Disc conversion...Bleedin Brakes

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Disc conversion...Bleedin Brakes

Postby Sleeper » Wed Feb 15, 2017 7:21 am

Dear All
Have just finished the front disc conversion,also a master cylinder swap ( for one I overhauled earlier ),and the problem is this...It takes one and a half presses of the brake pedal to get firm.
I have spent hours bleeding what seems like all the air from the system , noticed that the M/c I fitted is a 13/16" and the original was a 7/8" and neither had the valve seal in that one has to remove..

So,I suspect that the slight decrease in M/c bore has some effect,also the increase in front piston size may have some effect , but has anyone any suggestions re. this ?

Also,have fitted a servo,But vacuum not connected yet, Am I correct in thinking the servo just increases the pressure of the brake fluid and not the volume ?

Thanks

John ;)
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Re: Disc conversion...Bleedin Brakes

Postby Custard » Wed Feb 15, 2017 10:53 am

The remote servo does have a cylinder on it so overall fluid volume is increased.

Where is the servo mounted?

I have had issues before when mounted too high, as it becomes the highest point in the system and the nose should be mounted slightly upwards to aid air getting through and on to the wheels where it is bled out.

In certain positions I think air can get trapped in the servo. Depending how you have mounted it you may be able to move it slightly while you bleed the brakes then mount it back again afterwards.

Also are the rear brakes adjusted properly, if too loose you could be wasting travel there and every little thing adds up.

Sean.
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Re: Disc conversion...Bleedin Brakes

Postby Sleeper » Wed Feb 15, 2017 12:28 pm

Sean
Thanks,the brakes were non existent when I first drove this ( on the drive ) new handbrake cables and rears adjusted on day1, and I haven't driven it since ( waiting for the disc kit ) maybe when it's back together ( this afternoon - hopefully ) and I fire the engine up I can have a little tootle on the road and re-bleed the brakes with the engine running ( servo operating..)

DSC02045.JPG


John ;)
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I had a similar problem when doing Jeff, I got round it by jacking the front up high and leaving overnight, then re bleeding, as Sean says depending on how high the servo is this becomes the high point and can have a little trapped air,

A,
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Re: Disc conversion...Bleedin Brakes

Postby Custard » Wed Feb 15, 2017 3:05 pm

Is that an ABS system in there as well?

You may have some luck with the engine running, but the Hillman Hunters we had for taxis had a remote Lockheed servo and bled ok without it running.

Personally unless you have a pedal in one hit I would not take it on the road.

I would either jack it up as Woody suggests, but sideways as that is how your servo is mounted, or as you seem to have enough spare pipe slacken it of and tilt it. It does appear to be horizontal and I think the original instructions would have said at least 15 degrees or so of a tilt.

Sean.
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Re: Disc conversion...Bleedin Brakes

Postby Custard » Wed Feb 15, 2017 3:24 pm

Found a diagram here which shows mounting angles,

http://www.mg-cars.net/mgb-technical-bb ... 621649.htm

Sean.
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Re: Disc conversion...Bleedin Brakes

Postby Sleeper » Wed Feb 15, 2017 4:45 pm

Right
Got the engine back in and running so tomorrow is tidy-up day and loosen the servo to give it some angle and a good bleedin session...

Yes,ABS unit fitted,not fully plumbed yet ,waiting the escort back axle,need to run a brake-line to the rear-left,and not wired in yet,need to mount the sensors and sort out the wiring

Thanks
John ;)
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Re: Disc conversion...Bleedin Brakes

Postby Sleeper » Fri Mar 03, 2017 11:08 am

Finally back on the case,the Master cylinder pushes out 1000psi and after getting all the air out of the servo ( unbolting and bleeding in the vertical position ) , that is increasing the pressure to 1500psi ( or thereabouts as it's a 1.6 :1 unit )

John ;)
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