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MG MGA - I think I got a brake leak

Last nite I noticed there was some oil in the inside of the rear right tyre.

I though it was the dreaded axle oil leaking again.
However on inspection it seems to be brake fluid. I hate this stuff. IT seems that it is more than the occasional drop as it was puddling and softening the paint of the wheel.
I checked the fluid level and it has gone down a bit.
It seem to come from the inside of the brake drum, not from the steel pipe/fitting.

I guess the seal on the cylinder is leaking. I was wondering if any of you has had this happen.
I find it strand since I rebuilt the cylinders last year.
I can rebuild it again but I am afraid it can happen again. Is there anything specific I should take care about?

the car has been parked with the handbrake on for a couple of weeks.

Gonzalo Ramos

The same happened to me only a few months after getting my A - only I managed to drive to the end of the road before I found I had no brakes. I put a complete new cylinder on but made the mistake of only doing the one that leaked - and then a few weeks later the other one let go - so probably a good idea to do both sides at the same time - it's always quicker doing the second one by the way!
P.S. - I figured that a brand new cylinder was safer than playing about replacing the rubbers when the bores could be damaged/corroded etc.
Cam Cunningham

John Twist, in his video about rebuilding MBG rear brakes, recommends against rebuilding - says we should replace with new cylinders. I had a chat with Cecelia about cylinders yesterday. I was ordering a Lockheed cylinder - over $100, and she recommended the less expensive (about $30) replacement cylinder. She took one apart and says while the cylinder itself is made in Taiwan, the bore looked well machined and the seals are US Bendix. She says she's been selling them for awhile and has had no negative feedback. Leave it to Cecelia to talk you out of spending more money with her!

Here's the Twist video:

- Ken
Ken Doris

I don't want to sound cynical, but retailers and service shops have a vested interest in selling you new parts. The parts suppliers make more money selling you a new cylinder than a rebuilt kit. Service shops don't like taking a chance on rebuilding, because they may have to eat the cost of a subsequent repair is the rebuilt part might fail prematurely. Pro shops also have a relatively high labor rate compared to the cost of parts, so a pro rebuilding the part might cost more than a new wheel cylinder. An MGA master cylinder can almost always be rebuilt for less than the cost of a new one, even is you have to have it sleeved.

If you do your own service work you can often save some money by rebuilding hydraulic cylinders. Always do the diagnostic work first. You need disassemble the cylinder for a good look before you buy parts. If the cylinder bore is not pitted or badly scuffed, you can run a (cheap) brake cylinder hone in it to smooth it out. As long as it will hone out clean it can be repacked with new rubber seals. If the hone cannot remove deep scratches or pits in 5 minutes, then it's time to buy a new cylinder (or have a master cylinder sleeved).
Barney Gaylord

Barney - I agree that the general rule is to rebuild since it is typically much more cost effective. In this particular case, the rebuild kit is about the same price as the new cylinder (both in the $30 range). Also note I started out by calling Cecelia to order the new Lockheed part from her. That part lists for $117 on Moss; she sells it for a bit cheaper. She talked me into buying the less expensive one, costing her about $70 in sales. Cynically I might think she is overstocked with the cheaper part, but I've been dealing with her for years, and this is only one example of her advising against spending money, often to the point she tells me how get by without buying anything from her.
BTW, many thanks for your website. Once again it was the first place I go when I tackle an MGA problem.
- Ken
Ken Doris

Thank you for the answers but I don't think my original question was answered.
These were new cylinder that were fitted and the internals were fine 1year ago. Why would it not leak while parked?
I was wondering; I the adjuster was not correctly set (tight) the piston would move far enough to allow some of the fluid to leak?

I can rebuild it. That is not a problem, question is 'how to avoid it from happening again'....
Gonzalo Ramos

Sometimes sitting still is the worst enemy of moving parts. Depending on temp and humidity, the seals may have become less "intimate" with the bore and began leaking a bit. Also the salt air can corrode the bores more if not "washed" by the brake fluid fairly often

A "couple of weeks" doesn't seem long enough to me, but you have some extreme temp/humidity/salt in your area, so it's hard to say.

- Ken

PS: I feel for you as I'm going through similar problems right now. Can't take the A to Watkins Glen because of them, and worrying about getting it ready for the Solomons Regional GT because I'm working 6+ days per week on "real work" between now and then. I've just gotten all the parts for the brakes today, but now see a possible "dreaded axle oil leak" that you experienced earlier.
Ken Doris

I have seen a failure of brand new rear cylinders where the seal had a total rupture and subsequent failure. In fact, I was driving at the time. The car had less than a couple hundred miles in the 1 year since the cylinder was replaced. I would guess that up to that point, there would have been some slight leakage. I can't say for sure. it sure was wet after the failure. Disassembly showed the seal blew out in line with the slot for the brake lever. Since the seal doesn't travel that far out, I assumed it was a factory assembly error.

So new, doesn't necessarily mean trouble-free. Your new wheel cylinders may have non-standard seals and may need a different rebuild kit. You'll have to disassemble for inspection before ordering a rebuild kit.
Chuck Schaefer

If the brakes are maladjusted (too loose) isn't it possible for the brake cylinder piston to travel out too far and cock in the bore allowing a leak? I remember this from some conversation in the past...but it's foggy. I think it may have been a thread on the midget site from when I was working on my neighbor's Spridget a couple years ago. As I recall, I ended up rebuilding the cylinder, honing it, and reinstalling everything using the same rubber parts - which looked brand new - but the previous installer had botched it up somehow. Maybe one of the brake shoes was in upside down - I know it was something like that, but just can't remember exactly now...maybe it was just that springs were on the wrong side of the shoes, causing misalignment...

Perhaps the newer brake shoes are not machined correctly, allowing the longish travel? Guessing personal experience.

AJ Mail

MGA rear wheel cylinders are rather unique in that the parking brake lever goes through a slot in the side of the slave cylinder to push outward on a secondary metal piston. When completely assembled with the lever in place, the lever blocks outward travel of the primary slave piston. If you remove the brake drum and step on the brake pedal the slave piston will hit the lever and stop while the seal cup is still well into the bore to prevent escape of brake fluid. In fact if the brake linings are worn enough to allow lots of travel of the shoes, and the brakes are not adjusted properly, the parking brake lever will stop travel of the slave piston, and there may be no rear brakes at all, either hydraulic or parking brake.

The point is, on the MGA the rear slave piston should never be able to come out far enough to lose fluid, even with the brake drum removed. That condition (worn shoes and non-adjusted brakes) causing the primary piston to bump into the lever can cock the piston enough to cause damage to the cylinder bore (outboard from the seal area), but this should still not cause it to leak.

If the rubber boot on the lever is perished or not properly installed, then moisture and dirt can get past the lever into the bore of the cylinder in between the primary and secondary pistons. This can cause corrosion and wear to screw up the bore where the primary seal cup must run, which in turn can cause it to leak.

If it leaks fluid, the primary seal cup is not sealing against the bore, and it needs to be rebuilt or replaced. There have been some cases of bad rubber seal parts in recent years. Lockhead/Delphi parts are rather expensive now, while aftermarket cylinders are relatively cheap. If you have hobby time available it may be worth trying to hone and repack the cylinder once. If that doesn't last, then chuck the thing and buy a new cylinder assembly.

Gonzalo, -- When you had it repaired a year ago, was the cylinder repacked or replaced with a new one? If new, was it OEM type or aftermarket part?
Barney Gaylord

The cylinders were changed probably a year before I bought the car as they looked very need, but no sure if OEM or aftermarket. When I received it I rebuilt all the brake cylinders with Moss rebuilt kits.

I still have a couple of them left, so I will just go ahead and rebuild it, see what I find inside.
I which I could do it without having to re-bleed... ; )
Gonzalo Ramos

If only rebuilding one rear wheel cylinder, use two small sticks of wood and a ViceGrip to clamp off the rubber hose between battery carrier and rear axle. You will only lose fluid between the 3-way fitting an the one wheel cylinder. This makes follow-up bleeding very easy.
Barney Gaylord

Last night I took the brake cylinder off.
It seems like it has been leaking for a bit and the cylinder was full of a brown paste. Mixture of brake fluid and rust? or dust?
The boot was changed 1 year ago but I is already showing signs of perishing.

I did not find anything wrong with the seal and the cylinder look ok. Some small signs of pitting but nothing mayor.
I will go to buy a hone and hone it out just in case.
Looks like the fluid was leaking from the slow where the handbrake cable lever fits.

What I find is that the travel is of the seal is very small before it will leak.

Also the top piston (the one in contact withe adjuster) has a rubber seal on it and this does not allow this top piston to seat all the way down when at rest.

Its going to be an interesting weekend...
Gonzalo Ramos

It's not worth the effort to rebuild - the new cylinders are cheap and last ages.
dominic clancy

I'm with Dominic. After hit and miss with rebuilding wheel cylinders in years past, I just replace them now. It saves a lot of headaches, and possible failure that may come with a questionable rebuild.

L Poupard

This thread was discussed between 02/09/2011 and 09/09/2011

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