I just got the SR powered beast on the road (temporarily) and started finding some bugs in the brakes.

If you've followed along my SR buildup you'd see that I've installed front and rear disk brakes and a new master cylinder from a 1983 280ZX (Fairlady Z). Something funny is going on with the rear brakes now that I've gotten to drive it around some.

Basically what's happening is every time I step on the brakes, it's building up and not releasing pressure in the rear brakes. It takes a few pumps to get it there, but eventually the rear brakes get totally locked up. Just to be able to move the car I loosened the rear brake line on top of the brake bias assembly and sure enough brake fluid came squirting out under pressure.

The master cylinder is brand new as are all the brakes and rotors (calipers are used). The E-brake isn't even connected at this point either, but it still did it with it both connected and disconnected.

The master cylinder/brake pedal IS in fact returning all the way out when the brake pedal is released, so I don't see why it's holding pressure in those rear brakes. Could it be something internally in the master cylinder? Perhaps because it's new, one or some of the seals or valves are sticking that allows the pressure to bleed off when you release the brake pedal?

It had this problem when I first put the brakes on and bled them through, then a few days later when I came back the binding rear brakes seemed to mysteriously disappear....which I'm thinking the pressure buildiup finally slowly released itself over a few days, but then when I drove it around for a while it didn't do it at all......until today when I drove it.

Does anybody have any ideas as to what the problem could be? It's got to be something with the master cylinder, but I know that it's going through it's full travel.

I'm hoping it'll fix itself over a few days and more driving but I doubt that'll happen. I do have another spare used 280ZX master cylinder to try out if you guys think this new one is no good, I just don't want to have to take it all out again...it's so messy!

Let me know what you guys think the problem is! Thanks!

After driving it some more today I think I know what's going on. The turbo manifold and the brake master cylinder are really close to each other. While it's all heat shielded I think it's still getting too hot around the master cylinder, causing both the fluids and maybe even the seals inside the master cylinder to expand and clamp down on the brakes. The brakes only start to drag after I've been driving it a while ....in other words once everything gets heated up.... I didn't figure it out until today after driving it. It seems I can go about 15-20 minutes of driving before they start binding.....shut the car off and let it cool down for a little while and they stop binding...

So I'm going to do some more heat shielding, but ultimately I may have to just remove my beautiful Jet Hot coated mandrel bent stainless header-type manifold and install the stock manifold

Then at least I'll have more clearance on the brake master cyl. and also I could re-use the stock heat shielding. Man that's a lot of work replacing that stupid thing...I'm gonna have to go hunt down a new manifold gasket, turbine gasket, and outlet pipe gasket.

So much for a relaxing holiday weekend...

I had a similar problem once but it was my front disks sticking on. It was the pedel adjuster adjusted wrong. the pedal adjuster is the little bar that goes from the pedal into the boster. you probably have to shorten it a bit. If its not adjusted right then it stops the piston coming back far enough to let the fluid return back to the resivor and the system all seizes up. Your pedal probably goes very hard. Hope this helps. Olboy

The Z-Car had rear discs originally?

If so then ignore my comment.

It could be the residual pressure valve in the rear circuit in the master cylinder. Especially if the original car that the master cylinder came from, had drum brakes.

Chris

Yeah the 79-83 Z cars all have 4 wheel disk brakes stock. This is the reason I used the matching 280ZX master cylinder so that it would be valved properly.

I'm taking care of the heat issue tomorrow and actually killing a couple birds with one stone.

I figured since I will already be taking the turbo and manifold off to replace the cylinder head at the same time. You see, about 6 months ago I bought an AWESOME head that has at least $1500 worth of port work, polishing, and resurfacing. I forgot I had it so I'm going to throw it on at the same time along with a Nismo 1.2mm metal head gasket and a set of Tomei 256 PonCams and adjustable pulleys.

Anyways, back on track, I'm pretty confident that changing back to the stock manifold will fix the heating up and expansion of the brakes. Why else would it only do it after the car warms up and go away after you shut it off for a few minutes??? The exhaust manifold is practically touching the master cylinder....there's only about 1/8" clearance. I'm so excited to put that head on though!