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 RHD mini unable to bleed rear brake cylinder

 Created by: Minime1994
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 Posted: May 14, 2021 04:47AM
TK
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AU
always bleed from the cylinder furthest away. Could be collapsed rubber hose, Stuffed rear limiter, rusted brake line

 Posted: May 11, 2021 10:32AM
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US
+1 for rusted wheel cylinder. I had the same symptoms with mine a couple years ago. Buy new they aren't expensive.

 

 

 Posted: May 10, 2021 06:36AM
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US
I would start cracking lines loose from the wheel cylinder headed back towards the front... Crack a line and see if fluid comes out .
  If it does = the blockage is between that point and the end point.

 I would also wager bad wheel cylinder .  or rubber line collapse / blockage.

 Posted: May 9, 2021 01:05PM
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If you have DOT 3, 4, or 5.1 fluid (i.e. conventional brake fluid) in your system, you have to totally flush the system to switch to DOT 5. DOT 5 is not at all compatible with other brake fluids. And I mean totally purge the old fluid out.

My personal opinion is that DOT 5 is suited for vehicles that are mostly stored and rarely driven. Changing the brake fluid every 2-3 years solves the brake corrosion problem - the brake fluid is doing its job absorbing the moisture, which affects braking. Once it absorbs too much, it can start corroding because it's evenly distributed through the system. Braking power slowly declines, and declines more sharply if the brakes are used hard and often (because the heat boils out the water, making the pedal feel softer and softer.)

Moisture gets into DOT 5 brake systems too, it's just that DOT 5 doesn't absorb it and the water pools up instead, like water on oil. It likely won't corrode components because it's pooled up, but then braking can be strongly affected cold or hot.

DLY
 Posted: May 9, 2021 07:40AM
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You have a bad rear wheel brake cylinder because it rusted. You will need to replace it. Use DOT 5 brake fluid and you will eliminate the hydroscopic problems.

 Posted: May 9, 2021 07:30AM
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CA
It is unlikely that the pressure regulating valve is faulty as it serves both rear brakes and one is OK.
Generally the sequence for bleeding is to do the longest channel first as that gets air out of the long lines and any later branches are already partially bled. Brake pedal pressure should be applied gradually so as not to make the pressure regulating valve to react. Stomping on it will cause it to close.

You have tried removing the bleeder with no success. The logical thing is to disconnect the flexible hose at its output end and test for flow. If it does flow, test the hard line on the rear swing arm next. If not, remove its upstream end and test for flow again. If that doesn't work, separate the hard line from the regulating valve.

By process of elimination you should be able to isolate the problem,

.

"Hang on a minute lads....I've got a great idea."

 Posted: May 9, 2021 06:17AM
 Edited:  May 9, 2021 06:23AM
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Hi everyone: 

I replaced my master cylinder yesterday evening and bled the two front calipers and the rear passenger no problem. I get to the rear driver and there is zero fluid exiting. I left the bleed screw open with the tube and catch bottle attached and press on the brake pedal and still nothing. Finally  I removed the bleed screw entirely and not a drip. I have dual circuit MC with the pressure reducing valve at the rear. 

I'm asking what basics should I check before I start removing components? 

1. Bleed order - I started with front passenger, front driver, rear passenger, rear driver. Was this the correct order?
2. Flexible hose - maybe swollen internally?
3. Brake cylinder - I don't know what to check/inspect to determine a failing cylinder 
4. Clog in hard line from rear reducing valve to cylinder?
5. Failed or failing rear reducing valve? 

I replaced the MC because it would go soft after sitting for a couple weeks. I had no leaks but I figured it was either the MC internal seats or the brake servo. 

Any help is greatly appreciated. Thank you. 

Howard



RHD 1994 Mini dual SU