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MG TD TF 1500 - Smoking brake drum

Nice little trip out in the TF, but the further I went the more the performance dropped off. Engine sounded fine, but I was just going slower. Engine temp rose a little and I sensed what it was and turned for home. By the time I got there I was in second gear to make progress. Didn't dare stop or I might not start again. Struggled up the driveway and parked it - smoke from the offside rear drum. Got a watering can and sprinked a little water on it - steam everywhere. It took a few gallons to cool it down slowly. The car would then not move - rear brake seized. Jacked it up, remove the wheel and after a couple of hours battered off the drum unscathed with a block of wood and heavy mallet. What did I find? Nothing! Brakes set too tight, that is all it was. Slackened all the others just in case! What had I done to bring this on? Fitted a set of Eezi-bleeders and bled them just the once. Must have finally got rid of all the air. Brakes didn't seem set too tight, but clearly they were.
Dave H
Dave Hill

Sorry to hear of your trouble.
Any chance there was some crud in the slave cylinders preventing the return springs from doing their work? It doesn't take many months for black deposit to build up around the pistons.
I often check the drum temperatures at stops with my fingers to see if trouble is looming.

Matthew.
M Magilton

I really don't know. Yes I check the drum temps regularly as well. My usual finding is the front drums are very hot and the rears barely warm. Just taken a test drive this morning and a bit too much travel on the brake pedal, rears drums very cold, so have put one click back on each. Just a slight rubbing sound at one place on each rear wheel. No other harm apparent.
Dave H
Dave Hill

The best way to adjust brake shoes is to tighten down each adjuster all the way - hard - until the drum is locked, and then loosen one click at a time until the drum turns with just a little scraping. That takes up the free play on the pedal, and keeps the shoes tight without dragging.

Tom Lange
MGT Repair
t lange

Yes, the front are usually a little warmer. If the left and right sides match then they 'should' be reasonably balanced. I suspect there is a reason for your smoking drum that has not been discovered yet though. Were the pistons quite free?

Matthew.
M Magilton

Matt. You are right - I am going to have to look properly.
Dave H
Dave Hill

Well, crawling under the back and pulling on the lever it springs back nicely, just the same as the other side. I always set the rear brakes the same way - chock the front wheels, release the handbrake, jack up the back axle and rotate each wheel to check its free. Then adjust until tight and back-off until free (slight scrape ok). Finally check that both sides grip on the handbrake at the same point, if not re-adjust. Must have just set them a bit too tight. Bonded linings if it makes any difference.
Dave H
Dave Hill

You checked only half of the possible problem. The hydraulic piston is separate and further in than the one the handbrake lever presses on. You would have to disassemble the cylinder to check that. I have had front cylinders stick "on" due to corrosion and the springs aren't strong enough to pull it back.
George Butz

I'm with Matthew. I suspect you haven't found the actual problem. I suspect something with that slave cylinder at the wheel with the smoking drum.

I had a collapsing brake line on my rear axle that caused my rears to drag as the master cylinder would apply enough pressure to overcome the restriction, but the springs did not have enough to force it back. I doubt that's your issue since your problem appears isolated to one side.

Alex
Alex Waugh

Ok, its a possibilty there is problem with the cylinder. I too fear that I haven't got to the bottom of it yet, as things don't just happen. I'm using DOT5 and it was a new cylinder 3 years ago, so unlikely to be corrosion, but its worth dismantling to investigate.
Dave H
Dave Hill

How old is the flexible hose to the back axle. They can fail internally and work like a one way valve, so the brakes go on but don't release. And this can show up worse on one side of the car, speaking from experience!
Graeme
Graeme Fisher

The entire system was replaced about 3 years ago.
Dave H
Dave Hill

Three years can be plenty of time for deposit to build up on the pistons, especially if not driven very often.
M Magilton

I replaced every single part from the braking system on my TF last year. I thought I would be smart and smeared a little waxoil on the pistons and under the rubber boots to stop any water ingress and corrosion. When I came to move the car after winter storage the brakes were solid. The once fluid waxoil had solidified and was preventing the springs pulling the pistons back in. After a good clean and lubricating with the correct red, rubber grease everything is fine. Another outcome from this escapade I now have left and right hand dies to clean up the stub axle threads so if anyone needs them they are here to borrow.

Jan T
J Targosz

I will be dismantling it all today and will report here any findings. Thanks to all for your comments, its what this forum is all about.
Dave H
Dave Hill

Well its humble pie time from me! The brake cylinder was seized. A little bit of rust and some red crusty stuff, that was all it took. The red crusty stuff can only have been old red rubber grease, which I remember putting on the rubber boot and the outer rubber seal. I didn't know it degraded like this. Don't use it anywhere near brakes. I was able to clean everything up and reinstall it, lubricating with plenty of silicone brake fluid and silicone grease. Next step was to attend to the other side, which was well on the way to the same condition. It took me an age to bleed the system again and seal up the leaks, despite using new copper washers and tightening as firmly as I could. Thanks for all the helpful comments.
Dave H
Dave Hill

Apologies Jan, but I can only report what I found. No doubt about it at all.
Dave H
Dave Hill

Hi Dave,

Looks as though the root of our problems is the same - solidified grease. I think the key is to move the car and press the brake pedal each week during a winter lay up. If you are having trouble bleeding the brakes try jacking the front and then the rear of the car to raise the master cylinder above the hight of the wheel cylinder being bled. I haven't tried it myself but a Morris Minor owner said it worked with his car - they have a similar system to the MG.

Cheers

Jan
J Targosz

Actually, bleeding the brakes with the Eezi- bleeders is a lot better. The real problem was stopping the silicone fluid from leaking, having had it all apart. I had to tighten the everything with all the strength I could muster to stop it.
Dave H
Dave Hill

The other thing to add is that I had noticed several times that after a run out the front drums were very hot and the rears barely warm. Seems like the fronts were doing all the work and the rears nothing, I should have sensed a problem. On the day it all went very wrong, I went for a very brisk run and hurtled down a hill nearby (there aren't many!), pressing hard on the brakes at the bottom. Thinking on, it was only after that when I realised I had a problem. The rear brake cylinder must have already been partly seized, but the run down the hill had generated more heat and probably allowed the piston to advance further, but not retract. From them on I was driving with a dragging brake, which got progressively worse as it heated up. The warning sign was the dfferential in temp between front and rear brake drums.
Dave H
Dave Hill

Dave, I am having similar leakage problems with my rebuild after lying in pieces for 40 years. Mostly new fittings apart from banjos and a couple of good slaves plus dot 5. I have tried original (re-annealed) copper washers, new cheap ones ( bought a whole selection box but too much clearance around the bolts), new ones from a reputable source (much better fit but very thin) and am now waiting for some thicker ones from a brake specialist (he suggested a little loctite blue as well) and some special crush washers (though there is some doubt they will handle the pressure of a brake system). I polished the banjo surfaces but have been able to determine that one of the leaks is between a washer and the slave - leading me to wonder if the thread is truly perpendicular to the surface. I intend to check with feeler gauges. I also found I had to shorten one of the bolts and extend the thread as it was bottoming in the slave without fully crushing the copper. One website also suggests tapping the end of the banjos while tightening to improve the chances of getting a good seal. I am still open to any other suggestions!
PS if it hadn't been dot 5 I would have been having to repaint my chassis by now!
Chris
C I Twidle

I know what you mean, I spilt a lot of the stuff trying to seal it today. In the end I got there by tightening everything beyond the reasonable. Don't like the idea of crush washers or sealant.
Dave H
Dave Hill

You are onto something with the thicker copper washers. I decided to replace one of the rear brake cylinders today, and at the same time bought the correct new copper washers (all from B&G, which is fairly nearby). The new washers are much thicker than those I was struggling with and sealed straight away.
Dave H
Dave Hill

Dave,

I had a look at the B&G parts diagram and parts list and noticed that they have different part numbers for the inner and outer copper washers on the brake banjos.

The ones between the wheel cylinder and the banjo (same for front & rear) are part number 233220A – described as “copper washer brakes T A B”.

The ones between the banjo bolt and the banjo (same front & rear) are part number 3H550 – described as “copper washer brake banjo”.

As this was successful for you I thought I would do the same. The description “copper washer brakes T A B” seems a bit odd for the inner ones. Could you tell me what you got to do the job please?

Kind regards,
Michael
M R Calvert

Those are the ones that I used - they fit better than those that you find in boxes of general purpose copper washers. Slightly different size for each and one is thick and the other thin. I reused the banjo and connector piece. Their brake cylinders are also inexpensive.
Dave H
Dave Hill

Am I on the right track here, I would need 2 of each per side for the front and 1 of each per side for the rear?

Total of 6 of each per car?

Thanks.

Peter
P G Gilvarry

At the back one banjo per wheel, so one washer of each size per wheel. At the front there are two banjos per wheel so I imagine you need two washers of each size per wheel. That makes 6 of each size per car.
Dave H
Dave Hill

Thanks Dave, ordered, along with a few things I needed.

Peter
P G Gilvarry

Thanks Dave,

That is very helpful.

Kind regards,
Michael
M R Calvert

For anyone going through the full braking system it is worth noting that there is another of these copper washers between the master cylinder and the adapter at the rear that accepts the brake line.

B&G list it as: part number 233220A – “copper washer brakes T A B”

Michael

M R Calvert

If you are doing the remote fluid reservoir you will actually need yet another! The sizes are 5/16 and 3/8 ID. I bought a bulk set of various sizes which claimed to be imperial but were, shall we say, 'generously sized' so they didn't locate accurately on the banjo bolts.
I mentioned in a previous post that I had ordered some stat-o-seals and had some misgivings (reinforced by, I think, Dave) about whether they were suitable as the manufacturers specs rated them up to 200psi - a figure that is likely to be exceeded in our brake system. When they arrived they clearly state on the package 'Not for braking systems'. Pity it wasn't on their website....
Chris
C I Twidle

This thread was discussed between 01/06/2017 and 08/06/2017

MG TD TF 1500 index

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