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Brake Master/servo Issue


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#1 brandondonat

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Posted 01 August 2019 - 04:21 PM

I am currently having an issue with my Mini's brakes. They are spongy and the pedal is nearly to the floor before I get any braking power. When I do get braking power it is minimal. I have bled the brakes twice and it seems to fix the problem for a short period of time but in short time the issue is back.

I understand that I likely have a leak in my system somewhere which is allowing air to enter. Since I do not have a leak on any of the calipers or drums I presume it is an issue in either the brake master cylinder and/or the brake servo. Have any of you had success just changing the master cylinder on a servo setup and had any luck... or should I change the entire servo/master cylinder setup?

 

 



#2 Ethel

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Posted 01 August 2019 - 04:40 PM

You ought to get a good clue of what's leaking from the bleeding if you do R front, L front, R rear, L rear and check the pedal thoroughly each time. If it's the master it would take a while to bleed through.

#3 richmondclassicsnorthwales

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Posted 01 August 2019 - 05:11 PM

Hi

 

How old is the system ?

 

The brake hoses could have collapsed internally, the servo could be half knackered, could be a combination ?

 

One thing I do impose on people is that the brakes are designed to stop you, and not kill you - and will if you allow them too !

 

You need to have a look at the rear cylinders too, are these up to the spec ? The rear takes a pounding as our great British weather delivers us plenty of rain water.

 

Do a little investigating



#4 unburntfuelinthemorning

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Posted 01 August 2019 - 06:57 PM

Are the rear drums adjusted properly?  People sometimes chase air in the hydraulics when it's an adjustment problem.


Edited by unburntfuelinthemorning, 04 August 2019 - 07:03 AM.


#5 cal844

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Posted 01 August 2019 - 07:36 PM

I lock the rear drums solid then loosen them once it's bled and a good pedal. The front calipers aren't on the wrong side? Bleed nipples should be to the top

#6 richmondclassicsnorthwales

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Posted 01 August 2019 - 08:54 PM

How old is the system ?



#7 brandondonat

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Posted 04 August 2019 - 01:20 AM

Thanks for all of the responses.  All were helpful.  The Mini is an '89 with 1275 cc engine and servo brake setup. 

 

I first tweaked the adjustments in the rear drum setup.  Since only 1,000 miles or so have been put on the Mini since a full front/back brake job they were pretty spot on but it didn't hurt to do minor adjustments and I can see how this could cause a spongy feeling if not adjusted properly.  Nice recommendation. 

 

I then went through and bled each of the brakes individually and checking them after each bleed.  The flow from each brake was excellent with the exception of the right front.  Another good recommendation.  Since the right front had air I traced the line back to the brake limiter valve.  Initially there was not visible brake fluid but paint was bubbling from the right subframe tower mount location.  This cause me to look a little harder at the fitting that ran into the limiter valve from the right front brake setup and sure enough... I was able to tighten the fitting a slight amount and a small amount of brake fluid appeared.  Once tightened, I bled the right front again and it seemed to do the trick.  I am back on the road again, cheers all.   






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