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MG MGB Technical - Bleeding brakes on new system?

Morning All,
I am having a 'spot of bother' bleeding the rear brakes on my '72 B.

I've replaced the whole system. I used the gravity method for the front, but I can't get anywhere with the rear.

I could not find anything in the archives. I have also tried pumping while having a hose on the bleeder screw in a cup of fluid.

Any suggestions? Hoefully, without having to order some tool.

Cheers, Dave
David Steverson

The easiest way is to use a MityVac hand vacuum pumpand brake bleeding system. For about $40 you have an indispensible tool with many uses on your car. Otherwise, just keep pumping!
Jeff Schlemmer

I have always had the best luck bleeding brakes per the following. Open bleeder, have someone push the pedal down, close bleeder, release pedal. Repete until fluid with no bubbles is obtained. Once all have been bled, have helper push on the pedal hard, crack open the bleeder, the higher flow will get the last few bubbles. After 34 years, wife has gotten very good at this drill.
John H

I'm personally dicey about the physics of gravity only bleeding, despite the success some report with it - after all - gas rises, and the rigid brake lines and flexible hoses are all above the bleed points. I'll accept that bubbles may eventually get to the master cylinder, but it seems to me there are too many grottos where a bubble could lurk.

I also had a bit of trouble getting a good bleed (using a one-man kit) until I used this method:

1) Attach bleeder hose with valve or immersed in brake fluid.
2) Have an assistant pump the foot brake with normal braking pressure 4-5 times, then say 'hold' to keep the pedal in depressed position (again, using normal braking pressure on the pedal.
3) Open the bleed screw. Your assistant's foot pressure (stronger & cheaper than a Mityvac) will depress the pedal to the floor. Hold pedal down.
4) Close the nipple. Say 'release' to your assistant, who takes foot off pedal.
5) Repeat steps 2-4 until no bubbles appear.
6) Move onto the next nipple.

A couple of other pointers - make sure your rear brakes are adjusted up enough - overly backed off drums will increase pedal travel (but in differentiation from air in the lines, won't 'pump up').

Also, it seems there's debate about which bleed nipple to start with - the manuals say start furthest from the MC i.e. rear left on a RHD car, but Chris Betson from Octarin Services suggests start nearest the MC and work away. This makes sense to me, as new air-free fluid flows from the MC and around the system, whilst any returning air will leave via the master cylinder. Having said that, the last good bleed I did was starting furthest from the MC.
Curtis Walker

Gotta go with Jeff, although I use the vacuum brake bleeder from Griots. No mess, no hassle....truely a one man job.
Robert Dougherty

If you have power brakes - run the engine - cuts down the time.



If you don't have easy access to a second person consider using Speedbleeders. See
I have them on my A and have had good results.


Larry Hallanger

I have Speedbleeders as well, but they tend to aerate silicon fluids. The vacuum pump was still a necessity to prime the new system.
Jeff Schlemmer

I found a MityVac at AutoZone on the way home from work this evening. I guess it's worth the $30 price tag if it does the trick.

Working brakes would be nice...
David Steverson

This thread was discussed between 20/04/2006 and 21/04/2006

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.