andrew.carwithen
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| posted on 2/10/07 at 03:40 PM |
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brake pedal firmness
I'm having probs filling and bleeding brake system on my Avon ('though I've done it successfully enough on tintops in the
past.)
My brake set up is as follows:-
Stuart Taylor/Luego etc. type floor mounted pedals with dual master cylinders and bias bar. front m/c is .625" and rear .7"
Front are Cortina M16 calipers and rear are Sierra discs and calipers (with calipers orientated so bleed nipples are on top.)
Filling and bleeding the brake system for the first time, I used a hand held vacuum pump at each caliper (furthermost from M/c's first) to
initially draw fluid through.
Then used Gunson's easibleed kit and tyre pressure to bleed each caliper in turn until escaping brake fluid was free from air. (I've
actually gone through a full litre of fluid doing this to ensure no air in system.)
At no time was the M/C reservoir fluid level allowed to drop to anywhere near min. throughout bleed process and no leaks at any of the unions etc.
Problem is, there is very little (if any) brake pedal resistance and pedal travels fully to bulkhead (which, obviously, suggests air still in
system.)
How firm should the pedal be on my dual M/C set-up? (I was expecting it to be solid with little or no travel?)
I did significantly shorten and re-cut the thread on the M/C plungers in order for the brake pedal to sit upright when at rest (otherwise I would not
have had enough legroom.) Whether this has had any bearing on the m/c's not working properly?
How did others with twin M/C's successfully fill and bleed their brake system for the first time?
Any suggestions appreciated.
Andy.
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twybrow
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| posted on 2/10/07 at 03:58 PM |
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I have not driven it yet, but from playing in the garage, it feels very firm. When full of air, my pedal would drop a good few inches, with little
resistance. Since bleeding, it cant move more than about 3" in total.
I did them with one of those 'easibleed one man' kits. I had to do everywhere twice as I actually ended up swapping the two MCs around. I
only got through about ~500ml of fluid in total.
Are any of the fittings leaking? did you try to do each MC sepearatley or both together? Can you isolate each one and check?
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JAG
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| posted on 2/10/07 at 04:08 PM |
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It's the rear calipers.
Push the pistons in (needs a special tool) and GENTLY pump them out whilst rebleeding. Also tap the caliper all over the hydraulic housing with a soft
faced hammer. If you repeat this several times over you will eventually get a good, hard, short travel brake pedal.
The handbrake mechanism inside the caliper sits in the brake fluid and traps very small air bubbles all over itself. Needless to say it makes them
very difficult to bleed fully.
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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RazMan
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| posted on 2/10/07 at 04:27 PM |
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I have never had good results when I use my Eezibleed system and I suspect you may be getting the same problem. Try a conventional bleed with the help
of a second pair of hands (or foot in fact  ) Air can get trapped in the m/c and you need to pump them through their entire stroke to release it.
You also mention that you shortened the m/c rods - are they at 90 degrees to the pedal pivot point when all the slack is taken out? If they are
going over centre then you will reduce the mechanical lever advantage considerably.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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Mal
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| posted on 2/10/07 at 04:32 PM |
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Brake Bleeding
1. Have you set the bias to roughly in the central position?
2. When you press the brake pedal with the bleed screws open can you get the full travel of the pistons in the master cylinders?
3. Are you bleeding a front and rear cylinder at the same time? If not, as the one circuit develops pressure it will restrict the travel of the other
circuit being bled.
HTH
Mal
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BenB
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| posted on 2/10/07 at 04:47 PM |
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Pedal going to the bulkhead means something is wrong!!! You might have to press harder than normal in a non-servo car but the pedal shouldn't
move too far.
I've got a pretty identical set-up and yes, bleeding the brakes is a PITA!!! IT didn't help that my bias bar was long and consequently
catching on the edge of the pedal box (therefore only one MC was being compressed). Difficult to check when using the foot to press the pedal, I only
realised when I did so by hand.
I used 1L of brake fluid to fully bleed it. Tapping the calipers when bleeding helps to get rid of little air bubbles.
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britishtrident
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| posted on 3/10/07 at 07:40 AM |
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As already mentioned you need to pump the pedal at some point when bleeding even when using an easy bleed or vacuum bleeder.
Also the rear caliper bleeding problem is well known.
However in your case you may also find you have a slight fluid leak somewhere.
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