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No Brake Pressure - Rear Drum Issue?


Best Answer 20Drift , 18 November 2019 - 09:19 AM

Thanks all for your help.

 

Moke Spider was correct with the rubber grease theory, which seemed to have blocked the line between the master and the bias valve (26 in that diagram I posted). I replaced the line between the two and bled the master cylinder and that valve again.

 

Unfortunately a day after I noticed a puddle of fluid under the rear passenger wheel - the rear cylinder was leaking profusely into the drum so have just replaced that this weekend. Whole system bled with pedal pressure holding now. Life wasn't made easy due to all the brake lines and unions having underseal painted all over them, but thankfully no rounded unions.

 

Appreciate all the tips!

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#1 20Drift

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Posted 10 November 2019 - 02:38 PM

Hi all,

 

The Mrs has a 1986 Mini Mayfair 998cc which started leaking fluid from the master cylinder reservoir (yellow tag type) and eventually lost pedal pressure completely. I've just replaced the master cylinder with the replacement from Mini Spares (here: https://www.minispar...sic/GMC227.aspx), and set about bleeding the brakes.

 

Started in the usual order from rear passenger, to rear drivers to front passenger to front drivers, but I'm not getting any fluid out of the rear passenger, and a very minimal amount from the rear drivers. Just to rule out a dodgy master cylinder, I bled the fronts and got what I'd call the correct amount of fluid through from them.

 

I'm a bit stuck as to where to go from here - the handbrake works fine, and there's not evidence of fluid around the bleed nipples or casing of the rear drums. My next thought is to whip off the rear drums and have a look if there are any leaks on the cylinder within the drum, but not sure if there are any other valves which may have failed? Otherwise I was thinking of asking the garage to pressure bleed it in case there's an air lock (if that's possible?)

 

Appreciate any pointers!



#2 nicklouse

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Posted 10 November 2019 - 03:47 PM

First. There is no such thing as the correct amount of fluid.

the issue bleeding the rear is the slider bar thinking you have a leak and closing of the rear brakes. Press the pedal slowly when bleeding the rear or just open up the bleed nipples and let it flow. 



#3 Moke Spider

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Posted 10 November 2019 - 04:14 PM

If you are bleeding by the Pedal-down-open-nipple method, it's possible you are shutting off the Rear Brakes at the Shut Off Valve before the fluid gets to the Rear Brakes.

 

Try opening a Rear Bleed Nipple, put a hose on that to a jar, then Pumping the Pedal down, then lock off the Nipple before allowing the Pedal up. It'll be a 2 person job.

 

It may also be that the Master needs 'starting' too. When they assemble the new Master Cylinders, Rubber Grease is used and this can block the Ports between the Cylinder and the Reservoir not letting the fluid through. In this case, I find kicking off with a Pressure Bleeder, like a Gunsons unit works well.



#4 cal844

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Posted 10 November 2019 - 05:23 PM

Try simply crack the unions at the master cylinder then give a couple of pumps. Then work along each union on each line to the bleed nipples(front and rear)

When doing the bleed along each line, use the longest line first method. I've also used a couple of different methods... first of is 10 rapid pumps with the nipple open, make sure that on the last pump that the nipple is nipped closed. Any final bleed can be done with the open nipple, pump slow close nipple with pedal down.


Hope this helps.

Cal

#5 20Drift

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Posted 10 November 2019 - 06:18 PM

First. There is no such thing as the correct amount of fluid.

the issue bleeding the rear is the slider bar thinking you have a leak and closing of the rear brakes. Press the pedal slowly when bleeding the rear or just open up the bleed nipples and let it flow. 

 

Is the slider bar located where the circuit tees off near the middle of the car to each side?

 

 

If you are bleeding by the Pedal-down-open-nipple method, it's possible you are shutting off the Rear Brakes at the Shut Off Valve before the fluid gets to the Rear Brakes.

 

Try opening a Rear Bleed Nipple, put a hose on that to a jar, then Pumping the Pedal down, then lock off the Nipple before allowing the Pedal up. It'll be a 2 person job.

 

It may also be that the Master needs 'starting' too. When they assemble the new Master Cylinders, Rubber Grease is used and this can block the Ports between the Cylinder and the Reservoir not letting the fluid through. In this case, I find kicking off with a Pressure Bleeder, like a Gunsons unit works well.

Interesting, I might try the Gunson method then as a mate has one. Is the shut off valve the same as what nicklouse mentioned above?

 

 

 

Try simply crack the unions at the master cylinder then give a couple of pumps. Then work along each union on each line to the bleed nipples(front and rear)

When doing the bleed along each line, use the longest line first method. I've also used a couple of different methods... first of is 10 rapid pumps with the nipple open, make sure that on the last pump that the nipple is nipped closed. Any final bleed can be done with the open nipple, pump slow close nipple with pedal down.


Hope this helps.

Cal

Thanks - I will crack the union for the rear as I know the fronts are fine. I'm assuming rear is the top union as the fitting is smaller?



#6 Moke Spider

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Posted 10 November 2019 - 06:40 PM

 

 Is the shut off valve the same as what nicklouse mentioned above?

 

 

While Nick's posts are usually short, they do usually make sense, but in this case, I'm not sure what Nick is referring to.



#7 cal844

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Posted 10 November 2019 - 06:42 PM

Bottom is the rear brakes, as explained in the description on Minispares.

Ref the shut off valve there is two possibilities, you can have a rear limiter(mounts on the subframe) or the FAMwtf valve on the bulkhead below the MC.

Hope this is of some help

Cal

#8 20Drift

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Posted 11 November 2019 - 08:02 PM

Hi all,

 

Had another stab at this today - borrowed a Gunson Easibleeder off of a mate and used the spare tyre pressurised to 15psi.

 

Did a dry run with no fluid and everything held pressure fine, so assume that rules out any leaks. Put fluid into the vessel and re-pressurised and the level stayed constant in the bottle, and all bleed nipples and unions looked dry to me. 

I cracked the rear passenger side bleed nipple but again drier than ghandi's flip flop. Started working back, and cracked the feed from the brake limiter valve (26) where it enters the three way split (21). I had fluid come out of here.

 

I then cracked the passenger side outlet of the splitter (21), and had fluid come out of here to, at about the same rate as above. Same on the drivers side, and then around the same out of the rear drivers nipple.

 

I've checked the flexi hoses (13) and they're dry all the way along which confirms the system is holding pressure.

 

Any other ideas?

 

 

Brake circuit diagram:

xGXGzAT.jpg



#9 GraemeC

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Posted 11 November 2019 - 08:09 PM

How old are the flexies?

#10 20Drift

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Posted 11 November 2019 - 08:11 PM

How old are the flexies?

 

Got to be honest, no idea. I'd guess original. No cracks on them though.



#11 GraemeC

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Posted 11 November 2019 - 08:14 PM

There is a strong possibility they have broken down inside and blocked themselves.

#12 20Drift

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Posted 11 November 2019 - 08:24 PM

There is a strong possibility they have broken down inside and blocked themselves.

 

Interesting, hadn't thought of this. Wouldn't that still give some pedal pressure though? The only resistance at the moment is the spring on the end of the pedal



#13 Moke Spider

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Posted 11 November 2019 - 10:57 PM

 

There is a strong possibility they have broken down inside and blocked themselves.

 

Interesting, hadn't thought of this. Wouldn't that still give some pedal pressure though? The only resistance at the moment is the spring on the end of the pedal

 

 

Graeme has raised a good point here.

 

When the Hoses 'fail' they usually do so internally, blocking fluid passing through them.

 

It is recommended by the Brake Component Manufacturers that these be replaced every 3 years or 40 000 miles that these hoses and all other rubber parts in the Brake System.



#14 Rorf

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Posted 13 November 2019 - 07:04 AM

If the brake fluid hasn't been changed for years on end then it is possible that the rear brake cylinders are full of rust and have blocked up the bleed nipple holes. Considering the age of the vehicle and unknown brake fluid history I would suggest replacing the rear brake cylinders and rubber hoses - cheap enough. I assume the fronts are discs so usually no major problems there.

 

I am a great believer nowadays of changing brake fluid at least every 3 years and under this regime the hydraulics should last a good 20 years.

 

The old fashioned bleeding method with two people is t\still the best - open bleed nipple (plastic pipe into jar of brake fluid), push pedal slowly to the floor, nip nipple closed, release pedal slowly and then repeat, repeat, repeat until nice clean fluid comes through. Of course at all times ensure master cylinder reservoir does not go empty :proud:



#15 Ethel

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Posted 13 November 2019 - 09:46 AM

Hoses or slaves are both possibilities, but be aware if the pipework is as old you may find the unions have corroded on to the lines and you could end up doing a total refurb.

When the seals in the old master gave up the ghost they'll have created some debris which could have been pumped down the lines until it found a restriction to lodge in.

I use a syringe to pull air/fluid through when bleeding brakes. Lower pressure won't dissolve air in the fluid like a fizzy drink and it won't cause pressure limiting valves to close. You can also keep the reservoir topped up more readily than with a pressure bleeder.




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