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MG MGB Technical - Replacing brake discs

My '66 GT (wire wheeled) has just failed it's MOT because of an excessively scored nearside brake disc. Annoying, but I can't really complain too much as the tester warned me about it 7 years ago and it's sneaked through every year until now! I was going to replace the discs and pads on both sides, assuming like on a modern car it's a basic service item. However, once I read the workshop manual I'm not so sure! As far as I can tell replacing the discs involves removing the whole hub - the problem is the instructions start talking about shims, end-float and completely disassembling the bearings. This is all a bit scary and I'm not sure necessary!

I think I can probably get the thing apart assuming I only need to remove the hub by taking out the split pin and castellated nut and don't have to pull the bearing apart. Is that correct? When refitting, how do I know how tight to do the nut back up? I assume that's what alters the end float...

Also, am I right in thinking that I can use V8 pads with the standard calipers and discs? If so, does anyone know if the EBC green stuff pads are V8-sized (and recommended?)?

Many thanks in advance.

Tim
Tim Jenner

Tim. Yes, replacing the discs (rotors) requires the removal of the hub. Good time to clean and inspect the wheel bearings and races. If they are in good condition, regrease them with a good bearing greased and reinstall. If not (visible scoring or felt roughness) replace the bearings and races. In either case, a new grease seal on the back of the hub is highly recommended.

As to the shim set up process, Paul Hunt's website, "The Pages of Bee and Vee" has an excellent tech article on this process which many have used with great success. Not as difficult a job as it seems from reading the workshop manual and Paul's tech article makes things much easier to understand.

The workshop manual and Paul's article discuss the necessary reattachment procedure for the hub assembly. Basically, the spacer and shims form a strengthening assembly within the hub itself. As I remember it, there was a problem with the MGA front axle cracking under severe use and the spacer and shims were the solution to the problem. This system carried over to the MGB.

As to brake pads, I have been informed that the V-8 pads fit and have a set in my spare parts, but have not fitted them yet. Have not tried the Green Stuff pads, but remember others have either here or on the Sprite/midget board. You might check the archives on this subject.

This is a project you can do and, should you run into any problems, we are just an e-mail away.

Les
Les Bengtson

Triumph TR8 pads are a direct fit, too. Larger friction area. I've tried them but must admit that I don't remember noticing a difference. But I'm not hard on my brakes.

Pages of Bee & Vee:-

http://www.mgb-stuff.org.uk/suspensiontext.htm



Derek Nicholson

Tim,

As the others have posted, this is a readily doable job by the home mechanic...it looked a bit scary for me too, the first time reading the book, but go through it slowly, and it all comes apart logically and goes back together without too much fuss - I'd be surprised if you have to alter shims anyway - you should just be able to reassemble everything the way it came off. Give the hubs and bearings a good clean in petrol or deisel, and I'd advise picking up one of those wheel bearing greasers (look like two mushrooms stuck together) and new grease seals as Les suggests. Chances are you won't need to purchase any new races or bearings.

The V8 pads fit in the regular calipers, but are 'handed', meaning there's an 'inny' and an 'outy' on each side. The green stuff pads come in regular and V8 sized. I have the regular sized EBC pads, and can recommend them.

As always, do one side at a time, so you have a reference to put it back together again & good luck!


Curtis Walker

Many thanks for the comments, all. I think I have a better idea of what's involved and thanks to Paul's page it makes a little more sense! Would you suggest ordering new bearings and replacing as a matter of course (which, I assume, would mean a greater probability of needing to re-shim?) or just taking the old apart, cleaning and regreasing? Also - and this will sound like a really stupid question - how do you estimate the end-float? Paul talks about shimming until it's "perceptible" - is this by grasping the outside of the hub and wiggling it against the swivel axle, looking for slight movement?

Thanks again,
Tim
Tim Jenner

I don't install new bearings unless the old bearings are defective. I carefully inspect them for smooth operation and make sure they haven't turned blue due to overheating. Inspect the rollers for chips, pits or rust. If they fail any of these checks I replace them. Usually my wheel bearings pass all these tests and go back into the car. I think you have the right idea about Paul's description of end float.

Clifton
Clifton Gordon

I wouldn't bother with new bearings if there is no reason to suspect the existing ones, but of course changing one component could disturb another and subsequently cause a problem there. Neither would it need reshimming - unless it wasn't shimmed correctly to start with. Befoe you start dismantling I'd check the end-float, by waggling the disc/hub up and down, to make sure there is perceptible end-float, then make sure it isn't coming from worn king-pins and bushes!

I've not had to change bearings very often, but when I have I haven't found the need to alter the shims. The bearings themselves are precision items, I think the shims are more to deal with the wider tolerances in the other components like hub and spacer.

One problem I recall was undoing the disc nuts and bolts, something about them being recessed and my normal sockets and spanners not fitting very well.
Paul Hunt 2

You are right about the hub to disc bolts, I use a socket with an extender, and last time I did it the rachet need a hefty belt with the palm of my hand to get them started. I think I held the head of the bolt with a ring spanner while this violence was going on. Certanly I have changed discs and not needed to change shims in the past, not so lucky last time tho.
Stan Best

That reminds me, too (I was going to post it above, but forgot). Getting the nuts off the bolts between the hub and disc can indeed be a sod. I wound up using a vice to hold the disc (since they were getting replaced anyway), so I could squeeze thin walled socket over the nut, while using a breaker bar on the bolt. Then, of course, two of the bolts stripped off when reassembling, requiring a drill out! Was very careful not to reassemble above specified torque, and used antiseize after that (while carefully holding the new discs in a vice with cloth padding).
Curtis Walker

I found the following link of Paul's website:

http://www.mgcars.org.uk/cgi-bin/gen5?runprog=mgoc&p=emg/bearing1.htm

In combination with the rest of the good advice I've had so far I think I know what to do (and realise now I forgot to order new locktabs for the calipers!). However, like the rest of the instructions I've read this article assumes you want to replace the bearings at the same time as the disc. I really don't - so do I actually need to disassemble it at all? Can I just pull the hub in one piece, change the disc and bolt back on?

Thanks,
Tim
Tim Jenner

When you take the hub off there is nothing holding in the bearings, so they will tend to fall out of place. Also there is a risk of getting little bits of dirt into the bearings during the disc change. Best to remove the bearings, taking extra care to find and keep the shims, clean, regrease and replace when the new disc is on the hub ready to fit.

Iain

PS Check ahead of time you have a socket for the hub nut. It is larger than the average socket set covers. I thought it was 1"5/16, but it may actually be 1"1/8.
I D Cameron

The only part of the bearings that does not come out easily is the hub mounted race for the inner one. This is drifted out when you change them, just leave this bit alone apart from cleaning inpsecting and re-greasing it.
Stan Best

It really is worthwhile cleaning, inspecting, and regreasing the bearings while you have the front end apart. You are bound to contaminate the grease with rust and crud from the hub and rotor during disassembly. For the cost of a couple of new seals you will get some peace of mind that yet another part of your old car is up to spec.. Clean the bearings out by immersing them in Varsol/Mineral Spirits, then blowing them dry. (If you are using compressed air resist the temptation to make the bearing spin while doing this. It sounds cool, but is not good for the dry bearing!)To save the expense of buying a bearing greasing tool just put a blob of grease on the heel of your hand and push it into the bearing until it starts coming out the other side-very simple really, just fill the bearing with grease, then replace in the now clean hub with a new seal. (If the bearing race is loose in the hub you will either have to secure it or replace it which is really quite simple as well.
Good luck, let us know how it turns out!

Rich
R.J. McKie

Just did mine and like everyone else was a little aprehensive but it was pretty straightforward. Hardest part was getting the pistons back in all the way. You need a strong "C" clamp and a piece of metal to bridge the piston top.
P.J.F. Rogers

Thanks again for the comments, all. The experience on this board really is invaluable, and it's much more obvious once you start! I'm currently part way through and slightly stuck!!

It took a while to persuade the split pin out of the hub nut (what a stupid design...) but I've now got the disc and hub off the car, both bearings, the retaining washer, spacer, shims and oil retainer seal out. Fortunately both bearings and the races look to be in perfect condition - is a visual inspection all that's needed?

I managed to get the first 2 disc-to-hub nuts off without any problem and then made the mistake of thinking this was going to be easy. As a direct result, the other 2 have decided they're not giving up without a serious fight so I've left them soaking in penetrating oil. Think I might end up needing to find a 1/2" drive socket so I can use my monster ratchet on them... Failing that, is it worth trying to heat them to help them on their way? Everything else around seems hefty enough to not be affected by the heat.

Cheers,
Tim
Tim Jenner

Heat often realy helps, I seem to remember that the distance between the nuts and the inside of the hub is a bit tight as well. As I said before I resorted to violence last time, and that was having copper sliped the nuts last time I did the job. BTW on winding the pistons back. Remember to watch you do not force fluid out of the master cylinder and onto the paintwork. i use a small portable vise to do that job, it fits between the calipers nicley and gets on both sides of the piston at once.
Stan Best

When pressing the pistons back in it is best to open the bleeder valve on the caliper that you are working on. This prevents harmful debris, that has collected in the base of the caliper over the years, to pass harmlessly out of the brake system and not up into the master cylinder causing early failure. Ray
RAY

Have been away so have only just been able to carry on but thanks to the advice on this board have now finished one side! Hurrah! There's something deeply satsifying about seeing a nice clean new brake disc behind the wheels! Just the other side to do now, then we can have another go at that MOT...

Thanks again for the help.

Cheers,
Tim
Tim Jenner

Well, I should have known better! It was just going too well. The outer wheel bearing needs replacing on the other side - two adjacent ribs in the cage have broken off and the rollers can just fall out! As an aside, I'm curious how long this type of failure can go undetected and how long it would have been until it cause trouble?

Regardless, I can't get hold of a new bearing today (Sunday) so it's going to have to wait a bit longer. Question - do I have to change the outer race as well as the bearing (the one that presses into the hub) or can I leave that as-is (there's no visible wear) and just change the inner part?

Thanks,
Tim
Tim Jenner

Tim, You should definetly replace the outer race since the bearing and race are machined as a set. Simply tap it out using a long brass drift. Installing the new race is a reverse of the removal. Ray
RAY

I have used the old bearings to tap in the new race as you need to keep it square to get it to enter. When it seats you will hear the sound change. You may not be able to do this if your old cage has broken up.
Stan Best

This thread was discussed between 27/08/2006 and 17/09/2006

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