Stumped by MGA brakes

[malcolm]

You planning on putting up some pics of the car Malcolm?

It's dark out. Probably for the best - it was painted in cellulose 30 years ago and could do with being painted again with something better. Mechanicals and bodywork have held up well and it's normally no trouble.

 

[Tinbasherdan]

I’d try back bleeding it first. The air assist slave on the clutch on my Landy is an absolute pig to bleed unless you back bleed it

 

[frank horton]

the trick is to have the rear and/or front adjusters in the lowest position......
if it at max hight the slightest pressure will push the wheel cylinder pistons to the top of the bore and leave an air pocket
under the piston.....
with the pistons at their lowest position the springs will hold em down so all the air can exit the nipple....

 

[500e]

If the HB is incorrectly set it holds the first part of the cylinder out letting the hyd piston come forward trapping air, make sure the pistons are right in, remove hb clevis and make sure the pistons cannot move out when bleadin

 

[ajlelectronics]

You may be chasing your tail. In my long experience, that problem is caused by the flexi hoses. They degrade internally and bits of the hose inner become detached and act like one way valves. Unless the hoses are brand new, I would have a set of Goodridge in there double quick.

 

[daedalusminos]

I've never had so much air trapped to need two full strokes - in fact I can't imagine you'd actually get two full strokes and then go hard, when you release the pedal the air would just expand back.

What was the reason to disturb the brakes in the first place?

 

[8ob]

Doesnt look like there is any vodoo going on in there, could be the lack of spring (22) causing the issue if the piston is retracting

 

[tom2207]

if your still having grief ,,, take the shoes off and clamp the pistons in with a g clamp so they dont / cant move , and try bleeding the brakes .... that gets rid of another variable

 

[500e]

You have to have the pistons right in as Tom says if hb is holding first plunger out piston has air behind it, horid idea with the blead on Union.
Try pumping preasure in then releasing bleed and push piston back and locking off while holding pedal down, new hoses, with a car that age a must

 

[jsf55]

Always bench bleed the master before putting it back in, seems to help on all the swaps i've done

 

[dave h 2]

You may be chasing your tail. In my long experience, that problem is caused by the flexi hoses. They degrade internally and bits of the hose inner become detached and act like one way valves. Unless the hoses are brand new, I would have a set of Goodridge in there double quick.

Don't ignore the above post. The front brakes on Fiat Coupes would jam on due to inside decay of the brake flexi hose. The outside of them looks fine with no sign of cracking.

 

[ajlelectronics]

Don't ignore the above post. The front brakes on Fiat Coupes would jam on due to inside decay of the brake flexi hose. The outside of them looks fine with no sign of cracking.

I have had it on K1200LTs as well.

 

[RWD3M]

I changed the rear brake cylinders in my MGA last week. There had been a problem with the master cylinder which caused the pressure to stick on and blow the seals in the rear cylinders. I replaced the rear cylinders. Tried to bleed the brakes but couldn't get pressure. The master cylinder was suspected bad anyway so I changed that.

I've been trying all day to bleed the brakes again. I've put a litre of fluid through and there is no more air coming out. Rear brakes are adjusted tight so they don't travel. I still don't get pressure. The pedal goes down to the floor and takes another 2 full travels to become firm.

Logically it must be the rear cylinders as that's when the problem started. They are funny things that require an internal spring. I wonder if the aftermarket suppliers all include the spring. Maybe I'll order some reassuringly expensive ones from one of the major suppliers.

What else can I be missing? I've never had trouble bleeding the brakes on this thing before.

Hi Malcolm,

When it does be come firm, is properly firm (as in a normal feel) or still spongy? If firm, your issue isn't air, it's excess (slave) piston travel, somewhere.

 

[malcolm]

I bought some rear wheel cylinders from one of the mainstream MG suppliers. These do have the spring inside. Fitted them to the car this morning and I have a good brake pedal.

Must remember not to buy brake parts on eBay. The ebay ones did not have a spring inside. It was taking all the pedal travel to get them to the position they would have been already had the spring been present.

 

[Matchless]

A lot of BMC / Morris repro parts are made in India

I also have an MGA, 1600 mk1

 

[Robotstar5]

A lot of BMC / Morris repro parts are made in India

I also have an MGA, 1600 mk1

Some stationary engine parts are made in India as well, one batch of pistons had the crown separating from the body after a few hours running

 

[malcolm]

I think this was my bad. Inspecting the previous cylinders before sending them back I found them to have springs.

I was using the Easybleed kit that pressurises the master cylinder, and with the poor location of the bleed nipple before the slave cylinder it bled the lines but the slave cylinders were still full of air. I've not had this problem in the past when I had an assistant do the brake pedal pushing down style of bleeding. That probably provokes some movement in the slave cylinder that helps get the air out.

With the new cylinders I took the opportunity to open the bleed nipple and press the cylinder back with a screwdriver, close the nipple release etc 10 times or so until no air came out.

You live and learn.

On a more positive note that's 2 cars with brake problems fixed. One with a chassis problem fixed (replacement - not a quick job) and just the one in my avatar that has been a week away from being finished for the last 8 years.