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MG Midget and Sprite Technical - Bench bleeding brake master cylinder......

Hi folks,
I got a new brake master cylinder. It's on the bench to get bled. I hooked up short brake lines to each port (two) and bent them back into the reservoir.
Well, fluid is only shooting out of one of them.Is this correct ?
I switched over the two lines , in case one was plugged. Still only shooting out of one port.
Paul W 1976 1500

I should mention, it seems quite easy to push in the piston with my hand. Maybe I'm not pushing it in all the way ?
Paul W 1976 1500

I think the US spec is dual circuit brakes, yes? Try closing off the one that is squirting, maybe push a dowelling plug in it or crimp the end with a pair of pliers. Hopefully that will give enough back pressure to bleed the other side. At the moment the fluid is just taking the path of least resistance but when fitted to the car the pedal pressure should push fluid through both okay.
I think it should be reasonably easy to push the piston with no reaction pressure from the brake circuits.

Yes, dual circuit system.
I'll be darned if I could close off the working port. It's not a bolt thread that I can just bolt the hole closed. I've crimped the end of the brake line, bent the crimp, curled it up....still squirting out. The doggone workbench is a
I don't want to put this thing in if it's not going to work. According to the 'bench bleed' instructions, they say to hook up both lines, so I'm pretty sure both ports are supposed to squirt.
It's disappointing when you set time aside to get a job done, and then you can't do the job.
Unfortunately, I bought this MC early last year on a Rock Auto close out.
Thanks for the reply.......
Paul W 1976 1500

Well that's a headscratcher. With the piston in the "out" position I think it should be possible to pump fluid into the reservoir from the outlet port with a veterinary syringe (for example) provided you can get a good enough seal in the port, maybe using electrical tape. If not it's likely there's a blockage; possibly some internal component is out of place and blocking the port. A careful strip down and looksee might be the way forward.

I just remembered that I've heard that some dual circuit systems that are front/rear split instead of diagonally split have a valve built in to the m/c that isolates the supply to one circuit until pressure to the other circuit is enough to hydraulically open the valve. Possibly to prevent the rear brakes locking before the front brakes operate. I don't think I've ever seen one, just heard about it. It's more usual I think to have an external bias valve.
Is it possible you have an m/c with the valve built in? ISTR it should be possible to override it by opening it manually to bleed both circuits.

Yes, a strip-down might be the thing.
I remember though, trying to rebuild one of these, many years ago, there was a 'snap-ring' deeply recessed that held the piston in the bore. I had a hell of a time with that snap-ring. It seems to me that I scratched the piston in trying to get that darn ring out.
I'll have to have a look.
Paul W 1976 1500

I don't know if I have that valve in there or not.
Even if that is in there, when it would kick-in, there would be air in there.
Paul W 1976 1500

Old trick to shift deeply recessed snap rings is to ***very carefully*** drill a small hole through into the groove lining up with the break in the snap ring. Then poke the ring round until it covers the hole and a pin pushed through will lift the end of the ring so you can lever it out easily.

That sounds like a good trick.
I remember this one being so deeply recessed.....I'm just looking in my Bently MG repair manual and it calls for tool 18G-1112, for the removal of this darn ring.
Paul W 1976 1500

18G-1112 is just a pair of right angled internal circlip pliers. Common as mice - any toolstore will have a pair to fit.

I rebuilt a dual-circuit m/c many years ago. The Haynes manual forgot to mention the second circlip buried beneath the nylon spacer. When I eventually drilled and dismembered the spacer in order to discover the circlip, I then had to modify a pair of long nosed pliers in order to remove it. My usual circlip pliers wouldn’t reach it.
Dave O'Neill 2

Thanks guys. I'll have to get in there and get a look.
It seems to me I had to grind a pair of long nose pliers to get in there that far years ago. That was 40 years ago though, I can't really remember.
Paul W 1976 1500

Wow that is good info Dave. The BMC special tools catalogue just shows the pliers I mentioned, but the sketch suggests they have rather long jaws. I have a pdf of the catalogue but I can't post it from the phone.

I forgot momentarily that circlips are called snap rings in USA and the trick I posted is especially useful for the type of rings that are just plain spring steel wire without the lugs for the pliers. They're very common to retain gland blocks in hydraulic rams where they're not supposed to be removed at all, just "fitted for life", but the drill-and-pin method shifts them alright.

Before you pull it apart, it's probably only an air lock
Try pushing the piston in, then block the pipe that's not working with your finger over the end and slowly let the piston back--this will suck some fluid in from the reservoir- Release your finger,then push in again ,block and slowly let the piston back, release your finger, push,block,return ,release--do this a few times and it will suck the fluid up and you'll be away
William Revit

18G-1112 is just a pair of circlip pliers. Common as mice - any toolstore will have them.

If this link works you can scroll down and see a sketch of what you need.

Umm... Sorry about the repeat. That was something I tried to post last night and for some reason it wouldn't happen. Then lo and behold it popped up today. Anyway the link is carp - it just goes to a preview.

The problem I found was that the circlip was a long way down the bore, the bore is narrow and there is also the pushrod to contend with.

As well as modifying the ends of the long-nosed pliers to grip the circlip, I had to do some grinding to the outside to clear the bore and the inside to clear the pushrod.
Dave O'Neill 2


I don't mean to be insulting, but might as well explore all avenues. Are you sure that you have gotten both of the MC reservoirs filled? And when you try to bleed it, is the cylinder oriented like it would be if it were mounted in the car?

Next, I might consider filling a clean oil pump can with brake fluid, and see if you can pump the fluid into the pipe that is the problem.

C R Huff

I have struggled a lot with brake and clutch cylinders till I bought a suckling device; no more extra time spend with a helper, extra clutch drain lines etc.. No more mess. It is me and the device. My sucking device works with compressed air but you can also buy a hand held vacuum pump.


Flip Brühl

This thread was discussed between 22/08/2018 and 25/08/2018

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