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'69 B Brake Master Cylinder

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'69 B Brake Master Cylinder
#1
2992 Avatar
2992 Ron K
Tucson, AZ, USA   USA
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1969 MG MGB
Would you folks please confirm my diagnosis, I bled the system and initially have a good brake pedal but if I continue to put pressure on the pedal, it gradually goes to the floor with no leakage noted anywhere. I suspect that the Master is bad, I have owned this beauty since 1970 and don't think that I have ever replaced it, so I suppose that it is due. What do you guys think, rebuild mine or replace with a new one? As long as I have the assembly out would you also rebuild/replace the clutch master, also? Thank you in advance for your advice.

Ron

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Re: '69 B Brake Master Cylinder
#2
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chris Chris Roop (RIP)
Pendleton, OR, USA   USA
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You have a cylinder with an internal leak, assuming that you are not losing fluid. Consider rebuilding/replacing the hoses and wheel cylinders. Rebuilding the clutch master is a good plan.

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Re: '69 B Brake Master Cylinder
#3
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2992 Ron K
Tucson, AZ, USA   USA
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1969 MG MGB
Thanks Chris, I should have mentioned that I had just replaced both rear slaves, all flex hoses and the metal line between the rear brakes. Do you have any strong feelings one way or the other on a rebuild or replace?

Ron

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Re: '69 B Brake Master Cylinder
#4
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Gerry Gerry Masterman
Prairieville, LA, USA   USA
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The dual circut M/C have a circlip that is deep within the bore of the cylinder. Normal snapring removal pliers don't do a very good job of reaching it. Sometimes this ring is not so bad to pry out but other times it's all but impossible. My suggestion would be to buy new and keep the old to have a try at rebuilding for a spare.

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Re: '69 B Brake Master Cylinder
#5
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chris Chris Roop (RIP)
Pendleton, OR, USA   USA
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In reply to # 3431690 by 2992 Thanks Chris, I should have mentioned that I had just replaced both rear slaves, all flex hoses and the metal line between the rear brakes. Do you have any strong feelings one way or the other on a rebuild or replace?

Ron

For the dual masters, replace. For the clutch since it is working now, just rebuild.

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Re: '69 B Brake Master Cylinder
#6
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2992 Ron K
Tucson, AZ, USA   USA
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1969 MG MGB
Luckily I just noticed that when my wife put pressure on the brake pedal, fluid came out of the electrical connection on the "switch & body assembly" (the junction of the five brake lines). I cancelled my Moss order just in time and ordered the rebuild kit for that assembly instead. Sure hope that it solves my problem.

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Re: '69 B Brake Master Cylinder
#7
chris Avatar
chris Chris Roop (RIP)
Pendleton, OR, USA   USA
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In reply to # 3431768 by 2992 Luckily I just noticed that when my wife put pressure on the brake pedal, fluid came out of the electrical connection on the "switch & body assembly" (the junction of the five brake lines). I cancelled my Moss order just in time and ordered the rebuild kit for that assembly instead. Sure hope that it solves my problem.

That should do it! That is why I made the proviso that you weren't leaking! smileys with beer

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Re: '69 B Brake Master Cylinder
#8
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2992 Ron K
Tucson, AZ, USA   USA
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1969 MG MGB
You were correct, but who would have ever thought that it would leak out of an electrical connection. Thanks.

ron

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Re: '69 B Brake Master Cylinder
#9
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barry s Barry Stoll
Alexandria, VA, USA   USA
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1972 MG MGB GT
1974 MG MGB
1976 Triumph TR6
1980 MG MGB
A word of caution about the brake failure warning device. Getting the end bolt out of the assembly can be a PITA.
As you may have seen here before, an alternative is to simply insert a bolt and washer into the sensor hole. I'm one of those that believe that the warning device is of little to no use, trusting more the feel of the brake to assess a brake problem. As yours is leaking, it could not be functioning as intended, anyway. Luckily, the rebuild kit is pretty cheap should you decide to toss it in your spare parts drawer.

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Re: '69 B Brake Master Cylinder
#10
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selincs Simon E
Horncastle, Lincolnshire, UK   GBR
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1976 MG MGB "Poppy"
2017 MG MG3 "Midge"
If you haven't done so you will need to bench bleed the mc prior to fitting on the car - I did not do this so had to take it off again, also on a single line system you need to bleed the servo as well
Another tip I had from a member is to place a piece of wood between the seat and the pedal pressed down , leave the cap off the mc overnight as the pressure will eventually let any air in the system come up - works every time - don't forget to replace the cap in the morning !!

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Re: '69 B Brake Master Cylinder
#11
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barry s Barry Stoll
Alexandria, VA, USA   USA
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1972 MG MGB GT
1974 MG MGB
1976 Triumph TR6
1980 MG MGB
Simon - I think that you will find that you offer a 'minority' opinion on MC bleeding. This topic is/has been discussed many, many times. While I will not get any deeper into this< I will state that I have never bench bled an MG MC nor will I ever in the future.

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Re: '69 B Brake Master Cylinder
#12
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selincs Simon E
Horncastle, Lincolnshire, UK   GBR
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1976 MG MGB "Poppy"
2017 MG MG3 "Midge"
Thanks Barry
I could not get the pedal up with bleeding normally so on advice from one of my club members took the mc off bled it on the bench and it worked !!

Take care and thanks again

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