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MG MGA - Dragging Brakes

Well, its me again, getting to know my car...

The other day while I was driving I notices the car not free-wheeling as it should when driving and then putting it into neutral.
When I got home both the rear drums were red-hot! Must have been at least 200degC. Burnt my finger!

Now, I have been messing around tonight in my garage diagnosing the problem.

I was reading Barney's page on this specific problem;
and it seem like I have all the issues he describes.

I tried first setting the brakes again with the screw in the drum until they don't drag. So far so good.

With the rear jacked, I checked the handbrake cable and it is slack.
I pumped the brakes a couple of times, and BINGO, the wheels are locked and stay locked. I.e. the pressure is not being released.
I checked the rubber hose that connects into the T-junction at the rear and it looks like 10years old but is not broken...but maybe internally collapsed?
It takes about 1minute to release the pressure to unlock the wheels and a bit more to fully release.

Then I thought I'd check the front as well, so with the jack I lifted the front right wheel. Pumped the brakes and the it 'seems' like the front wheel also drags a bit...but only for a couple of seconds. Meanwhile the rear wheels stay locked.

So I checked the master cylinder and saw there was no play all in the push rod and apparently there is supposed to be a bit. So I shortened the push rod 1 turn. This did not seem to make any difference.
The vent in the reservoir cap is clear.
I believe the master cylinder is releasing properly, and the is no chaffing in the steel pipe delivering the fluid to the 5way junction.

The rubber dust cups on the rear drums are perished (and I have a replacement), but the hand-brake lever seems to operate properly when the pressure is completely released. So I don't believe there is a deficiency in the drum slave cylinders.

After messing around pumping here and pumping there, I realised the rubber hose that is connects the T-juntion in the rear had some brake fluid coming out. i.e. a leak.

I am going to order a new hose, but my question is;
- Does this collapsed hose account for a the front wheel locking momentarily just after the initial brake pumping? or should I look for something else?

Since I have to change this particular hose, the rubber cups, and bleed it make sense to take the opportunity to change to DOT5 fluid? How well would I need to flush it?

That was long story! Now I'm going to bed.

Quick picture showing all of this is worth it.. ;0

G Ramos

Gonzalo -
Replace all three hoses while you are at it. Hoses are dated if made in the last 25 years or so. No dates = real old! 10 years = too old. 3 years = recommended change interval (nobody does it).

Fletcher R Millmore

If you are going to go from DOT3 to DOT5 change all rubber bits at a minimum. There is a whole can of worms I'm not getting into on this. Suffice to say I have run DOT3 and DOT5 in the 16 years I've had my "A" and both have been fine. I currently use DOT5 only because if I do have a leak at the MC I do not have to worry about paint.

BTW -- for the problem you describe above, I'd replace the hoses, and check your rear wheel cylinders.

Christopher Wilson

Gonzalo, Very pretty! And the car looks great as well!
Now, what was that about a brake problem?
BM Gannon


I would recommend (as above) you change the hoses and all seals; master cylinder, slaves and callipers (do the clutch parts at the same time). I would also recommend DOT5, to flush I just ran through the system at each bleed until it was clear.

I did exactly the same when I bought my current driver some years ago.

Neil McGurk

Gonzalo, In over 30 years of MGA ownership I have had one instance of a brake hose turning itself into a one-way valve (the internal lining collapsing due to using silicone brake fluid) but far more common is the master cylinder not allowing the fluid to return (due to the rubber seal expanding and blanking the return port, also due to the use of silicone brake fluid-I grind off about 30 thou from the forward end of the piston to prevent this recurring and this has absolutely no deleterious affect to the braking system). As you may have guessed, I no longer use silicone brake fluid even though modern rubber brake components may well be more compatible with it. Brakes are important (and MGA brakes are very effective) so I would replace all of the rubber components (and the cylinders, or resleeve them) and generally overhaul the system. Modern resleeving, using stainless steel or even brass, makes the use of silicone brake fluid practically redundant.
Barry Bahnisch

I went to rescue a midget Sunday, brake hose collapsed internally, kept the LF on. Last year I had an MGB with two of three hoses blocked, and the third restricted.

Fletcher R Millmore

The front caliper hoses are new so I don't think these should be a problem. I will check for a date...
The master cylinder is also new. It must be 1year old, so I was hoping it was working fine.
But I have a funny feeling the master cylinder could be the culprit. I will see if I can find some info in order to chech it.

The calipers were also rebuild by the PO.
I have ordered a replacement hose for the rear and I will take appart the rear slaves to see what I find.

Judging from the comments I might just stick with DOT3 until I perform a frame-off rebuild, which may not happen in until many years...

Thanks guys!
G Ramos

Gonzalo -
Do you now have the requisite bit of clearance on the master cyl pushrod?
If so, did that fix the front brake problem?

In back, while you are changing the hose, we know your car was just transported via truck, so examine the steel pipe along the axle very carefully. It can be surprisingly difficult to see the little dent(s) that causes this problem. Run your fingers along the line, especially either side of the axle/spring u-bolts, since those are the usual tie down points.

Fletcher R Millmore

I gave it a turn of additional clearance in the pushrod, but so there is like 3-4mm of clearance, but that problem still persists.
I also had a look yesterday when I was looking for dents on the line but didn't find anything. I will have a closer look, but surely if one side was dented, that would make only one of the read wheels lock up and not both.
I suspect the pressure is not being released by the MC. I fear I will need to take it appart to see what condition the rubber and the fluid return valve is in...
G Ramos

If it was the master cylinder causing the problem, both front and rear brakes would be affected equally. Since only your rear brakes stay locked it would seem to be a rear hose problem or stuck pistons in the rear wheel cylinders. If you loosen a bleed screw on one of the rear wheel cylinders to release the pressure do the brakes release? If they do, that would indicate that it is a hose problem and not stuck pistons in the wheel cylinders.
Ed Bell

Thanks Ed. I will do the test.

Just one more embarrassing/scary question...
When I got the car I bled the brakes and I added some DOT4 fluid in the reservoir.
The DPO didn't know what he had put in, he said that it was what MOSS recommended.

The fluid that came out was yellow, and corrosive on paint. So I assumed it is not DOT5.
It possible there could be a mix of dot3 and dot4 in the reservoir? if so could that be deteriorating the MC piston rubber and hoses?
G Ramos

Well I thought the car was going to be quite a challenge when you bought it as I said at the time and as we can all see it is living up to expectations.

However I will say this Gonzalo nothing is too much for you to tackle and I like the way you address everything with a lot of mechanical ability and enthusiasm. I am convinced that you will sort out this car and wish you good luck, on this particular problem I would do as Ed has suggested.
Robert (Bob) Midget Turbo


I believe DOT4 is the the same as DOT3 and can be mixed, but sometimes there may be an issue with seals in cars designed for a specific fluid.

Moss sells DOT4 as well as silicone and synthetic.

You would be wise to use one type of fluid but I don't think this will be the root of your problem. NEVER mix DOT3 and DOT5.

Christopher Wilson

Ok, thanks for the advice Chris.

Bob, I guess this one of those No pain, no gain situations! ; )
G Ramos

Dot3 and Dot4 are compatible so don't worry about that. You should ask the PO if he used silcone (Dot5) because that would be a problem. Ed is spot on with his advice. Don't fret about the "MG Midget's" opinion about your car, you have a great car for the money . He is right about the fact that you are exactly the right type of individual to carry on the MG tradition. Keep at it, you are doing all the right stuff. We're here for you..:)
G T Foster

Also, to add to the complication, there is DOT 5.1 which is not silicone based and is compatible with DOT 3 and 4.
Malcolm Asquith

I had binding brakes after a collapsed rear brake hose; my bet it on the hose.

I think disk brake calipers always drag a bit after braking because of the way they are constructed. There is no return spring, so the clearance comes solely from the flexibilty of the rubber pistonseals and they have to push back the piston and brake fluid, so they will bind for a few seconds?

The upside is that they are self-adjusting because of the way they are constructed.
Willem vd Veer

I don't want to insult any one or start a flame war over brake fluid but the information in this post is absolutely false and must be countered. Any decisions based on this opinion are is error.
"In over 30 years of MGA ownership I have had one instance of a brake hose turning itself into a one-way valve (the internal lining collapsing due to using silicone brake fluid) but far more common is the master cylinder not allowing the fluid to return (due to the rubber seal expanding and blanking the return port, also due to the use of silicone brake fluid-I grind off about 30 thou from the forward end of the piston to prevent this recurring and this has absolutely no deleterious affect to the braking system). As you may have guessed, I no longer use silicone brake fluid even though modern rubber brake components may well be more compatible with it."
Silicon fluid does have some disadvantages but those noted here are not real. Silicone brake fluid does NOT attack rubber, conventional fluid does.The same chemical action that EATS paint is what attacks rubber components.
The disadvantages of synthetic fluid are:
#1 synthetic is more compressible that standard fluids. This gives a slightly "softer" brake pedal.
#2 Synthetic is molecularly smaller and hence has a greater tendency to leak.
#3 synthetic is not recommended for anti lock brakes. This does not matter to our application.
The differences are:
#1 synthetic fluid won't absorb water. This can be good or bad. Good because it won't deteriorate with the absorption of water and boil sooner. Bad because water sits at the bottom of components and can further rust.
#2 the fluids are incompatible with each other.
The advantages are:
#1 Won't attack paintwork.
#2 Won't attack Rubber.
#3 Lasts longer.
#4 higher boiling point.

In summary for me.
I use it because:
The advantage of not attacking paint is the deciding factor for me. I also like that it DOES NOT attack rubber either. I will put up with the softer pedal, hardly noticeable IMHO, that it is harder to bleed air out of system and does leak a bit more.

The hose damage listed above could not be a synthetic fluid problem.
The master cylinder situation could be related to silicone fluid but for different reasons. Silicone does not soften the rubber like standard fluid this makes the seals stiffer and not as "slippery". The return spring inside the master should be stretched a little to make it stronger so the pieces return completely. Errors in assembly are more common when using silicone fluid because it does not slip together as easily.
Silicone IS more work but in my opinion well worth it.
Randy Brown.
MGA owner since 1976 and auto repair shop owner since 1981
R J Brown

My post regarding silicone fluid provoked such a savage response that I wondered if I was mistaken and/or out of date and therefore contacted the three main brake specialists in this city. Each told me that reputable brake specialists have never, and will not, use silcone brake fluid, principally for the reasons explained in this thread. Silicone brake fluid was withdrawn from commercial sale in Australia some years ago and whilst one of the companies (an Australia-wide franchise) advised that they may still be able to get it in (to special order) they had not done so for a long time since the demand for it had practically ceased. The previous thread reminded me of a problem that I had with s friend's TC (during my silicone fluid era) in that the brake pedal would not return. Instead of trying to stretch the spring (which I would call a "bodge") I took off the master cylinder (again) and honed and/or polished the bore so that the piston/seal would move in the proper manner. It is regrettable that threads such as these, which are designed to attract constructive comments and/or experiences, are seized upon by some individuals to air their knowledge, or more often (as in this case) lack of it.
Barry Bahnisch

Barry my response was not intended to be "savage" and I apologize if you feel offended. But to help those with no direct knowledge recognise an Old Wives Tale. Silicon does have its shortcomings but attacking rubber is NOT one of them.
The rubber bits slip and slide better with conventional fluid BECASUE it softens rubber.
Prove me right or wrong by throwing identical bits into a bottle of each and checking them periodically. Then tell me which piece feels gooey.
I understand your well intentioned post and how you could arrive at the conclusion you did. But I believe that when misinformation is published as advise to a newcomer it must be challenged.
Professionally I would NEVER use silicon fluid in a customers car. To do so would be both unwise and unsafe. I also would never use it in my modern cars.
The design of the master cylinder on our MGAs guarantees that they will leak fluid. The location of that leak will ruin paint.
The decision on what type of fluid people choose to use is not open and shut obvious. Each fluid has advantages and disadvantages. To make an informed decision it must be based on the facts. I tried to be balanced in my post and show both sides of the story.
R J Brown

Well I have progressed and I spend most of the morning performing a braking system overhaul.

I have now changed the rear hose, cos I am not sure if it was collapsed, but it was very very old and had crack. It spent most of the time trying to undo the nuts off the old one! Anyway that job is done.
By the way, I am still not 100% sure if the fluid in my car is DOT3 or DOT5. It is yellow. I put a drop of it on some the car paint in a non visible area and it did not seem to eat it immediately, maybe takes more time. I would like to use the same fluid as is in there as I don't want to have to change all the rubber in the system for the moment, and keep the variables to a minimum.

Then I had a rebuild kit for the rear drum cylinders and since I was doing the brakes I thought I might aswell rebuild them too.
The cylinders don't seem to be in bad condition, and the inside of the bore is smooth with very minor corrosion.

So I cleaned all the components. There was a brown sludge lodged in the piston channel (looked like grease but probably not..) which I removed.
The inside was kind of dirty and with brown fluid.

Now 3 questions;

1 - should I put any grease in the bore where the piston moves or just leave it dry (will probably get some brake fluid).

2 - In the bottom of the bore there is a washer with holes attached to a spring. In the rebuild kit I got a similar washer that is plastic/rubber (white).
Should I use the original or the new plastic ones.

3 - There is a rubber washer that came with the kit, but I am not sure where that should go...
I couldn't find a page on MGAGuru with the rear cylinder rebuild.

Your advice appreciated here... ; )

BTW yesterday I successful complete the change of the steering ball joints and rack rubbers. Next I need to fill it will oil...
G Ramos

#1 There is a special assembly lube that can be used. Do not use grease. Without lube just wet it with fluid.
#2 Use either throw other in spare parts bin.
#3 apicture would help.
paint damage is not always immediate. It softens the paint over time.
If the PO did not know it probably is not silicone.
R J Brown

DOT 3 or 4 is soluble in water, DOT 5 is not. Try washing it off.

#1 Repair kits used to come with a sachet of "Red Rubber Grease", just for the purpose. I guess you didn't get any, another sign of the decline of civilisation! Might be able to buy similar separately.

Fletcher R Millmore

Ok thanks! Will try to find some of the red rubber grease, so I didn't get any.

I think I got all the info I needed.

I will test the fluid further, but as RJ said it is probably not silicone.

I will post picture of the rubber washer, but suspect it is for the plunger seal (part that actually pushed the brake shoes)... but the size and shape does not look the same.

Aaaaaah, another wonderful day tomorrow under the MGA... ;)
G Ramos

I am often amazed at the discussions here on brake problems.

I have a very simple and basic rule for brakes. Always buy brand new parts and change the service parts (hoses and fluid) on schedule. I check for seal condition when doing a service. Even though I use silicon fluid, I still flush the fluid every three years. Hoses etc. are inspected for damage and condition every service. We only live once.... That people continue to skimp on $15 hoses beggars belief!

To say that the MGA MC is predestined to leak is (sorry to be harsh) absolute rubbish. If it is correctly assembled and in good condition, it will be dry and stay dry. All my braking cylinders are now over 20 years old (replaced with new ones when restoring the car), and are ***completely*** free of leaks. When I replace the seals (about every 8 years) I replace the MC gaskets too, and the system has never leaked a single drop. If the MC is leaking between the cover and the casting, remove the cover, sand it flat and replace the gasket and you will cure the leak. Easy really.

As to assertions that Silicon fluid attacks rubber, I have to say that I have never seen any evidence of that. The reason that hoses collapse is that they are old and way overdue for replacement. The reason that Si fluid is not used in modern cars is that they have ABS, and if any air is present in the system it forms micro bubbles in the fluid that can only be purged by purging the fluid. That obviously affects brake performance. But any well maintained braking system should have no air in it anyway.
dominic clancy

I suspect that the compounds used in braking systems seals and/or hoses has changed over the years. My observation is that newer ones look different, they are "shinier" and "blacker" than older ones. In the "old days" the standard practice when using silicone fluid in MGA 1600's (if not 1500's as well although they have the benefit of brake shoe return springs on all wheels) was to grind about a sixteenth of an inch off the forward end on the piston because the swollen seal fouled the return port and the brakes "dragged". Upon dismantling, these seals would look "puffy" and soft after using silicone fluid.
Barry Bahnisch

See my earlier testing results for determining whether I had Dot 5 or Dot 4 fluid.
Mike Ellsmore

This thread was discussed between 30/03/2010 and 05/04/2010

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