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Almost No Brakes-Bad Vacuum Servo?

brakes

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#1 HowardMiniMe

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Posted 08 September 2019 - 01:55 PM

Hi,

I acquired a 1993 Mini a few months ago and I’m just finding the time to sort it out. I noticed the brakes were really spongy and I figured there is air in the lines. I bled the brakes and didn’t see any air bubbles, and when I checked the brakes were still spongy.

I hooked up my motive power bleeder and put air into the system. I hear a hissing sound coming from the vacuum servo. I’m guessing there’s an issue with seals inside the unit. Are these rebuildable? Or maybe I should ask is it even worth rebuilding and I just replace it? Thank you.

Howard

#2 cal844

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Posted 08 September 2019 - 02:28 PM

Check everything else is correct before rebuilding or replacing the servo.

Make sure the front brake caliper bleed nipples are at the top. If they're at the bottom you simply swap them sides.

Make sure the rear wheel cylinders and the brake proportioning valve aren't leaking. If the car is dumping fluid suddenly it could be the master cylinder needs replaced.

To test your servo is functioning correctly pump the pedal until it gains pressure(if at all possible) then keep the pressure on the pedal.... now start the engine, the pedal should drop about an inch whilst still maintaining firmness.

Hope this helps

Cal

Edited by cal844, 08 September 2019 - 02:29 PM.


#3 expat_cat

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Posted 08 September 2019 - 03:22 PM

Poor or no servo usually has the opposite effect i.e brakes feel harder (but don't stop you!).  So as per Cal's suggestion above.  Also run engine, turn it off.  Then try the brakes.  For the first one or two pedal-presses you should hear a short "hiss" with longer pedal travel, then the pedal should get harder.

Of course, if you have air in the system, then the "harder" bit might not be too noticeable.



#4 HowardMiniMe

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Posted 08 September 2019 - 11:50 PM

Cal the bleed valves are at the top. I performed the vacuum test and it passed.

I figured I should bleed it again. This time i let a lot more fluid come out of each bleed valve. That solved it as my brake pedal is now hard and it stops like it should. Thank you to both of your for your assistance.

Howard

Edited by HowardMiniMe, 08 September 2019 - 11:51 PM.


#5 Ethel

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Posted 09 September 2019 - 08:24 AM

I'd be removing the pads and checking the condition and operation of the calipers, discs & wheel bearings (play in the discs) for starters.

The spongy pedal suggests a hydraulic fault that will probably be elsewhere, but the above's quick and easy and without the front brakes in decent condition you won't be stopping quickly anyway.

Hydraulic leaks are most common and easiest to spot on the rear wheel cylinders, so eliminate that before stripping down the master. They can be rebuilt, but it's worth inspecting the bore first to see if just replacing makes more sense.





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