New brakes binding

[Ruairidh Dunford]

The tool fits on in place of the brake drum.

The bar moves up and down to suit the heights of linings etc. The bar is clamped tight and allows the shoe to be set up straight against it, you then rotate the tool removing any high spots it comes up against. Once high spots are removed the tool can be adjusted down slightly and further lining removed until it turns right around the axis of the hub freely.

[Chris KC]

For what it's worth, there ain't no such thing as 'perfectly round'. A brake drum produced by modern mass-production methods might have a tolerance of 0.5 thou or so for roundness and 1 thou for concentricity with the axis. But it would also be substantially stiffer than an A7 drum and clamping up to something much flatter than a 90 year old hub. New drums are very good, not perfect!

[Steve Bryant]

Once upon a time new brake shoes had to be trued up prior to installation by "arcing " them on a machine similar to a drum sander. The shoe was clamped and the pivot point adjusted  to  to give an arc of the same diameter as the inside of the drum. The shoe was then rotated on this set pivot point  or "arced" against the sanding drum to remove any high spots.

This gave a true curved surface that allowed the shoes to make full contact immediately without a bedding in period.

Stephen

[GK5268]

Check that the new drum is sitting perfectly flat on the hub, I had this issue with my new drums several years ago (part of the kit for hydraulic brake conversion), the front drums needed to have its inner radius filed where it contacts the hub (rears were fine as they had new hubs and were machined to match) and once done, fitted flat onto the hub flange.

I did not notice this at first, it wasn't until I could see that the wheel rotation was out of truth (difficulty in setting up the tracking) that I had to investigate and spotted this problem. The profile of the angle on the drum differed to that on the angle of the hub - this has a curve - the drum is square - and once they matched it was fine, it is hard to see at first, only has to be slightly out, if the drum rocks slightly before the screws are fitted, then that is your problem.

Good luck!

[Tony Press]

Check that the new drum is sitting perfectly flat on the hub, I had this issue with my new drums several years ago (part of the kit for hydraulic brake conversion), the front drums needed to have its inner radius filed where it contacts the hub (rears were fine as they had new hubs and were machined to match) and once done, fitted flat onto the hub flange.

I did not notice this at first, it wasn't until I could see that the wheel rotation was out of truth (difficulty in setting up the tracking) that I had to investigate and spotted this problem. The profile of the angle on the drum differed to that on the angle of the hub - this has a curve - the drum is square - and once they matched it was fine, it is hard to see at first, only has to be slightly out, if the drum rocks slightly before the screws are fitted, then that is your problem.

Good luck!

If I understand what you are saying- the new front hubs have a sharp corner where the flange meets the body - technically not a good thing, promoting a failure at this point ?

[Zetomagneto]

Check that the new drum is sitting perfectly flat on the hub, I had this issue with my new drums several years ago (part of the kit for hydraulic brake conversion), the front drums needed to have its inner radius filed where it contacts the hub (rears were fine as they had new hubs and were machined to match) and once done, fitted flat onto the hub flange.

I did not notice this at first, it wasn't until I could see that the wheel rotation was out of truth (difficulty in setting up the tracking) that I had to investigate and spotted this problem. The profile of the angle on the drum differed to that on the angle of the hub - this has a curve - the drum is square - and once they matched it was fine, it is hard to see at first, only has to be slightly out, if the drum rocks slightly before the screws are fitted, then that is your problem.

Good luck!

If I understand what you are saying- the new front hubs have a sharp corner where the flange meets the body - technically not a good thing, promoting a failure at this point ?

No, GK means the inner edge of the drums were not radiused.You certainly want a radius on the hub though, as you say

[Tony Press]

Check that the new drum is sitting perfectly flat on the hub, I had this issue with my new drums several years ago (part of the kit for hydraulic brake conversion), the front drums needed to have its inner radius filed where it contacts the hub (rears were fine as they had new hubs and were machined to match) and once done, fitted flat onto the hub flange.

I did not notice this at first, it wasn't until I could see that the wheel rotation was out of truth (difficulty in setting up the tracking) that I had to investigate and spotted this problem. The profile of the angle on the drum differed to that on the angle of the hub - this has a curve - the drum is square - and once they matched it was fine, it is hard to see at first, only has to be slightly out, if the drum rocks slightly before the screws are fitted, then that is your problem.

Good luck!

If I understand what you are saying- the new front hubs have a sharp corner where the flange meets the body - technically not a good thing, promoting a failure at this point ?

No, GK means the inner edge of the drums were not radiused.You certainly want a radius on the hub though, as you say

Hi Zetomagneto,

Yes- but he also said -

 (rears were fine as they had new hubs and were machined to match)

which seems to indicate the hub had a sharp corner ?

Tony.

[GK5268]

Check that the new drum is sitting perfectly flat on the hub, I had this issue with my new drums several years ago (part of the kit for hydraulic brake conversion), the front drums needed to have its inner radius filed where it contacts the hub (rears were fine as they had new hubs and were machined to match) and once done, fitted flat onto the hub flange.

I did not notice this at first, it wasn't until I could see that the wheel rotation was out of truth (difficulty in setting up the tracking) that I had to investigate and spotted this problem. The profile of the angle on the drum differed to that on the angle of the hub - this has a curve - the drum is square - and once they matched it was fine, it is hard to see at first, only has to be slightly out, if the drum rocks slightly before the screws are fitted, then that is your problem.

Good luck!

If I understand what you are saying- the new front hubs have a sharp corner where the flange meets the body - technically not a good thing, promoting a failure at this point ?

No, GK means the inner edge of the drums were not radiused.You certainly want a radius on the hub though, as you say

Hi Zetomagneto,

Yes- but he also said -

 (rears were fine as they had new hubs and were machined to match)

which seems to indicate the hub had a sharp corner ?

Tony.

To avoid any confusion, the front hubs were the originals and they are radiused between the flange and the hub projection, the rears, which were brand-new (supplied by A7 Components) are less radiused, so that the new brake drums fitted perfectly on the rear, but at the front, the edge of the central mounting hole had to be filed to suit the radius on the hub, once this was done, the drum fitted onto the flange perfectly square. 

Just fitting the drums as supplied, it was not self-evident that these were out of truth, they fitted and screwed up ok, all seemed fine until I had problems setting up the tracking - the wheels were of course wobbling away - my first thought was the wheels (which had been re-built) were out of truth, but checking the drums with a dial-test indicator showed there was a run-out and then taking it all apart, the fitting of the drum onto the hub was found to be the problem as the drum was riding on the radius and not making full contact across the flange surface. Once closely inspected it was obvious what the problem was. Once the edge had been filed to suit, the drum fitted perfectly.

So, if the new drum is out of truth with the hub, not only could this affect brakes, but also the tracking and handling!

[Steve Jones]

If the brakes only bind when the drum screws are fitted and tightened, try filing a small angle on the outer top edge of each lining. I've just had this issue and found that when tightened up, the outer top edge of the linings were binding on the corresponding radius inside the drum.

Steve

[John Mims]

Having digested all the ideas and advice in this thread, I managed to get up to my shed and try to sort out the binding front brake.

Firstly, I established as best I could that the drum was round and not distorted. Then I checked the profile around the central hole that Gary Edwards mentioned. This was fine, too.

Satisfied that the drum was not at fault, I tried Reckless Rat's method of chalking the shoes to see where they were binding. On tightening the three screws, I encountered exactly the problem that Steve Jones mentioned in the previous post, and so I chamfered the edges of the linings. This didn't completely overcome the problem, and the chalk indicated that the top sections of both shoes were binding. At some time in the past, the pivot has been repaired by drilling and tapping through its axis, and then bolting through the backplate. Perhaps this was slightly off centre, raising the shoes slightly.

I would have liked to make an adjustable gauge like Ruairidh's, but just didn't have the time, so instead I made a slightly less elegant copy of Derek Sheldon's sanding drum, but using a strip cut from cloth-backed sanding belt rather than emery cloth. A few turns, a little packing and a few more turns, and voila! problem solved.

Many thanks to everybody for their help