Hot brakes

[bluez]

Hi guys,

Seem to be having an issue with brakes getting too hot, on my 12/70 Z.  This occurs when barely using them. The front rotors get very hot, so much that the wheel hub is almost to hot to touch. While the rear drums get a bit warm. This happens after a short drive, 10-15 miles. Car will easily roll without resistance. 

I have the early style original Tokico m/c (recently installed) and Nabco differential brake switch. Car previously had a Sanyco m/c, which I swapped out for the original.  

So is it normal for brakes to be hot, when not using them?

[SteveJ]

Hot is relative. Use an IR thermometer to say what the temps are. How freely can the fronts spin with the tire off the ground? Shoot a video of you spinning the wheels by hand. Post it on YouTube and link it here.

[Zed Head]

14 hours ago, bluez said:

The front rotors get very hot, so much that the wheel hub is almost to hot to touch.

Maybe it's not the brakes.  Could be wheel bearings.

[bluez]

Will check temps tomorrow.  Previously checked wheels, the fronts spin freely, about 1.5 rotations with minimal effort. 

[Mark Maras]

 That's quite a bit of wheel rotation for the problem to be the brakes. I'd jack up a front corner, grab the the top and bottom of the tire and push on the top while pulling out the bottom, then reverse the direction several times. If you can feel any looseness take a look at the wheel bearing and check to see if it's just loose or trashed.

[bluez]

Had checked all bearings last winter when everything was disassembled, cleaned and repacked them. Issue started after redoing brake system. Even rechecked the brake push rod to 3.5mm spec.

[Zed Head]

Might be that you have a hydraulic pressure buildup or hang up, not releasing quickly, but releasing slowly.  So you're not catching it by the time you get a wheel lifted.

You could lift the front end and confirm that the wheels spin freely then drop it down and go for a drive using only the parking brake.  Check for heat.  That would tell you if the pads are dragging all of the time or only when you pressurize the hydraulics.

Or you could just let them cool down and go for a drive using only the parking brake.  If it's a slow leakdown you'll get the same result.

[bluez]

Thanks for all suggestions.

Yes, am thinking pressure maybe being released to slowly, thus causing binding and heat. Will take a drive using e-brake only.
So if there is residual pressure, what’s the root cause for all 4 brakes getting hot? M/C or differential switch?

 

 

 

[Racer X]

6 hours ago, bluez said:

Thanks for all suggestions.

Yes, am thinking pressure maybe being released to slowly, thus causing binding and heat. Will take a drive using e-brake only.
So if there is residual pressure, what’s the root cause for all 4 brakes getting hot? M/C or differential switch?

 

 

 

You said you recently changed the master cylinder.

Did you check and adjust the vacuum booster pushrod? There needs to be about 0.020” clearance between the booster pushrod and the cup inside the master cylinder piston.

If the gap is too large, there will be excessive pedal travel and the brakes will feel soft.

Not enough gap, and the vacuum booster will be partially applying the brakes, causing them to drag, and heat up.

 

 

[dutchzcarguy]

Very old brake flexible brakelines can clog up, every time u use the brakes the pressure in the brake cylinders (on the wheel(s) ) get released to slow and warm up.. new rubber lines are the only solution to this.

I'm not saying that's the problem but you can check for it by lifting front wheels and let someone brake hard and you checking the wheels after brakes are off. (after relaesing the brakes the wheel should turn very easy.)

[bluez]

7 hours ago, Racer X said:

You said you recently changed the master cylinder.

Did you check and adjust the vacuum booster pushrod? There needs to be about 0.020” clearance between the booster pushrod and the cup inside the master cylinder piston.

If the gap is too large, there will be excessive pedal travel and the brakes will feel soft.

Not enough gap, and the vacuum booster will be partially applying the brakes, causing them to drag, and heat up.

 

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.

 

[bluez]

4 hours ago, dutchzcarguy said:

Very old brake flexible brakelines can clog up, every time u use the brakes the pressure in the brake cylinders (on the wheel(s) ) get released to slow and warm up.. new rubber lines are the only solution to this.

I'm not saying that's the problem but you can check for it by lifting front wheels and let someone brake hard and you checking the wheels after brakes are off. (after relaesing the brakes the wheel should turn very easy.)

Had previously replaced all 4 rubber lines as part of refresh.