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75 620 L20b engine issues Please read!


HntnFsh

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19 hours ago, Stoffregen Motorsports said:

What's the casting number on the intake manifold? A46? Looks like and early (desirable) intake.

 

The round port exhaust manifold is not worth using, unless you have a round port head.

Checked the intake manifold. Looks like an A85.

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Its alive!!!

I got everything put together last night and took it for a spin. Other than a bit of a rough idle Its running pretty good. I'll double check the timing, vacuum leaks etc. I actually think it has more power than his old motor.

I had a bit of a what the heck moment when I first went to start it. I couldnt get it to pick up any fuel. I knew the fuel pump was working when I pulled it off the old motor. I was sure the new motor had an electric fuel pump because it had a plate covering the fuel pump hole. That got me to wondering if the previous owner removed the eccentric cam that drives the fuel pump. Pulled the valve cover and sure enough, it was missing. Went over and pulled the old one off. Put it on the new motor and away we go!

 

I really need to adjust the brakes tonight. They are pretty bad. It has new pads etc. I also dont think the vacuum boost is working. In fact I dont think it has for a long time. It takes way too much effort to apply the brakes, and make the truck slow down. The pedal kind of feel like its sticking part way down. Then frees up a little before activating the brakes. I'm pretty sure I will be searching for a new booster. In the meantime, I am going to get a few small items ironed out, get the truck washed up, and let my sisters know that I will deliver it to Dad tomorrow afternoon, in case they want to be there.

 

At least he will have it home while I figure out the vacuum boost stuff. I am going to do some research on how to check that out, if any of you have any input. I am all ears!

 

I did a quick search last night. So far the only thing I have found is California Datsun will rebuild this one for $400. I'll do more investigating to make sure thats the issue, and try to locate one.

 

I'll post another update later!

 

 

 

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The earlier L16 and most L18s were only desirable because they didn't have the attached EGR manifold and were coolant cooled. They have smaller runner diameter than the similar '78-'80 L20B manifolds but these did have the EGR. 

 

If you have the '75-'77 co joined intake/exhaust I'm not sure if there is room to run an early or late intake above it. Easy enough to seal the exhaust if separated as there is a metal block off plate to seal and separate them.

 

You can run a round exhaust port W58 head with the earlier square port exhaust manifold. Use the square port gasket. You can run the opposite, square exhaust port into a '78-'80 round exhaust port manifold but why would you want to?

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Yeah, haven't heard much good about them.

 

 

To test the booster step on the brake several times to exhaust any residual vacuum, if any. Step down on the pedal and hold. Start engine.

 

What should happen is the pedal will drop slightly as intake vacuum builds and the booster diaphragm applies extra effort on the master. This is normal. If engine falters when you step on the brake while running the booster diaphragm is leaking intake vacuum. After engine shut off there should be vacuum present in the booster. You may hear a hissing sound if you step on the brake, this is normal. You may get 2 or 3 pumps before it's all gone. This allows brake assist even if the engine quits while driving and the intake vacuum is zero. Obviously don't pump the brakes and use it all.

 

If it doesn't pass this test, check for any vacuum leaks and check the in line check valve. You should be able to suck air through it from the engine side but not from the booster side. I had my hose off from an engine swap and over the winter bugs nested in there and the valve was stuck closed and had to replace it.

 

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17 minutes ago, banzai510(hainz) said:

California Datsun??I be leary of some of this guys stuff.

 

400 and a junk collector Datsun guy will have one in the back yard for 50

Definitely dont use that guy....

I think I'm one of the few who got lucky buying off him, before I knew not to...  Lucky for me the part was fine but all the information he gave me was wrong...

He outsources everything anyhow, he is just a parts guy...

You can probably get it done cheaper going right to a rebuild shop... 

Hopefully someone will chim in about a brake booster rebuild company....

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Thank you for the info on Power Brake Sales. And also the warning on Cailfornia Datsun! Much appreciated.

I checked for any vacuum leaks today and couldnt find any. The vacuum and check valve for the brake booster worked good. But I checked to see if the booster is working and by all signs its dead. I couldnt tell any difference in how the pedal reacts or any sign of the booster working. The booster looks pretty rough. I think I will try to find a used one and go from there. Its still idling a bit rough, but runs great down the road. Not sure if a bad diaghram or something in the booster could contribute to that. But seems reasonable to my untrained mind! 😄

 

I got her all washed up and will run it down to Dads tomorrow after work. He can keep it there while I search for a vacuum booster!

 

I hope you guys dont get tired of me telling you all thank you for the help and advice. I just appreciate it that much!

 

I'll give updates when I make more headway!

http://liZtJNo.jpg

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Forgot 2 show a pic of the booster.

Ive been doing some research and I think there may be a couple different ones. I am wondering if either will work or do I need to stick to this exact 1? I couldnt get a number off it anywhere. Hoping for some direction on what exactly to look for?

Does this one look rebuildable? I wouldnt want to send it out to here it isnt any good.

http://dYCz3uc.jpg

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The rust between the master and booster indicate is one sign of a bad booster, but also of a leaky master. If the master is allowed to leak into the booster, it will take out the booster.

 

If there are no holes in it, it's probably rebuildable.

 

For now, just disconnect the booster vacuum from the engine and plug the vacuum port. This way, you'll be able to tune the motor.

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8 hours ago, Stoffregen Motorsports said:

The rust between the master and booster indicate is one sign of a bad booster, but also of a leaky master. If the master is allowed to leak into the booster, it will take out the booster.

 

If there are no holes in it, it's probably rebuildable.

 

For now, just disconnect the booster vacuum from the engine and plug the vacuum port. This way, you'll be able to tune the motor.

Thank you, I was hoping to get ahold of Power Brake sales but didnt get a chance. I will call them tomorrow.

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  • 2 weeks later...

Pulled the booster off the other day. Cleaned it up with a wire brush and sent pictures to Power Brake Sales. They said they can rebuild it! Very nice ladies there to deal with. Got it sent of today. Should have it back in 2 or 3 weeks.

Will keep you posted!

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  • 5 weeks later...

Another update and looking for a part.

I got the vacuum booster back last week. Was able to put it and a new master cylinder on the other day. I did a bench bleed on the master cylinder and then a pneumatic bleeder to get all of the wheel cylinders. I got brakes, but they were almost to the floor before they started working. I ran out of time so went and picked up the truck this morning and got it my shop and up on stands.

 

I adjusted the pedal to about 1/16" freeplay. I bled the master cylinder again and feel like I got a good bleed on it. Then used my bleeder set up to go through the brakes again. When Ive used the brake bleeder in the past I take the bleeder screw out. Wrap a little bit of pipe tape on the threads, making sure that I am only on the threads. Then I screw the bleeder in and back it out a 1/4 turn or a hair more. I then put a dab of silicone grease on the rubber adapter that goes over the top of the bleeder screw. This has always worked great in the past. Ive not had any issues with pulling air past the threads and I am confident that I wont get any tape in the brake lines. And i get a good seal on the adapter.

 

I went all the way around the cylinders. RR, LR, RF, and then LF. I was hoping I would have a good pedal. No luck. Popped the wheels off and then the drums. The front brakes werent put on properly and the RF wheel cylinder wasnt working. Dad happened to have a set of wheel cylinders so I changed the wheel cylinder and put the brakes on in the right orientation. Bleed that cylinder and it works. Still have a lousy pedal.

 

I decided to pull the rear drums off to have a look. Both cylinders are bad. Oriellys is getting a set in for me tonight or in the morning. While I had the drums off I decided to clean and lube the adjusters. The left rear was seized and while trying to get it loosened up I got too rambunctious and broke the back off of it where the retaining clips attach to hold it in place. Now I amin need of a working adjuster for the left rear. I believe left side front or rear will work from any 520, 521, or 620 pickup. 1968 to 1979.

 

I am hoping somebody on here would have one they would be willing to sell!

If so please shoot me a msg. and I can paypal payment.

 

Thanks,

Rick

 

 

 

 

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2 hours ago, HntnFsh said:

This is the adjuster i am looking for. You can see where I broke the retainer off the back!

 

 

 

 

 

 

 

 

Brake adj..jpg

 

I've done that too on my 521. Have a look on the inside frame rail under the passenger seat for a NLSV (load sensing valve) The '76 and up had them so check your '75, you never know. It also has to be bled I think before the rears are done.

 

Try loosening off the wheel adjusters so there is lots of shoe travel when bleeding. Then set the wheel adjusters so the shoes just rub when spinning the wheel. Be sure to stomp on the brake between adjustments to center the adjuster on that slide slot on the backing plate. If shoes are not adjusted properly it takes way more pedal travel to move the shoes.

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I looked for the NSLV. It doesnt have one. Thank you for the advice on bleeding and adjusting. I picked up the new wheel cylinders tonight at Oriellys. 

I cant believe some dipstick put all of the shoes on wrong. Front and rear. But I guess I have to, because I'm pretty sure I did it a few years ago!🤣

I'm learning. A bit slow, but I really am learning!

Edited by HntnFsh
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Does the 620 use a proportioning valve? I assumed there was one somewhere on the truck. If it's anything like the generic domestic vehicle valve, it may have a floating safety valve that needs to be locked in place before bleeding. I don't recall Nissan using anything like this, but maybe I'm wrong.

 

image.png.575ca1164f1ef6ef48e902bd53f22ad6.png

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14 hours ago, datzenmike said:

 

Try loosening off the wheel adjusters so there is lots of shoe travel when bleeding. Then set the wheel adjusters so the shoes just rub when spinning the wheel. Be sure to stomp on the brake between adjustments to center the adjuster on that slide slot on the backing plate. If shoes are not adjusted properly it takes way more pedal travel to move the shoes.

This is the opposite of my experience. I get the shoes tight and sometimes even pull the parking brake lever before bleeding. I don't want the wheel cylinders moving at all while bleeding.

 

If there is a prop valve in the truck, it may have a bleeder on it. If so, it needs to be bled before the wheel cylinders can be bled.

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I don't think there are proportioning valves used. It's easier to engineer the system properly. For one, the front brakes are the first to come on when the pedal is depressed and there is a spring between the first and second piston and one at the front that must compress to allow the rear piston to move forward. The first (front) piston has to move a certain distance before the rear piston begins to move and apply rear brakes. In addition the rear cylinders can be sized to increase or decrease braking. Fronts do the majority of the braking because weight shifts forward increasing the weight on the front tires increasing their traction. The opposite is true on the rears where weight lifts off decreasing traction.

 

As to loosening the rear before bleeding I was against a wall. Nothing seemed to work bleeding my rear 710s brakes. Loosening seemed to work though it may not be correct.

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