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MG MGB Technical - Bleeding brakes, read archives but...

Hello all,
I hate to bring up this old problem again, but I've had no joy after reading the archives. I have a totally new (including lines) brake system on a '67.
Problem is I have a low, spongy brake pedal. Air must still be lurking somewhere.
I bled the system with the old easy-bleed, using Valvoline SynPower fluid, set parking brake to run rear shoes out, front calipers are installed on proper side. I did not bench bleed the MC.
Any suggestions, please?
Many thanks, Dave
David Steverson

Try:

raising the front of the car on stands/ramps, and bleed as normal

and/or

stamping on the pedal with engine started and without (bleed nipples closed), then bleed as normal

and/or

using the old-fashioned tube and jam-jar method - press the pedal VERY slowly

and/or

try different sequences (some books/people say front first, some say furthest first, etc)

and/or

start the engine so the remote servo gives you full travel when bleeding

One of these worked for me, but I cannot remember which. I did not 'bench bleed' the master cylinder - never ever have done on any car and don't see the point.

I've not had much luck with the Easybleed either.

Neil

Neil Lock

One trick with the eezibleed -- make sure to
use a low tire pressure of 10 PSI or even less.

I found that with the recommended max of 20 PSI,
the eezibleed would inject air bubbles into the
system.

I always bleed starting with the longest run
first (right rear) then left rear, right front,
finally left front.
Ronald

I have never been very successful at bleeding a fresh dual brake system unless I bled the M/C first at the bench. For whatever reasons, perhaps their relative complexity, I have had the same problem as you are encountering if I didnot bench bleed the M/C first before installing. If yours is a new M/C, save the caplugs that protected the outlets and once bench bled, stick those into the outlets quickly and before moving the unit to the car. They will make life a bit less messy and less chance for the bled fluid to leak out recreating the bubble internally again.
Good luck.
Bob Muenchausen

Anyone out there ever try speed bleeder? They look like the cat's meow.
Fred Horstmeyer

Thanks everyone for their input on this!
By the way, mine is the simple single line system, not the dual. I've bleed this thing 3 times over the last couple of months. It doesn't seem to be getting any better. I think I was using too much air pressure with my Easybleed.
Maybe I'll resort to manual bleeding. But, I know I've not had this problem before with other cars where I replaced the entire brake system. I just feel I'm missing something that's going to be painfully obvious.
Cheers, Dave
David Steverson

I just bled both my brake and clutch master cylinders last night. I had installed a new brake MC, and did not bench bleed. I had tried bleeding alone with a VISIBLEED, with no success, so waited until my daughter was home for semester break to help me. I started with the rear, and moved to the front. I had her pump 6 times, slowly to avoid air, hold and release. I did it in 3 bleeds per wheel in 2 seperate sets (a total of 6 bleeds). I simply attached a rubber hose and directed into a can I finished with a high pedal, using silicone fluid. I had more problem with the clutch. After finally getting good movement at the slave cylinder, after 6 attempts, I ran the cylinder dry and sucked air and had to start over again. So keep an eye on the clutch master when you bleed, it doesn't hold much and goes dry faster than the brake master. You may not have had to remove the clutch master on the earlier models, but I found no easy way to remove the brake master alone, so I had to pull both out. Good luck!
Joe

Another method that does work, if you have the time and Patience is to simply fill and keep full the resevior, and then open all the bleeder nipples (connected to hoses into jars as per standard practice), and then let gravity do the job. It takes a while, but it can lead to a very good bleed job. Perhaps it is because there is no cavitation of the fluid in the M/C or just why, but it works. You can look into the archives for more on this method. FWIW.
Bob Muenchausen

The only way I have found is to bleed normally e.g. with a gunsons which leaves a spongy pedal, then get an assistant to stand on the pedal while I rapidly open and close each front bleed nipple. With my 73 roadster and 75 V8, both single-line systems, this always gets an additional 'lump' of air out and after that the pedal is fine.
Paul Hunt

For Fred,
I put a set of speed bleeders on - fronts were OK but the rears gave me trouble. They have a coating on the threads that provides a seal when you have the bleeder loosened. The fronts (large diameter) sealed ok but the rear (small diameter) would leak air/fluid past the threads. I liked the check valve concept and they worked very well, after I added some additional sealer on the rear units.
John Zeiler

I am with Joe. I used the almost identical technique, except that I used glass mason jars, clear vinyl line, and Valvoline Syntec. You can "clearly" see when the air bubbles are gone. And slow and easy on the pedal pumping. Your young asisstant will feel like they are part of your hobby now too!
PS If you have wire wheels the Moss 1/4" spoke wrench is handy for the rear bleeders.
Andrew Blackley

Dave, try this method. It works on my 73B and dozens of other cars I have worked on through the years.
Leave your EZ bleader on the bench. Hve an assistant pump the pedal while you bleed at the wheels.

Instruct your assistant to pumb the brakes 3 or for times and hold it down hard. Slowly loosen a bleeder and close it before all the preasure is released. Have the aassistant release thge pedal. Repeat this a few times at each wheel or untill bubbles no longer appear in the fluid.

If this does not give you a solid brake pedal you may have a bad master, soft hoses or a fluid leak. I have had a few cases of "good masters" not being so good after being flushed with clean fluid. Suspect that the sludge did most of the sealing.

A learned this trick from a master mechanic in the 70s. By always keeping preasure in the system while bleeding air can not sneek back past the bleeders. Also compare a few pounds behind an easy bleeder to the hundreds of pounds behind a strong foot. the air does not stand a chance.

Cheers. Doug
Doug Gordon

Thanks to all for your excellent advice!
I had a chance to try the gravity bleed for maybe an hour last night. I found that if I had all 4 bleeders open with hoses on, 1 front and 1 rear seemed to have much more fluid through than the other 2.

So, I switched to just one bleeder open. An amazing amount of bubbles were coming through the clear line I had attached.

My pedal is better. I wonder how long the gravity bleed might take? I suppose it's directly based on how much air is still in!
Cheers to all, Dave
David Steverson

Dave,
Once had a similar experience with a '67 bug. Went through many quarts of fluid...also replaced the rubber lines, master cylinder, etc.. Still kept getting air. I discounted that the culprit might be wheel cylinders. After all, if the cups or the cylinder bores were defective, I should see a leak, not suck air. Well, to make a long story short, I replaced the wheel cylinders out of desparation...nothing left to do. Problem immediately solved. Best of luck!

Dave Tye
David Tye

This thread was discussed between 29/12/2002 and 02/01/2003

MG MGB Technical index

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