Technical Overheating brake

[gordinir8]

So after i changed my master cylinder with new i also replaced rear drums, (this was the last part of the car i think i had to replace with new). Braking is much better than before but i am dealing with two problems. When i hit the brakes hard, nose of the car with blocked wheels goes straight but tail wants to turn to the left. Also i have noticed that rear drums got very hot and especially the left one. At the same time front drums are normal to touch. I have changed the drums but not the pads since they are new and have checked that retaining springs are in place, cylinders moves with no problem when i apply the brake with drums off the car and hydraulic fluid has a normal flow during bleeding so no blocked line here. In general all brake parts are new. Also rear wheels turn with hand almost free and i put the drums in place with almost no problem since i reset the springs that auto-adjust the pads. Is it normal for new drums to overheat for the first kilometers of use or there is something wrong.

 

[gordinir8]

I have done another test today, took it for 5-6 kilometers ride with almost no braking and rear drums still very hot. Removed the wheel and i can turn the drum with hand but i can feel a friction from the shoes. I am thinking two things, to grind down the top part of the shoe that touches the cylinder slot (this will close shoes about one millimeter so maybe they stop touching the drum) or take the shoes down a bit wit a block and sandpaper to give some clearance. I can see that shoes are polished at their top and lower ends so i guess this is the touching point that causes the heat.

 

[the hobbler]

From your description Thomas, it sounds as if the shoes are not quite 'round'---hence them touching at the top and bottom of the shoe. A careful sanding off of the 'polished' sections might just be the answer---I hate pattern parts!

 

[F123C]

Hi Thomas,

I don't think I'd remove any metal from the tip of the shoe that touches the cylinder slot.

Have you re-adjusted the handbrake cables?
(these would have been adjusted to suit the old perhaps worn and therefore larger inside diameter brake drums).

The brake shoes should automatically retract from the drums by an amount equal to the clearance between the bore of the automatic adjuster and the pin on which it fits. Did you perhaps not back off the shoes in their adjusters before fitting the new drums?

Whenever I work on rear drum brakes, I apply a tiny amount of lubricant (e.g. copper grease/Copaslip) where the brake shoe web/spine touches the brake cylinder and also the fixed abutment so that the brake shoe can move up or down a little to find it's own position. There's also iirc 2 or 3 spots on the edge of the brake shoe that contact the brake backing-plate that can benefit from a very tiny smear of copper grease, to ensure free and easy movement (mainly retraction) (these 2 or 3 spots on the edge of the brake shoes are iirc dimpled).

After fitting the brake drums and adjusting them, if I find there is a slight rubbing sound, I usually tap the brake drum at the top and bottom with a soft hammer to centralize the brake shoes. If they're still binding, it might be necessary to back-off the handbrake adjusters until the shoes have bedded-in.

I know that even a very tiny amount of rubbing can result in a brake drum getting very hot without it even being used.

I'd agree with your other plan of action and 'the hobbler''s advice to sand the shiny sections (high spots) on the brake shoe linings.

Regards,

Al.

 

[gordinir8]

Thank you guys, it is really nice to get some help when something is driving you nuts. Anyway I have done all the above Al mention except the grease thing which I did now.I grind the shoes down so the wheel could spin free for a couple of turns. Back in the street and done the same distance but faster. Front brakes almost cool, rear hot again but not as before, more like well used. Also brake pedal has a very limited travel. I think I will live it as is and do some short distances around for a few days to see how it will go, besides it is forbidden to go outside because of the covid19 except you have a serious reason. What could it be more serious than 500 testing??

 

[gordinir8]

Have a s,mall update here on my overheating aft brakes. Removed drums again and saw some polished spots again on the pads so more sanding off and back to the road. Problem still remains :bang: Also aft brakes are much stronger than fwd but that's another story. Hands up

 

[the hobbler]

The rear brakes often seem to be better than the front, especially on a 500. When you brake hard, the weight of the car transferes forward, so the front brakes have more work to do, but the rear brakes, because the rear of the car has become effectively lighter, are much more easy to 'lock-up'---hence my oft repeated belief that disc brakes on the rear of a 500 are a waste of time, and money.

 

[1500500]

Have a s,mall update here on my overheating aft brakes. Removed drums again and saw some polished spots again on the pads so more sanding off and back to the road. Problem still remains :bang: Also aft brakes are much stronger than fwd but that's another story. Hands up

. You could try swapping shoes From front to back and back to front and see if You have the Same problem.

 

[gordinir8]

That might be an option although just checked my papers i have use exactly the same type of shoes (high quality made in italy) according to the dealer i bought them.
I will give another round of bleed to see if there is any improvement.

 

[rusty500]

I'm having the same problem as described in this thread. New shoes and drums on both rear wheels. Pretty clearly pads are just a little too thick in places or drum diameter is a tiny bit too small. Or both. (It's definitely not an issue with handbrake setting. Its cable is loose when disengaged.)

My question is, What the risk is of letting the pads wear themselves in rather than sanding them down? Is there a temperature that I shouldn't let them exceed? The hottest I've measured on the drum with an IR sensor in my initial testing is 200F.

(In the front I only replaced shoes, and they seem to be fine.)

 

[bugsymike]

I'm having the same problem as described in this thread. New shoes and drums on both rear wheels. Pretty clearly pads are just a little too thick in places or drum diameter is a tiny bit too small. Or both. (It's definitely not an issue with handbrake setting. Its cable is loose when disengaged.)

My question is, What the risk is of letting the pads wear themselves in rather than sanding them down? Is there a temperature that I shouldn't let them exceed? The hottest I've measured on the drum with an IR sensor in my initial testing is 200F.

(In the front I only replaced shoes, and they seem to be fine.)

I have fitted literally thousands of brake shoes in the past.
The most common problem is what ever form of brake adjuster used is not backed right off when new shoes fitted.
Secondly shoes fitted wrong , either upside down or on the wrong side, as a rough guide there is a leading and trailing shoe, if looking at the shoes on the car with the wheel cylinder at the top the leading shoe is fitted on the side towards the front of the car and is recognised by having a space before the friction material starts on the shoe i.e. it has less material compared with the trailing shoe. This part is fitted nearer to the cylinder.
Thirdly the handbrake has not been de adjusted / backed right off, causing the handbrake lever inside the brake drum to be partly on .
All this is assuming the brake springs have been fitted correctly and not damaged or stretched, they must be holding the shoes back tightly against the wheel cylinder, that the handbrake crossbar is fitted as it came off correctly and moves freely.
The last and very unlikely is that the new shoes do not match the old, either to wide and dragging on the edge of the drum in which case you should see marks on the drum edge, or physically longer overall meaning where it touches the anchor point or the wheel cylinder. If in doubt when changing shoes take a photo before removing and compare new with old.
If every thing else is correct but they grab or lock on early, it is possible to file away slightly the leading shoe edge nearest the wheel cylinder.

 

[bugsymike]

I have fitted literally thousands of brake shoes in the past.
The most common problem is what ever form of brake adjuster used is not backed right off when new shoes fitted.
Secondly shoes fitted wrong , either upside down or on the wrong side, as a rough guide there is a leading and trailing shoe, if looking at the shoes on the car with the wheel cylinder at the top the leading shoe is fitted on the side towards the front of the car and is recognised by having a space before the friction material starts on the shoe i.e. it has less material compared with the trailing shoe. This part is fitted nearer to the cylinder.
Thirdly the handbrake has not been de adjusted / backed right off, causing the handbrake lever inside the brake drum to be partly on .
All this is assuming the brake springs have been fitted correctly and not damaged or stretched, they must be holding the shoes back tightly against the wheel cylinder, that the handbrake crossbar is fitted as it came off correctly and moves freely.
The last and very unlikely is that the new shoes do not match the old, either to wide and dragging on the edge of the drum in which case you should see marks on the drum edge, or physically longer overall meaning where it touches the anchor point or the wheel cylinder. If in doubt when changing shoes take a photo before removing and compare new with old.
If every thing else is correct but they grab or lock on early, it is possible to file away slightly the leading shoe edge nearest the wheel cylinder.

Also never drive with brakes binding, they will NOT wear away to fix the problem, they will seriously overheat causing warped brake drums, potential boiling the brake fluid making a spongy pedal and very hard to stop and damage the friction material reducing stopping capability etc.
After correctly fitting shoes it should be possible to spin the wheel with minimal resistance after pressing the brake pedal hard and pulling the handbrake hard also then releasing them both.
Finally after a road test it should be possible to touch all four wheels without burning your hands!

 

[bugsymike]

Also never drive with brakes binding, they will NOT wear away to fix the problem, they will seriously overheat causing warped brake drums, potential boiling the brake fluid making a spongy pedal and very hard to stop and damage the friction material reducing stopping capability etc.
After correctly fitting shoes it should be possible to spin the wheel with minimal resistance after pressing the brake pedal hard and pulling the handbrake hard also then releasing them both.
Finally after a road test it should be possible to touch all four wheels without burning your hands!

If none of the above, I see you fitted new drums are they the same internal diameter?

 

[gordinir8]

I'm having the same problem as described in this thread. New shoes and drums on both rear wheels. Pretty clearly pads are just a little too thick in places or drum diameter is a tiny bit too small. Or both. (It's definitely not an issue with handbrake setting. Its cable is loose when disengaged.)

My question is, What the risk is of letting the pads wear themselves in rather than sanding them down? Is there a temperature that I shouldn't let them exceed? The hottest I've measured on the drum with an IR sensor in my initial testing is 200F.

(In the front I only replaced shoes, and they seem to be fine.)

What I did in the end is that I pretended that everything was fine, just ignore the problem and after a few days or weeks I am not sure problem gone, shoes probably took their shape and everything come to neutral shape. I just did small distances at the time as I usually do in the town I live. Sometimes life is better when you have no idea about what is going on with your car.