dmottaway
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| posted on 29/10/06 at 08:41 PM |
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OT/bleeding brakes
basic question about bleeding brakes. if you remove both the master cylinder resevoir cap and a bleed screw at a wheel cylinder, should the fluid
flow freely though due to gravity?
The situation: 1957 Nash Metropolitan (aka Austin Metropolitan) recently (6 months, about 100 miles ago) had its brakes serviced. Take it out for
its semi-annual spin through the neighborhood and find its has NO brakes.
Check the resevoir and find it is dry! Top it up to commence bleeding. I attach my "one man bleeding tool (hand powered vacuum pump) and
cannot draw any fluid at all through the first wheel cylinder. So, I take the bleed screw completely out, figuring it would just drain through.
NOPE.
Does this sound like the line may be clogged. or maybe the master cylinder is dead? or what?
Shop that did the recent service now says they only worked on the rear brakes. Those are the ones that have brake fluid trails on the tires(!) and
not the fronts. Now they want us to bring it in again (more$), but we need to make it driveable, first. at least basically.
So, the big question is: does the master cylinder sound bad, or is my inability to draw fluid though by vacuum "normal."
If it is normal, then the tool is worthless. Oh well.
tia
dave
Somewhere, in Texas, a village is missing its idiot.
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stevec
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| posted on 29/10/06 at 08:59 PM |
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First question is where has the fluid gone?
Fill the res and put the nipples back in,
Undo the furthest nipple from the Mcylinder quater turn and slowly pump the pedal and the fluid should come through, when it does flow with no air in
the fluid hold pedal down and tighten the nipple, repeat for all corners,
Keep the res full at all times. If you get a pedal put pressure on and look for a leak.
Steve.
[Edited on 29/10/06 by stevec]
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nitram38
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| posted on 29/10/06 at 09:02 PM |
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Also check that the master cylinder piston is returning as your inability to draw fluid could indicate that the piston is sticking.
[Edited on 29/10/2006 by nitram38]
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lexi
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| posted on 29/10/06 at 09:02 PM |
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If car has been lying up then brake lines could have crud in them from bottom of dirty old master cylinder. It sounds like you may have to overhaul
system. First off did you press pedal with bleed nipple off? Dont press it more than an inch or two. Does any fluid come out?
Rubber flexi houses could be defective, collapsed inside and blocked or kinked. wheel cylinders may be rusted seized solid. Can you bleed rear
brakes with pressing of pedal if so then MC may be OK
When using old fashioned method of pressing brake pedal with bleed nipples open DO NOT press pedal to floor as it will take sealing rubber past any
ridge in metal cylinder causing damage to seal. If no joy I would strip MC for a look at seals
Alex
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mookaloid
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| posted on 29/10/06 at 09:04 PM |
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I have always had good success using one of
these
Cheers
Mark
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oliwb
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| posted on 29/10/06 at 09:05 PM |
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An old trick for bleeding brakes is to remove the reservoir cap and undo the bleed nipple a little.....put a bit of pipe or similar to jam the brake
pedal hard down against the bulkhead and wedge it like this against the seat....leave it over night and then finish bleeding it the conventional
way....not too sure of the physics behind this but can confirm it does work on a '79 series 3 landrover! Oli.
If your not living life on the edge you're taking up too much room!
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Peteff
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| posted on 29/10/06 at 09:59 PM |
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Put some fluid in a jar, slacken your bleed nipple and put a tube on with the other end in the jar of fluid, get someone to pump the pedal while you
watch the jar for bubbles. Keep the M/C topped up and lock the nipple off with the pedal still pressed down.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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mark chandler
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| posted on 29/10/06 at 10:27 PM |
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To answer the original question, even without removing the master cylinder cap the fluid should gradually drain due to gravity.
If the master cyinder is empty then you must have a leak at a lower point in the system or the seals have gone in this item in which case you may have
a wet pedal.
Brake bleeders that draw fluid from the axle ends work well, although it can be hard to identify if its pulling air as this leaks around the nipple
threads. Sometimes you have to remove the bleed nipple, grease the threads with copper ease and screw back to stop this.
Regards Mark
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dmottaway
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| posted on 30/10/06 at 01:06 AM |
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thanx Mark and Nitram, these are the answers I was looking for. confident in my ability to do the job, just needed confiming that I was
experiencing a problem.
So, next I will be taking out the master cylinder. Oh, joy. It is under the floor beneath the driver. and so is the clutch master cylinder.
answer to an early question - the car is parked over a "drip pan" (mostly engine area) and it appears that most of the fluid is in this
pan. Some of it, however, appears to have run down the insides of the rear tires (leaky wheel cylinders) and these are the brakes the shop was
supposed to have serviced!
Now for a truly obscure question - anybody know what master cylinder is suitable? Parts people around here depend far too much on their computers and
have not even heard of Nash, or Austin, or Metropolitan. There can't be that many variations in master cylinders in 1957. The car was built in
England, by Austin, and probably used something that was also used in other cars.
Any Ideas???
tia
dave
[Edited on 30/10/06 by dmottaway]
Somewhere, in Texas, a village is missing its idiot.
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britishtrident
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| posted on 30/10/06 at 03:39 PM |
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If memory serves me correctly this car has a Lockheed system similar to the later Austin A30 , A35 and Frogeye Sprite. Knowing these systems from your
descrition the odds are you have a leaking wheel cylinder, look for wet brake back plates.
As to bleeding Lockheed master cylinder of this period are really easy to bleed just do it the old fashioned way by ---s-l-o-w-l-y pumping the pedal
with one nipple at a time open, lose the nipple with the pedal held down to the floor.
When bleeding any brake system even with a pressure or vacum bleeder it is really really important to pump the pedal a few times or else the master
cylinder won't get primed.
If you must use some kind of bleed tool use a pressure bleeder that put the pressure head onto the mastercylinder resevoir -- ie Gunson EaziBleed
[Edited on 30/10/06 by britishtrident]
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lexi
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| posted on 31/10/06 at 12:20 AM |
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Obviously my references to NOT pumping brake pedal to floor do not apply to a new M/C as there is no wear ridge on it.
Not so much a prob damaging a seal with a Girling or Lockheed as repair kits are cheap.........But Jap ones aint.........if you can get them.
Alex
[Edited on 31/10/06 by lexi]
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britishtrident
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| posted on 31/10/06 at 08:15 AM |
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Very important Pedal always MUST be pushed all the way down, pushed down slowly and returned very slowly.
quote]Originally posted by lexi
Obviously my references to NOT pumping brake pedal to floor do not apply to a new M/C as there is no wear ridge on it.
Not so much a prob damaging a seal with a Girling or Lockheed as repair kits are cheap.........But Jap ones aint.........if you can get them.
Alex
[Edited on 31/10/06 by lexi]
[Edited on 31/10/06 by britishtrident]
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lexi
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| posted on 1/11/06 at 05:24 PM |
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quote:
Originally posted by britishtrident
Very important Pedal always MUST be pushed all the way down, pushed down slowly and returned very slowly.
I think that is a disagreement then Andy. The way you describe is the way I did it for years. This other method I have used since taking the
advice of Car Mechanics mag and I know that I have destroyed one in the past by going past the ridge. I think a lot of these auto bleeding devices are
to overcome the dangers of pedal bleeding as well as being time savers.
Alex
quote]Originally posted by lexi
Obviously my references to NOT pumping brake pedal to floor do not apply to a new M/C as there is no wear ridge on it.
Not so much a prob damaging a seal with a Girling or Lockheed as repair kits are cheap.........But Jap ones aint.........if you can get them.
Alex
[Edited on 31/10/06 by lexi]
[Edited on 31/10/06 by britishtrident]
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britishtrident
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| posted on 1/11/06 at 06:32 PM |
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Just to point out you will never get a distinct wear ridge on a drum brake master cylinder as the postion the piston stops moves all the time as the
shoes wear.
With a brake master cylinder on car with disc brakes any wear ridge is at start of the piston travel, which kind of disproves the theory.
Take anything written in that particular magazine with a very very large pinch of salt as they come away with some real howlers such as on an article
on Rover 800s they insisted Rover fitted later 820 with 2 litre 4 cylinder k series engines when of course a 2 litre K series just dosen't
exist and the only KV6 engined fitted to the 800 was the early version of 2.5.
Seals in Teves (ATE) master cylinders can be damaged by incorrect bleed -- the pedal must be very pumped slowly to avoid seal reversal on the up
stroke. Teves cylinders are best bled by pressure bleeding from the top -- but even them the pedal must be pumped through full stroke at some point,
the extra posative pressure keeps the seals expanded and in full contact with the bore on the return stroke.
[Edited on 1/11/06 by britishtrident]
[Edited on 1/11/06 by britishtrident]
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lexi
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| posted on 1/11/06 at 11:43 PM |
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Good stuff Andy.
Alex
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