Trouble Bleeding Brakes following MC Rebuild

Please restrict your questions and replies to Capri related technical issues!
Post Reply
EightyFive
Posts: 175
Joined: Mon Jul 13, 2015 7:52 pm
Car(s): Ford Capri 2.0 Laser 1985

Trouble Bleeding Brakes following MC Rebuild

Post by EightyFive »

Hi all,

Decided to give rebuiding my Master Cylinder a go using the great guide on the laser page. All seemed to go okay, seals in correct way etc but for the life of me I can't get any fluid to come out of the calipers.

I primed the MC by letting brake fluid pour out of the 3 union pipes on the reservoir etc. before I attempted to bleed. I then went to bleed the brakes and whilst some fluid was coming out I suspect this was just the old stuff. After a few pumps there felt like some resistance, followed by a 'dong' sound, in any case it didn't feel right.

Since then I've been unable to get any fluid to come out of the calipers. I have removed both bleed nipples for an hour to see if the fluid would find it's way out and nothing... Whenever I push on the peddle I can hear the suction from the caliper, but maybe a spittle of fluid comes out at best.

Is this a case of there just being way too much air in the system, or could one of the pistons have become stuck? Is there anything I can try before having to drain the system and inspect the pistons again?
User avatar
Peter-S
Donator
Donator
Posts: 7180
Joined: Mon Jul 28, 2008 7:57 am
Car(s): 1985 Capri 2.0
1983 Capri 2.8i
Location: Kent
Contact:

Re: Trouble Bleeding Brakes following MC Rebuild

Post by Peter-S »

Sounds like fluid isn't coming out of the master cylinder. If you have a helper to hand I would disconnect a caliper input pipe and get them to press the brake pedal to see if any fluid comes through
ImageBanner by Peter Smith, on Flickr
STEVEW
Posts: 200
Joined: Sun Dec 30, 2018 10:10 am
Car(s): Ford Capri 2.3S
Project

Re: Trouble Bleeding Brakes following MC Rebuild

Post by STEVEW »

Hi EightyFive,

I’m in the process of overhauling an “ATE” master cylinder which is slightly different to the one described in the Laser Page however, they must be similar in operation.

You say,
After a few pumps there felt like some resistance, followed by a ‘dong’ sound, in any case it didn’t feel right.
a) The small 4mm screw which holds the “locating cone” of the stronger spring could have let go.
b) The ATE master cylinder has a piston travel stop-screw, which is located externally under the master cylinder. If yours has one: it could have snapped or fallen out.

That ‘dong’ sound could be accentuated by the drum-like servo or from the servo itself. I would remove the master cylinder and inspect the inside of the servo and the rod which pushes into the rear of the master cylinder and try locating it again into the master cylinder.

I hope this helps. Please let me know how you get on.
All the best.
Not_Anumber
Donator
Donator
Posts: 870
Joined: Sun Jan 15, 2017 3:54 pm
Car(s): 2.8 Injection 1983 5 speed, weekend car. Audi A7 daily driver Slowly restoring a 1979 MGB. Previously owned 2 Capris.

Re: Trouble Bleeding Brakes following MC Rebuild

Post by Not_Anumber »

It sounds very much like my experience trying to bleed the brakes on my other old car. Though not a Capri it's from the same era with a very similar braking system layout. I'd had the master cylinder off the car for a year or so whilst I was working on the engine bay and wrongly just assumed this couldn't be a problem. because of that i ignored the signs and carried on trying to bleed the brakes for days without success. Almost no fluid was getting through to the calipers and rear cylinders. I tried all the usual workarounds after that, left the bleed nipples open, left a bit of timber holding the pedal down all night etc to no avail.
Luckily recon master cylinders for this car happened to be easy to get hold of and not expensive. Within 15 mins of having replaced it I had the brakes fully bled. For the hell of it I dismantled the old master cylinder but couldn't see any obvious signs of failure on the seals.
Mc Tool
Donator
Donator
Posts: 1834
Joined: Sat May 17, 2014 8:34 pm
Car(s): 1980 mk3 capri 2l ohc T9 , Toyota Blade Master 3.5l V6, Paso , 850T,rd400, 900ss
Location: Invercargill New Zealand

Re: Trouble Bleeding Brakes following MC Rebuild

Post by Mc Tool »

Another thing that can happen is the rear seal in the cylinder can fail . This can be awkward as it usually sucks air in and doesnt actually leak fluid . Pita when trying to bleed as it sucks air in as fast as you can bleed it out at the other end . Not usually enough to cause complete failure but enough to give a spongy pedal that wont go away.
As the pedal is pressed the piston moves forward the pressure in the cyl holds the seal lip out and it seals. When the pedal is released and the piston moves back there is slight vacuum in the cyl and this can draw in a small amount of air into the rear of the cyl. Damage or rust to the outer end of the cyl bore can do this too . Brembo motorcycle pumps ( what they call the clutch and brake master cyls )are good at this . 🙂
Sometimes I talk to myself ... and we both have a good laugh
User avatar
Noel
Donator
Donator
Posts: 508
Joined: Thu May 19, 2011 7:57 pm
Car(s): Capri 2.8i
Range Rover
M140i
Location: Twickenham

Re: Trouble Bleeding Brakes following MC Rebuild

Post by Noel »

Mc Tool wrote: Wed Nov 10, 2021 1:57 am Another thing that can happen is the rear seal in the cylinder can fail . This can be awkward as it usually sucks air in and doesnt actually leak fluid . Pita when trying to bleed as it sucks air in as fast as you can bleed it out at the other end . Not usually enough to cause complete failure but enough to give a spongy pedal that wont go away.
Oh man that's exactly what my cars like at the moment, been bled and bled again but still spongy. Brakes all standard. Hoping not the MC but kind of resigned to the fact that it might be past it's best.
Mc Tool
Donator
Donator
Posts: 1834
Joined: Sat May 17, 2014 8:34 pm
Car(s): 1980 mk3 capri 2l ohc T9 , Toyota Blade Master 3.5l V6, Paso , 850T,rd400, 900ss
Location: Invercargill New Zealand

Re: Trouble Bleeding Brakes following MC Rebuild

Post by Mc Tool »

Things have changed since I was young and was a great one for repairing stuff . Now Im thinking that if you can get a new one at a good price Id do that , specially if its got a few miles on it or its been sitting for a while unused.
I dunno your situation there but a seal kit here is about $50 ,and a whole mc is about $150
Sometimes I talk to myself ... and we both have a good laugh
Not_Anumber
Donator
Donator
Posts: 870
Joined: Sun Jan 15, 2017 3:54 pm
Car(s): 2.8 Injection 1983 5 speed, weekend car. Audi A7 daily driver Slowly restoring a 1979 MGB. Previously owned 2 Capris.

Re: Trouble Bleeding Brakes following MC Rebuild

Post by Not_Anumber »

Personally I would change the MC for a new, recon or good 2nd hand one rather than replace seals as i would be concerned about corrosion inside the cylinder wearing and tearing the new seals before they had even bedded in.
EightyFive
Posts: 175
Joined: Mon Jul 13, 2015 7:52 pm
Car(s): Ford Capri 2.0 Laser 1985

Re: Trouble Bleeding Brakes following MC Rebuild

Post by EightyFive »

Appreciate the suggestions guys. Unfortunately haven’t had much time to work on the capri so it’s been sat untouched. Will have one last look/ attempt tomorrow before I just bite the bullet and buy a new MC. Not got the time to faff around ad would rather just drop £50-£70 than waste more time!

For whatever reason I do suspect the piston isn’t going back into it’s original position.
User avatar
Major_Tom
Posts: 8151
Joined: Mon Jul 28, 2008 8:21 am
Car(s): 2.0S

Re: Trouble Bleeding Brakes following MC Rebuild

Post by Major_Tom »

MC Rebuild sounds like a mechanic turned 90s rapper.
I'm the one that leaves all those shoes in the carriageway.
tazla
Posts: 392
Joined: Tue Mar 10, 2015 7:25 pm
Car(s): Mk2 3.0s stardust silver

Re: Trouble Bleeding Brakes following MC Rebuild

Post by tazla »

I changed the seals on mine and it didnt work i then sent it off and they resleeved it and its now fixed and works a treat
Post Reply