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Brakes, bleeding, MBCs and ABS pumps

Community Veteran
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Registered: 01-08-2007

Brakes, bleeding, MBCs and ABS pumps

This is kind of a follow on from a previous thread i started moons ago.

So i've got our renault moved across the residential car park and up onto its axle stands. Wheels removed and i'm going for the bleeding again.

First of all let me give you some insight as to what got me into this position. The car has been sat five years due to technical faults, bad health, lack of money etc. Now I have a small income to do things i started working on it last year - removing all the rusted shocks / springs / subframe etc, wire brushing them, repainting etc. Unfortunately in removing the rear subframe one of the old steel brake pipes that had badly corroded decided to give up and snap off. Worse, while having the front calipers apart (and disconnected) those brake lines also lost fluid.

Now it's all back together and i refilled it with fluid however the brakes were incredibly spongy. When I say this I mean it would take the car approx 10m to stop... from 5mph. Now over the months this has slightly improved to the point where the brakes will hold the car in D or R (it's an auto) but only just. This clearly won't go through an MOT.

So today i've tried bleeding again but only got two nipples done and frankly having no assistant to look at the rear nearside wheel / pipe for bubbles i can't be sure i'm even pumping enough fluid down the line via the pedal.

So guys, how am I going to determine if its simply trapped air in the line somewhere, a dodgy MBC or an ABS pump full of air? - Will the ABS pump even make any difference if its not in use / triggered? Would an MBC suddenly fail just because it was empty of fluid for a while? (to me that seems unlikely but i'm no expert). My logic says that the MBC was functional before the fluid emptied and so it should still work but i've not done brakes to this extent before.

Any ideas?

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12 REPLIES
Community Veteran
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Re: Brakes, bleeding, MBCs and ABS pumps

When bleeding brakes, you should start with the one nearest to the master cylinder reservoir... then proceed to the next nearest, and the next until the final wheel furthest away from the master cyl.

 

From what you say, you are using the old "tube & jam jar " technique, where it really requires two people to do the job... one to push the pedal 4 times and hold, while the second person unscrews the nipple slightly, to bleed through... 

 

You should be able to buy a "one man bleed kit"... from reputable Motor Factors, and these are very good...

 

Basically... you just need to keep topping up the fluid, until the brake pedal feels " right "..  you may need to go round the bleed procedure two or three times...but it should work out in the end... 

It may sound a bit "expensive"... but you should not return "used" brake fluid to the master cylinder after it has been pumped through, because it MAY contain minute bits of rustd/dirt/grit that can seriously damage your rubber seals, long after you have passed your MOT... and this could result in brake failure, when you least expect it.....

 

P.M. is still effective. Smiley

Community Veteran
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Re: Brakes, bleeding, MBCs and ABS pumps


shutter wrote:

When bleeding brakes, you should start with the one nearest to the master cylinder reservoir... then proceed to the next nearest, and the next until the final wheel furthest away from the master cyl.

 


 The problem I'm having there is that some people say that you should start with the wheel that is furthest - so i am still at a loss here. Others say you should do them diagonally... i'm stumped as to what to trust.

 


shutter wrote:

From what you say, you are using the old "tube & jam jar " technique, where it really requires two people to do the job... one to push the pedal 4 times and hold, while the second person unscrews the nipple slightly, to bleed through... 


 Similar yes, a friend gave me a bleeder tube that has a one way valve on it that i can just leave hanging in a plastic container. Trouble is that even he didn't realise i'd need a second person to watch for the bubbles of air.

 


shutter wrote:

 

You should be able to buy a "one man bleed kit"... from reputable Motor Factors, and these are very good...

 

Basically... you just need to keep topping up the fluid, until the brake pedal feels " right "..  you may need to go round the bleed procedure two or three times...but it should work out in the end... 

 


 The problem is i'm not sure its ever going to feel 'right'... and thats my problem. I'm stuck in between a rock and a hard place (as usual). But I will look into this kit.

 


shutter wrote:

 

It may sound a bit "expensive"... but you should not return "used" brake fluid to the master cylinder after it has been pumped through, because it MAY contain minute bits of rustd/dirt/grit that can seriously damage your rubber seals, long after you have passed your MOT... and this could result in brake failure, when you least expect it.....


 I wouldn't recycle the fluid - i've got a big 4L bottle of the stuff for the job and being that the brake lines are quite thin the system doesn't seem to use much from that 4L bottle. The problem is though that i've no idea when to stop pumping it out. I do recall though that when we first refilled it and was pumping it through to the back end, it did seem to take an age for the fluid to get from the reservoir to the nipple - i think it was about 5 minutes.

 


shutter wrote:

 

P.M. is still effective. Smiley


No thanks.

I need a new signature... i'm bored of the old one!
Community Veteran
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Re: Brakes, bleeding, MBCs and ABS pumps

If the car has been standing around that long it could well be a seal allowing air into the system, not sure if you can still buy kits that allow you to refurbish the MBC or other seals such as those in calipers etc.

There comes a time with most cars no matter how attached we are to them that it is not financially viable to keep them on the road unless you have deep pockets in which case you can rebuild almost anything.

One last thought, can you get a MCB from a local scrapyard or reconditioned one with a guarantee .?

 

Community Veteran
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Re: Brakes, bleeding, MBCs and ABS pumps

On some ABS systems a scan tool is required, you may wish to check out if this applies to your car.

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Re: Brakes, bleeding, MBCs and ABS pumps

If you start at the shortest first...you eliminate the air bubbles in that line...then proceed to the next and so on....  ( logical thinking... new fluid pushes out old fluid and bubbles... ) ( as you elimnate it in each pipe in order of shortest first, the shorter pipe is full of "good" fluid, and will remain so, while you bleed the next.. )

 

However,

 

Old seals could well be a source of injecting "new" air bubbles,...thus making your task more difficult to complete effectively.

David_W
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Re: Brakes, bleeding, MBCs and ABS pumps

I don't know if it works on a car (works on a bike, sometimes) but you can reverse bleed, get a syringe and put it over the nipple, push the fluid back through the system pushing the air out of the system.

 

I just bled my brake using a 1 man kit, the right side (I have two, once each side on my front wheel) was perfect, open, close, no air at all, left side?  Air, Air, Air, Air, Air.  What you could easily do, put a one man kit on the rear wheel, pump 3 or 4 times, top up, pump again, top up, pump again, top up, you *will* go through a lot of fluid, for just my two calipers it took almost a whole bottle before the air was gone.

 

Final option (and most expensive) is a vacuum pump, stuck it on the nipple and it'll suck the fluid and air out, I tried it with a syringe and a lot of air did come out, pretty much constantly, for reference, my left hand side is furtherest from the MC and Haynes manual states to bleed the right hand side first.  Don't worry about using all the brake fluid btw, you can't store it (it's now exposed to air, which is bad for the fluid, so next time you bleed them you'll need a new bottle of brake fluid, it's not something you can keep in the shed for 6 months).

 

/edit - also, keep an eye on the fluid, if it goes too low it'll let air in.

jockwav
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Re: Brakes, bleeding, MBCs and ABS pumps

Don,t you start furthest away from the master cylinder?.Huh

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Re: Brakes, bleeding, MBCs and ABS pumps

So that you push any air bubbles into the longest pipe  , from the shorter ones...  ? ?  

 

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Re: Brakes, bleeding, MBCs and ABS pumps

Think of EACH pipe as a closed system, once you have closed the bleed valve no more air can enter or leave that pipe, so you should start at the longest one and move forward, each time you are cleaning air from the pipe to the junction box (if there is one) or the mcb. Till you get to the shortest and you have the least air to remove.
You may need a new mcb as has been said. I had a Renault that had a similar issue, no matter how much I bled them it was still spongy. New mcb was the cure, I could have tried a seal kit but the difference was minimal for a replacement.

Its the same with a water radiator system, if you put a bung in the feeds (usually in the attic) then you can remove any of the radiators without it leaking water.
PowerLee
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Re: Brakes, bleeding, MBCs and ABS pumps

The correct order to bleed the brakes in will be stated by the car manufacture.

Normally you start furthest away from the master cylinder but not all systems are the same.

If air gets trapped inside the ABS hydraulic modulator then diagnostic computer may be needed to activate the valves during bleeding.

What car / ABS system is it?
jockwav
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Re: Brakes, bleeding, MBCs and ABS pumps

I have always bled brakes starting at the furthest away from the master cylinder for a lot of years without any problem.Smiley

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Re: Brakes, bleeding, MBCs and ABS pumps

Hi Guys,

Yes I thought it was the furthest away from the MBC however today i just settled for that... and then anything random lol.

So I went and bought an eezibleed thing from Halfords to do this job and nearly cried at the loss of £20 (having just paid a plumber silly money to unblock a drain). Anyhow after faffing about for a couple of hours the eezibleed seems to have paid off as the brakes are now functional. The rear drivers side nipple was the only one to let out any air through the pipe... but when it did, it did so in spectacular style. I kid you not, there was LOADS of it coming out and bubbling up through the silicon tube and when I say loads, it must have been around 15-20cm in length. Not quite sure how that would have affected the other brakes though ... and there was a very significant loss of braking power..

The others produced tiny little bubbles but nothing significant. What I did find odd though was that the fluid flow seemed quite slow on most of the wheels... except the rear drivers one where the air was.. where it flowed a fair bit quicker.

 

Anyhow its working now, braking seems back to its powerful usual sluggish self - it's a big old renault luxo barge... great car but it's always had [-Censored-] brakes (and we've had three of them and they were all the same).

Now i need to get to grips with what is causing the ecu to throw a wobbly...

Thanks for everyones help!

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