spottedog Posted September 21, 2011 Report Share Posted September 21, 2011 Should have said 1980 Datsun Could not edit. :unsure: I have owned this heap for about 10 years and never have the rear drum brakes worked with a s**t! Parking brake also wont hold. :o The drums have been machined, recent shoes and wheel cylinders, proportioning valve removed and bypassed, I have thrown time and money at this problem for years. Today I took it apart again and noticed something strange.... My front shoes on both sides (the brake shoes facing the front of the truck) are grey in color (the friction material on the shoe is grey and fresh looking) but the shoes facing the rear of the truck are much darker in color. It kind of looks like only one shoe (on both sides) is making any real contact with the drums! See oics. No leaks, everything is dry, new master cylinder. WTF? I think I am repeating some kind of mistake over and over..... :blink: :blink: Help (please) http://im1.shutterfl...3D550/ry%3D400/ http://im1.shutterfl...3D550/ry%3D400/ Quote Link to comment
wayno Posted September 21, 2011 Report Share Posted September 21, 2011 This is a datsun classic Quote Link to comment
wayno Posted September 21, 2011 Report Share Posted September 21, 2011 Should have said 1980 Datsun Could not edit. :unsure: I have owned this heap for about 10 years and never have the rear drum brakes worked with a s**t! Parking brake also wont hold. :o The drums have been machined, recent shoes and wheel cylinders, proportioning valve removed and bypassed, I have thrown time and money at this problem for years. Today I took it apart again and noticed something strange.... My front shoes on both sides (the brake shoes facing the front of the truck) are grey in color (the friction material on the shoe is grey and fresh looking) but the shoes facing the rear of the truck are much darker in color. It kind of looks like only one shoe (on both sides) is making any real contact with the drums! See oics. No leaks, everything is dry, new master cylinder. WTF? I think I am repeating some kind of mistake over and over..... :blink: :blink: Help (please) http://im1.shutterfl...3D550/ry%3D400/ http://im1.shutterfl...3D550/ry%3D400/ I don't beleave that the 1980 720 has a proportioning valve anywhere except maybe in the master brake cylinder itself. There is a load sensing unit near where the e-brake system separates near the carrier bearing. To edit the title, click on "use full editor". Quote Link to comment
izzo Posted September 21, 2011 Report Share Posted September 21, 2011 The 1980 has the proportioning valve. Its on the passenger side of the frame rail, real close to where the cab and bed meet. My 80 720 had it. Quote Link to comment
wayno Posted September 21, 2011 Report Share Posted September 21, 2011 The 1980 has the proportioning valve. Its on the passenger side of the frame rail, real close to where the cab and bed meet. My 80 720 had it. I don't beleave that is a proportioning valve izzo, that is a load sensing unit, it is supposed to add more rear brake pressure when the truck is loaded, I also thought it was the proportioning valve till I seen it labeled as a load sensing unit/something in a photo with discriptions of everything. Quote Link to comment
izzo Posted September 21, 2011 Report Share Posted September 21, 2011 I see. I didn't see it hooked up to anything but the brakes, wonder how it could tell if there was some weight back there. Good to know, though. Quote Link to comment
wayno Posted September 21, 2011 Report Share Posted September 21, 2011 I see. I didn't see it hooked up to anything but the brakes, wonder how it could tell if there was some weight back there. Good to know, though. I have started looking for the diagram with the labels, but I am not sure if I will find it. Quote Link to comment
datzenmike Posted September 21, 2011 Report Share Posted September 21, 2011 Izzo, you sure it isn't the pressure differential switch? Did it have an electrical wire going to it? It lights the red BRAKE light if there is a failure (pressure drop) in either the front or rear braking systems. Usually the front rear bias is accomplished by matching the wheel cylinder size to the master piston size. Quote Link to comment
datzenmike Posted September 21, 2011 Report Share Posted September 21, 2011 brakes worked with a s**t! Parking brake also wont hold. :o Check and see if the brakes work better backing up than going forward. Humor me. Quote Link to comment
wayno Posted September 21, 2011 Report Share Posted September 21, 2011 OK, I found the name of it, it is called the, "NLSV", which stands for "Nissan Load Sensing Valve", still looking for the diagram. Quote Link to comment
izzo Posted September 21, 2011 Report Share Posted September 21, 2011 Izzo, you sure it isn't the pressure differential switch? Did it have an electrical wire going to it? It lights the red BRAKE light if there is a failure (pressure drop) in either the front or rear braking systems. Usually the front rear bias is accomplished by matching the wheel cylinder size to the master piston size. my 720 had a wire coming off the master, never knew what that was for until i bought a 510 wire diagram. Then when i got my current 510 running, and the pedal hit the floor. it lit up :rofl: There was no wire running to it. it had a few brake lines going to it, and a few going out to the back. two bleeders. Quote Link to comment
datsunaholic Posted September 21, 2011 Report Share Posted September 21, 2011 Pretty sure by the pictures that you have both rearward shoes on one side and both leading shoes on the other. Quote Link to comment
wayno Posted September 21, 2011 Report Share Posted September 21, 2011 Here is a link to a NLSV removal. http://community.ratsun.net/topic/26288-nlsv-removal/ I suppose it could be a proportioning valve of sorts according to the kingrat, he discribes how it works in this thread, and why you need one. Quote Link to comment
izzo Posted September 21, 2011 Report Share Posted September 21, 2011 Here is a link to a NLSV removal. http://community.ratsun.net/topic/26288-nlsv-removal/ I suppose it could be a proportioning valve of sorts according to the kingrat, he discribes how it works in this thread, and why you need one. Damn Wayno, good job on digging that up. Good info to know, and now i know what it is and how it works :cool: Quote Link to comment
datzenmike Posted September 21, 2011 Report Share Posted September 21, 2011 Pretty sure by the pictures that you have both rearward shoes on one side and both leading shoes on the other. Doug, that's exactly why I asked this. I learned it from you. Check and see if the brakes work better backing up than going forward. Humor me. Quote Link to comment
spottedog Posted September 22, 2011 Author Report Share Posted September 22, 2011 Doug, that's exactly why I asked this. I learned it from you. It turns out I DO have "trailing" or "secondary" brake shoes on both sides. I was sold four "trailing" or "secondary" brake shoes by Carquest and previously by Napa. All four are identical, no short shoes, just four long shoes. So I guess this is why my "self energizing" rear brakes don't energize! :rolleyes: I gotta start buying critical parts from Courtesy Nissan! Quote Link to comment
carnuck Posted September 23, 2011 Report Share Posted September 23, 2011 Check the manual adjusters aren't stuck. Adjust them out till the brakes drag, then slide the adjuster back and forth through the backing plate and adjust again. I used to do that a LOT on the old Sunraders. Quote Link to comment
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