Mrs. Cold

YAY! It was the booster check valve. I got one off of Amazon for a who knows what and plumbed it in. The brakes work (OKish) and the truck will move in both directions. I think my goofy check valve bypass setup put so much vacuum in the booster that it held the calipers shut even when my foot was off the pedal. Not sure why it moved in reverse but maybe it's a much lower gear than 1st and it overpowered the brakes but the F gears didn't give enough torque. That's my story. So, on to the next thing. Wheels and tires. Electrical. Legal.

Nah Wayno, I am a dude. I came up with the name because of how much the SD-22 misses when it's cold. Mrs. Cold...

After sitting an hour, the truck moves forward again. I think Wayno's speculation that the diaphragm was actualting the brake is correct and it was the higher RPMs doing it. The reverse gear is so low that I just let off the clutch slowly to start moving, first gear is taller and needs some RPMs, I think the extra vacuum caused the brakes to grip. Really weird. Off to find a working valve...

Here's a new one for me. I am slowly troubleshooting everything my 720 needs to get back on the road. I just finished putting in a fresh engine and started working on the brakes. Yesterday I was able to drive the truck forward in 1-3 gears and reverse. The brakes were really bad so I started working on them. I bled all four brakes, no help. Truck still goes both F and R. Today I started checking the brake booster. Bad valve between the vacuum source and the booster. No vacuum is passing. So I bypass the valve and hook the vacuum directly to the booster. And then I backed up about ten feet. The brakes work fine in this config. Then I try to go forward and the truck stalls. I start it and go forward again and this time as I let off the clutch, it begins to stall so I push the clutch back in. Each time I try to go forward, the truck acts like the E-brake is on. As I let off the clutch, RPMs fall until it stalls. If I rev up, I can feel the car straining, as if I am trying to drive over a cinder block or push something heavy, and then the revs fall until the motor stalls. But not in reverse. In reverse the truck acts just like normal. Thinking that futzing with the brakes caused this I unplugged the vacuum from the booster. No change. Thinking that there was a wheel somehow stuck that could spin only in one direction I jacked the truck up and spun them by hand. All wheels spin freely both ways. I am thoroughly flummoxed.

Hi everybody, My name is Christian, I am posting under the name "Mrs. Cold" because that's what my SD-22 does. I've got an 81 720 with an SD22 that I recently had rebuilt. Got new bearings, pistons, liners. Had the head welded in a heat tank and then totally rebuilt. I got everything put back together with help from Wayno on the datsun diesel site but there's very little traffic over there and the engine is running like a top now, so what I need is truck help more than motor help and I am hoping there will be more traffice here. This is the truck: Hmmm, I tried to post a pic but I don't have permission, here's a link to it https://lh5.googleusercontent.com/-y_n1SydzprA/TlHFXNTXrmI/AAAAAAAAAWY/oMuV1UehWM0/w800-h533-no/IMG_3368%2B%28Medium%29.JPG