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Brake bleeding question.

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gphackney Avatar
gphackney Silver Member Gregory Hackney
West Linn, OR, USA   USA
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1969 MG MGB GT "FrankenGT"
1969 MG MGB GT "Betty"
I had brake work done on my wife's B a while ago.
It definitely was better, but never seemed quite as good as it should be.

I decided to try bleeding the brakes.
I bought a harbor Freight Pneumatic Brake Fluid Bleeder.
http://www.harborfreight.com/brake-fluid-bleeder-92924.html
It seemed to get decent reviews. The refill bottle didn't fit between
the Master Cylinder reservoir and the hood, so I enlisted the help
of my lovely assistant.

I started on the left side rear. There seemed to be a lot of air
bubbles for a very long time. I thought that perhaps the
fitting on the bleeder did not make a good seal on the bleed nipple.

It's been a long time since I bled brakes, but I don't remember
it taking that long to clear a line.

My lovely assistant reported that she had used about a third
of a 500ml bottle of fluid (Moss 220-400 Lockheed Brake Fluid)
to keep the reservoir filled. The bottle on the bleeder has about
half that much.

On the right rear. Lot of bubbles to start, but cleared much
faster. Right front took longer than the right rear but not
nearly as long left rear. Left front cleared fairly quickly.

In the end, my lovely assistant had use 2/3 of a 500ml bottle.
The bleeder bottle looked to me to have about half that amount.
The fluid in the bleeder bottle has quite a bit of crud in it.

Since it is her car, my lovely assistant took it for a test
drive and reported that the brakes seem to be about 30-40% better.

Questions:
Is this a case of the shop not bleeding the brakes or doing a half-assed job of it?
Should I be looking for some other problem?
Is the crude in the fluid indicative of something?

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Jim K Avatar
Jim K James A. Krasnansky
Liberty, KY, USA   USA
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1970 MG MGB GT "Chloe"
1971 MG MGB GT "Roscoe"
1972 MG MGB "Camilla"
Wow.

I think you have the answer. Not that hard to do, especially when you have a lovely assistant.

Personally, I never let any "automotive technician" touch my MG's.



Jim K is a grease-stained wretch

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ghnl Avatar
ghnl Eric Russell
Mebane, NC, USA   USA
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1961 MG MGA "Calvin"
IME, the rear brake cylinders can be difficult to bleed because the fluid enters so close to the bleeder. The inside of the cylinder can have air trapped that doesn't get pushed out.

And, are the bleeders for the front calipers facing upwards? The calipers can be installed upside down (bleeders facing down) and the fronts will never be properly bled.



Eric Russell ~ Mebane, NC
1961 MGA #61, 1981 Alfa Romeo GTV6, 1984 Alfa Romeo Spider, 1991 Honda ST1100

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gphackney Avatar
gphackney Silver Member Gregory Hackney
West Linn, OR, USA   USA
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1969 MG MGB GT "FrankenGT"
1969 MG MGB GT "Betty"
So can the brakes work at all with 150ml of air in the lines?

Is the amount of crude in the bled fluid indicative of a problem?

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Jim K Avatar
Jim K James A. Krasnansky
Liberty, KY, USA   USA
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1970 MG MGB GT "Chloe"
1971 MG MGB GT "Roscoe"
1972 MG MGB "Camilla"
No air in brake lines. That's the whole point of bleeding them. What you MIGHT have had is air in one circuit. But what you describe, I don't think so. If your brakes worked at all, you were just lucky.

Not sure about what you mean in your second comment.



Jim K is a grease-stained wretch

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gphackney Avatar
gphackney Silver Member Gregory Hackney
West Linn, OR, USA   USA
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1969 MG MGB GT "FrankenGT"
1969 MG MGB GT "Betty"
OK, so lets back up.
We put in 2/3 of a 500ml bottle of fluid.
I extracted about half that.

My math indicates that we replaced 1/3 of 500ml in the lines that was not fluid.
Must be air.

That means there was 150ml of air in the lines.
Will the brakes work at all with that much air in the lines?
If so, I'm surprised.

I don't remember the fluid coming out so dirty the last time I bled brakes.
Of course that was more than 30 years ago, so my memory may be wrong.

Is dirty fluid indicative of another problem?

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Fairfield, CA, USA   USA
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My procedure is to inject fluid at the brake cylinder, forcing air up into the master. I use a 60 ml syringe, available at farm/vet supply/ebay. (about 25 of them for $12 or so awhile back, and they've been used for a huge number of different purposes by me and the 3-4 folks I gave some to).

It takes about 2 syringes full to clear the line from the rear. Less from calipers in front. Your LA has to keep tabs on the master and remove the excess (another syringe works for that).

I found that the fitting HF included in their kit that was supposed to fit onto the bleed fitting was fine, hooked up the plastic hose from syringe to it and it was great.

This procedure is ignored by most, including a friend who actually did it with me. But...genius is not usually recognized while life remains.<G>

(works even better for bleeding clutch)



1973 Pale Primrose Roadster. A nice 10-footer!
SUs, Datsun 5-speed

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jjonns74 Avatar
jjonns74 Gold Member John Dailey
Indianapolis, IN, USA   USA
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1974 MG MGB "Athena"
1974 MG MGB "Apollo"
X2 for Mac's reverse fill method (with an added tip)

Do Driver Rear first. GO SLOW - give the air bubbles some time to work their way up to the MC.

TIP: Leave pump connected to Driver Rear (bleed valve open), open Passenger Rear bleed valve & just bleed other 3 feet of rear line. Rear done.

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tomkatb Avatar
tomkatb Larry Baygents
Dayton, Ohio, USA   USA
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1963 MG MGB
In a fifty year old car it is common to have multiple items that need replacement. If any of the components are more than ten years old almost anything is possible. If I open the hydraulic system I like to replace a lot of stuff.

Difficulty bleeding is often just another worn out item you did not replace.

Brakes should be flushed every three years. Minor crap is then removed. I buy a quart and a pint to do it. Castrol LMA is the same fluid. Available at "European". Car parts places. Your fluid should look clean!

Can we assume you did step one, adjust the rear brakes. Makes a difference.

Bled the system again. You might get lucky.

Brake bleeding systems are hit and miss. I have had no luck with vacuum bleeders. My wife is trained. I also own a Motive power bleeder that is easy.



L.W.(Larry)Baygents
63B
77 Spit

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HiPowerShooter Avatar
HiPowerShooter James Booker
Lake Winneconne, WI, USA   USA
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1973 MG MGB
I've used the "reverse bleed" method as well on both the clutch and brake. I also have one of the pneumatic bleeders from HFT. I found that I could use both and be very successful as long as I was careful not cracking the bleeder too much. Rather than a syringe I used an old oil can which I cleaned out and filled with brake fluid. It was an old, metal type...very sturdy...but did the job well.



"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...

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ghnl Avatar
ghnl Eric Russell
Mebane, NC, USA   USA
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1961 MG MGA "Calvin"
In reply to # 2974033 by gphackney So can the brakes work at all with 150ml of air in the lines?

Seems unlikely. How much fluid was in the reservoir before vs after. That could account for much of the difference.

Quote: Is the amount of crude in the bled fluid indicative of a problem?

It could indicate very old fluid, break down of the rubber seals or contamination with an incompatable fluid (petroleum based oil or even DOT5 sliicone brake fluid) or water (brake fluid is hygroscopic - it absorbs H2O even right out of the air).



Eric Russell ~ Mebane, NC
1961 MGA #61, 1981 Alfa Romeo GTV6, 1984 Alfa Romeo Spider, 1991 Honda ST1100

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gphackney Avatar
gphackney Silver Member Gregory Hackney
West Linn, OR, USA   USA
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1969 MG MGB GT "FrankenGT"
1969 MG MGB GT "Betty"
In reply to # 2973912 by ghnl IME, the rear brake cylinders can be difficult to bleed because the fluid enters so close to the bleeder. The inside of the cylinder can have air trapped that doesn't get pushed out.

And, are the bleeders for the front calipers facing upwards? The calipers can be installed upside down (bleeders facing down) and the fronts will never be properly bled.
Air in the rear brake cylinders would explain the weakness.
The bleeders on the front calibers are facing upwards.

In reply to # 2974178 by ghnl
In reply to # 2974033 by gphackney So can the brakes work at all with 150ml of air in the lines?

Seems unlikely. How much fluid was in the reservoir before vs after. That could account for much of the difference.
That is what I thought. So maybe I opened the bleed nipples to much, or the bleeder attachment didn't seal well.
There was more in the reservoir after bleeding.

In reply to # 2974178 by ghnl
Quote: Is the amount of crude in the bled fluid indicative of a problem?

It could indicate very old fluid, break down of the rubber seals or contamination with an incompatable fluid (petroleum based oil or even DOT5 sliicone brake fluid) or water (brake fluid is hygroscopic - it absorbs H2O even right out of the air).
OK. More things to check.

In reply to # 2974137 by tomkatb In a fifty year old car it is common to have multiple items that need replacement. If any of the components are more than ten years old almost anything is possible. If I open the hydraulic system I like to replace a lot of stuff.

Difficulty bleeding is often just another worn out item you did not replace.
Good point. I have no idea how old the MC is. Maybe I should replace that and
anything else I can get too.

In reply to # 2974137 by tomkatb Brakes should be flushed every three years. Minor crap is then removed. I buy a quart and a pint to do it. Castrol LMA is the same fluid. Available at "European". Car parts places. Your fluid should look clean!

Can we assume you did step one, adjust the rear brakes. Makes a difference.

Bled the system again. You might get lucky.

Brake bleeding systems are hit and miss. I have had no luck with vacuum bleeders. My wife is trained. I also own a Motive power bleeder that is easy.
I've owned the car for less than a year, so I have no idea when the last
time the brake system was flushed. To flush it, do I just run more fluid
through it? I have another 500ml bottle.


Thanks to everyone that answered.

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tomkatb Avatar
tomkatb Larry Baygents
Dayton, Ohio, USA   USA
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1963 MG MGB
If you fluid looks crappy then it has Been a long time.

500 ml is more than enough to flush. Bleeding a system usually takes more fluid. The wife and I do it easily. 33 years of practice. The Motive power bleeder is great, however the cleanup is a pain.

LR, RR, LF, & RF. fluid should be clear.

I give the commands, down, she responds down, up, up. Etc. as I open and close the bleeder. I do not need to remind her not to bury the pedal or fill the master.

No need to lift the car. It is easier with all four wheels off. Takes longer.



L.W.(Larry)Baygents
63B
77 Spit

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