Need help with dragging rear disc brakes.

[rejracer]

I've had the 280zx rear brakes on my car for 10 years, and I've always gone through pads on the rear. I bet I've had the same probllem and just never knew it.

 

Thanks for posting this.

[Miles]

Re: Residual check valves in the 280ZX MC

 

I opened up the outlet ports on two 280ZX MCs I have. Both the front and rear outlet ports have residual check valves behind the flare seats (cone shaped part). The 280ZX has four wheel disk brakes so you would think that using a 280ZX MC on a 240Z with 240Sx rear disk brakes would be ok. One of the 280ZX MCs I bought from MSA new and the other I bought from a wrecking yard to use as a core so I doubt that anyone added the check valves.

 

The check valve issue became of interest to me because ever since I replaced a failed 280ZX MC with a Wilwood 1 inch MC in my 240Z, which has the 240SX MM rear disk kit, my rear brakes don't seem to be doing much work. My brake pedal is soft and low since I did the Wilwood MC install in which I also removed the residual check valve per Wilwood instructions. Before the 280ZX MC failed and I replaced it with the Wilwood MC my brakes were fine.

 

So why would the 280ZX MC work in a 280ZX with disk brakes, but not a 240Z with 240SX rear disk brakes?

 

Everything I have read says that residual check valves are for drum brakes only and not to be used with disk brakes and yet, there they are in the 280ZX MC.

Based on my finding with the 280ZX MC I was considering puting the check valves back in the Wilwood MC, but after reading the above posts about the rear brakes dragging I am having second thoughts.

 

 

 

 

[rejracer]

I don't know if that's a good comparison as both the front and rear calipers are different on those 2 cars. Also the 280zx booster is much more powerful than the 240z unit.

I used to have the 280zx (15/16") MC in my 240 and I went back to the 7/8" master cylinder as I found the pedal to be too firm and not give as much braking control. The 240sx calipers have a smaller diameter piston compared to the 280zx.

 

It does not sound like the problem you are facing is the difference in this piston diameter though. It appears that there is something fundamental wrong. When you say "do not work" can you be more explicit? How do you know that they are not being as effective as they should be? A good way to check is with a pyrometer for temp or the tried and true slam on the brakes and see how far apart the front and rears lock up.

 

It sounds like there is still air in the MC itself. Those side ports on the MC are for bleeding it. Google Bench bleeding a MC.

[Miles]

I have installed the front and rear check valves in the Wilwood 1 inch master cylinder. I haven't noticed any change in pedal stiffness or legnth of travel. The brakes do not drag.

[Arcmeister]

On ‎3‎/‎12‎/‎2012 at 12:40 AM, Cannonball89 said:

Stock 240z master cylinders have a residual pressure valve in the rear circuit. This was installed to keep slight pressure against the drum brakes at all times. When you do a rear disk brake swap, the residual pressure valve must be removed, or you will have the slight dragging that you are describing. The valve is in the assembly under the rear reservoir.

 

Here is a picture from zcarnut's 1" master cylinder thread. The ones in the stock 240z master cylinder look similar and are in the same place, but there is only one in the rear circuit, not the front.

 

 

I hope this solves your problem, and while your at it, you may want to make sure that the handbrake master cylinder you installed doesn't have a residual pressure valve too.

 

P.S: You may want to think about upgrading to the 1" master or at least a 15/16" master. I have 280zx rear disks on my 240z which are a pretty similar piston size to the maxima's you have, and with the stock 7/8" master the brakes are very "squishy". I liked the firm pedal feel that the drums had, but the disks stop much better now that I have dialed them in with a prop valve. A larger master would bring back the firm pedal feel that the drums had I think.

 

Are the springs part of the check valves and get removed?

Or do you just remove the rubber nipple/tab?

Thanks