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MG MGB Technical - Front brake hose, Internal failure.

A few months ago I noticed my 74 roadster would pull to the left for a few seconds after
using the brakes. The brake hoses were replaced about four years ago, the calipers were
not rebuilt then. So thinking my calipers needed a rebuild, I ordered caliper kits and pistons
and rebuilt the calipers. On a test drive brakes worked ok. I went on a club tour to WV last
week and noticed the short duration pull again while enjoying the nice WV sports car roads.

Yesterday I jacked up the front end, applied the brakes, tried to spin the front wheels,
the LF was locked, RF free. About 30 seconds later I checked the LF again and the wheel
was free. I put a wrench on the bleeder screw, had my wife press and release the brakes.
LF Wheel locked up, opened the bleeder screw, wheel free. I removed the brake hose and
replaced it with a used but known to be good hose I had in the tool box, after bleeding
the brake it checked ok. Brakes ok on a short test drive. I'll know for sure during the British
Car Days South Rally today where the brakes will get a good workout.

I'm passing this information along because we may be getting poor quality replacement
hoses and it may be a good idea to replace them every three or four years. BTW, I have
always used DOT 4 Castrol fluid in the brakes. Last month I switched to Valvoline
SynPower fluid with the caliper rebuild.

Regards,Clifton



Clifton Gordon

Clifton: I hope your brake hose problem was an isolated case. I just replaced mine last week with new AP Lockheed hoses. I am also using the Valvoline fluid. Could you do a "forensic" analysis, i.e. disect the offending hose to see if there are any obvious defects, little flaps, collapsed walls, or whatever?
Regards, Andy
Andrew Blackley

Cliff,
Many times the inside of the brake hose will go with no indications from the outside, they get soft inside. Usually this will result in a locked up brake, but a brake that is late to grab is also possible. I have found that it is not uncommon for brake hoses to only last 5 years, I'd replace the one you just put on with a new one, that old hose may look good on the outside but is ready to go on the inside.
Robert Dougherty

Andrew; I'll cut it open and see what I can find. I drove 225 miles today and the brakes
are now fine. The car did ok on the rally but the navigator and driver missed a route
marker and it was all downhill from then on. Still enjoyed the drive, great day mid 70's.

Robert; New brake hoses are on my list of items to pick up tomorrow at the British Car
Days South show. I took the old hose off my 68 GT because I didn't know how old it
was so it will come off the car next week.

Clifton

Clifton Gordon

Hey guys, Just a side note, but on our older with natural rubber seals the brake fluid we choose is fairly important. I'm no expert here, but it stands to reason that since natural rubber doesn't stand up well to petroleum distillates, fluids containing such an ingredient should be avoided. This would be your conventional DOT 3 fluid. DOT 4 is a better choice (of which the LMA Castrol is one) since its chemical composition does not cause the disentigration of the lines and seals. There is also a DOT 5 Silicone based fluid available as well, which is said to not harm natural rubber, but is completely incompatible with DOT 3 and 4 fluids. For this reason, it should not be used except in a freshly rebuilt system. Basically, though, a DOT 4 is the way to go in an older car with antiquated rubber seals.
Mike Lord

What we need is a web site like the one for virus hoaxes, for sports car myths. With all due respect Mike, you have not only been told a very old myth, but it has been told to you 180° out from the original. Ever since I have had an MG (starting in 1959 with a TD), the story has been circulated that all British cars have natural rubber seals and anything but AP Lockheed (DOT 3) fulid will cause the seals to swell, the brake cylinders to fall off the cars and other such scare stories. Interestingly, I was told the exact same story by the service manager of the local Audi dealership, when I asked him why the shop manual said not to use DOT 5 fluid in the brake system of a 1980 Audi that I owned.

I don't know about many years ago, when MGs were first manufactured, but nowdays, all cars use the same brake components. One can go to the auto parts houses and get a 7/8" wheel cylinder cup and it will be speced for MG, Ford, Chevy, Honda, or any other car that uses that same configuration cup. All DOT 3 and DOT 4 fluids are glycol based fluids and react to seals, paint, etc. in the same way. The DOT 4 fluid has been formulated to absorbe moisture at a lower rate than DOT 3 and has a higher boiling point, but otherwise it is the same type of fluid. Mike, you are correct in saying that DOT 4 and DOT 5 are better fluids to use, but this is because they absorbe less or no moisture and therefor cause less corrosion than DOT 3 fluid, not because one or the other will cause the seals and lines to swell and disintegrate. Over the years, I have progressed from Lockheed fluid, to generic DOT 3, to Castrol LMA (DOT 4), to silicon fluid in my braking systems. While all of the brakes have suffered from wear, I have never had a system fail due to swollen or disintegrated rubber components.

I don't know where this myth started, but with apologizes to our British friends, I would not be suprised if it was right after WW II. If you have read about the history of the MGs, you will find that, in an effort to bolster a shot economy, the British started a massive export effort to bring fresh money into the country. The motto was "Export or Die". What better way to sell a product such as brake fluid overseas, than tell the world that "you have to use our brake fluid in our cars or your brakes won't work"... ;).
Cheers - Dave
David DuBois

Hi Guys,

Interesting stuff on these brakes. The front nearside brake on my 78 roadster jammed on yesterday and got really hot before I could smell burning and pulled over. I couldn't free the pads from the disc so (rightly or wrongly) I poured water on it all to cool it off and limped home without any further burning. I removed the pads today and pressed the brake to push the pistons out a bit to check for dirt and alignment etc. I couldn't see anything wrong so re-fitted the pads and tried the brake. Jammed again. I've now removed the pads again and I wanted to check the movement of the pistons but I can't push one of them in by hand or even with a lever.
Is this normal?
I wondered if I'd have to bleed the system to relieve the pressure and then push it in?
I will replace the hose after what's been said here but could there be other causes such as the seal perishing and fouling the bore? I realise I might have to remove the whole caliper and take the pistons out and inspect them but I'm concerned that they might be tough to get back in after what I experienced today. Are they?!

All suggestions / comments gratefully received.

Cheers
Matt
Matt

David; Thanks for your comments, I too am of the opinion that DOT 3 brake fluid will not harm an
MG brake system, just because it is DOT 3 fluid. I'll stick with that opinion until someone can show
me some evidence that is is harmful.

That said, I do not use DOT 3 fluid to repalce fluid fluid in any of my vehicles. Why? I use DOT 4
fluid for it's a higher boiling point and less moisture attraction. As I stated in my initial post I used
Castrol LMA in the suspect brake hose from the time it was new. I still think 4 years is a short life
for a brake hose. It failed prior to my switching to Valvoline SynPower.

I cut the suspect hose open and the it had internally partially collapsed near the caliper fitting. It
was keeping the caliper on for a few seconds after brake application, not a lot of fun in the twisties.
I bought new hoses today and they will be replaced next week.

Matt; When the caliper locks up loosen the bleeder screw and see if the brake caliper unlocks, if it
does the caliper is probably ok and the problem is in the brake lines, hoses or master cylinder. If you
have only one caliper locking up I would check or replace the hose for that caliper. You should be
able to push the caliper piston in with a C clamp, unless the line or hose to the caliper is blocked.

Regards, Clifton
Clifton Gordon

Clifton - Yes, DOT 3 fluid makes a good penetrating oil to loosen rusted bolts. At the conclusion of the restoration of our TD close to 20 years ago, I put silicone fluid in the braking system. This fluid has never been changed out since then and it is as crystal clear now as when I put it in. The only failure that I have had was the cup in the master cylinder wearing out. This has definitely sold me on silicon fluid.

Matt, I believe that Clifton is correct, your problem is more likely a failed hose rather than a caliper. One would have to have a really large chunk of something floating around inside the caliper to cause the kind of problem you are having.

Good luck - Dave
David DuBois

Just a thought: if you look at the orginal B maintenance schedule it specifies that the entire hydraulic portion of the brake system should be replaced/rebuilt about every 5 years (xx thousand miles). This includes replacing all three brake hoses, seals in rear brake cylinders, seals in the front calipers, and the seals in the MBC.

John
J Long

David,

I would be concerned about your braking system. The reason is that since Silicon fluid does not absorb water it will collect little "bubbles" of water. That can have a catastrophic effect on your braking ability.

So let's start with the bubbles and the source. Your master cylinder will collect water over time (20 years esp.). This can come from general humidity to the reservoir sweating due to changes in temperature.

With the water-absorbing fluids, the water gets into the fluid and reduces the boiling point. Over time you have to flush the system to get back to "fresh" braking abilities. But the water does not stay as a drop, it's part of the fluid.

With silicon the water just stays as a drop and eventually works its way into the braking system.

Since the water is held as a drop, from where the drop sits it begins to rust the brake lines from the inside out. This means that a perfect looking line may rupture without warning. Hopefully it will drip first, but that's leaving a lot to luck.

Or it can work its way to the caliper and then you have good brake fluid that boils at 500+ degrees and a bubble of water that boils at 212+ (due to pressure) degrees. The weakest link means that under heavy strain/heat you may loose braking ability well before that of a clean silicon system.

This does not mean that silicon is bad, it just means that using the same stuff for 20 years is asking for trouble. The water needs to be flushed out every so often.

Some good reading from a BMW forum on braking systems:

http://forums.roadfly.org/bmw/forums/e46m3/archives/forum.php?postid=394999&page=10


Lin

This thread was discussed between 08/06/2002 and 11/06/2002

MG MGB Technical index

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