Rear brake drum won't slide up to the hub

[philthehill]

I am certain that the only difference between the 7" and 8" snail cam brake adjusters is the size of the snail pin which fits into the hollow of the brake shoe.
The 8" pin is of a larger diameter than the 7" pin which means the slot in the 8" carrier is also slightly larger.
I have both 7" and 8" adjusters but cannot do any lifting at the moment to get at them to measure the height and the size of the pin.
Check that the snail pin fully fits into the hollow of the brake shoe.
You may have to run a file through the hollow to suit the adjuster pin.

[svenedin]

I am certain that the only difference between the 7" and 8" snail cam brake adjusters is the size of the snail pin which fits into the hollow of the brake shoe.
The 8" pin is of a larger diameter than the 7" pin which means the slot in the 8" carrier is also slightly larger.
I have both 7" and 8" adjusters but cannot do any lifting at the moment to get at them to measure the height and the size of the pin.
Check that the snail pin fully fits into the hollow of the brake shoe.
You may have to run a file through the hollow to suit the adjuster pin.

I think I have some adjusters in the house to compare. I'm not venturing out to the garage in the cold!

I think they have the same diameter spindle but a larger diameter cam.

We shall see......

Stephen

[svenedin]

The answer is, the spindle of the 8" adjuster is larger than the 7" and therefore the slot in the adjuster mask is also larger as Phil said....

In fact, the difference in spindle diameter is quite considerable.

Stephen

IMG_2978.jpeg (708.34 KiB) Viewed 42512 times

IMG_2979.jpeg (1.07 MiB) Viewed 42512 times

[philthehill]

Stephen
Many thanks for confirming my view.
Phil

[geoberni]

I posted a load of detail about the cams back in 2022, including the original part numbers.
Even the original 7" front and read were different parts.
https://board.mmoc.org.uk/viewtopic.php ... 63#p677763

[philthehill]

As regards part numbers - BMC were well known for providing different part numbers for the same part.
For example - the Minor front suspension rubber eye bush and rear spring rubber eye bush are one and the same part but have different part numbers.
As regards the number of teeth on the snail cam - it is not unknown for different manufactures of BMC parts to have different styles of part but all having the same outcome. For example I have several gearbox front covers by different manufactures and they all have different styles of casting but all have the same part number and outcome. Therefore I would consider the number of teeth on the snail cam to be irrelevant/a red herring.
Basically there are just two factory snail adjuster cams the 7" and the 8" size and style. The larger after market snail adjuster should be considered as an afterthought solution to a after factory problem.
Phil

[mike1864]

So the snail's spindle diameter determines the minimum adjustment, ie the shoes away from the drum as far as possible?
I have lust measured the slot in some new ESM front shoes. It's an interference fit around a 9mm diameter drill bit.
So, going back to Stephen's photos, the spindles are approx 8mm front and 5mm rear?
And presumably a rear snail would fit in the front (albeit sloppy), but not vice versa?

[geoberni]

So the snail's spindle diameter determines the minimum adjustment, ie the shoes away from the drum as far as possible?
I have lust measured the slot in some new ESM front shoes. It's an interference fit around a 9mm diameter drill bit.
So, going back to Stephen's photos, the spindles are approx 8mm front and 5mm rear?
And presumably a rear snail would fit in the front (albeit sloppy), but not vice versa?

By no definition of 'Fit' does a Cam for a 7" fit the Mask of an 8"...

That's like saying a 15mm socket fits a 12mm bolt, but it's just a bit sloppy...

[svenedin]

So the snail's spindle diameter determines the minimum adjustment, ie the shoes away from the drum as far as possible?
I have lust measured the slot in some new ESM front shoes. It's an interference fit around a 9mm diameter drill bit.
So, going back to Stephen's photos, the spindles are approx 8mm front and 5mm rear?
And presumably a rear snail would fit in the front (albeit sloppy), but not vice versa?

Comparison of rear (left) and front (right) Micram snail cams

IMG_2983.jpeg (722.31 KiB) Viewed 42080 times

Spindle diameter rear Micram (all models, 7" brakes)

IMG_2984.jpeg (1.17 MiB) Viewed 42080 times

Spindle diameter front Micram (8" front brakes)

IMG_2985.jpeg (1.13 MiB) Viewed 42080 times

[mike1864]

So the snail's spindle diameter determines the minimum adjustment, ie the shoes away from the drum as far as possible?
I have lust measured the slot in some new ESM front shoes. It's an interference fit around a 9mm diameter drill bit.
So, going back to Stephen's photos, the spindles are approx 8mm front and 5mm rear?
And presumably a rear snail would fit in the front (albeit sloppy), but not vice versa?

By no definition of 'Fit' does a Cam for a 7" fit the Mask of an 8"...

That's like saying a 15mm socket fits a 12mm bolt, but it's just a bit sloppy...

I was assuming each snail was in its correct mask, and the slop would be between the rear's spindle and the front shoe's slot.
That said, Stephen's 9.98mm would seem to be too big to go into my front shoe's slot. But - without an adjuster to hand - maybe i'm mis-visualising the design.

[svenedin]

So the snail's spindle diameter determines the minimum adjustment, ie the shoes away from the drum as far as possible?
I have lust measured the slot in some new ESM front shoes. It's an interference fit around a 9mm diameter drill bit.
So, going back to Stephen's photos, the spindles are approx 8mm front and 5mm rear?
And presumably a rear snail would fit in the front (albeit sloppy), but not vice versa?

By no definition of 'Fit' does a Cam for a 7" fit the Mask of an 8"...

That's like saying a 15mm socket fits a 12mm bolt, but it's just a bit sloppy...

I was assuming each snail was in its correct mask, and the slop would be between the rear's spindle and the front shoe's slot.
That said, Stephen's 9.98mm would seem to be too big to go into my front shoe's slot. But - without an adjuster to hand - maybe i'm mis-visualising the design.

Ah but to confuse matters, if you look at my picture, the spindle diameter in between the cams is not the same diameter as the rest of the spindle. The spindle in between the cams is narrower. I didn't measure the spindle there.

Stephen

[mike1864]

Hi Stephen. I thought that might be the case. Dimensioning off your photo gives ~8.6mm diameter for the inside section of the "axle". Fine for my shoe's slots. But, on the next strip-down, I'll check the right ones are in place.
But do any of these findings explain the OP's eponymous issue?