Hot brakes

[Racer X]

34 minutes ago, bluez said:

Yes, as stated above push rod was set at 3.5mm (within factory spec).  Am using a thinner reaction disk.  OEM was about 1/4” thick, made one 1/8”, pedal travel is ok.

As long as there is a gap, about 0.020”. If there is no gap, the booster will (slightly) apply the brakes without depressing the brake pedal.

[Zed Head]

15 hours ago, bluez said:

So if there is residual pressure, what’s the root cause for all 4 brakes getting hot?

Any mechanical component from the brake pedal to the MC piston could be too tight.  Each contact point is meant to have a small amount of play.  The play at the pedal to MC can be hard to get right because of cramped quarters.  I used to adjust mine so that I could feel when the MC rod was just contacting the MC piston and the clevis pin was loose in the holes.  You can adjust the rod with a pair of pliers while everything is connected.  It will spin when the locknut is loosened.

People have had problems using the FSM numbers on their booster rod because of the variety of aftermarket parts and gaskets and adapter things.  There's a tool you can get that will measure the depth then transfer it to the rod if you're not confident of your measurement technique.

Somebody has posted it in the past, here's an example.  

https://www.amazon.com/Sunyat-Power-Booster-Pushrod-Adjustment/

[bluez]

Thanks for everyone’s suggestions.  
Okay, so took car for a 5 mile drive, without using brakes. Got home and found only front passenger side disc was slightly warm.  The other 3 sides were basically cool. So this confirms something is causing both front and rears to not fully release after applying pressure. Leaves me to think the m/c is causing the issue, as I don’t think the differential switch could cause brakes to bind.  
The person I bought the m/c had said it had recently been rebuilt. It appeared fine when I took it apart.
Does anyone know where I can order new seals? Someone is selling a kit for early Z’s on eBay, but it includes new reservoir caps that I don’t need.

[Yarb]

Try looking for A Beck Arnley new MC.

[bluez]

1 hour ago, Racer X said:

As long as there is a gap, about 0.020”. If there is no gap, the booster will (slightly) apply the brakes without depressing the brake pedal.

Per the FSM it states “the measurement between the face of the mounting flange and the end of the pushrod is between 0.138 and 0.177 in (3.5 to 4.0mm)”. There’s no way to adjust down to 0.020. 

[Zed Head]

I don't think that you're talking about the same measurement.

[Racer X]

13 hours ago, bluez said:

Per the FSM it states “the measurement between the face of the mounting flange and the end of the pushrod is between 0.138 and 0.177 in (3.5 to 4.0mm)”. There’s no way to adjust down to 0.020. 

0.020” (inches) = 0.508mm (millimeters).

Edited August 9, 2022 by Racer X

[Racer X]

15 hours ago, bluez said:

Does anyone know where I can order new seals? Someone is selling a kit for early Z’s on eBay, but it includes new reservoir caps that I don’t need.

Rockauto has multiple brands of new master cylinders, including Beck Arnley (about $65). You most likely can get one at your local NAPA auto parts store.

I still think it is the vacuum booster rod adjustment. It only needs to be off a tiny amount to cause the brakes to drag (not release fully).

 

Edited August 9, 2022 by Racer X

[bluez]

Okay, progress made I think.. Pulled m/c off booster and rechecked the push rod. Found it was about 4.5mm instead of the 3.5mm. I think my previous measurement was off due to the m/c being in the way of my ruler. 🤬 This time I made sure the ruler was level & square against the pushrod rod. So that resolved that issue.

So all I needed to do was screw the bolt in 1mm. Easier said then done. Found that when I previously removed the bolt last year, it was frozen, had to resort to some heat to loosen it.  Well turns out that between being in place for 50 years and too much heat caused the bolt to twist a bit, so it can no longer be screwed in that extra 1mm.  Ended up making a new bolt to the fit inside the m/c. With everything back in place, took car for ride without using brakes to confirm no more dragging. Got home all 4 sides were cool. Went out again for a quick drive, this time using brakes. Got home it appears all is good.  Will take a longer ride tomorrow to confirm.  

Zed Head was right on target.  Thanks to all for the input.

My goal is to keep car 100% original (other then points/coil) so will be sticking with the original m/c.    Now if I could just find 4 “D” hubcaps..

[Captain Obvious]

11 minutes ago, bluez said:

 Ended up making a new bolt to the fit inside the m/c.

I'd be a little careful with this. The original actuator tip was hardened, heat treated.

I'm not exactly what you meant about making a new bolt, but if you started with an off the shelf bolt made out of mystery metal, I'd be a concerned.

[bluez]

Agreed, I had a bolt and welded a nob on the end, then ground it down close to the original.  Will be looking a new rod for long term.