All I get is air when bleeding the rear brakes. : MGB & GT Forum : The MG Experience

All I get is air when bleeding the rear brakes. #1
fixingmymomscar Evan D Rutherford, NJ, USA Sign in to contact 1979 MG MGB	Topic Creator (OP) May 29, 2015 09:28 PM Joined 8 years ago 188 Posts

I tried bleeding the rear brakes on the '79 B for fifteen minutes of having my helper press the brake, I open the bleeder, close and release. Every time I opened the bleeder, it was just air. I took the plastic line off to make sure something was coming out, and it's just air. It makes a release noise, so I can tell the brake is working to push stuff out, but the rear brakes just will not show any fluid. I don't know if there's just a lot lot lot of air in the lines, but I think it would have come out with the amount of bleeding I was doing. What could make this happen?

Also, the wheel cylinders and flexible line is brand new, and the front brakes bled perfectly.

Edited 3 time(s). Last edit at 2015-05-29 09:30 PM by fixingmymomscar.

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Re: All I get is air when bleeding the rear brakes. #2
Ex-Calif Dan D Dayton, OH, USA Sign in to contact 1968 MG MGB GT "Bart - Yellow And Naughty" 1977 MG MGB "Red Betty" 2006 Suzuki Grand Vitara "Suzi Q" 2012 Jeep Liberty "Tommy The Tank"	May 29, 2015 09:42 PM Joined 8 years ago 8,992 Posts

I did mine (77B) last week and it went fine using the procedure you describe.

Is the fluid level going down in the reservoir? If so keep bleeding (and topping up the reservoir).

Was the system emptied? i.e. Why are you bleeding them? Replacement of master cylinder or something else?

The goal - Reliable summer driver interspersed with mechanical tinkering...
Motto - "Driving fifty in the twisties..."
On Mods - It's your damn car - Do what you want. Haters gonna hate...
On SUVs - Drive your B like a soccer mom is texting her friends about how she wants to kill you...
Red Betty - http://www.mgexp.com/registry/GHN5UH418165
Bart - http://www.mgexp.com/registry/GHD4U146898G

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Re: All I get is air when bleeding the rear brakes. #3
rntanner Roger N. Tanner (Disabled) Oxnard, CA, USA Sign in to contact 1970 MG MGB 1977 MG MGB	May 29, 2015 09:52 PM Joined 15 years ago 4,348 Posts

Assuming your Master Cylinder reservoir is full, you should be able to bleed the brakes:

1) Have a helper open the bleed screw on the most distant (left rear) wheel cylinder, open the bleed screw and "you" push the brake pedal to the floor.....stop...hold the brake pedal down until the next step is completed.

2) Helper close bleed screw on the wheel cylinder.

3) Repeat (1) and (2) until you get nothing but clear brake fluid from the wheel cylinder. Some will find it easier to see just clear brake fluid if a 12 inch ..or so...piece of clear vinyl tubing that fits tightly on the "opened" bleed screw, shows nothing but brake fluid. Close the bleed screw.

4) Repeat on right rear wheel cylinder-Repeat (2) after pedal is pushed down

5) Repeat on right front caliper.Repeat (2) after pedal is pushed down

6) Repeat on the left front caliper Repeat (2) after pedal is pushed down

Roger N. Tanner
Professional Engineer, Retired

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Re: All I get is air when bleeding the rear brakes. #4
fixingmymomscar Evan D Rutherford, NJ, USA Sign in to contact 1979 MG MGB	Topic Creator (OP) May 29, 2015 09:57 PM Joined 8 years ago 188 Posts

Thanks guys. The car was sat in the garage for ten years, I'm just fixing it up now. The master cylinder was completely full when it was put up, but emptied a bit when I put the new flexible lines in. I filled it back up. Now that I think about it, not alot of fluid came out when I replaced the wheel cylinders. Daniel, I'm bleeding them because of the new lines and cylinders, and cause the sitting brake fluid was very dirty, though it was crystal clear in the master cylinder. I did every step just like that Roger, but I'm just getting air.

Edited 3 time(s). Last edit at 2015-05-29 09:58 PM by fixingmymomscar.

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Re: All I get is air when bleeding the rear brakes. #5
curtis7420 Curtis Wright University City, MO, USA Sign in to contact 1975 MG MGB "The "B" 2003 Toyota Highlander 4WD 2010 Jeep Wrangler	May 29, 2015 10:11 PM Joined 13 years ago 4,032 Posts

well, the fact that you're getting air would cancel out a crushed brake line, which was gonna be a guess of mine. also, the cylinders have been replaced, which would be my other guess.

as other's have stated, keep trying. maybe use a syringe to pull the fluid through? you can also get a bleeder from Autozone or Advance Auto Parts through their tool loaner program.

good luck

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Re: All I get is air when bleeding the rear brakes. #6
Ex-Calif Dan D Dayton, OH, USA Sign in to contact 1968 MG MGB GT "Bart - Yellow And Naughty" 1977 MG MGB "Red Betty" 2006 Suzuki Grand Vitara "Suzi Q" 2012 Jeep Liberty "Tommy The Tank"	May 29, 2015 10:35 PM Joined 8 years ago 8,992 Posts

In reply to # 2999709 by fixingmymomscar Daniel, I'm bleeding them because of the new lines and cylinders, and cause the sitting brake fluid was very dirty, though it was crystal clear in the master cylinder. I did every step just like that Roger, but I'm just getting air.

You still didn't mention if the fluid level is going down while bleeding rear and getting air. If the fluid level is not going down - double check all the connections on the rear lines for tightness - you may have a loose one. If the nuts are all tight we may have to suspect the master cylinder or try pressure bleeding fro the bottom up.

If the fluid level is going down keep replenishing and bleeding - that's progress.

The goal - Reliable summer driver interspersed with mechanical tinkering...
Motto - "Driving fifty in the twisties..."
On Mods - It's your damn car - Do what you want. Haters gonna hate...
On SUVs - Drive your B like a soccer mom is texting her friends about how she wants to kill you...
Red Betty - http://www.mgexp.com/registry/GHN5UH418165
Bart - http://www.mgexp.com/registry/GHD4U146898G

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Re: All I get is air when bleeding the rear brakes. #7
fixingmymomscar Evan D Rutherford, NJ, USA Sign in to contact 1979 MG MGB	Topic Creator (OP) May 29, 2015 10:36 PM Joined 8 years ago 188 Posts

You're right Daniel, I didn't even check whether the fluid level had gone down. Guess I'll find out tomorrow.

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Re: All I get is air when bleeding the rear brakes. #8
freetors Nick H Collinsville, OK, USA Sign in to contact 1973 MG MGB	May 29, 2015 11:12 PM Joined 11 years ago 214 Posts

After just replacing my master cylinder and having this exact same problem, I finally bled them after much head scratching. I drained the system first so it was an essentially dry system. I had to use my vacuum pump on one of the wheel cylinders to get fluid to flow. Having a very good seal around the bleeder threads is essential for this, I use Loctite 567. After hitting it with vacuum, both wheel cylinders bled out normally.

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Re: All I get is air when bleeding the rear brakes. #9
Wayno Wayne Lueth Vancouver, WA, USA Sign in to contact	May 29, 2015 11:34 PM Joined 9 years ago 434 Posts

You need to confirm that you have fluid in the rear reservoir circuit.

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Re: All I get is air when bleeding the rear brakes. #10
Basil Adams About 12 miles from Sears Point, CA, USA Sign in to contact	May 30, 2015 12:39 AM Top Contributor Joined 17 years ago 12,276 Posts

Remove the brak failure switch and re center the shuttle valve. It ounds like it it tripped and no fluid is getting to the rear brakes at all. Best of luck. Basil 707.762.0974 basiladams@yahoo.com

Basil C. Adams
1956 MGA Coupe (Show Car)
1957 MGA Roadster (Driver)
1958 MGA Coupe (Racecar)
1959 MGA Coupe (unrestored)
1960 MGA Coupe (unrestored)
1960 MGA Roadster (Driver)
MKIII Elva Courier (E1056)
1967 427 Cobra
1972 Alfa Romeo Montreal
A coupla late MGBs
1960 Austin Healy BN7
More Cars than Brains

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Re: All I get is air when bleeding the rear brakes. #11
newmgbdan Dana Yingling Mechanicsburg, PA, USA Sign in to contact 1979 MG MGB	May 30, 2015 06:35 AM Joined 13 years ago 428 Posts

When I replaced the rubber line and new rear wheel cylinders, I could not bleed them. Went to my local foreign car repair shop, they had to use a vacuum pump to get the air out.

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Re: All I get is air when bleeding the rear brakes. #12
2150john John L Nolensville, TN, USA Sign in to contact 1974 MG MGB MkIII	May 30, 2015 06:44 AM Joined 12 years ago 468 Posts

I'd try Basil's suggestion first. Common problem... although the fact that you are getting air contraindicates that. If that doesn't work then try vacuum.

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Re: All I get is air when bleeding the rear brakes. #13
flash75 Clifton G Summerfield, FL, USA Sign in to contact	May 30, 2015 01:06 PM Joined 17 years ago 3,094 Posts

The brake failure switch for a 97 is on the master cylinder. I think the shop manual calls
for loosening the failure switch 3 1/2 turns to bleed the rear brakes. It worked years ago
for someone in a club I used to attend.

The type shuttle valve that is located under the master cylinder in earlier cars does not need
to be centered to bleed the brakes. Moving it either direction does not block fluid flow. It can
move in either direction dependent on whether a leak or problem is (front or rear). If you
recall the master cylinder for those cars has a divider in the reservoir to keep the fluid in the
good circuit.

Clifton

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Re: All I get is air when bleeding the rear brakes. #14
Nicecar Gary (ex "Harv") G Victoria, BC, Canada Sign in to contact 1980 MG MGB "Red On Red On Red"	May 30, 2015 01:20 PM Joined 13 years ago 8,390 Posts

#3 "Have a helper open the bleed screw on the most distant (left rear) wheel cylinder"

I've heard this before and am confused by it. As MC is on left side, in my mind the farthest away is right side rear, but nobody has corrected Roger.

???

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Re: All I get is air when bleeding the rear brakes. #15
forestghost07 Marco Sinai FL, USA Sign in to contact 1972 MG MGB GT "Viajero" 1999 Chevrolet Blazer "Works For Gas"	May 30, 2015 01:35 PM Joined 12 years ago 4,174 Posts

In reply to # 3000112 by Nicecar #3 "Have a helper open the bleed screw on the most distant (left rear) wheel cylinder"

I've heard this before and am confused by it. As MC is on left side, in my mind the farthest away is right side rear, but nobody has corrected Roger.

???

The length of piping makes the L/R brake furthest away; remember it's fitted more to the pass. side and traverses the axle.

~ Marco and Viajero ~

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All I get is air when bleeding the rear brakes.

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