31 replies to this topic

[Jimmer 84mayfair]

Hi all,

 

A strange thing that someone on here may have experienced,... and have hopefully found an answer.

 

Firstly, I have plenty of experience with brakes and have bled many systems before, but this one has me stumped. It is an all drum system, so that is different, but the principles for expelling air surely have to be the same!

 

I decided to replace my braking system completely on Mini Mayfair, after the brakes were failing,... going soft. The old system looked tired and there was obviously fluid leaking from one or two of the wheel cylinders.

 

I have now replaced everything on the system, the pipes, master cylinder, brake limiter valve, springs, all connectors, washers, wheel cylinders, bleed screws,... the lot (from Mini-spares). i have now completed this task, but now I am still having very similar problems to before! I have used new brake fluid on each occasion, and have used a one man Gunson bleeding kit connected to a tyre to push the fluid through the system into a jar with aid of a one way valve bleed pipe.

 

After opening the bleed screws in correct sequence, the system is seemingly flowing free of air bubbles. Yet after a day or two of driving the peddle starts to drop and there is now no pressure left.

 

I have bled the system three or four times thinking that this time the pressure was up to scratch, and all balanced and cannot see any leaks coming from anywhere on the system, only to find a day or to into driving the peddle slowly dropping.

 

There are no puddles or visible wetness on any joints. This must mean air is getting in, or there was still air trapped that is taking its time to move elsewhere which has an effect on the system.

 

I am worried that the new master cylinder is faulty,  only because it was a bastard to put in, the room in the footwell for putting in the retaining split pin through the clevis pin was one of the fiddliest things I've ever experienced. This is worst case scenario, so I will ignore this until all other possibilities are pursued.

 

I have followed the manuals bleeding sequence, I have even tried tightening up all the brake adjusters, bleeding, then backing off the adjusters as some have advised on other sites.

 

What to try folks?

 

I am a sod for getting a job done and I do not want to give in and 'take the car to a garage'.

 

I am sure many of you may have had similar experiences, there must be something I am missing. The fact that it takes a day or so to fail could be telling, but offers no obvious resolve, like a puddle on the floor!

 

Any suggestions...

 

thanks, Jim

 

 

 

[cal844]

What I'd now do is chase the air back up the pipes to the master cylinder,

bleed the nipple, then loonsen the car end of flex pipe(let some fluid weep out),

then tighten the flex, now go to the compensator valve(on bulkhead, if fitted) open the top and bottom unions allowing fluid to weep, tighten unions and then close the bleed nipple...

Bleed order( im sure you know this!)

rear left
Rear right
Front left
Front right.

A critical point:: protect your paintwork from brake fluid!!

A long post but hope it helps

Edited by cal844, 15 December 2016 - 03:40 PM.

[Cooperman]

If you pre-pressure the system before opening the bleed screws on the rears, the pressure regulator can shut off the full fluid feed to the rears.
This may be your problem. Ditch the pressure bleeder and get someone to push the pedal down AFTER the rear bleed screws are undone in turn.

[Jimmer 84mayfair]

What I'd now do is chase the air back up the pipes to the master cylinder,

bleed the nipple, then loonsen the car end of flex pipe(let some fluid weep out),

then tighten the flex, now go to the compensator valve(on bulkhead, if fitted) open the top and bottom unions allowing fluid to weep, tighten unions and then close the bleed nipple...

Bleed order( im sure you know this!)

rear left
Rear right
Front left
Front right.

A critical point:: protect your paintwork from brake fluid!!

A long post but hope it helps

thanks for the reply,...

I like the idea that I could bleed the brakes the opposite direction back to the master rather than down via the regular bleed valves.

however I am not sure how this is can be done...

What I'd now do is chase the air back up the pipes to the master cylinder,

do you mean close of all the regular bleed valves once bled in the regular fashion, then loosen each of the connections to the regulator, then to the master cylinder until they weep clear of bubbles?

Firstly should I pump the brake whilst doing this or should there be enough pressure present to expel any air?

Should I do this with the master cylinder cap loose fit or tightened up?

It's a shame the master cylinder does not have its own bleed nipple on the top... if this is a common problem.

 

If the above is not right i am confused about the sequence and possibly the terminology of some of what you have described.

loosen the car end of flex pipe

the car end of flex pipe?

 

I have been bleeding the brakes in the order you have described...

 

rear left
Rear right
Front left
Front right.

 

thanks, Jim

[Jimmer 84mayfair]

If you pre-pressure the system before opening the bleed screws on the rears, the pressure regulator can shut off the full fluid feed to the rears.
This may be your problem. Ditch the pressure bleeder and get someone to push the pedal down AFTER the rear bleed screws are undone in turn.

thanks for the reply,

I can see how the regulator maybe closing off whilst using the pressure bleeder system, although wouldn't the same happen when using the pedal?

The fluid seemed to flow out freely before ok when i was opening the nipples using the air pressure system.

I tried using the foot pedal method before using the air pressure system, it seemed to lose the pressure after a day or two the same then, that's why I tried the air pressure because I thought at least the pressure was constant.

Maybe if I opened both rear bleed nipples at the same time there would be no unbalance between the two. i have two clear tubes and jars.

 

Ditch the pressure bleeder and get someone to push the pedal down AFTER the rear bleed screws are undone in turn

Is this not the same as bleeding with the foot pedal, not sure how this instruction is any different?! to usual bleeding.

 

The secret has to be to try and bleed the brakes without the pressure regulator closing off one side of the system and trapping air in the process.

Ideally it would see that all bleed nipples should be opened simultaneously to prevent any unbalance and movement in the regulator.

[cal844]

What I do is keep the bleed nipple (on wheel cylinders) open, then bleed from the unions along each pipe to the MC, then once you get the fluid out of every union, close them all off and do a final bleed from the nipples

I've never ever used a pressure bleeder, always just opened the nipple and have another person work the pedal, be sure to tighten the nipple with the pedal fully down!

Edited by cal844, 16 December 2016 - 04:49 PM.

[Jimmer 84mayfair]

I've been working on this problem again today... I have two problems, the new master appears to be leaking, there is a small patch of fluid forming after a number of pumps after bleeding the system. I cannot see clearly if the leak is coming from between the plastic reservoir and the metal body seals or dribbling down from the cap and down the back of the reservoir. The pipe joins are dry.
Another problem is... I had a hunch that the new backplate adjuster were moving once I had bled the system and used the brakes so I marked each of the adjusters with tipex and then marked it on the body of the backplate,... sure enough after a number of pumps of the brakes 10-20 the adjuster had turned away from the set mark by 2-3mm. I filmed the front-front brake adjuster doing this, but then realised my camera disc was full! But this was definitely the case, the adjusters are moving! These are new backing plates, my old plates had worn round adjusters so thought I had better swap them out, this does not help. How am I supposed to adjust the brakes if they back off on their own!? I need to know they are not going to move after tightening them up, otherwise what's the point!
I am fairly sure that a combination of these two problems is at the bottom of the problems I face, but what to do next?
I am thinking of clearing the memory on my camera and filming both again, I may then upload them onto YouTube and put a link up.

[Jimmer 84mayfair]

Film of the new master cylinder leaking...

https://youtu.be/t8S3inP53RE

[AlexMozza]

If the adjusters back off on their own, then ditch the back plates and get new ones, assuming you mean it's the fronts that are backing off
I have seen some poor quality back plates before, causing no end of issues.

[Jimmer 84mayfair]

It's a shame, I chucked the old ones. Can anyone recommend where to get some from, these were from Mini Spares Centre Ltd. I do not want to replace like for like.

[AlexMozza]

All the major suppliers will use the same manufacturer.
But you could try Somerford Mini, as I fit the stuff we sell in the workshop, the recent back plates I've fitted have been without issue.

[Jimmer 84mayfair]

Will do thanks

[Jimmer 84mayfair]

They look a bit different to my current set up. There are what looks like retaining clips by the master cylinders, the springs also look different. I will try Minispares first, see if they will swap the current backplates and the master cylinder. Otherwise I will need to replace the whole lot it would seem.... an expensive and unnecessary change as I have already bought new pipes, backplates, cylinders, shoes and springs for the front. This part replaces the lot in one go rather than individually.

My car is August 84 so wonder if they will fit ok.

http://www.somerford...oducts_id=16903

[AlexMozza]

They look a bit different to my current set up. There are what looks like retaining clips by the master cylinders, the springs also look different. I will try Minispares first, see if they will swap the current backplates and the master cylinder. Otherwise I will need to replace the whole lot it would seem.... an expensive and unnecessary change as I have already bought new pipes, backplates, cylinders, shoes and springs for the front. This part replaces the lot in one go rather than individually.

My car is August 84 so wonder if they will fit ok.

http://www.somerford...oducts_id=16903

It would fit.
You could however just change the backplate.

[Jimmer 84mayfair]

I wonder if they would sell just the backplates, I can give them a call. First I will try and get these current ones swapped, see if the problem is inherent in all of them, or just this pair.