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Author Topic: Brake bleeding after MC replacement - Conflicting procedures  (Read 445 times)
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JASPER_40
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« on: May 26, 2024, 02:56:29 PM »

Hi,

Apologies in advance as it seems there is much discussion about this but there seems to be several conflicting procedures for brake bleeding on this forum which are also in conflict with the Haynes manual.
I was hoping that there is a "never fails" procedure that someone can tell me about.

I have just bought a 1982 coupe and I replaced the Master Cylinder to remedy a spongy brake pedal issue. I fully understand that spongy pedal is almost certainly air in the system but had read that spongy pedal is also a possible symptom of a bad MC, so I thought I would replace it anyway. Good job I did as the MC internal bore was rusty and the seals looked scored. Must surely have been the problem for my spongy pedal !!

However, now everything is back together and brakes bled using a pressure bleed apperatus attached to the reservoir (30 psi) and 2 litres of Dot 3. The brake pedal feels exactly the same as it was before.

The bleeding procedure I followed was as per Haynes.......With just the front of the car off the ground, I bled the system in the following order :

1. Front drivers side outermost bleed screw (closest to the disc)
2. Front passanger side outermost
3. Rear driver side (therefore furthest from the Master Cylinder
4. Rear passanger side
5. Front driver side innermost (furthest bleed screw from the disc)
6. Front passanger side innermost

Before fitting the MC, I did attempt to prime it on the bench before fitting.

I would appreciate any suggestions / techniques on how to get stubborn air out of the system

Cheers,

Steve

Is it possible to bleed the MC in situ in case the air is stuck there ?
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peteracs
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Peter Stokes


« Reply #1 on: May 26, 2024, 03:08:20 PM »

Hi Steve

I replaced all the brake parts on my Spider when restoring, used a pressure bleeder and simply worked furthest to nearest to MC. Nothing special, it just worked. So I suspect you may have a problem with a seal of flexi pipe. What else have you replaced and if you repeat do you still get any air coming through? I assume you have flushed the old fluid?

Peter
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JASPER_40
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« Reply #2 on: May 27, 2024, 02:50:29 AM »

Hi Peter,

Thanks for your response and to answer your questions....

Do I still get air coming through if I re-bleed ? Not sure so I will try this today and report back.

What else has been replaced ? I purchased the car in Jan where the sellers description included "drives like a new car" which was the most appauling mis-description ever....but anyway. As concerns the braking system, the flexi pipes on the front appear to have been renewed and also has new discs and pads on the front. When I bleed any of the front circuits then the fluid flows freely as you would expect. What has always struck me as strange is that the front discs still have all the machining marks from manufacture which suggests to me that the front brakes are just not gripping with any kind of force making the braking performance quite poor. So, my theory is that the air in the front circuits is making the pedal spongy and the front brakes ineffective.

There is also evidence that the previous owner has done something with the calipers as they have been cleaned but it doesnt look lihe the seals have been renewed as the piston seals looks quite old.

There are no fluid leaks from any of the joints throughout the entire system.

Your last question about flushing all the fluid ? Yes twice.

Everything I have done on the car to-date has revealed so many jaw dropping bodges so I think my only cause of action is now to remove the front caliper to see if they are working correctly. The pistons definitely move as they grip the disc enough to stop the wheel from rotating when the pedal is applied.

My best guess at the moment is that there is air trapped in the front calipers somehow.

What do you reckon ?


Cheers,

Steve
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SanRemo78
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« Reply #3 on: May 27, 2024, 08:59:51 AM »

You could still have air trapped in the rear circuit which would give a spongy brake pedal? What's the grip from the rear callipers like? And what condition is the rear brake balance compensator in? If it's seized (especially in rear wheels off the deck) it'll make bleeding harder. You may need to peel back the rubber boot to see if the actuator piston on the compensate is moving and also disconnect it from the rear ARB?

Have you ever been able to lock the front wheels under heavy braking? If not that strongly suggests that there is air in the system somewhere or seals in the master cylinder allowing fluid past the pistons.

Guy
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JASPER_40
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« Reply #4 on: May 27, 2024, 11:18:16 AM »

Hi Guy,

The grip of the rear calipers is hard to determine as all I can do is see is the brakes stop the wheel rotation when the wheels are off the ground...which they do....so the pistons actually do move.

The brake balance compensator is pretty crusty inside the dust cover and I doubt it works as I get a good flow of brake fluid when bleeding the rears with the wheels unsupported and off the ground. I have also tried bleeding the rears with the actuaror arm disconnected from th ARB and fixed up as if the wheels were on the ground.

Today, I tried to reverse bleed the fronts and when attempting the drivers side I easily managed to pump fluid back up into the reservoir using a simple syringe. I am thinking that this could have cleared any air in the Master cylinder for both circuits ?
However, on the passanger side it was having none of it (both circuits) and I just couldn't force fluid back up to the reservoir. I did think afterwards that I could have inadvertantly closed the bleed screw when attaching the bleed syringe pipe to the bleeder nipple. surely not and not on each circuit !! I am going to have to re-try the passanger side before I do anything else just to check and save me dismantling anything unnecessarily. strange though as yesterday, I was easily able to bleed the passanger side with my pressure bleeded attached to the reservoir.

I seem to be using up all the supplies of DOT3 in Western Australia....Doh

The saga continues.......
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JASPER_40
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« Reply #5 on: May 27, 2024, 11:20:00 AM »

Hi Steve

I replaced all the brake parts on my Spider when restoring, used a pressure bleeder and simply worked furthest to nearest to MC. Nothing special, it just worked. So I suspect you may have a problem with a seal of flexi pipe. What else have you replaced and if you repeat do you still get any air coming through? I assume you have flushed the old fluid?

Peter

Hi Peter,

No, I didnt get more air coming through when I tried to re-bleed today.

Cheers

Steve
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peteracs
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Peter Stokes


« Reply #6 on: May 27, 2024, 10:44:31 PM »

Hi Steve

All very frustrating. If it was me with your scenario I would try to isolate each section u til you find the problem. A bit of a pain as you need to blank off segments of the brake circuit and make sure no air is left in it.

I would start with the MC a check the new one is actually ok. You say the pistons on the front calipers are moving, but that could just be the second circuit and the primary circuit could be at fault, are the rear pistons moving ok when you apply pressure?

Also if you pump the pedal does it go hard and stay solid or does the pedal go down eventually?

Sorry, just thinking as I writeÖ

Peter
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JASPER_40
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« Reply #7 on: May 28, 2024, 02:25:31 AM »

Hi Peter,

first things first....Today, I am going to re-do that reverse bleeding on the front passanger side as I must surely...surely have inadvertantly closed the bleed nipple (on both circuits !)when fiddling with the syringe......or could be that the brake pedal didnt reset fully after I tested the pedal when I did the drivers side reverse bleed. I understand that if the pedal doesnt fully retract then the passage back to the reservoir is closed off. I have noticed the brake lights staying on sometimes as the pedal doesnt retract by a small fraction...could be just enough to close the passage to the reservoir maybe. I will make sure the brake lights are off before attempting the reverse bleed again.

Note : The brake fluid flowed freely when I did the initial pressure bleed from the reservior.

If I pump the pedal it does not make any difference to the sponginess and pedal travel. If i push the pedal hard it reaches a point and stays there. It does not gradually go to the floor.

This problem situation is exactly the same when I got the car and so with the old MC in place. This brand new MC seems to have made no difference to the sponginess despite thinking that I had found the smoking gun.

Is there a simple way to isolate sections of the braking circuits ?


Cheers,

Steve
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JASPER_40
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« Reply #8 on: May 28, 2024, 10:42:37 AM »

Hi,

Today I tried again to reverse bleed the brakes and managed to pump fluid via all 6 bleed screws back into the reservoir using my trusty syringe. I only pushed about 100ml in each but figured this would be enough to purge the MC of any air. I tried the brakes and they were still as spongy.

Next I pressure bled to whole system from the reservoir ......still no different

I then had a look at the rear brake compensator and disconnedted it from the ARB. I pulled back the rubber boot and could see that the arm that was connected to the ARB was not acting on the compensator plunger at all. I am thinking maybe the plunger is pushed out by the hydraulic action of braking whuch then interacts with the lever connected to the ARB ?

Is this compensator device known to trap air especially if inoperative ? The device itself is pretty crusty but I was able to lever out the plunger with a screwdriver 3-4 mm (took a bit of doing though.

Just as a shot to nothing, tomorrows job is to remove this device and dismantle to see if this may be causing my problem.

Does anyone have any experience with thse compensation devices ?


Cheers

Steve


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peteracs
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Peter Stokes


« Reply #9 on: May 28, 2024, 10:51:41 AM »

Hi Steve

Mine was also very crusty and as they are pretty inexpensive, just replaced it. No idea why it would cause your issue unless leaking?

As to previous question re isolating, not trivial as you would need to make up blanking pieces which also need to be able to bleed as well.

One point on the reverse bleeding. I tried to use a vacuum bleed originally and found it sucked in air via the bleed nipple thread when they were loosened, so made it impossible  to see if you have removed all the air. So I would be much more confident with positive pressure from the MC.

Peter
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JASPER_40
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« Reply #10 on: May 30, 2024, 03:12:14 AM »

Hi Peter,

I managed to remove the rear brake compensator. Bit worried about the 40 year old connections being siezed and possibly having to make new brake lines but needent have worried as the whole thing came off easily.

I couldn't dismantle the unit itself by removing the big screw plug at the back so decided to just bench test it instead.  I found that wiggling the plunger made the action smoother and it gave about 4mm of movement. I then forced compressed air into the inlet port and got the full force of the air blowing out of the exit port. I then used plyers to pull the plunger out whilst blowing in air and the exiting air was significantly reduced. So the unit seems to be working as it should.

I can only assume the hydraulic pressure under braking pushes the plunger / piston and the "torsion bar" connection to the ARB then inhibits the plunger movement accouring to the ride hight at the back.

I am pretty sure that this device would not trap air and therefore be the cause of my spongy brake pedal but I can see that it could have an affect on the abaility to bleed the rear calipers if the wheels are off the ground (as stated in Haynes).

so....no closer to solving my problem of spongy brakes.

Today, I am going to try reverse bleeding the MC directly....still desperate for any help or suggestions.


Cheers

Steve


PS. I discovered a handy hack on the inerweb which was to use something to press down the brake pedal just a little such that the MC piston shuts off the passage back to the reservoir. This then prevents brake fluid from leaking out under gravity from any disconnected unions. I literally only lost a drip. I am sure everyone already knows this....so just me then  !

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squiglyzigly
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« Reply #11 on: May 30, 2024, 08:20:45 AM »

Hi Steve,
Just coming at this from a different direction to consider.
Maybe there isnít any air in the system and you have successfully bled the system.
Maybe there is a mechanical issue introducing Ďplayí into the system. If a calliper isnít sliding correctly in the cage then after you release the pedal pressure the calliper will settle back too far from the disc and the next time you press the pedal you will have to take up the play again.
On many cars with different calliper sliding designs they can experience seized sliders which would give uneven pad wear Ďandí a spongy pedal.
Maybe, just maybe some mechanical part of the system is flexing, assembled incorrectly or simply not seated properly.
Presuming you have a right hand drive car? Then you also have a fair amount of linkage from the brake pedal to the master cylinder on the opposite side of the car. Many times I have found excessive play in these linkages which spoil brake pedal feel. RHD cars are more like factory converted LHD than true RHD cars in some ways.

If you can safely drive the car to a test station and put it on the brake testing rollers it will show you what is and isnít doing itís part of the work.


Good luck
Ian
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JASPER_40
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« Reply #12 on: May 30, 2024, 10:35:42 AM »

Hi Steve,
Just coming at this from a different direction to consider.
Maybe there isnít any air in the system and you have successfully bled the system.
Maybe there is a mechanical issue introducing Ďplayí into the system. If a calliper isnít sliding correctly in the cage then after you release the pedal pressure the calliper will settle back too far from the disc and the next time you press the pedal you will have to take up the play again.
On many cars with different calliper sliding designs they can experience seized sliders which would give uneven pad wear Ďandí a spongy pedal.
Maybe, just maybe some mechanical part of the system is flexing, assembled incorrectly or simply not seated properly.
Presuming you have a right hand drive car? Then you also have a fair amount of linkage from the brake pedal to the master cylinder on the opposite side of the car. Many times I have found excessive play in these linkages which spoil brake pedal feel. RHD cars are more like factory converted LHD than true RHD cars in some ways.

If you can safely drive the car to a test station and put it on the brake testing rollers it will show you what is and isnít doing itís part of the work.


Good luck
Ian


Interesting....When I bought the car 5 months ago I have never since driven it on the road except to a roadworthyness testing station ( Western Australian equivalent of the M.O.T). When the car was delivered to me in the first place the front discs and pads were almost new so the previous owner had done some work on the fronts. This is such a simple job to change the disc and pads so cant imagine what he might have done to mechanically compromise the brakes. Having said this he did neglect to fit any spring retainers for the pads which is so typical of the sort of carelessness of all the other problems I have had to fix.

However...thanks for the advice, I will test out the mechanical operation of the fronts to ensure the carrier slides and centres. I will also remove a pad to ensure the piston is moving in and out smoothly, The previous owner had definitey some other work as the caliper has been cleaned or even replaced and also put on new flexi hoses.

Also, not sure how the linkage from the pedal is supposed to be set up. The previous owner may have tampered with this although I suspect not as there would ne no reason to.

This is all driving me nuts although I now understand the primative operation of the brake compensator device and have cleaned it all up and changed the bushes......just because that is we all do.

Cheers,

Steve



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JASPER_40
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« Reply #13 on: June 03, 2024, 11:49:40 AM »

The saga continues........

I have now plumbed the 2 bleed scews on the passanger side front caliper back into the reservoir and then  contunually pumped fluid using the pedal. To ensure I was not drawing in air fron the bleed screw threads, I had an assistant pump the pedal whilst I opened and closed the bleed screws on each pump. There were no air bubbles visible and so I locked off the screws after about 40 pumps. I then pressure bled the entire system using 2 litres of fresh fluid.

and...would you believe it........made no difference to my spongy pedal whatsoever.

I then did the 2 man bleed just for sh**s and giggles. Made no difference at all.

However, I did notice that there was quite a bit of movement of the front flexi pipes when the brakes were being pumped...virtually nothing at the backs. Got me thinking that maybe the The hydraulic action was being lost as a consequnce of the flexi pipes moving. This can only because the pipes are stretching and/or expanding. Amplifying this over both fronts and to a far lesser extent the rears, then could this not give rise to a spongy pedal with too much travel ? The flexi pipes do give a little under normal circumstances but maybe not supposedly this much.

The front flexi pipes are new (by previous owner) but could be so cheap and nasty that they are creating this spongy pedal effect. The pipes also do not have the clips to carry the wear sensor wire suggesting that they may be non standard or an incorrect specification of flexi pipe for the Beta. (note the front caliper pistons move freely using just finger pressure)

I am tempted to order a set of braided flexi pipes all round to conclusively eliminate this issue and the more I think about it....this is a plausable expalation for my problem....is it not ?

I have money to waste ...NOT !! so would apprecate any advice before I take the plunge in desperation

Cheers,

Steve

I have another italian classic from the 80's and the braking system layout is virtually the same in that the pedal action is transmitted to the other side of the car to the the master cylinder. The pedal on this car is rock solid. The reason for mentioning this is to eliminate the possibility that this is a natural symptom of 80 braking systems on italian cars.
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JASPER_40
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« Reply #14 on: June 03, 2024, 12:32:02 PM »

Oh and......just did same test on my other italian (only has a single front circuit) and the front flexi brake pipes do not move at all when the pedal is pushed hard.

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peteracs
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Peter Stokes


« Reply #15 on: June 03, 2024, 07:05:50 PM »

I would change them. I used braided and never had an issue and should not be an expensive purchase.

Peter
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« Reply #16 on: June 04, 2024, 05:45:27 AM »

I would change them. I used braided and never had an issue and should not be an expensive purchase.

Peter

Yep, agree. Have ordered a set of F & R braided hoses from Mark at Betaboyz. This will conclusively eliminate the flexi pipes as the culpret. I have a video clip of the front pipes "flexing"when the pedal is pumped....will add this to the thread if poss.

Cheers Peter.

Steve
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