Problem bleeding rebuilt brakes

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MilesnMiles
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Joined: Fri Nov 04, 05 8:40 pm
Location: Cornwall

Problem bleeding rebuilt brakes

Post by MilesnMiles »

After my brake system failed last year I rebuilt all 4 drum corners with new cylinders and a new bench bled master cylinder. Me and a mate started to bleed the system, got half way through (he’s a busy guy) bleeding and then Lockdown happened.
Three months pass and I tried to gravity bleed today. However, when I inspected the MC before starting I found it had emptied. How or where I don’t know as everything is new and tight and no leaks apparent.
I then filled the MC and tried gravity bleeding with no luck, almost nothing comes out.
Am I going to have to remove the MC and bench bleed it again?
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Dave999
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Re: Problem bleeding rebuilt brakes

Post by Dave999 »

probably


but what was in there probably replaced AIR trapped in the pipes.


fill it up
open farthest bleed nipple just a smidge i.e manufacture just a small leak at the nipple
Pump it through
repeat for the other 3, you want that old stuff out

no luck....
loosen the connectors slightly at the T fitting on the axle and pump some out there
do the same at the master cylinder connectors
the Knack is to nip them up while still flowing before the pumpee lets the peddle back up

then bench bleed the master if you need to

the other method
replace nipple with a Grease fitting that has had the ball picked/pushed/hammerd from the other end, out, and pump it in with a big plastic syringe and plastic pipe.... from the wrong end

https://www.ebay.co.uk/itm/300ML-Large- ... %3A2334524


last but not least

buy a mityvac vacuum bleeder
ignore the distructions and again use a modified nipple like a grease fitting i.e one that doesn't leak via the threads once loose

if you use the orginal you will need to tape up the threads so the air can't just suck in down the threads and out again via the nipple

obviously remove and replace with real nipple when done while someone very slowly compresses the peddle or at least holds it still, semi compressed

easier to use a mityvac single handedly, if you tape the gun the little vacuum pot with the syphon tube etc to a flat bit of wood with reams of duct tape... build some kind of stand for the thing you need 6 hands otherwise

stops the pot falling over every time you touch the vacuum gun

handy for testing vacuum advance as well avoids you inhaling vacuum advance breath as you suck on the pipe

basically they bleed up fine and you get hard peddle on the attempt After you nearly smashed the car to bits with a big hammer

Dave
The Greater Knapweed near the Mugwort by the Buckthorn tree is dying
MilesnMiles
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Joined: Fri Nov 04, 05 8:40 pm
Location: Cornwall

Re: Problem bleeding rebuilt brakes

Post by MilesnMiles »

Thanks Dave, plenty to think about there. I do have a vac pump, need to check if I still have the little cup thingy for it.

Hers a thought on the M/C. Maybe it wasn’t fully bench bled correctly by me.
So....with the MC still fitted to the car I figured I could redo the exercise, but with a syringe. Undo the one brake pipe, sqirt fluid up into the MC until air stops. Plug the port with the plastic fitting that came with the MC. If I’ve done it correctly I should get full pedal pressure, right?
If so, then I turn my attention to the rest of the bleeding process. This way I’d know the MCis not the issue, right?
The big hammer is already on hand💀😉
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Blue
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Re: Problem bleeding rebuilt brakes

Post by Blue »

No, you don’t get a full stroke on the master cyl when it’s attached to the pedal. That’s why you bench bleed and bottom the piston so there’s no air getting trapped under the piston.
“This ain’t no party, this ain’t no disco, this ain’t no foolin’ around”
MilesnMiles
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Re: Problem bleeding rebuilt brakes

Post by MilesnMiles »

Thing is Blue, when I read the odd 1,000 posts on bench bleeding there’s always the school of thought that says by using too much of a pushrod stroke on the bench it can damage the seals inside the MC. No one seems to agree.
The idea of removing air via syringe came from Leeds Brakes who recommended it on their site.
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Blue
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Re: Problem bleeding rebuilt brakes

Post by Blue »

Can’t see how it can damage the seals, both ports are open so you are generating very little actual pressure. The syringe method might well do the trick, never had cause to try it.
“This ain’t no party, this ain’t no disco, this ain’t no foolin’ around”
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MattH
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Re: Problem bleeding rebuilt brakes

Post by MattH »

If it is drums all round, possibly adjust them right up to locked.
Land Rovers are good for this, it's not trapped air but excess pedal travel, or the pedal travel prevents pushing the air out.
Remove the ability for wheel cylinders to move by adjusting up the brakes, then try bleeding.
Triumphs are similar, in that the handbrake holds the wheel cylinder away and you get too much play when trying to bleed, so you have to disconnect handbrake to ensure the cylinders are properly in contact with the shoes.
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MilesnMiles
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Re: Problem bleeding rebuilt brakes

Post by MilesnMiles »

Good points there Matt, thanks. I’ve left the handbrake off, but don’t recall tightening up the adjusters beyond where they’re we’re before. I’ll nip them up and try again. Now you mention it I recall replacing a wheel cylinder before and having a floppy pedal until adjusted up.
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MattH
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Re: Problem bleeding rebuilt brakes

Post by MattH »

MilesnMiles wrote: Thu Mar 11, 21 1:20 pm Good points there Matt, thanks. I’ve left the handbrake off, but don’t recall tightening up the adjusters beyond where they’re we’re before. I’ll nip them up and try again. Now you mention it I recall replacing a wheel cylinder before and having a floppy pedal until adjusted up.
It took us days of bleeding the Land rover to sort it, it was all down to too much adjustment on the shoes. Pedal needed two pumps all the time just to get the slack out when driving, so if the cylinder is moving it is less likely to push the trapped air through.
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mygasser
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Re: Problem bleeding rebuilt brakes

Post by mygasser »

as dave suggested i also use a mitivac vacuum bleeder as it's a 1 man job.
they are bloody dear these days though but luckily there are cheaper copies like this https://www.ebay.co.uk/itm/Car-Hand-Hel ... SwUldgHQuI
rather than swapping the bleed nipples for something else i remove them and smear grease on the threads and this stops air sucking past the threads.
neil.
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