Is my master cylinder knackered?

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davidimurray

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Building: Haynes Roadster

posted on 11/5/13 at 08:59 PM

Is my master cylinder knackered?

I am having a hell of time trying to get my brakes nice and firm. At the moment the pedal goes firm but if you use all your might you can get the pedal to reach the bulkhead.

Master cylinder, front calipers and rear drum cylinders are all new.

I always suspected the problem may be at the rear so released the handbrake and set the adjusters so the drums only just fit over.

I've been using a easibleed and started on the passenger side rear(furthest from master cylinder) and I have put 20+ easibleed bottles through. Just using the easibleed I don't get any air, but if I pump the pedal I get lots of tiny air bubbles in the fluid.

I then moved on to the drivers side rear and got loads of slugs of air out.again put 5+ easibleed fills through with still loads of air coming through.

Very confused I then disconnected the rear brakes at the master cylinder and fitted a bleed nipple into the port for the rear brakes.pressing the pedal it was harder that last time but would still almost go to the bulkhead when using all the force I could apply.

I then tried bleeding the rear master cylinder port, using both the easibleed and traditional method.when using the traditional method I can hear popping inside the master cylinder and I get air coming out in every stroke. Reservoir is full and with 20+ stroke every one had air in. When I pressed the pedal I did notice that the fluid level rose slightly in the reservoir and then dropped again when released.

Based on this is my master cylinder knackered?if so is it better to get a rebuild kit or a whole new unit?

As I've been re-using the brake fluid as I go along.I've got two containers which I alternate to give the air a chance to escape from the fluid. Is this OK to do?

All help much appreciated.

Dave

rodgling

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posted on 11/5/13 at 09:45 PM

Is it a good idea to use all your might after the pedal goes firm to force it to the bulkhead? Won't that knacker your m/c seals?

Could maybe be hoses expanding under excessive pressure - are you using hoses or copper pipe?

davidimurray

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posted on 11/5/13 at 09:56 PM

I'm assuming that the iva man will want to press it until it goes solid.my pedal goes firm but never solid.

System is all piped in copper except for flexis to wheels which are home made rally design braided items

[Edited on 11/5/13 by davidimurray]

snapper

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posted on 12/5/13 at 03:44 AM

I would put bleed nipples in all the master cylinder outputs and do the test again
If you still get to the floor you need a new master cylinder
Could master cylinder seals could be worn bore
Best way is to get a new master not a rebuild
On my kit I used 2 master cylinders (second hand) and had the same problem until I bought a new one
Check also all joints for weeping, a little nip up helps but do go all King Kong on them
Old clean fluid can be used for lots off bleeding but use new out of the bottle for a final bleed through as fluid in air absorbed water and that will boil at only 100c

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davidimurray

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posted on 12/5/13 at 09:41 PM

Had planned to have a full day on the car but was greeted with drains overflowing over the patio

A couple of hours with the drawn rods then playtime.

Plugged off all the master cylinder ports, bled the front ports without a problem, but kept getting air through the back port. With the ports blanked off the pedal was still spongy. Removed and stripped the master cylinder. Seals looked fine but there was some dirt in there.cleaned and refitted, bled all the ports then hooked up the rear brakes, bled through adn got a nice solid pedal

Going to hook up the fronts tomorrow so fingers crossed.

Litemoth

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posted on 12/5/13 at 10:47 PM

I refer you to my answer here:

http://www.locostbuilders.co.uk/viewthread.php?tid=168494&page=2
Could be worth trying the old trick of loading the brake pedal overnight. This flares the master cylinder seals and improves the fit.

[Edited on 12/5/13 by Litemoth]

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