1978 620 Brake, Suspension, Engine, etc... Update/Upgrade?

[]2eDeYe]

I have a 15/16 on a disc/disc 620 and a disc drum 620 and it works well on both trucks. 

You can change out the residual valve to match what you have. 

 

It is essentially the same as the stock 13/16 master, just has a bigger bore, you can pull the residual valves from that one for a drum application. 

[FrankRizzo]

I bought my brand new 15/16 vertical MC from Dave at Airizonazcar.com. But it's $129...

 

I had the old 3/4 M/C on 4 wheel disks for a while before changing and it was just fine. IMHO you can save some $$ by getting a 7/8" M/C for a '77-78 280z ...  those cars had dual piston disks with rear drums and it is vertical.

 

 

http://www.arizonazcar.com/brake.html

 

 

 

.....

[Spawn]

On 4/5/2019 at 8:50 AM, datzenmike said:

Adjust the rear drums! If they have to move too far to start braking it will eat up huge amounts of pedal travel. Try this.... pull the emergency brake out so slightly dragging while driving and then try the brakes. If improved, they are in need of adjusting.

 

Self adjusting rear brakes started in around '81 on the next generation 720 truck. YOU will need to adjust them every 3-6 months depending on use. Don't forget the fronts.

 

'Soggy' brakes can also be air trapped in the system but if initially bled properly air can't get in and it's likely in need of adjusting. It can also be from an increase in caliper size. Larger caliper needs more fluid to activate them. In this case going to a larger master will help, but it won't help if the rears need adjusting or there is air in the system. to begin with. Check these first.  

 

The emergency brake should always be adjusted or checked after setting the brake adjustment. It your last chance to get stopped if something should go wrong with your brakes. Think of it as a reserve parachute.

 

datzenmike, so was I correct in how to adjust the rear drum brake cylinders, by pulling the rubber access plug off the rear of the plate and then reaching in with a screwdriver to adjust the notched wheel so that when you try spinning the wheel & tire, as it's off the ground, you feel dragging?  As for the emergency brake, I know that my friend had tried adjusting it when we put in new shocks, but he wasn't able to get it to adjust.  The kit that I got off of ebay is only the rear half of the whole setup, so I'm hoping that is the portion that is unable to be adjusted any further (cable stretch over time?).  I have a feeling, however, that I will have to remove the drums from the rears in order to detach the old emergency brake cable and attach the new emergency brake cable, correct?  I don't have front drums anymore, so I don't have to worry about forgetting them. 😎

 

As for the original master cylinder question, does the 15/16" 1979-1982 Z master cylinder directly swap out for any year of 620?

[Spawn]

On 4/5/2019 at 9:52 AM, ]2eDeYe said:

I have a 15/16 on a disc/disc 620 and a disc drum 620 and it works well on both trucks. 

You can change out the residual valve to match what you have. 

 

It is essentially the same as the stock 13/16 master, just has a bigger bore, you can pull the residual valves from that one for a drum application. 

 

Redeye, what and where is the residual valve that you are referring to?  As I read through your post a few more times, I'm thinking that this is something directly on the master cylinder?  I'm just wanting to upgrade the master cylinder (if it needs it, which will probably be determined if I am able to adjust the rear drums at all), and I was thinking that RockAuto would probably be the best spot to locate one. So I want to make sure that if I do go that route that I am getting one that will simply bolt right on without needing any adapters or spacers, etc.

[]2eDeYe]

Here you go :)

 

 

Essentially you swap everything below the cylinder for the circuit you want to change

[Spawn]

Redeye,

 

So if you have discs up front and drums on the rear, the residual valves will be different for each?  If I manage to get one of the 1979 280ZX Master Cylinders from RockAuto, then I would just have to ensure that I swap out the residual valves from my current setup to the new one to have it work properly for my setup?

[datzenmike]

19 hours ago, Spawn said:

 

datzenmike, so was I correct in how to adjust the rear drum brake cylinders, by pulling the rubber access plug off the rear of the plate and then reaching in with a screwdriver to adjust the notched wheel so that when you try spinning the wheel & tire, as it's off the ground, you feel dragging?  As for the emergency brake, I know that my friend had tried adjusting it when we put in new shocks, but he wasn't able to get it to adjust.  The kit that I got off of ebay is only the rear half of the whole setup, so I'm hoping that is the portion that is unable to be adjusted any further (cable stretch over time?).  I have a feeling, however, that I will have to remove the drums from the rears in order to detach the old emergency brake cable and attach the new emergency brake cable, correct?  I don't have front drums anymore, so I don't have to worry about forgetting them. 😎

 

As for the original master cylinder question, does the 15/16" 1979-1982 Z master cylinder directly swap out for any year of 620?

 

Yes.

 

After you feel the shoe dragging be sure to pump the brakes several times to center the shoes. This may cause them to be loose again, so continue adjusting and pumping the brakes till there is no change and the shoes just barely drag.

 

The 15/16" ZX master has vertical mounting bolts and I think all years of 620 are also. The '82-'83 ZX are horizontal and thats why not mentioned.

 

The ZX master is for all wheel disc brakes and will have only disc brake residual valves in it. For use on a 620 with front disc and rear drums, put your 620 rear residual valve in the ZX master and you are good to go. Have a care as the rear circuit is on the FRONT of the master and will be marked R.

 

Disc brake pads are in constant contact with the rotor and a 2 pound residual valve is required... just enough to keep the rotor clean and the pad close to it. Drum brakes are much different and need 3 or 4 times this amount of pressure. A drum residual valve on a disc brake can cause  over heating of the rotor and can even lock it. A disc brake residual valve can cause the rear drum brakes to be mushy. So don't mix them up they all look identical....

 

 

It's the little coil spring. I have a 15/16" in my rear drum 710. Just swapped a rear residual valve into the ZX master.

[Spawn]

datzenmike, Redeye & FrankRizzo, thank you very much for the details and information.  This is exactly what I was needing/looking for.  I wasn't aware that the rears needed to be adjusted every 3-6 months, so I will definitely be trying this first, as the brakes hold pressure once they've been pumped 2-4 times while driving, but lose the feel and have to be redone each time.  This makes me think that the rear pads are just too far away from the drums and when pressing the pedal the fluid is pushing the drums out as much as it can, causing the mushy feeling until it starts to either grab slightly or reach the point where the fronts are doing all the work.

If adjusting doesn't work, then I'm going to probably swap out the master cylinder with the ZX unit, and then change the rear residual valve to ensure the rear drums aren't mushy.  I'm also hoping that if adjusting the rears works that it will also return some functionality to the emergency/parking brake.  If not, then I may end up calling on your expertise again to try and get it functioning again as I've never been a huge fan of leaving the transmission in gear when parking, but that's the only way I can keep it from rolling when parked on an incline anywhere I go.

Edited April 9, 2019 by Spawn

[]2eDeYe]

General rule of thumb on a drum brake 620, adjust the brakes every oil change.
This will keep them operating at peak performance and also keep the adjuster mechanism in good working order. 

You may find that you have to tear down the brakes to get the adjusters un-seized.
Some grease on the threads when you reassemble it will make it almost a pleasure to adjust them. 

 

That said, I no longer have those style brakes on my trucks, because adjusting brakes sucks.  lol