshly rebuilt. Hard to find a rebuild kit for them even. But the 15/16" is the one you want. RockAuto has a Cardone MC for less than $30+core right now. Get it! Quote Link to comment
heretic Posted July 15, 2013 Report Share Posted July 15, 2013 Did you bleed the Load Sensing Valve.? I personally don't think that the bigger MC is required, besides the 15/16" is exspensive and damn near impossible to find/rebuild locally. I put D21 dropped spindles & twin piston calipers on my red 78' 620 & used the stock 13/16" MC with ZERO issues. The pedal is only slightly lower than stock. On my green 78' 620 I'm going to use a 7/8" MC just to see how much it brings up the pedal.... only because I'm curious & it needs a new MC anyhow. Quote Link to comment
Bulletside_Bomber Posted July 17, 2013 Author Report Share Posted July 17, 2013 Rock auto is offering a rebuild service for that MC for $30 if you send one in, not the MC itself. But thanks for the info. Let the search begin Quote Link to comment
hawaii_620 Posted January 24, 2014 Report Share Posted January 24, 2014 Bulletside Did you ever get your brakes working correctly? I would like to know what your solution was. Quote Link to comment
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