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MG MGA - Master cylinder help please

Be really grateful for some help with my master cylinder. Sorry if its a bit long winded.
My brakes work well but I noticed a little weeping of fluid on the brake push rod of the MC. I was thinking I should just renew the rubbers but am concerned about the the body around the MC (see pic), as it has lots of surface rust (it's quite good everywhere else). Even some on back panel behind, so its unlikely to be from refilling and suggests some other leakage problem?
I could replace the entire MC but at 250 (MGOC) I want to be as sure as I can that it cures the problem. I read in the archives that possibly it could just be that the plastic cap should have a (cork?) seal in it, or would this just be wishful thinking (i.e. too easy a fix)? I was wondering if anyone had similar experiences? I should add I have not needed to refill the MC in last year.
With regard to fluid, I have only had the car a year, and have no idea what fluid is in the system. Is there a universal fluid or is it best just to flush everything right through regardless?

I renewed MC seals many years ago on another car, only to find all the slaves leaked very soon afterwards and guessed this was down to increased pressure from the MC. If this is true I imagine it makes sense to renew the slave rubbers as well, and then bleed just the once?

Finally, I have seen a master cylinder for sale at 85 on ebay (mg services heathrow) anyone know if they are any good as considerably cheaper?



Graham M V

Graham,
It would be worth a try just to replace the seal. If it works great and cheap. If not then probably your MC is probably pitted and will need to be sleeved. Before you buy on ebay you need to know if the cylinders are ok or do they need sleeves. If your fluid is purple it is probably DOT 5 but it looks like it is probably DOT 3 or 4 by the rust/no paint around the MC. Have a good day!

John
John Progess

Changing the master cylinder does not change the pressure and cause the other components to fail. An old wives tale. The pressure is a factor of the size of the parts and does not vary. The reason other components soon fail is because they were just as old as the master. Age and filthy fluid are the killers of the rubber bits in the system.
That said if it was me I would clean, hone and replace the rubber parts. Then flush out all the old fluid and see what happens.
R J Brown

As the fluid level rises and fall somewhat in normal use, the cap must be vented. The cap should have an internal piece, inner and outer vent holes, and a fluid trap in between. Fluid should not be escaping from the cap unless it was overfilled.

The visible rubber caps in front are dust seals. The fluid seals are inside on the moving pistons. When it leaks you have to disassemble it to replace the seals inside.

If the bores are clean and smooth (rarely), you might install a new seal kit and banish the leak. I would always hone the bores lightly to remove any dirt or rust or glaze or scuff marks. If you cannot hone it to a clean buff finish (remove all pits and scratch marks), then it needs to be bored and sleeved, which is still cheaper than a new master cylinder (usually).

If the whole system is of unknown age, and one cylinder leaks, it may be a good time to rebuild all cylinders as good preventive maintenance. Also a good idea to change all rubber seals in the whole system if you are changing fluid type.
Barney Gaylord

Thanks for input. I intend to replace all seals but what I am really bothered about is the state of the rust which is quite bad. I have checked the cap to see if it's as Barney describes, and it does have a fluid trap so its unlikely to be that. There is no obvious leak other than the weeping on the push rod (can be seen in my photo) and I cant see how this would have created damage all the way round and high up the back wall. A leak between the mc and expansion top might explain, but nothing I can see. Hmmmm.....?
Graham M V

Graham, the rust is entirely normal considering all the fluid that must have been spilled over the years. Most are a lot worse than yours!

One of the first jobs I did after buying my current driver was change the master cylinder, rubber hoses, slave seals and calliper seals. I also refilled with silicon fluid and although I would highly recommend that I know that opinion is divided on the forum. I also rebuilt (new seals and polished the bore with wet & dry paper and metal polish) the master and used on another car. Absolutely no problems to date.

I bought my master cylinder on eBay, but it had the cheese head screws for the cover and front plate as original. It may have been a lockheed unit, it wasn't the cheapest on eBay, I paid about 110. Here is one:
http://cgi.ebay.co.uk/GMC-112-3-4-BORE-DUEL-MASTER-CYL-BRAKE-clutch_W0QQitemZ360214873357QQcmdZViewItemQQptZUK_CarsParts_Vehicles_CarParts_SM?hash=item53de7ac50d#ht_500wt_956

But I am not sure it is better than the Lucas TRW units at half the price.

Neil
Neil McGurk

Brake fluid is hygroscopic, and it sits on panels and IN the paint, absorbs water from the air, and causes rust for years. And it continues to diffuse through the paint, which acts as a holding sponge for the fluid. The damage you see may be from the first fluid that was spilled on it 50 years ago - still there. The prevention is to always wash spilled fluid off with large amounts of running water ASAP.

Scrape off any loose paint, especially at the limit edges, wash thoroughly. Lots of water will also get the brake fluid out of the harness braid so it doesn't eat the new paint. Until you are ready to take it apart and repaint everything, spray a wax based rust preventative on the bare metal. When you do repaint, use a moisture cured urethane, which will not be affected by the fluid. POR is such, though I use Masterseries CT.

It is even possible to save paint that has had fluid spilled on it by washing thoroughly without touching it and washing the fluid out of the paint if you are quick enough. I once changed the pads on a MkVIII Jag, pushing the pistons back without checking the reservoir - when I came out from under, the fluid had squirted up onto the bonnet underside and run down the wing to the front valance. There was about a 6ft long x 2in wide strip of nicely lifted immaculate lacquer all wrinkly. I screamed and my boss screamed back "Don't touch it" and came running with a hose. Twenty minutes of water and an overnight rest - we waxed it - good as new!

FRM
FR Millmore

Graham
I have exactly the same problem my MC leaks minutely at the clutch piston I have bought new seals and have not yet got around to tackling this job.
I understand the procedure is to remove the front bolt and tilt the MC upwards ( after removing the pins that connect to the pedals)can you just remove the pistons? does one have to remove the front plate as well ? then is it simply a matter of replacing all the rubbers amd refitting after possibly polishing the pistons.A step by step guide from the experts on this forum would be appreciated
Forgive ones questions but I have never tackled this job before and am somewhat wary with safety sensitive parts.
I have also bought new flexibles (the high performance ! metal covered ones) which I intend to replace as I am uncertain as to the age of the existing rubber ones.
Once the leak is cured I intend to clean up the area around the MC and have got the message about brake fluid needing copius washing off!
Paul
P D Camp

Paul

Yes you have to remove the front plate as that holds the pistons in place. You can replace the seals in situ by tilting the MC as you describe, but first syphon off the MC fluid first to avoid spillage on the bulkhead. Place clothes underneath the MC to catch the odd drop.

Steve
Steve Gyles

Barney, the white plastic cap that came with my m/c has a very small vent hole but no inner piece. What's the inner piece for -equalising pressure somehow?. I know the original caps had an inner piece and have wondered what's its job is?
JP, Dot 5 has been described as purple before but my Automec Dot 5 is yellow/brown - what product do you use?
J H Cole

FRM/Neil, that is very interesting. So you're saying I may be trying to find a leak that was fixed many years ago!
If so I will probably just renew the mc rubbers. Am I correct in thinking it's just as easy to do this on the bench rather than fiddle arround with it in situ? (as it will also give me a better opportunity to clean up the metal work). I read in the archives that someone said if done in situ, no need to bleed, but I find that hard to believe.
Paul, Since we live nearby, maybe its worth comparing notes, I will email.

JHC - I understand the inner piece is to catch fluid so it doesnt overflow
Graham V

Graham
I have just removed my MC as I wanted to clean it up & replace the rubber fume excluder. I took the opportunity to replace all seals, gaskets, copper washers & lid securing screws. All items were available at MGOC. What I didn’t realise was that the gaskets came supplied with the seal kit but noticed that the separate ones I ordered were much thicker. Due to reported leakage problems from the top lid I decided to use the thicker cork gasket.
Only problem I had was sticking pistons after reassembly but managed to free these with the aid of a foot pump connected to the outlets. I also purchased an Ezibleed as I have read some good reports on this kit. I will let you know how I get on when I re-install the MC & bleed the system some time next week.



r a evans

Doing it on the bench is a better way to do the job. That way you can clean the master cylinder AFTER you hone it.
These brake/clutch master cylinders will ALWAYS leak some fluid.
So unless you like the paint damage replace all the rubber in the whole system and use silicon fluid.
R J Brown

Graham -
I was only addressing the paint/rust issue.
If you have " a little weeping of fluid on the brake push rod", then you need to fix it.
I can't really believe anyone actually thinks In-situ repair is appropriate, other than as a temp emergency thing. You simply cannot get things clean and correctly examined/repaired and CLEAN in the car. Not to mention that working with brake fluid in the car near all that shiny paint is pretty silly.

FRM
FR Millmore

Thanks that all makes good sense. I have managed to source a very well priced master cylinder so wont even bother with replacing the rubbers. Just take out the old one, clean up bodywork and replace.
Do the push rods just slide in to the new mc or is there some fixing? - cant see from from Haynes.
Graham M V

I stuff a small rag under the MC so that early weeps do not damage the paint. If done "properly" the rag is not seen.
Barry Bahnisch

Graham

They just slide in through the dust cover.

Steve
Steve Gyles

I'm with you Barry. Although my master cylinder doesn't leak (yet) I like the added insurance of knowing that my paint is safe in the event of a weep occurring.

I also make a point of checking the master cyclinder pushrods for leaks as often as I check the oil and water levels (usually every time I take the car out on the road!)

Cheers

Steven


S HILL

Some of you may remember my saga when I had leakage around the front plate/pushrods. In an attempt to seal everything up I put jointing compound between the front plate and MC body. In time some of this compound dissolved into the bores and contaminated the seals! Therefore do not use sealant in the MC. When I replaced the seals afterwards I took the opportunity to flatten all the mating surfaces (front cover and top + MC). I was surprised that all were considerably out of true. No leaks now.

Steve
Steve Gyles

Steven, your car looks very nice (and correct, too!), no wonder you are trying to protect the firewall paint! Steve, I might be missing something but the rubber piston seals should prevent fluid from reaching the plate?
Barry Bahnisch

Barry

Yes, I agree with you. In theory it should be dry back there, but as you will see from comments above there are plenty of instances of damp rods etc. talking to James at Bob West the other week he was saying that many cars he sees have weeps round that area. Mine is now dry after fitting new seals, so I guess it takes just a little bit of wear in the seals and/or bores for the fluid to find its way back there.

Steve
Steve Gyles

Steve,
I seem to remember reading in the archives that you had a really serious problem from a disolved felt washer in the master cylinder (maybe not you & if so, apologies)?
Graham M V

Is there a clear coat paint that is "DOT3 proof" ?
Art Pearse

Art its called DOT5. DOT3 will melt any paint you use. DOT 5 has been leaked and spilled on this one for over 22 years. The MC has been redone 2 times during that period. NO MELTED PAINT. Check out next picture!


R J Brown

A wet paper towel with dish soap got it this clean!
I don't even care WHEN I spill brake fluid cause it is purple. The mess I just cleaned a little of has been sitting like that since last summer.
USE DOT 5!!! DOT3 MELTS PAINT!!!
Anyone stubborn enough to still use DOT3 deserves the melted wrinkled paint on the rusty shelf that they get.
There is no argument!!!


R J Brown

RJ, has your clutch push rod got a crank in it -puzzled?
J H Cole

This car has a 82 Mazda RX7 engine and trans. I had to limit the movement of the clutch because RX7 slave cyl is smaller in diameter than the MGA part. I made the part you see.
You can see the slave cylinder on top next to the oil filter.
The paint is PPG Deltron no clear coat. Dot 5 has been spilled on it since it was painted in 1988.
I HATE DOT 3.
R J Brown

image refered to above


R J Brown

Hi Graham,
Installed the MC after seal replacements & bled the system today. Only problem I had was one of the outboard bleed nipples was blocked, but I guess I managed to extract any air out of the inboard nipple as the brakes are working fine. No problems with clutch either. That Ezibleed is brilliant, only wish I used one back in the 60’s……………I can still remember lying under the car & shouting at the girl friend (now my wife) “pump, pump………… don’t forget to top up.”

I decided to keep to DOT 4, I hope this isn’t a decision I will live to regret!

How did you get on with your MC replacement, DOT 4 or DOT 5?

Richard
r a evans

Richard
Good to hear you have got the job done and the car now stops. Always a good thing.
I haven't started work on mine yet as was delighted to get my refurbished carbs back quicker than expected, so that's my current job.

I have decided to stick with dot 4 as I am only planning to renew the mc. I am also thinking of buying an eezibleed kit and encouraged that you got on so well with it. Like you, many years ago, my wife would help me with the job but she no longer pretends to be interested in my hobbies and for some reason, thinks sitting in the garage at 0 degrees in mid winter is not fun.

Can I ask, when you disconnected the brake line at the 4 way fitting, any trick to prevent fluid going everywhere?
Graham M V

Graham
I disconnected the brake line at the rear of the MC, not at the 4 way fitting.

After removing the clutch line I removed both front & rear securing bolts on the MC, this allowed me to withdraw the unit enough to remove the brake line at the rear.

I put some rubber dust caps over the ends of the lines to stop any dripping of the fluid whilst I was working on the unit.

The Ezibleed was used to pressure test the MC @ 20PSI & then reduced to 15PSI to bleed the system.

One word of warning: I almost forgot to disconnect the pressure from the tyre prior to disconnection at the MC……… I hate to think of the consequences!

Good luck

Richard



r a evans

Richard
Thanks thats a good tip. I will try that and see if I can disconnect the brake line at the top. As well as putting up with the mess, I think you need Twizzle's arms (if you remember that TV character from the 60's) to reach the 4 way union joint. I will let you know how it goes but want to get the engine running first!
Graham M V

Richard

I have done that one! Fortunately I use silicon fluid so I now have the most rust free MGA bulkhead in the world. It sprays everywhere.

Steve
Steve Gyles

This thread was discussed between 15/02/2010 and 23/02/2010

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