Drum brakes - binding in one spot

Quote:

---

Originally Posted by JDNSW

I think, if I understand the situation, that there is a lot of barking up wrong trees.

If the brake is binding in only one spot during rotation of the wheel, the only possible cause is that the braking surface of the drum is not concentric with the axis of rotation.

This can have several possible causes. Working out from the centre:-

1. Bearing issues - worn, or not sitting square in the hub, possibly due to dirt or a bit of metal on the seat, or faulty manufacture of the hub.

2. Mounting surface for the drum is worn, damaged, got dirt or rust on it, or poor manufacture of the hub.

3. (most likely) Mounting surface on the drum is damaged, oversize, rusty, or not concentric with braking surface.

4. Drum is warped, cracked, or otherwise damaged.

I had to replace a new drum on my County, because the mounting circle was not concentric with the braking surface.

Any alignment issues with the shoes, backing plate etc will result in lost motion and poor braking, but cannot result in binding at one point in the wheel rotation.

---

Thanks John. The drum being at fault was my first thought but swapping them left to right makes no difference - the tight spot remains on the one side and the other side adjusts up perfectly with no binding which is why I’m scratching my head at the moment. All bearings, drums, backing plates and shoes are new. Will have a play today and if I have no luck, I’ll buy another drum and try it.

Well I found the issue within 5 minutes this morning...

Looked over the drums to see where they were rubbing - the only spot I could find is right on the outside on both. Checked the shoes to see where this would be on them - and found my answer - NOT the shoes that were grabbing, but just touching the backing plate in one spot - see pic below.

So, the bracket isn’t quite on centrally - which is not really my fault as these were off the shelf laser cut plates that sat tightly on the axle so I didn’t think anything of this. There isn’t any wiggle room on the backing plate mounting bolts so it is where it was always going to be - twice as I redid it thinking I was at fault.

So, a tickle with a flap disc and I have no rubbing any more. This also shows the drums aren’t perfectly concentric either, but having adjusted both sides now, they both work fine and when the brakes are released, they go back to where they came from and the drums spin free.

What a PITA... Will throw the axle back in and may take the van for a spin this arvo if I have time and make sure everything is as it should be.

Thanks for everyone’s input and ideas - I really appreciate it. 👍😊


https://farm5.staticflickr.com/4902/...56db79b0_k.jpgUntitled by Gavin Gregory, on Flickr

I have exactly the same problem on the trailer I just converted from no brakes to 4 wheel electric. One wheel locks up & only way to unlock it is to come to a stop & reverse . I only put the brakes on to be Legal. So have backed the right off for now. I'll get around to fixing it one day but thanks for the clues .

When making the drums, the only critical measurement is the centre hole and the braking surface - unless the backing plate is too close! The "proper" fix would presumably have been to turn the edge of the drum so it didn't "wobble".

I have a lathe in my sights so maybe able to do this at some point. The drum is designed to run this close to the backing plate - the plate has a lip that the edge of the drum runs in. The outside of the drum right at the edge is turned down and runs inside the lip presumably to keep crud out of the brakes. There’s plenty of clearance for this but less on the inside where the raised bump is that was rubbing.

Great HS. Result.

It's a bugger when this happens & best to go inside the house & make a Cuppa T
When you come back out with fresh eyes/brain new things seem to happen.

Oh, the time we waste on what we think is an insurmountable problem. [smilebigeye]