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MG MGA - Where's the Air? - Brake bleed problems

Hi there.
I spent the last weeks rebuilding all the brake system, following the dragging brakes issue I had.
This is what I had done;

- Rebuilt master cylinder
- Changed rear hose (front ones are new)
- Rebuilt rear drum cylinders
- Rebuilt front calipers

I spend most of today putting the last pieces together and bleeding the brake system.

I started with the rear right wheel cylinder, then rear right, front right, front left and then clutch.

During the first bleed obviously a lot of air came out and the pedal started to go harder progressively.

After I bled the system, the problem I have is that the pedal travels all the way down on the fist stroke, and then on a second stroke and further ones it gets hard as it should.
I understand that this happens because of the non-return valve in the MC.
My hypothesis is that there is still air in the system, on the first stroke the air-bubbles get compressed and on the subsequent ones they stay compressed hence the system stay pressurised.

Since this was happening I went ahead an bled it one more, but not much air came out just some tiny bubbles in the fluid.

I am not using any fancy pressure bleeders, just a bleed bottle which I attach to the nipple while my helper (i.e. wife) pressed the pedal.

Do you have any ideas about what do to next? Do you think there is still air in the system or could it be the MC which is not working properly?
I suspect the air could be in the center section of the pipes or in the rear wheel cylinders.

I also spent some time adjusting the rear brake adjusters and that reduced slightly the travel, but the problem is still there.

I will sleep over it, see if I or you come up with some ideas.

Gonzalo










G Ramos

If you rebuilt the front calipers and reinstalled them, you may have switched them, right to left etc.. This would put the bleed fittings on the bottom. They need to be on the top. You'll never get rid of the air with them on the bottom. Been there and done that.
Tom Newton

Usally if the pedal pumps up hard after a few pumps it is the brake shoes out of adjustment but you say you've covered that. Hopefull you have your calipers on correctly. A pressure bleeder may be the way to go. I've tried the mity vac where you pull a vacuum on the bleeder and found with even with teflon tape on the bleeder threads to create a good seal I still could not get all the air out. I have used the pressure bleeder from Motive Products with great sucess. They don't have a adaptor for the MGA master cylinder but its easy to make one out of a used plastic MGB cap and a 1/4" hose barb. In fact thats what I do for all my cars, get an aftermarket or used mc cap and attach the hose barb. Its cheaper than buying all there adaptors and what a difference it makes in flushing out all the old fluid.
Charles O'Brien

Tom,
Caliper have the bleed nipples on top... no worries there.
Charles, I will see if I can maybe get a pressure bleeder locally...or on rent to finish the job.
I guess that is the only other solution.
G Ramos

Gonzalo -
As Charles says, this sounds like an adjustment problem.
Lock both rear adjusters dead tight and see what happens. You should get a rock solid pedal, right at the top.
With adjusters locked, the only movement should be the required bit of free play at the MC pushrod. I always bleed with adjusters locked, usually by myself & by gravity.
If it still feels squishy, there is still air in it, or there is deflection at a front caliper from a sticking piston or pad, which causes the disc to flex. You should be able to see deflection if you look while the Lovely Assistant stomps on the brake. Since you rebuilt the calipers, most likely cause here would be a pad hanging up a bit.
Once you get the air out, you back off the adjusters enough to let things turn freely. Disturbed or new shoes and pads take a little while to recenter correctly, so a subsequent readjust after a short drive may be called for.

FRM
Fletcher R Millmore

Gonzalo, Buy a pressure bleeder they are not that expencive and they really do work making it a one man job in the process, Vin
Vin Rafter

Spent the afternoon messing around again doing a third bleed...without success, so I will go an get a pressure bleeder.
Which type do you recommend? pressure or vacuum?
G Ramos

Hi Gonzalo
There must be hundred if not thousand people who bled the brakes just as you did. Look for something else. I do not think that pressure bleeder will help. And if it will you have problem for next time. Beside I would like to know WHY? My life depend on it. Can you plug the front, bleed the rear,see if it works. Plug the rear bleed the front. I suspect the calipers. Did you do them? or had them done?

Martin
m zazvorka

Gonzalo,
I have bled brakes with a helper operating the pedal many times. The way I do it is to open the bleed nipple on whichever wheel I am working on and yell to the pedal operator "down", making sure that they hold the pedal down until I tighten the bleed nipple, then I yell "up" and wait for them to tell me the pedal is in the up position. I repeat this until I am convinced that no more air is in that particular place, and then move on to the next wheel. I have found that if you don't close the bleed nipple before allowing the pedal to start it's return to the up position some air can be sucked back in around the threads of the bleed nipple. I have made myself a pressure bleeder using a plastic master cylinder cap and now don't have to hunt up a helper in order to bleed my brakes. Both methods have worked well for me.
Ed Bell

I will have to give it another go then.
Indeed it could be the calipers, I need to re-check them.
Indeed my life will depend on it.
The problem I see is that there could be air in the T-junctions where the brake switch is (or any area around there) and the bubbles there will never go down the brake line as the yfloat...

I will see if I can clamp the rubber hoses successfully in order to see where the air could be. Do you suggest a particular method to avoid damaging the hose?
I was thinking vicegrip with some sort of protection for the hose?
G Ramos

FWIW. My clutch worked properly. After sitting for a few days - nothing. I used the EZ Bleed system that uses air from a spare tire to pressurize the system. I opened the bleed for the clutch slave cylinder and after about 5 seconds a large "burp" of air came out.

I'm sure you've done this but there is no brake fluid leaking anywhere.

Good Luck.
Lmazoway

Hi Gonzalo,

One of the reasons for using the pressurised or vacuum bleeders is that they force enough movement into the fluid to dislodge the bubbles and push them down the pipe.

I did my brakes with an Eezibleed too and the pedal is rock solid.

Barney's site has a piece about making your own pressure bleeder with a garden sprayer or similar pressure vessel.

You can buy hose clamps that aren't too expensive but I've also seen manuals recommend two coins in the jaws of self-clamping grips. Obviously the objective is to avoid applying any sharp metal edges to the hose or pressure that is too localised. The coins spread it over a wide area. But don't clamp too tight.

Good luck!

Malcolm

Malcolm Eades

Chapter IV of the amateur MGA mechanic.

So I went and bought a mityvac bleeder, and spent most of the evening messing around with it (since my wife is fed up of helping me).
I tried the 'suction at the nipple' tecnique, but I found there is too much air coming through the bleed nipple threads... I guess that some air came out.

Then I did the reverse bleed, suction at the MC and put a bottle full of fluid at the nipple and suck the fluid upwards. Some air came up the MC, but you also put some air into the system cos it is difficult to have both the bottle and tube full of liquid.
Then I did a regular pressure bleed with some positive pressure at the MC...
In the end I got fed up. And the floor was full of patches of brake fluid...disgusting stuff.

The pedal seems to be a bit firmer but still too much travel compared to before.
Next step will be to clamp the hoses to see where the spongyness is coming from.

Maybe I should have got the Eeazybleed, but couldn't find it locally. I think the mityvac does not produce much positive pressure.
Ah, the joys of the MGA.

G Ramos

The Mityvac is a waste of money - most useless tool I ever bought except for testing vacuum gauges.

The easibleed is on the other hand an excellent tool that makes bleeding hydraulics a really easy job.
dominic clancy

Gonzalo, the problem is with the rear brake cylinders. The bleed nipple is on the bottom and the air is trapped at the top. I tried the mitivac and it was useless, air came in around the bleed nipples even with teflon tape around them. The easibleed worked better but still left air in the rear cylinders. I put through about 1 gallon of brake fluid and the peddle still pumped. I got the best results with a helper who pumped the brakes 3 times before I opened up the rear bleed nipples. This helped by mixing the air in the fluid before it was pushed out. They work OK now but still need doing again to be perfect.

Andy

60 coupe
Andy Preston

I had that trouble once with my father's Mark 7 Jaguar and it turned out to be the booster. They were notorious for this. I assume that you do not have a brake booster (not original equipment).
Barry Bahnisch

Hello Gonzalo, if you want to solve the problem stop messing around and buy a gunson ezebleed pressure bleeder, not expencive and as i said (third masage in the thread) it will do the job for you, good luck, Vin.
Vin Rafter

Eezibleed is on its way from the UK!
Couldn't find it in the US.
Thanks you chaps for the responses!
Can't wait to get the A out.
G Ramos

With the Eezibleed it is quite easy to spill or leak brake fluid as it is under pressure. Just in case, it is a good idea to wrap an old towel or piece of cloth around the master cylinder to catch any escaping fluid.
Malcolm Asquith

"In fact I took the drum off today cos as you may have read on the other thread I have some issues bleeding the brakes.
On the right rear wheel the travel is too much... and in fact I run out of adjustment before the drums bind..."

Gonzalo,
I saw this comment on the other thread. If the shoes cannot be adjusted properly it would cause excessive pedal travel that would firm up with pumping just as you describe. No amount of bleeding will cure that.

Have you measured the drum? If it is worn or ground too far oversize it would cause this problem. Are the brake shoes new? There are some threads in the archives that talk about lack of adjustment even with only slightly worn shoes. They talk about putting a shim on the back of the adjuster, but I don't know anything about that.

Also, if the shoes are new it is possible they don't match the radius of the drum. If that is the case then they will contact the drum in one spot and then flex, again giving excessive travel that firms up with pumping.

Jeff
Jeff Schultz

Gonzalo
It sounds like you are rapidly becoming an expert mechanic for an MGA, you will very soon be helping us with our MGA problems. I have to admire the way you have got right in there and tackled everything your car has thrown at you.
Back to your brakes ( Im assuming you have front discs and rear drums on your car)
On the subject of bleeding the brakes, it seems to me that you dont have to adjust the rear shoes up hard before you bleed them, just pulling the handbrake on hard will do the same thing.
Then you can bleed the brakes until you get a hard pedal.
If you dont get a hard pedal and there are no fluid leaks, then you either have a faulty master cylinder or the brake hoses are soft and expanding.

If the system bleeds ok and you get a hard pedal at first but when you release the handbrake the brake pedal goes soft (it usually can be pumped up solid after a few strokes) then you have too much clearance between the rear brake shoes and the drum.
This can be fixed by fitting a shim onto the brake cylinders (see Vin Rafters recent posting, he has uploaded some excellent pictures showing these)
Hope this may help
Colyn
Colyn Firth

The brake shoes on the rear are not new, didn't measure them. They are the ones that came with the car, and the have about 4-5mm still of pads. Not sure if that is a lot cos I never saw a set of new ones...

I will follow your advices one this and do one complete new bleed once I get the Eezibleed. I have to take it easy cos my wife is starting to complain I spend too much time on the stupid car.

I would tend to disagree with you Colyn on the 'pull the handbrake, it does the same'.
The way the rear cylinder is constructed the outer piston will move up when the internal lever pusher it, but the hydraulic piston will not stay down as it will be moving free internally. My understanding is that you want the least volume in the rear cylinders so no air can stay trapped. This is achieved generally by adjusting the brakes solid onto the rotor.

If it is that I have run out of adjustment I might look into doing what Vin suggested with the shim, but I don't think that is necessary as the pedal was quite solid before I took the fluid out.

Anyway I am going to wait for the Eezibleed before I waste more time on it, and will let you know how I get on.
Thanks guys and girls!
G Ramos

Im not an expert Gonzalo but applying the handbrake locks the the shoes onto the drum by moving the cylinders along the slot in the back plate.
Adjusting the shoes up using the adjuster does the same thing but from the other side of the brake cylinder.
Either way it takes up all the free movement from the rear brakes.
(I have noticed that my brake pedal is a fraction harder when the handbrake is applied than when released)
It sounds though from your earlier posts that your problem should be sorted once you have bled all the air out.
I would recommend some knee pads ( or sit on a wheel ) and a cold pack of Coronitas or Buds to help things along.
Best of luck
Colyn
Colyn Firth

Gonzalo

I have been a bit out of circulation for a couple of weeks - Thank you volcano.

What I have noticed when catching up with the threads is that you are now one of us - an MGA addict.

Great stuff. I remember your first post when looking for an MGA; and now here you are an MGA widower, wife losing interest with the oil and the muck!!

Keep at it, you will have a great car at the end of the day and it will be all your own work.

Steve
Steve Gyles

Yep, MGA widower.LoL. Now
I geat a restriction of how many days a week I can work on my car... :)
Gonzalo Ramos

Gonzalo - Did you try Moss for the Eezi-bleeder, I bought one there a couple of years ago and they still show on their web site. Great to use but then again I never had trouble using a helper.
Mike
Mike Ellsmore

Today I received the Eezibleed and I did the bleedin.
Woow. What a difference it made, it was fast and clean.

I think i'll never bleed the brakes the old fashioned way.

Now the pedal is firm. Just need to fiddle with the rear adjusters to reduce the travel.
I will probably do another bleed after I have done some more miles to get an even stiffer pedal.

That's one thing solved. I'm going driving! ; 0
Gonzalo Ramos

This thread was discussed between 17/04/2010 and 29/04/2010

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