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MG MGA - MY A has the dreaded dragging front brakes

So I did the test today of raising up the front end and trying the brakes. Locked on solid and takes a long time to release and they're always dragging severely. This has been going on since purchasing the car last year which had a total restoration with all new lines and..... silicone brake fluid!
Recently I had a new master cylinder installed after the old one started leaking. Silicone was used again and the front brakes continue to lock on and drag.
So I suspect the brake fluid as opposed to both front lines collapsing. I'm doubtful that modifying the gasket on the front of the master will help. So if I decide to switch to dot 4, do the internals of the hydraulics need to be replaced or can I just flush copiuous amounts of dot 4 throught first?
R emgeeaa

When I used to use silicone brake fluid (not any more, too many problems and stainless steel m/c sleeving overcomes the main reason for using silicone!) in my MGA's I found it necessary to remove about an eighth of an inch from the front of the master cylinder piston. The reason is that when some (if not all) of the rubbers swell (due to the use of silicone fluid) they block the return port in the master cylinder. The consolation is that the brakes still work perfectly, notwithstanding the m/c mod, since I reverted to conventional fluid many years ago.
Barry Bahnisch

I would really look at replacing the front rubber hoses first if you haven't already - or if they are older than 5 or 10 years.

I have DOT 5, but all new rubber parts, and my brakes release just fine. I don't see any reason why DOT 5 alone would cause brakes to drag. With new rubber parts, the pistons may not want to return all the way forward if they are hanging up in the bores - but just exercising them a bit seems to solve that. Since your MC is new, I am guessing that the bores are in good shape and the rubber is new. Did the piston want to return all the way forward when the system was dry? You can check by opening up the bleed nipples and purging the system of fluid and then cycling the piston.

The hoses are a quick swap and easy enough to do for little $$$, and if you go through all the trouble to drain, flush (with alcohol), refill and bleed them and still have the problem, you'll kick yourself in the head for not doing this part first.

The other issue of changing the front gasket is also a 10 minute job, and I would do that next if needed - or actually, I would do it while I had the hoses apart before rebleeding the system - no harm done if it didn't need doing.

Before you do anything else, though, make sure that you check the adjustment of the brake linkage rod to make sure that it is correct. Mine was not. Make sure that when the pedal returns the piston has returned all the way to the correct position at the front of the bore, and that the rod then has about 1/16 to 1/8 of fore and aft play.



Good luck!


JIM in NH
AJ Mail

I should mention that I have an MGB front disc brake and suspension swap on the car.
Thanks Barry. I read about the 1/8" rod shortening mod. Maybe an option.
R emgeeaa

Thanks Jim. The hoses, etc were all replaced by the PO when he restored the car a few years back. There are hardly any miles on the car since then.
Maybe I should consider trying the gasket mod. I did check the end play in the pushrod.
R emgeeaa

I note the enthusiastic support for silicone brake fluid by our USA colleagues! I, too, used to be an advocate until one of my (fairly new) MGA front hoses turned itself into a one-way valve and caused serious dragging (trying to get the car home the wheel bearing grease caught fire--lucky that I did not lose the whole car!). I had to repaint the wire wheel and some of the front suspension. Silicone brake fluid, once readily available here "off the shelf", is now off the market and, at last enquiry (some time ago), was only available to specific order in advance. In fact, by now, it could be unobtainable in Oz. It was never adopted here in the trade probably due to the various problems that us "amateurs" encounter.
Barry Bahnisch

Sorry, I have just re-read the previous threads. It has nothing to do with the rod (which I think is adjustable anyway) or the gasket (which is really superfluous if you think about it), it is the piston that can cause the trouble. I suspect that the (earlier ?) soft black rubber seals may be more susceptible to swelling than the later (?) shiny ones? Either way it doesn't matter (to me anyway) any more!
Barry Bahnisch

The main reasons that people give for changing to silicone fluid is that normal brake fluid is hygroscopic (absorbs water) and damages paint.
The paint damage problem can be avoided by just being careful.
The water absorption can be eliminated by using the method which is used on most modern cars, fitting a bladder inside the master cylinder.
The water gets into the fluid because of the constant rising and falling of the fluid level when using the brakes and the dropping of the fluid level as the brake pads wear.
When the fluid level drops air containing moisture is drawn through the air vent into the master cylinder, the strongly hygroscopic fluid absorbs the moisture. When the level rises the now dry air is expelled.
This cycle is repeated thousands of times.
The solution is to use the modern car method.
Have a short tube fitted to the inside of the cap at the air vent.
Fit a bladder (party balloon?) to the tube and then inside the master cylinder.
Air drawn in and expelled only goes into the bladder.
The bladder also expands as the brake pads wear.

Mick
M F Anderson

Since going back to "conventional" brake fluid I stuff a rag under the master cylinder so that "weeps" do not damage my firewall paint (I have seen firewalls almost completely devoid of paint in the m/c area!). If "strategically" placed, the rag cannot be seen and the cause of the weep must be attended to at the first sign.
Barry Bahnisch

Always do the diagnostic work before you spend more money. At least open a bleed nipple to see what happens. My bet says it has absolutely nothing to do with fluid type, so do try to figure out what the real problem is before you change the fluid and all of the rubber bits (and then maybe find you have not fixed the problem).

Start here:
http://mgaguru.com/mgtech/brakes/bt101.htm
http://mgaguru.com/mgtech/brakes/bt101a.htm
Barney Gaylord

Surely there must be a clear coating that is resistant to DOT4 ? In my youth we used "fuel proofer" on model aeroplanes to prevent attack by methanol / nitromethane fuel on the cellulose nitrate paint.
Art Pearse

So I tried bleeding one of the front calipers once the brakes were locked on and in fact it released both front wheels. I then adjusted the pushrod on the master to give it even a little more clearance and I may be imaganing it, but it does seem to release the wheels sooner than before(under 10 seconds). I know this is nowhere near optimum.
So it must be a master cylinder issue.
R emgeeaa

Sorry for the typo;'imagining". I also think the residual drag is still more than it should be. But again, the back brakes are not being affected at all and work fine!
R emgeeaa

So I took the car out for a spin. No change. The knock offs are so hot they can't be touched. Jacked up the car and the fronts are both locked on and the back wheels are totally free.
R emgeeaa

the problem is likely with the front hoses, then...even if they were changed or you think they were...

Mine were at least 10 years old, though I think they had very little actual mileage on them and they were bad.

JIM in NH
AJ Mail

When opening one bleed nipple releases both front brakes immediately, the hoses are okay and it is a master cylinder problem not allowing fluid return. Since it is a single line braking system, the rear brakes should be locked up along with the front ones due to residual hydraulic pressure.

If the rear brakes are never locked up, they may be grossly out of adjustment, or may have some other reason why hydraulic pressure is not actuating the rear shoes (rear brakes not working at all). Perhaps a totally clogged rear hose or smashed steel lines on the rear axle housing. When you bleed the brakes, can you get fluid to go through to the rear cylinders?
Barney Gaylord

Hi Barney, the rear brakes are working fine and I've adjusted the shoes to one click from binding. When I had the rear jacked up and spun the wheels, I quickly went to the brake pedal and apllied, rear brakes are working fine! It was the shop that installed the new master that would've bled the system initially and they did not mention any issues with bleeding the brakes. I haven't bled the system since.
R emgeeaa

The reason that front disc brakes bind before the rear ones is that the drum shoes at the rear have quite strong return springs which force the pistons in the wheel cylinders back to the rest position whilst the front disc pads rely (theoretically) on the return to normal shape of the rubber seals.
Barry Bahnisch

Hi R,
Where are you and your car in BC? My good friend Rod and I would be happy to come and drink your beer. Sorry, I mean help you! At least then you would not have to run from the rear of the car to the brake pedal.
Rod and I have three A's and a B between us, so might be able to help with the diagnosis. My A coupe has MGB discs on the front, and I have had no problem with them.
Email me directly with more info. We are both south of the river in the Lower Mainland, but willing to travel.
Peter.
P. Tilbury

Hi Peter, I'm on west side of Vancouver, Oak and 16th ave area. You're in Surrey?
R emgeeaa

I bored you all to death a year or so ago with my identical dragging front disc brakes. I carried out all the work suggested above, shortening the MC brake piston, replacing MC seals, replacing front hoses etc.

I eventually changed the MC to one recommended by Bob West; made by Caparo using the Lockheed tooling. The problem went away in an instant. Bob advised me that the 'cheepo' MCs on the market are rubbish and he has endless numbers of customers coming to him with similar brake issues. He only ever now fits Caparo MCs to his rebuilds.

By the way, I will speak up in favour of Silicone fluid. Brilliant stuff. The main issue with it is that it cannot be mixed with other fluids. Many people who have converted to silicone have failed to flush their system correctly before putting it in. Ideally, it should be used only with a brand new system and it will then give many years of trouble free use.

Steve
Steve Gyles

I had this trouble and was advised on previous thread to use two gaskets on the front of the master cylinder. It worked like a charm!
H L Davy

As others above raised the issue of silicone fluid, all dismissing it as a suitable fluid, I thought you may be interested in the following article written over 12 years ago by Derek Stevson:

"Foremost among the problems of conventional glycol fluids, is their hygroscopic properties - when exposed to air, glycols absorb up to 12% water by volume. The water lowers the boiling point. Under normal driving conditions, a car, driven daily, or even weekly, will heat up the brake fluid and evaporate a significant amount of the absorbed water. At higher percentages of water the brake cylinders corrode rapidly leading to early brake failure (probably due to electrolytic action as the mixture conducts more). This occurs in cars that have not been driven for several months. On being driven, the rust or corrosion soon causes one or more seals to fail.

The other effect, lowered boiling point, does not usually bother the ordinary driver. It does, however, cause problems under extreme braking conditions, such as in racing at Le Mans where the brake discs can be seen to glow in the dark. Silicones were first used at the 12-Hour Endurance Race in the sixties on the Chaparral, an innovative ground effects race car. Most club racing never approaches this kind of heat load from braking.

The U.S. Army undertook a long term study of the problems of brake failure, primarily due to-corrosion, extreme heat (desert conditions), and extreme cold (arctic) conditions. They were experiencing an enormous maintenance problem. The average Army vehicle logs only about 2000 miles per year, with most of the mileage occurring in short bursts followed by long periods of inactivity. They found that, invariably, vehicles that had been sitting for several months had brake failures after being driven a few miles. They then evolved an elaborate scheme of draining, flushing and refilling the brake system with a non-hygroscopic preservative for storage, and then a similar reverse process for getting the vehicle ready for use. This was expensive and delayed 'readiness' but cost less than the continual overhauling of brake systems.

After extensive study they found that silicone fluids (DOT5) could be used instead. All U.S. Army vehicles with hydraulic brakes now use silicone with an attendant savings of in excess of $20 million per year over the flush-refill protocol. An additional benefit was the wider range of temperature extremes the silicone had over glycol based fluids. The U.S. Postal Service also adapted silicones for the same reasons.

Silicones do not attack natural rubbers and most synthetic rubbers and vinyl, and are often used as rubber vinyl preservatives (as in many car care products). In addition, it does not attack auto paints! The earlier U.S. version of D0T3 would destroy the natural rubber used in early Lockheed and Girling brakes from England. Only Girling "Crimson" and Lockheed "genuine" fluids were usable, and they were hard to get in the US. The later US D0T4 specification seemed to overcome this, as did the change to synthetic rubber for the seals. CASTROL-LMA (Low Moisture Absorption) did better than most.

DOT5 silicone fluid does not attack British made seals. An exception seems to be with some German manufactured synthetic seals (such as lately used on Mercedes). These compounds do react with silicones and more readily with ozone (the sidewalls of tyres seem to age more rapidly than those manufactured in other countries).

I have used DOT5 Silicone brake fluid in my 1962 MGB (both clutch & brake) since 1984 and in my TF 1500 since 1986. In both cases, I have added fluid only once since (a slight topping off). I have had no hydraulic problems with either car. On the other hand , I have had to replace or rebuild cylinders on my other cars filled with DOT4 glycol based fluid, invariably after the car was laid up for other reasons.

When I switched over to silicone on the MGB, I first attempted to simply flush of the system by adding silicone and bleeding the brakes. This sounds like it should work since the two don't mix (are immiscible), and was the method suggested by the supplier. I found, however, the following:- the old brake fluid contained a lot of water, which in contact with the silicone, separated into three layers: water, silicone, glycol. Ordinary bleeding procedures, designed to remove air, left water in the bottom of the wheel cylinders. A sure invitation to corrosion and failure in time. However the brakes work fine at first, since any "non-compressible" fluid or mixture will work. (See the Army emergency procedures for loss of coolant or hydraulic fluid under combat conditions, using readily available fluid from every soldier in the unit. Note that a complete overhaul is then necessary to minimise corrosion afterwards).

I have found that the best way to switch over is with a complete system overhaul. The brake lines should be flushed with acetone which dissolves the glycol gummy residues and removes any trapped moisture. The lines should be dried by blowing with air (ethyl alcohol can also be used, it is not as flammable and won't injure paint). All flexible lines and seals should be replaced so that all rubber that has been exposed to the glycol is removed. I think that the problems some have had with silicone may arise from not doing this. It may be that the problems come from the interaction of the different swelling agents in the silicone with those used in the glycol based fluid.

Some time ago, an article appeared about the dangers of using silicone. It was written by (I believe) a sales engineer for a company who markets DOT4 type fluid. The myths created by this have been widely quoted since. Among the myths is the fact that silicone is 3-times as compressible as glycol (TRUE) and that this leads to excessive pedal travel, such that the pedal will travel as much as 3cm further (FALSE). While it is 3 times as compressible, the compressibility is still a very small number. With the volume of our brake systems, the additional compressibility would at most add 0.1mm to the pedal travel. Most of the problems with "soft" pedal arise from air bubbles entrapped, and poor bleeding. One should take the precaution of pouring carefully so as not to introduce air bubbles. Wait for 10-15 minutes for any bubbles to escape, and then bleed the brakes."

Steve
Steve Gyles

R,
Give me a call - my number is 604 889 5067, and I'm sure we can arrange to come to your place now the rain has stopped for a few days.
Yes - I'm in Surrey, and Rod is in North Delta.
Peter.
P. Tilbury

This thread was discussed between 17/07/2011 and 18/07/2011

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