The Stovebolt Site Forums The Shop Area Driveline Overheating Disc Brakes on Restomod

Sorry for the long story here, but you'll want all the data...
I recently acquired a 1946 Chevy Pickup Resto-mod, with a 350 Engine and front disc brakes. When I drive for any length of time, the front brakes get really really hot. I drove only about 10 miles the other day and the front wheel hub was 122 F. That is way hotter than I drink my coffee so it is way too hot.
This truck was built out about 20 years ago with some "not-so-professional" build quality. I have fixed a multitude of issues and am stuck with this brake problem/concern. They used the 1980 Pinto front end, which is the same as an early '74-'78 Mustang II. This truck has front disc, and rear drum but I suspect the rear drum brakes are not doing any work as I haven't opened them up yet, but they spin freely when up on jacks and have no overheating problem. Therefore, the focus is on the fronts.
When I first looked in the master cylinder (2 chambers, one for back, one for front), there was so much rusty color in the fluid that it freaked me out. And the front calipers were looking pretty gross. So, I replaced everything with new. New Master Cylinder, New Vacuum Booster, New Front Calipers, New Pads. And I bled the whole thing 3 times so I am confident there is all new fluid in the lines and no air.
When I drive 2 or 3 miles, the fronts are nice and cool. But, when I jack up the front, the wheels do not spin freely - about 1/4 turn when I spin them.
- There is no Proportioning Valve.
- The truck drives perfectly straight and stops perfectly straight.
- Pinto Brake Cylinders don't use the 2 slide pins like I am use to. It is a Wedge thing that you have to hammer in place. Seems like questionable way from a Mechanical Engineering perspective to allow the caliper to back off.

I am looking for you experienced people to provide suggestions.
- '46 trucks have a huge front wheel well. Could the engine heat be circulating in the wheel well heating up the fronts? Has anybody ever heard of putting small fans on the front wheels?
- Should I just swap out the fronts with a newer style calipers that use guide pins?
- should I re-do all the brake lines and route them along the side frames in stead of under the engine. Currently one line for the Fronts where there is a splitter under the engine. so both Left and Right have same travel distance.
- Any ideas?

Bluesky, not quite so Blue today

Most overheating of brakes (when not really using them) is cause by binding. if the rotors are purple hue. Then it has been binding. uneven brake pad wear is a caliper sign I would look at the calipers first. You said it stops at 1/4 turn on wheel spin. that may be a indicator if you really putting a good spin on them. IF it is a uneven heating one side is way cooler than the other. I would suggest a caliper is binding. If both are the same hot temp then you may have a fluid not returning well issue. Since you have to use the brakes to stop after a drive test. And since the fundamentals of brakes is that you are removing energy using heat. do this test.
Find a nice straight road section or even a emergency lane . Drive for a few miles without using any brakes. Then coast to a stop without using any brake. Then get out and check temp. I used a thermal scan on the rotors and caliper works really well. while wheel is off while its running have someone push hard on brakes then release. Make sure the caliper piston is releasing if its not its a sticking piston
I like sliding calipers on pins. easy check to see if its moving. Hot hubs could be a bad bearing and not the brakes. which is why i use the thermal scanner.

Check the rod from brake booster to master cylinder. It needs to have some free play. Its not much. but if there is none or it's too long, the pistons in the master cylinder never return enough to open the return ports which holds pressure on the calipers. Since it stops straight, you can rule out one side or the other, follow the lines back to where they connect.

A simple test is to drive 4 or five miles till you know they are hot, lift it up and spin the wheels to verify they are tight, then open the bleeder and see if they loosen up. If it does, you have pushrod issues or master cylinder issues. If the do not loosen up, then the slides are the issue. If it is the in the master cylinder, both front tires should loosen up at the same time.

Another problem could be the master cylinder is plumbed wrong. It could be applying the rears first as most due, but since the lines are backwards, the fronts are always working the hardest. Be sure the rear shoes are adjusted up to the drums and you have a slight drag. Have a helper slowly apply the brakes as you rotate the tires, run back and forth from front to rear and see which one applies first ( a third helper would be handy ). I plumbed mine backwards once, it makes for some strange stopping.

Is the master still under the floor?
Are there residual pressure valves for front and rear? What pressure are they ( should be different)
Chuck

If you have to hammer the wedges in, then something is wrong with your brake mount or the caliper.

Ford used that design on a lot of things from the 60s to at least the 80s.

There should be a snot-load on brake lube on the sliding surfaces of the caliper. If that is not lubed proeprly, the calibers will freeze up and the brakes will not disengage properly.

I would also recommend checking the free play in the brake pedal to brake booster rod and the brake booster to master cylinder rod. If either of those are too long, you will get issues like this.

122 degrees (or maybe a lot more) is normal for a disc brake, since the pads ride on the rotors all the time. As long as the front wheels will spin, even a little, without a lot of effort, you don't have a problem. Brakes work by converting kinetic energy (movement) to thermal energy (heat). If they don't get hot, they're not working at all. It sounds you're searching for a solution to a nonexistent problem. Even after a few stops, the rotors will be too hot to touch.
Jerry

Thank you for the valuable, and quick responses. A couple of people posted on the free play at the master cylinder input rod. I knew to check that when installing the system and I definitely had free play when connecting the brake pedal lever, and double checked that later just to make sure.
when I had the calipers off, the wheel spins like a dream so I know its not the bearings.

I really am curious about Jerry's (Hotrod Lincoln) input that hot rotors are normal. I've never had a car where the front wheel hub gets to 120 degrees. They might get warm... but that seems way too hot. I had an old time Mechanic also tell me that I am overthinking this thing.. but realistically the wheels should spin freely, or at least be able to spin a full turn. But, since I wanted to report out something.. I took it out for the drive test a few minutes ago.
I jacked it up before the drive and with the wheel on, it spins about 3/4 around. Much easier with the wheel on (extra mass).
I then drove it for about 6 miles with limited stops. But, I live in Florida and there is a stop light every 1/2 mile whether you like it or not. I then checked the temp - nice and cool 92 degrees at the wheel hub.
I jacked it up and it spins about 3/4 around. So.... this is like taking your car to a mechanic. With all of you guys watching, there Doesn't Seem to Be a Problem!!! WHAT IS WITH THAT?
but last weekend with the AC running on a warm day (85F), the engine was getting closer to 180 Degrees. Most of the time it runs right at 160 degrees (with a 160 thermostat).

I am going to try this all over again on a warmer day (next week) And drive further... Will keep you all posted.
Thank you again for being here and helping. I love the Stovebolt!

Bach when I taught auto mechanics (a little over 30 years' worth) I'd have my students calculate the amount of fuel an average sized car needed to burn to accelerate to 60 MPH, and then break down the dissipation of energy required to stop it again. One of the laws of physics is the concept of "conservation of energy"- - - - -energy is neither created nor destroyed, it simply changes its form. After accounting for things like rolling resistance, wind resistance, and other energy dissipating factors, the amount of energy the brakes absorb during a single stop from 60 MPH is roughly equivalent to the heat needed to MELT a 9 inch cast iron skillet! Brakes get hot, but the heat is mostly dissipated by air passing over the drums and/or rotors. Brake "fade" where there's lots of pedal pressure but no stopping effect happens when more energy is trying to be absorbed by the brakes than they can dissipate to the surrounding air.
Jerry

By nature, disc brakes get hotter than drum brakes. That is why you must use high temp brake fluid and wheel bearing grease. As long as they don't get hot enough to warp the rotors, there is nothing to worry about. Brakes turn kinetic energy into heat. The faster they do it, the more heat. I use ventilated brake rotors to dissipate heat faster.

Don't know if this helps, but (my experiences only):
1. Master cylinder push rod was not releasing fully when installed, needed adjustment (my 57 truck)
2. Flexible front brake lines that go to the caliper, collapsing (this is a common problem with JK Jeep Wranglers. I had to replace left and right).
They looked fine externally (30K on the Jeep), but replacing them worked.
Not sure this is true, but someone suggested that pressing the brake (fluid) overcomes the collapsed line, but there is not not enough pressure
upon release to overcome the collapsed line, hence sticking calipers.
Just some thoughts to possibly spur additional ideas.
don

Brake hose flaps are very common, but both at the same time would be kind of unusual. Hope it turns out to be something simple.

I’m with Jerry here. Not convinced that your hub temp is anything but totally normal. Unless I’ve missed some detail in your posts that gives some better context.

Disc brakes get way hot. It’s impossible for some of that heat not to be transferred to the hub area.

Not sure if this has been mentioned, but I suppose you could have a look at your wheel bearings and maker sure something isn’t funky. Make sure the preload is right and such.

You don't have a combination valve in the system? Combination valves include a metering valve that slows the application of the front disc brakes until the rear drum brakes catch up.

Description of Metering Valve

The key will be to check how the tires roll before driving and while cool, then go drive till they are hot and check how they roll. If its much tighter, then you have a drag issue, if it's about the same, then it's just normal heat.