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MG MGB Technical - Overnight bleeding

I don't know who to thank, but the overnight bleed has given my B great brakes. Thanks a lot
Bob

R Etches

Can you direct us to the tread with the details?
Thanks,
Pete
Pete W.

Pete.
You'll find it in the archives, but basically it says" depress the brake pedel overnight remove the cap of the m/c and thats it" What I did was jam the brake pedal as far as it would go with an adjustable rod against the drivers seat.
It works.

Bob
R Etches

One potential problem with this method is that it may put unusual, prolonged pressure on your master cyclinder, still, I guess you'd rather it fail in this circumstance than on the road.
Curtis Walker

You are welcome!! Myself, I discovered it be accident. Thankfully I was running silicon fluid, or the paint would have been off the wheels! I do not claim to be the originator of this idea, just one of many who brings it up when someone can't get a firm pedal.

I think it only works on early cars, but I may be wrong.

Pete
Pete

Pat, Mines a 1978 model roadster, so it apparrently works on all models. Thanks again

Bob
R Etches

Hi Pete,

You said,..."Luckily I as running silicon fluid, or the paint would have been off the wheels!". Does this mean you had the wheel cylinder bleeder valves open too?

Please clarify, as I think I'm going to try this tonight.

Thanks,
DT
Danny T

"Does this mean you had the wheel cylinder bleeder valves open too?"

Surely not, it would have emptied the master cylinder.

I've not tried this method as I like to get my cars finished in one go, not leave something overnight and possibly have to get under it again next day. For a spongy pedal that pumps up what works on both my cars is after normal low pressure bledding by either pedal or gunsons EeziBleed, is to get someone to stand on the pedal (i.e. apply heavy constant pressure) while I rapidly open and close each caliper bleed nipple in turn. This always blast an extra lump or air out and after that the pedal is fine, and the job is finished.
Paul Hunt 2

Letting the master cylinder vent overnight will allow harmful moisture to enter the system.
S Rechter

The clutch and master cylinder caps should always be vented. Particularly in the case of the brakes if an unvented cap is used (if one can be found) when the brakes heat up the fluid expands, which unless there is a vent in the cap will pressurise the air above the fluid. This means that the fluid is also pressurised which will cause the brakes to bind. I've read of a case not too long ago where the vent became blocked and the resultant brake drag and overheating took some time to diagnose. If the clutch cap is blocked it will cause excessive wear on the release bearing, which will take much longer to come to light than dragging brakes.
Paul Hunt 2

Danny:

You have to keep in in that it was not overnight, only long enough to enjoy a social beverage and have someone point out "Is there supposed to be fluid under that tire?" Both rears were open as I had previously made sure the bleeder were not stuck. And yes, I was low on fluid.

Pete
Pete

Bob,In your first popst you mention the b now has great brakes. Did it have a problem before this was done?
just curious.
Chere , Pete (Australia not Canada).
Peter Thomas

Pete, Previously the brakes would lock the wheels, but it always felt as if there was need to pump them once to get a satisfactory feel.i.e there seemed to be too much travel when first applied. The system had been bleed as per the book, when the fluid and brake pipes were renewed. This overnight bleed seems to have removed the last remmnants of air and I've got what I would consider a good brake.
Bob
R Etches

I just can't go along with this method at all. To me it makes no sense that we should have to wait until the fluid percolates all through the system. That'a just too much faffing about. The normal brake bleeding method whether it be by using an Eezibleed or not works just fine and it seems that you are missing something if you cannot get results by these methods. Have a look at the thread lower down entitled "Bleeding Brake Adjustment 67"
Iain MacKintosh

I've used this method a couple of times. Results first time were great, with a much firmer brake pedal than I'd achieved with an ezbleed the day before. Second time it killed the master cylinder, just as Curtis suggested. It may have been ailing already, but this technique finished it off.
Steve Postins

This thread was discussed between 11/03/2006 and 13/03/2006

MG MGB Technical index

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