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Brake Master Cylinder Bleeding

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blue64 Avatar
blue64 Paul Hanley
Eastern Chesapeake Bay, MD, USA   USA
Greetings, I am having a bit of difficulty getting the air out of the system as I finish a full brake refurbishment. Both rear calipers and the original style master cylinder are fresh from a Whitepost rebuild. I cleaned and lubricated the known-good front calipers and replaced the pads and crossover pipes. All three hoses were renewed.


I had an assistant lend a hand bleeding but, I still have a spongy pedal. We bled LR, RR, LF, RF...twice. Though the technique may not have been perfect, we did the "open bleeder--down pedal--close bleeder--up-pedal technique, to only slight improvement over my one-man gravity bleed.


Two different local mechanics asked whether I bled the master cylinder on the bench. Was I supposed to bleed the master on the bench? I simply installed, (well, not simple but that's another story) filled and kept it topped up with DOT 3/4 during the process.

As a helpful hint: I used a fresh, clean and dry catsup squirty bottle (restaurant tech term) to refill the master, with very little spillage.


Thanks for your insights, suggestions and tips.


Paul Hanley
YD3 818

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TRex73 Avatar
TRex73 Rex DeShon
Saint Joseph, MO, USA   USA
1973 MG MGB
I used the pressure EZ bleed. But I had to buy an extra cap from eBay. I just bought the complete plastic reservoir it was like 12 bucks so I could have an extra cap since you can't buy a cap with an o-ring.

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blue64 Avatar
blue64 Paul Hanley
Eastern Chesapeake Bay, MD, USA   USA
Rex, did you find a EasyBleed cap for a Twin Cam? I have the device but cant get a hard seal on the master cylinder.

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TRex73 Avatar
TRex73 Rex DeShon
Saint Joseph, MO, USA   USA
1973 MG MGB
I just happened to be looking on eBay and found the whole plastic reservoir for my car which is an MGB 1973 maybe yours is different but try searching eBay just for the whole plastic reservoir. The whole reservoir was like 12 bucks.


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Gary E Avatar
Gary E Silver Member Gary Edwards
Kernersville, NC, USA   USA
I us a EZ bleed on my MKII and 67 MK1 MGB. The new kit may have a cap that fits my old one did not. Made the cap by removing the plastic liner on the regular cap and drilling a hole in top. I had to make a new washer for the cap as the original and rubber washers did not do the trick. I used a heavy piece of gasket material and that worked The original cap has a ridge that prevents a good seal. Years ago I made one from of a bottle top but they don't make bottles the same any more.



Gary

Hammer: Originally employed as a weapon of war, the hammer nowadays is used as a kind of divining rod to locate expensive car parts not far from the object we are trying to hit.

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blue64 Avatar
blue64 Paul Hanley
Eastern Chesapeake Bay, MD, USA   USA
Thanks Rex. I am sticking with the original Twin Cam master cylinder. I just had it rebuilt by Whitepost.

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ghnl Avatar
ghnl Silver Member Eric Russell
Mebane, NC, USA   USA
1961 MG MGA "Calvin"
Bench bleeding usually helps by making sure the master cylinder bore is full before connecting the brake line and thus being able to push only fluid (vs air & fluid) down the lines. That said, the major downside to not bench bleeding is you might need to use more brake fluid to get all the air out.

Since you have the master cylinder installed and are still having difficulty getting all the air out, you can try this: crack open the connection at the master cylinder (say 1/2 turn) and pump the pedal 2 or 3 times. Note that DOT 3 & DOT 4 brake fluid will eat away at paint so wrap the cracked open connection with a rag and have a spray bottle of soapy water handy. After the 2-3 pedal strokes, remove the rag, tighten the connection then spray the soapy water in the general vicinity to wash away any errant brake fluid.

Also try bleeding the calipers thusly: have your assistant pump the pedal a few times then hold pressure on the pedal. Now open the bleed screw. The pedal will go to the floor and the extra pressure can help encourage the trapped air to move along. It might take 2 or 3 repeats at each caliper to move trapped air to the bleeder.



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

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Blueosprey90 Avatar
Blueosprey90 Jeff Sienkiewicz
New Milford, CT, USA   USA
Billman's trick:

Wedge the brake down pedal overnight. Forces all the tiny air bubbles to the master cylinder or to the wheels. Bleed again the next day.

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bobs77vet bob K.
northern Va, VA, USA   USA
twice isnt enough....you are on the right track just keep doing it.


and yes bench bleeding is always a good thing.

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Gary E Avatar
Gary E Silver Member Gary Edwards
Kernersville, NC, USA   USA
Those all sound like really good ideas but with a ez bleed it only takes minutes to do the job.



Gary

Hammer: Originally employed as a weapon of war, the hammer nowadays is used as a kind of divining rod to locate expensive car parts not far from the object we are trying to hit.

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RoyS Avatar
RoyS Roy Sperbeck
deptford, NJ, USA   USA
You can buy a mini vac hand pump on ebay it has a brake bleeder attachment .Its best to have 2 people bleed the brakes .if you crack the bleeder with a hose on it into a container you can watch the fluid come out . A trick is to pinch each rubber hose with vice grips it the pedal is hard then you will know the problem is at one of the cyls.

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kirks-auto Platinum Member Robert Kirk
Davenport, IA, USA   USA
Speed bleeders made brake wheel bleeding a one man chore.



Regards,
Robert Kirk

kirkbrit@yahoo.com
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