mm rear brakes

[namass1]

Help needed urgently.The rear brakes on my 1951 mm appear to be jammed on.I removed the castellated nut and spent an age tapping the drum all round with a rubber mallet to no avail.How can I shift the rear brake drum?The tapping method used to work fine on the 1098 model I had years ago, but it does not want to work on my mm.What am I missing?I need to get this problem sorted out as quickly as possible.

[bmcecosse]

Start by slackening off the handbrake cables, remove them from the cylinder levers if you can - and then tap the levers gently into the backplate - and then hit the drum HARDER. ! Use a lump of timber to protect the drum - and good wallops with a 'wee heavy' lump hammer.... I believe some in the past have suggested pouring boiling water over the drum - not something I have ever tried - or had to consider.

[HarryMango]

You could try using a puller on the drum or levering off with large screwdriver or small jemmy.

Rog

[mike.perry]

Have you slackened off the brake adjuster?
Does the drum rotate?
To avoid damaging the half shaft thread slacken but do not remove the castellated nut.
Rotate and tap around the side of the drum with a club hammer
Tap around the back of the flange but not too hard or you may brake the flange
There is a service tool 18G 304, Manual section Q7

[namass1]

Thanks for all your help.I tried to check that the brake adjusters were backed off,but when I lined up the adjuster through the hole in the wheel I could only see half of the screw,so it could be that the adjuster screw has broken.I seem to have 2 options.I can either smash off the drum and buy another or would it be possible to remove the back plate and drum as one unit hopefully releasing the pressure on the springs to enable me to dismantle it?Advice welcome, please.

[blues2rock]

If you are going to hit the drum "hard" as suggested, make sure to wear eye protection.

[bmcecosse]

Don't smash the drum! These are 'not common' now. If you can turn it enough to line up the adjuster - it WILL come off. Just keep turning and thumping. And as indicated above - protect the drum with a lump of timber.

[gtt1951]

These are not just brake drums but an integral Drum/Hub that contains the HUB bearings - it could be that the bearings are seized to the half shaft stub. As already mentioned earlier - do not smash the hub as these are now like Hen's Teeth to get hold of.
Try to heat the hub/drum up - it you are going to use a gas torch/blow-lamp, then drain off ALL the brake fluid as this is flammable. Use a hub puller, if you have one that will fit into the wheel bolt holes.
If you can see only half a screw head on the adjuster screw, then the other edge has snapped off (happened to me) - if the drum/hub rotates, then the shoes are not what is causing the jam (unless the lining has worn a groove in the brake drum mating surface.
Try removing the other side - if that comes off OK, then you will see how the whole fits together and can then work out what to attempt on the jammed side.
Good luck, George.

[mike.perry]

The rear wheel bearing is not part of the drum, only the front wheel bearing. The rear drum is located on the half shaft spline. I doubt that you could remove the drum and back plate as the outer bearing case is bolted through the back plate to the axle casing and is usually separated with a fine taper wedge once the brake assembly has been removed.
At car no. 131858 RHD Ref Service Parts List, threads changed from BSF to UNF and it is my belief that the spline dimensions changed slightly. Ideally a BSF drum should fit a BSF half shaft and the same with UNF drums and shafts when the splines would be a good fit with no excess movement between the drum and shaft. Mixing BSF and UNF parts can result in the drum being a loose fit or a very tight fit on the half shaft.

[gtt1951]

Mike, it is integral on my '51 MM - I don't have a picture to hand, at the moment, but see below for an image of the spline shaft. The hub/drum, when removed, has 2 ballraces inside it - one on the outside lip and the other on the inner lip[frame][/frame]
I have a March '51 short bonnet (the high-light version of the low-light original series MM). The Workshop Manual does not show a clear image of the drum/hub.
Image of my front hub is below and the rear one looks very similar, but with a slightly larger diameter "hole"[frame][/frame]

[mike.perry]

Sorry to disagree George but the rear brake drum is not integral with the rear axle bearing, when the drum is removed from the half shaft spline the bearing remains in its cage attached by the four bolts to the axle casing. The front brake drum when removed contains the inner and outer ball races.

[bmcecosse]

It can't be 'integral' - the half shaft must carry the bearing loads - the drum appears to be just perched on the rotating cantilevered halfshaft ! I can well see why they changed the design on later models! So the 'splines' are probably the main holding force - perhaps a good dosing of release oil up the splines wouldn't go wrong. And careful use of a puller.......

[gtt1951]

Sorry to disagree George but the rear brake drum is not integral with the rear axle bearing, when the drum is removed from the half shaft spline the bearing remains in its cage attached by the four bolts to the axle casing. The front brake drum when removed contains the inner and outer ball races.

Mike, I stand corrected. Compared with the later assemblies, it looks integral. The later ones have a separate drum that screws onto the half-shaft end plate, like the later front drums screw onto the front bearing hub.
My point remains that the whole "hub" may not want to be released because the bearing races are "stuck" to the shaft.
Namass - what are you going to try next?
Please refer to my rear hub/brake thread on the Series MM Register thread http://www.mmoc.org.uk/viewtopic.php?f=19&t=53447
Regards George.
P.S. I have to take my rear hubs off, again, to refit the brake shoes correctly - I'll take photos then and post them on this thread.

[bmcecosse]

But there can't be any 'bearings' in the drum/hub - it just slides on the rotating halfshaft. If the shoes are not holding it - then it must be the splines.

[gtt1951]

But there can'y be any 'bearings' in the drum/hub - it just slides on the rotating halfshaft. If the shoes are not holding it - then it must be the splines.

Roy and Mike - my memory has been having some "senior moments". In the glorious sunshine that Farnborough has had today, I took both rear brake drums off (to put the brake shoes in correctly).
No bearings - just the hub/drum rear shape looked a bit like a bearing race (memory!). What it really looks like is this[frame][/frame]
Removal sequence, for Namass1's benefit
Hub cap off and split pin about to be removed[frame][/frame]Split (cotter) pin removed, castellated nut loosened and then wheel removed[frame][/frame]
Castellated nut and large washer removed[frame][/frame]Drum removed (shown in 1st picture above), then brake assembly revealed[frame][/frame]Replacement brake shoes and new springs fitted[frame][/frame]
Namass1, if your drum is still not pulling straight off, then try to squirt some Plus-Gas (not WD40) into the spline ends (see below)[frame][/frame]
Plus-Gas is designed as a "freeing" agent, WD40 is a Water Displacement agent (can do a bit of freeing too).
Please let us know how you are getting on?
Regards, George.

[namass1]

I will try some more hammering on the drum and also try to lever the shoe off the adjuster. If that fails(Which is quite likely-I will keep you informed) I will get a puller but as I may never need the puller again,hopefully,I am loath to buy one, but I will see how it goes.

[bmcecosse]

The puller is nothing fancy - just a length of decent angle iron with two holes in it will do - and a couple of long screws or studding and nuts to fit the wheel stud holes. I don't know the thread size of these - but someone who does will be along in a minute! Protect the end of the half shaft. Tighten the screws/nuts and then some more 'tapping' !

[mike.perry]

The thread is BSF, 7/16 x 18 tpi or UNF, 7/16 x 20 tpi, you will just have to check.
George - Point to note, the split pin should be removed and castellated nut slackened then wheel bolts slackened before the car is jacked up, but you knew that already.
Also I think that you have fitted the wrong long spring. The Service Parts List shows a long spring with continuous coils, similar to the short spring

[gtt1951]

...
Also I think that you have fitted the wrong long spring. The Service Parts List shows a long spring with continuous coils, similar to the short spring

You mean like the ones I have just removed - see picture of "brake assembly revealed"? The new ones never did look correct.
The new shoes and springs came from a bona-fide parts supplier. The short spring is the one that has given me so much trouble as being too "robust".
George.

[bmcecosse]

The easy way to get a bit more leverage on it - is to put the wheel back on and use it wiggle the drum back and forth - with turning. The 'short' spring looks fine - it IS super strong.