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MG MGB Technical - Front brakes getting warm

This is happenning intermittently after a longish run. The hubs are warm to the touch, but not painfully hot and there is a 'hot brakes' smell.
The brakes still work fine, even when hot, and they release ok when the pedal is released.
Flexi tubes were changed less than a year ago, so the problem is most likely the master cylinder or calipers. Any ideas on how to go about testing these items, or should I just replace them?
Car is a late model BGT with dual circuit brakes and integral servo. Is the servo on the list of suspects too?
Grateful for your thoughts,
Stephen Elster
SJ Elster

If you are getting a hot brakes smell then I'd expect the hubs to be too hot to touch. 'Warm' just seems normal to me, although it's going to be down to how many nerve endings are in our respective fingers. I had a caliper stick on after an emergency brake and that made the car slightly sluggish, gave a whiff of brakes, after the second whiff I stopped and the disc had turned blue.

If they are binding, and it's both of them, then the probable cause is master cylinder or servo and my first suspect would be the latter. Certainly if it had been the earlier remote servo which is known to stick, but I don't have experience of the later integral. It would be unusual for both calipers to be doing the same thing at the same time, sometimes and not others.

When the remote servo sticks the pedal gets higher and harder so is pretty obvious, and tapping it usually releases mine. I'd expect - maybe wrongly - the same effect on any hydraulic braking system if something is maintaining pressure in the system.

If something is preventing the master cylinder piston from coming back far enough to clear the bypass passage up to the reservoir, fluid expansion with heat will apply the brakes. But that would be more noticeable after a session of heavy brake use rather than just a longish trip, and will make the wheel hard to turn with the pedal released.

Without any other external factor pointing to fluid pressurisation, and despite my comment above, I'd bang them on hard and see whether the pistons retract as they should from seal tension i.e. does the wheel spin relatively freely with just light rubbing or are they jammed on. Also looking at the pistons to see how easy they are to press back, and whether any are reluctant to come back out with very gentle pressure on the pedal.

paulh4

"Flexi tubes were changed less than a year ago ..." - I can't remember hearing of problems with these but never assume that just because it's a new part that it can't be faulty or not fully functioning.

Many modern made parts are of piss-poor quality and the're supplied by all the usual suspects and the smaller ones too - bur as I put I've not, that I can remember, hear this about brake flexi-hoses, others might know differently.
Nigel Atkins

One would hope that brake hoses aren't suffering from deteriorating quality, but one never knows!

But like calipers sticking, it would be surprising to have both sometimes causing the problem and others not, both sides together.
paulh4

I'm not entirely sure what the problem is here.
Brakes work by converting kinetic energy to heat energy!
How hot the discs, and therefore hubs, get is down to how much braking you do on a journey and how hard you lean on the pedal!
Don't go feeling how hot the discs are unless you fancy a trip to A & E.

If you want to double check, jack up the front wheels and see if there is any suggestion of binding.
If the servo air valve sticks after you have come to a halt, then you won't move much as the fluid pressure stays in the brake lines.
Allan Reeling

Servos probably vary, but the one in the roadster can stick just from slowing the car. The drag is obvious, but it doesn't stop the car moving. Tapping the pedal releases it in my case, but a pal's V8 was so bad touring Ireland we had to disconnect the servo hose and plug it with a spare spark plug. If one braked hard to bring the car to a halt and it stuck then, maybe you wouldn't move, but that hasn't happened with mine.

As for heat, I certainly wouldn't touch the hubs after a bout of heavy braking, but coming to a halt after 'normal' (for me) driving they are no more than warm.

And being intermittent, you would have to test the rotation of the wheels when you don't have the problem and compare it with when you, to see if they are binding or if it's something else.
paulh4

Stephen,
how old are your tyres (regardless of how much tread are on them)?

Tyres are an often neglected but important part of braking, steering, road holding, handling, noise and comfort.

Picking up on Allan's point about braking, driving style, techniques and experience with old cars can make a big difference to wear on parts and components like brakes, clutch and engine. If the following doesn't apply to you then please don't take offence because I don't know your experience.

Owners who are more used to modern cars and don't always drive their classics much or far so may not drive them appropriately and lack experience with the car from basically lack of use.

I sold my rubber-bumper roadster V8 conversion to a younger chap who was a motorcyclist with 11 points on his license and he wanted a classic so he would drive (a car?) slower, about three weeks later he rang me to ask if I'd ever experienced brake fade on the V8 (which had an appropriate brake upgrade and with brakes, tyres and suspension all in good condition). I told him to slow down and how to drive the car for braking.

Do you have a copy of the relevant Driver's Handbook, and in relation to this post, read how to properly start the car - you don't have the clutch pedal pressed down, use the overdrive - switching in or out you don't press the clutch pedal or fully lift off the accelerator pedal, correct tyre pressures, changes of brake fluid, servicing requirements.

I make no apology for stressing the following - brakes are THE most important thing on a vehicle, they should be your first thought as you approach the vehicle to use and everytime you lift the bonnet (not the engine or carbs with classics).

"WISDOM
It makes no difference how quickly your MG will accelerate if it cannot stop! The proper functioning of your brakes must ALWAYS be at the top of your list of priorities. You owe this degree of safety to yourself, your passenger, and all others on the road. John H. Twist (Fall, 1980)"

Sorry, it always sounds preachy, perhaps it is. :)
Nigel Atkins

Or as Andy Green has said "Going faster is optional, slowing down is compulsory"
paulh4

Not heard that but I like it - and from someone who would really know!
Nigel Atkins

Thanks to all for the advice and wisdom. I had another look at it today and really couldn't find anything wrong, I cannot make the brakes bind no matter what I do and the brakes, steering etc are working perfectly well. Drove about 40 miles today, checked the hubs several times but never more than slightly warm.
I will just keep an eye on it for the time being and see if I can spot a pattern in when they heat up. Certainly the last time I noticed it happenning was on a warm day and a bendy road.
Agree totally about that safety is always the highest priority, and also that we cannot expect to treat our old cars as if they were new cars.
Just for the record, I do have quite a bit of experience driving old cars. I learned to drive in 1964 Ford Escort and passed my test in 1969 Vauxhall Viva. They were not classic cars then, just the kind of second hand cars most people had back then.
Excellent point about the tyres - they are in very good condition tread wise but coming up to 6 years old so will change them soon.
All the best,
Stephen Elster
SJ Elster

Stephen,
my first three cars were from the early 60s (in two years in the later 70s, then no cars until mid 1980s).

6 years old isn't old by what I meant, some ride on tyres that are decades old (showing how little the car is used).

In case I gave you the wrong idea I expect these cars to be driven enough and maintained enough to be driven in a spirited or very spirited fashion with confidence.

For the brakes, having the rear drums adjusted properly makes a difference, and to the handbrake (though it'll have less difference to pedal feel with the servo perhaps) and changing the brake fluid at the required intervals.

With the brakes, tyres, steering and suspension in good condition and set up correctly the cars should brake well, not in the same way as modern cars but still effectively and in a way that give you confidence in them.

If the car hasn't been used a lot and/or for a good while perhaps the brakes have gone hard with age/lack of use. Or perhaps just a good clean out would help, front and rear and adjust rear.
Nigel Atkins

Stephen
Ifyou only get the smell when you've been on a bendy road (more braking ) then I would tend to think you haven't got a problem
It's a bit difficult to imagine how much smell you're getting, but some softer disc pads will smell easily without a lot of braking effort
Do you know what brand / grade of pads you have and have they been recently fitted. If they are newish ,maybe they just need a good workout to bed them in

willy
William Revit

Correction to previous post. My first car was a cortina, not an escort. Not sure how I could have muddled that up:)
SJ Elster

My second car, bought within weeks of my first which was my first but not only car buying mistake, was a pre-63 Ford Consul Cortina Mk1, 1200cc, with the very long gear lever and Starsky & Hutch white stripe which I tried to remove.

Willy as always make a good point about new pads and bedding them in. I bedded in some Mintex 1144 on my midget before going on a driving holiday over the Welsh mountains and thought I'd give them a final test over the Long Mynd on the way. After the bottom of the Long Mynd I waited for our friends to catch us up and my wife noticed steam at the front of the car, it was smoke off the brakes so I got going again to cool them down without using them unless I had to stop. They were fine after that over the Welsh mountains and remained so. I thought I'd fully bedded them in before Long Mynd but I wasn't hanging about on the test.

Nigel Atkins

I have had the brake smell problem at times after moderate use on the left side after fitting the green pads from Moss. Took out the pads and sanded the edges of the steel backing plates as I felt they were a bit tight and so far so good
R J Pemberton

The only binding I have had was corroded pistons. I put stainless steel MGOC ones in 20 years ago and no problems since.
Stan Best

This thread was discussed between 27/08/2019 and 19/11/2019

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