rear brakes get too hot

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cudarudy

cudarudy

cudarudy
Joined
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Fremont, Ohio
I have noticed after driving several miles with just normal braking no panic stops the rear brake drums are too hot to touch . backed off the adjusters no change. The car(s) is a 69 Barracuda with front power k/h disc rear drums 8 3/4 suregrip rear . I have also noticed same thing on my 67 cuda with drums front and rear 7 1/4 rear. After driving home from work 27 miles rear drums too hot to touch front drums warm, also checked my Ranger after a drive home from work rear drums only warm. Any ideas , anyone else experienced the same thing ?
 
On the front disc car, do you have a manual proportioning valve? That would change the bias more to the front if set correctly. As I understand the factory valve is a bit rear happy.
 
^^^ My thought too.... gear oil topped up in the rear axle? Any bumping of the wheels at low speed?

- Also, is this a changed out rear axle? What size drums are back there? Need to know both diameter and shoe width.
- Need to know front pad/shoe and rear shoe types; pad/shoe materials being non-standard on either end could make the coefficient of friction high on the rears or low on the front, that will make the rears do more braking and hotter.
- Need to check the diameter of the pistons in the rear wheel cylinders and the front wheel cylinders for the all drum car. The fronts being too small or the rears too big will do this.
- Also see if the fronts are actually working properly and are completely bled of air.

Yeah, lots of things to check that can be doing this.
 
27 miles on the highway can generate a lot of heat from multiple places.
The rear gears and bearings tires and brake drums all generate heat just under normal running conditions.
Try checking the entire rear end when you pull in from the drive.
(Is it by chance uniformly hot from tire to tire?)

Also, "to hot to touch" isn't that hot for brakes at all so this could be a normal condition since we can't feel it.
 
Does it have a residual pressure valve in the system? Has the master cylinder been replaced recently?
 
Do you use the emergency brake..??

There's a possibility that the emergency brake cables are binding,, and every time you apply the emerg.. it tightens the brake, but doesn't release enuff, and causes the brakes to drag,,

hope it helps
 
Have you checked for a collapsed brake hose? Had that happen on my 69 Dart, replaced the hose and all was good again.
 
Brakes will be hot to touch after normal driving....


TrailBeast said:
27 miles on the highway can generate a lot of heat from multiple places.
The rear gears and bearings tires and brake drums all generate heat just under normal running conditions.
Try checking the entire rear end when you pull in from the drive.
(Is it by chance uniformly hot from tire to tire?)

Also, "to hot to touch" isn't that hot for brakes at all so this could be a normal condition since we can't feel it.
Click to expand...

I agree X2
 
let me try to give more info. I have not used parking brake on either car , parking brake not causing excessive drag. Front and rear brake hoses and wheel cylinders have been replaced on both cars in last few years. 69 cuda has rebuilt calipers and new replacement master cyl. and booster. My main concern is with the 69 the 67 I only drive to work a couple times a week ( future project ). Gear lube in rear full 10 inch drums all parts store replacement shoes wheel cyls. and hoses no mix/matched parts or high performance parts. I do have " green axle bearings " in the 69 plan on changing back to tapered bearings. Don't want to start a bearing debate but had a green bearing fail possibly due to excessive heat from brakes. What is the correct wheel cyl size for the rear and can anyone suggest a slightly smaller dia. cyl. size if this might correct problem ?
 
Ima gonna make a suggestion that some might not agree with, but it will lead straight to a logical conclusion.
Defeat the rear brake workings and re-roadtest it.
I have done this by clamping the rear hose off.If the "excessive heat" is still there, I would remove the rear shoes and all their hardware. A roadtest in this condition will prove exactly where the heat was or is coming from.
Clamping and old line is never a good idea. The inside may be crushed and ruined. A new line has always survived for me. Besides, at $95 per hour typical shop-rate, this is the fastest way to a solution, and rear hoses are (were?) cheap.
Bear in mind that, brakes work by translating friction into heat.They are pretty good at doing that. But the drums also have to be able to shed that heat, to the surrounding air. So if they are somehow shrouded,or painted, or the air cant get to them, excessive heat could be expected.The better they are at shedding heat,the better will be their performance, and typically their running temp.
 
I think "too hot" to touch should be better defined,, an accurate temp reading from a infra red gun etc would be far more accurate.. The fact two Darts (apples) run hot and another type of vehicle (orange) doesn't, is not relative..

Get a gun and shoot the temps, both sides, so another member can measure his,,
(apple),, and a practical comparison can be made..

What you are calling hot,, might not be so... jmo

A customer came in thinking his car was running too hot, cuz he couldn't hold his hand on the rad hose,, temp was 185*.. jmo
 
Only way I can explain it better right now is after driving I can touch front brake drum on 67 car with 4 wheel drums without fear of burning skin but rear drum so hot you immediately remove your hand . Rear drums on 69 cuda same . My thinking is front brakes would normaly be hotter than rear.
 
I think you have something wrong, dragging brakes, sticking parking cable, hoses, prop valve problem, or axle bearings set up wrong. I don't know what. When I first read this thread that's what I thought, and I think that now.

Try THIS Get yourself to an open highway. Try to take a direct route. Don't make too many stops and try to be easy on the brakes. STOP before you get on the highway and check all four wheels. Drive 10 mi, recheck, 20 if necessary, and recheck.

What happens? With rear jacked up? Does everything turn freely? Try applying brakes with rear jacked up, do they immediately release?
 
Since normally the front brakes do more work than the rears, the rears being hotter is a sign that they are doing too much, especially with the same sized drums front and rear.....is the the case for that car?

Not near any data for the wheel cylinders sizes; they would be in my old Chilton's book... that is 500 miles away. I assume the FSM would certainly have the sizes; is there one online for you? For the '67 with the stock system components, I would expect (just from general principles with the same F and R MC pistons) the front cylinders to be 1/16' to 1/8' larger than the rears.

I would not change the rear wheel cylinders unless they were the wrong size. The sizes are set to work with the car weights and MC piston diameters to set the basic F/R proportioning.

If you jack up the car and spin the wheels, are the rears dragging in any way? Also, any chance that this started occuring with the new MC? I am following up on RRR' thought about a residual valve; might be missing on the front and letting the front shoes back way off. But the pedal wold move more than normal if that was the case. Is the pedal action normal?
 
It could be the "proportioning valve", which is integral with the "combination valve" in your 1969 is not doing its job. It should reduce pressure to the rears so they don't brake as much and lockup, thus spinning out on a sharp turn. If so, that is dangerous. You can buy new ones for ~$75 (Inline Brake and such).
 
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