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Author: Subject: Brake bleeding help - please!!!
contaminated

posted on 28/3/11 at 10:06 AM Reply With Quote
Brake bleeding help - please!!!

Forgive the long post – but I need some help!

Last year I had all sorts of problems trying to bleed my rear brakes. I had M16 calipers on the front and what I thought were sierra on the rear (turns out they are VAG). I was running a single Ford master cylinder and a servo. Try as I might I could not bleed the rears – the pedal would just hit the bulkhead. Eventually 7 Indulgence bled them for me, but even they struggled and I had loads of pedal travel. They never inspired confidence.
Recently I decided to replace all the pedals with a decent bias bar pedal box. It’s all installed and the clutch and throttle are lovely. I have the same VAG callipers on the rear and M16 on the front and again I’m getting:

1. Quite a bit of pedal travel
2. The brakes just don’t stop the car – no chance you could lock the brakes;
3. They don’t pump up with repeated brakes presses – they are constant as above.

I have tried removing the callipers and ensuring the bleed nipples are at the top. I’ve bled with handbrake mechanism attached and detached. I’ve used both the Easibleed and SWMBO’s foot methods. I have wedged the pedal down over night. I have cracked open the connections on the master cylinders and given them a little bleed. The brake pedal continues to travel a couple of inches before firming up but won’t stop the car.
I’m after some suggestions now because I want to be able to sort this out myself if I ever have to take it apart again. Things I’ve thought of are:

1. Residual pressure valve – the master cylinders are pretty low compared to the callipers. Thing is though if this was the issue surely the brakes would just be spongy as opposed to not stopping the car? Also would they not pump up?
2. Using one of those vacuum things to remove engine oil through the dipstick to pull the fluid through from the callipers;
3. Removing the callipers and letting the pistons pump out an inch or so which bleeding, and then winding them back.

Other than the above can anyone think of anything? This is the only thing preventing me from going for the MOT and getting back on the road!

Dan





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RichN

posted on 28/3/11 at 11:22 AM Reply With Quote
Have you got vacuum going to the servo i.e. servo assistance?

I remember years ago a garage trying to bleed the brakes on my sisters Metro after changing a rear wheel cylinder and they couldn't do it until they had the engine running.

They we saying the master cylinder needed replacing, my Dad told them to run the engine and then bleed, it worked !

May be worth a try?

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ashg

posted on 28/3/11 at 11:29 AM Reply With Quote
its all about angle of the dangle dan. wind them back remove them wand face the bleed nipples up. you need to stick a block of wood in each caliper to stop them moving.

if you need the windback tool or an eazy bleed, vacuum bleeder let me know i have all of them.





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contaminated

posted on 28/3/11 at 12:34 PM Reply With Quote
quote:
Originally posted by RichN
Have you got vacuum going to the servo i.e. servo assistance?

I remember years ago a garage trying to bleed the brakes on my sisters Metro after changing a rear wheel cylinder and they couldn't do it until they had the engine running.

They we saying the master cylinder needed replacing, my Dad told them to run the engine and then bleed, it worked !

May be worth a try?


I've ditched the servo set up now - so it's not that.





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contaminated

posted on 28/3/11 at 12:36 PM Reply With Quote
quote:
Originally posted by ashg
its all about angle of the dangle dan. wind them back remove them wand face the bleed nipples up. you need to stick a block of wood in each caliper to stop them moving.

if you need the windback tool or an eazy bleed, vacuum bleeder let me know i have all of them.


Not sure I understand all of that Ash mate! I have the tools, just not the talent. You'd be very welcome to pop round and educate me!





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Frosty

posted on 28/3/11 at 02:21 PM Reply With Quote
Are you sure the master cylinder is correct for the callipers, or if it's functioning correctly? It doesn't sound like air if you can't pump the pedal up.

Does the pedal improve with the handbrake on?

Double-check that the rear pads are fitted correctly. The Sierra rear pads have a nipple on them which must perfectly align with the piston. If it's off, the pad does not get pressed correctly and you get stacks of extra travel.





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contaminated

posted on 28/3/11 at 02:25 PM Reply With Quote
Are you sure the master cylinder is correct for the callipers, or if it's functioning correctly? It doesn't sound like air if you can't pump the pedal up. The pedal box and master cylinders came as a set and it's the same as many others use on here.

Does the pedal improve with the handbrake on?
I've not checked actually, but I will - ta.

Double-check that the rear pads are fitted correctly. The Sierra rear pads have a nipple on them which must perfectly align with the piston. If it's off, the pad does not get pressed correctly and you get stacks of extra travel. I'll check that as well.





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flibble

posted on 28/3/11 at 02:31 PM Reply With Quote
What ash was saying was to slide the calipers off the brake disc, stick a bit of wood between the pads (so they dont close up when you pump the pedal) and hold the caliper so the bleed nipple is at the top, then bleed.
Of course this is only relevant if your nipples arn't at the top already

I know I've had to do it like this on a few of my bikes that have the bleed nipple near the bottom of the caliper, I'd guess that the air thats floated to the top edge of the caliper won't naturally find its way downwards.

[Edited on 28-3-11 by flibble]

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britishtrident

posted on 28/3/11 at 02:49 PM Reply With Quote
quote:
Originally posted by flibble
What ash was saying was to slide the calipers off the brake disc, stick a bit of wood between the pads (so they dont close up when you pump the pedal) and hold the caliper so the bleed nipple is at the top, then bleed.
Of course this is only relevant if your nipples arn't at the top already

I know I've had to do it like this on a few of my bikes that have the bleed nipple near the bottom of the caliper, I'd guess that the air thats floated to the top edge of the caliper won't naturally find its way downwards.

[Edited on 28-3-11 by flibble]



Thats exactly right nipples must be at the highest point of the caliper when bleeding.

The other thing is of course after bleeding to release the tension fully in the handbrake cable and pump the pedal several times before readjusting the handbrake cable.

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daviep

posted on 28/3/11 at 02:55 PM Reply With Quote
Is it definately the rears which are the problem? Now that you have twin MC's can you see which one is travelling excessively?

When you say you can't lock the wheels is this beacuse the pedal hits the floor or you can't push it hard enough?

Have you looked to see if there are any of the calipers flexing on there mounts? It's quite easy to get a long pedal if a caliper is flexing 1mm will give quite a spongy pedal.

How are your calipers mounted?

Have you tried clamping of the flexi pipes to each wheel in order to diagnose which wheel is the problem?

Regards
Davie





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contaminated

posted on 28/3/11 at 02:59 PM Reply With Quote
quote:
Originally posted by flibble
What ash was saying was to slide the calipers off the brake disc, stick a bit of wood between the pads (so they dont close up when you pump the pedal) and hold the caliper so the bleed nipple is at the top, then bleed.
Of course this is only relevant if your nipples arn't at the top already




I've tried this several times already sadly - but not letting the pistons travel out a bit yet.





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contaminated

posted on 28/3/11 at 03:04 PM Reply With Quote
Is it definately the rears which are the problem? I am pretty sure this is the case. I will know later because I'm going to block off that master cylinder with a bleed nipple and see if the fronts work. Now that you have twin MC's can you see which one is travelling excessively? I've tried, but it's not easy to see really. I did wonder whether with a balance bar I should be bleeding the front and rears at the same time so that the system that isn't being bled doesn't prevent total pedal travel during bleeding?

When you say you can't lock the wheels is this beacuse the pedal hits the floor or you can't push it hard enough? Can't push hard enough, pedal doesn't reach the floor. Last year it was the opposite problem!

Have you looked to see if there are any of the calipers flexing on there mounts? It's quite easy to get a long pedal if a caliper is flexing 1mm will give quite a spongy pedal. I think this is ok - they worked originally and I've not changed anythinh here. I will check though.

How are your calipers mounted? Almost identical to sierra ones i.e. on sliders.

Have you tried clamping of the flexi pipes to each wheel in order to diagnose which wheel is the problem? I can't really. Everthing is solid or braided.

Thanks for the help so far chaps.

[Edited on 28/3/11 by contaminated]





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Frosty

posted on 28/3/11 at 03:10 PM Reply With Quote
quote:
Originally posted by contaminated

When you say you can't lock the wheels is this beacuse the pedal hits the floor or you can't push it hard enough? Can't push hard enough, pedal doesn't reach the floor. Last year it was the opposite problem!

Have you given the brakes some abuse? My brakes were shocking until I had got them nice and hot. I had to press the pedal so hard to get the car to stop, so I went out to a dual carriage way and bedded them in.

Lots of 60mph to 30mph stops in blocks of five, and then let them cool for a bit, then again, and again. It introduced the friction material onto the discs and the car worked fabulously after that.





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contaminated

posted on 28/3/11 at 03:21 PM Reply With Quote
quote:
Originally posted by Frosty
quote:
Originally posted by contaminated

When you say you can't lock the wheels is this beacuse the pedal hits the floor or you can't push it hard enough? Can't push hard enough, pedal doesn't reach the floor. Last year it was the opposite problem!

Have you given the brakes some abuse? My brakes were shocking until I had got them nice and hot. I had to press the pedal so hard to get the car to stop, so I went out to a dual carriage way and bedded them in.

Lots of 60mph to 30mph stops in blocks of five, and then let them cool for a bit, then again, and again. It introduced the friction material onto the discs and the car worked fabulously after that.


I'll try that - but I've not changed the pads so they should be fine really.





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daviep

posted on 28/3/11 at 03:33 PM Reply With Quote
quote:
Originally posted by contaminated
When you say you can't lock the wheels is this beacuse the pedal hits the floor or you can't push it hard enough? Can't push hard enough, pedal doesn't reach the floor. Last year it was the opposite problem!

[Edited on 28/3/11 by contaminated]


What sizes of MC are you running?
Which size is going to which circuit?

If you can't press the pedal hard enough then it doesn't sound like a bleeding problem to me, I'm suspecting that your MC's are too big or hooked up backwards.

To go from a single servo'd MC to twin is pretty dramatic change, unless you've gone for very small MC's then you may have increased the piston area which in effect lowers your mechanical advantage, and then you have ditched the servo which will make the brakes feel even heavier.

Davie





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contaminated

posted on 28/3/11 at 03:46 PM Reply With Quote
What sizes of MC are you running? 0.7 and 0.625
Which size is going to which circuit? 0.7 to the rear

If you can't press the pedal hard enough then it doesn't sound like a bleeding problem to me, I'm suspecting that your MC's are too big or hooked up backwards. Surely not? Funnily enough the MCs connections are ar$e about face in my view - the connection to the resevoir being furthest from the bulkhead and all. I'm sure it's righ though.

To go from a single servo'd MC to twin is pretty dramatic change, unless you've gone for very small MC's then you may have increased the piston area which in effect lowers your mechanical advantage, and then you have ditched the servo which will make the brakes feel even heavier. Point noted, but I think pleanty of others are using this setup.





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daviep

posted on 28/3/11 at 03:56 PM Reply With Quote
When bleeding are you getting a nice easy free stroke of the pedal all the way to the floor?

Do you have a gap at either side of the pedal on the bias bar so that it can pivot in the pedal?

The only thing I can think of is that something is physically binding and all the force isn't being transmitted to the MC's

Regards
Davie





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macc man

posted on 28/3/11 at 04:09 PM Reply With Quote
I just checked my master cylinders and indeed the resevoir does feed the furthest inlets on the cylinders. I had same problem with spongy brakes and it was the rear caliper bleed nipples being at the bottom. bled off the car with nipples inverted and problem sorted. I beleive the self adjusters on the rears can cause problems. Might be worth taking apart to make sure all ok inside. I remember fitting a larger master cylinder to my Anglia and had the effect of making pedal effort worse. Best of luck.






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contaminated

posted on 28/3/11 at 04:31 PM Reply With Quote
quote:
Originally posted by daviep
When bleeding are you getting a nice easy free stroke of the pedal all the way to the floor?

Do you have a gap at either side of the pedal on the bias bar so that it can pivot in the pedal?

The only thing I can think of is that something is physically binding and all the force isn't being transmitted to the MC's

Regards
Davie


Yes and yes. I'll give it all another go later and see what happens.

Dan





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plentywahalla

posted on 28/3/11 at 04:43 PM Reply With Quote
I had a similar problem on the wifes tintop. no amount of conventional bleeding would give a firm pedal.

I got a spare reservoir cap from a breakers, drilled and fitted a tyre valve into the top, turned the compressor regulator down to 5 psi, used a long neoprene tube on the bleed nipple and gently pushed a whole reservoir of fluid through the line with a tyre inflator.

Amazing how much air came out even though we had been pumping conventionally for hours. Instant solution!

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Frosty

posted on 28/3/11 at 05:33 PM Reply With Quote
quote:
Originally posted by plentywahalla
I had a similar problem on the wifes tintop. no amount of conventional bleeding would give a firm pedal.

I got a spare reservoir cap from a breakers, drilled and fitted a tyre valve into the top, turned the compressor regulator down to 5 psi, used a long neoprene tube on the bleed nipple and gently pushed a whole reservoir of fluid through the line with a tyre inflator.

Amazing how much air came out even though we had been pumping conventionally for hours. Instant solution!

Basically an Eazibleed system then

The reason this works so well is because the pump of a pedal only moves a very small amount of fluid (by the time the mechanical reduction has been factored in). Any trapped air moves a little bit with the fluid, and then moves straight back to where it was again. If it's trapped in a high-point, it will stay there because the air bubble will not move far enough with a pump of the pedal.

The easibleed keeps all of the fluid moving constantly though, so the air gets flushed out. The Easibleed system can be had for about £15 delivered on eBay, and it's worth every penny IMO. It saves having to remove callipers and all of that messing around.





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mad-butcher

posted on 28/3/11 at 05:56 PM Reply With Quote
Helped a fellow builder once with a similar problem, problem became clear as soon as I as got under the car rear brake line came out of the master cylinder along the top of the transmission tunnel to a T piece mounted on top of the diff. no amount of normal bleeding was going to shift that, easibleed well sorted it.
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contaminated

posted on 28/3/11 at 06:47 PM Reply With Quote
I've Easibled it to death!





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ashg

posted on 29/3/11 at 12:24 AM Reply With Quote
if its not sorted by the weekend i will pop down and take a look. think mark has issues as well so if we can crack one of them it may help the other.





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