Bleeding brakes doing my nut

[Moseley]

I've never had a problem bleeding brakes on any car in the past, but this has got me stumped as to where to go next.

The system was working fine prior to being dismantled - and all I've done in 'dismantling' is to break into the front and rear lines for fitting of new parts, and then re-connected back up. Drums have also been adjusted when putting back together, although without cantering the pads at this stage.

So, I've come to bleed, and started at the front as per Bentley. (It's a 70 bay with a dual circuit MC, no servo. As far as I can see, the lines go direct to all wheels). Should also mention, the pedal has the free play, although the spring isn't great, so it does require manually lifting the pedal with each pump.

The fronts bled fine, lots of clean, air free fluid flowing.

However, the backs, especially the drivers side isn't playing ball. I am getting a continual stream of bubbles through the line despite the new fluid being well flushed through. The bottle is kept topped up throughout, and I can't see any leaks anywhere. The pedal has not gotten any better despite all the air coming out, so it seems like air is getting in somewhere. The pedal is completely soft until about the last inch of travel where it goes solid with all nipples closed.

Is it possible for the MC to draw air in? Have I just got extremely unlucky that it has broken just as I've come to bleed it? Any other ideas as I'm at a bit of a loss with this one, and don't just want to start replacing bits willy nilly.

 

[67panel]

if the seals are tired then yes air can bypass them ,also as you have pushed the piston further up the bore it could have stuck.might work with reverse bleeding .thats presure bleed from the bleed nipple back .remember fluid will come out of filler bottle.

 

[subheatadey]

If the hoses are old maybe a good thing to replace?

 

[neilswheels]

Not sure about the Bentley manual, but i've always bled the one furthest away from the MC first, so for me, LHD, off side rear, then ns rear, then os front then ns front. Always worked for me.
I've heard that pushing the peddle down and holding it there for a long period, i.e, over night, gets rid of alot of air in the system, never tried it myself tho.

 

[yoda]

it does sound as if the master cylinder is at fault. have you tried bleeding the master cylinder. Then bleed the brakes starting at the closest wheel. Also clamp off all the brake hoses and see what effect this has on the pedal, then release the clamps one at a time to see what happens. Then reclamp and try another wheel. good luck.

 

[Moseley]

Cheers for the replies - just to respond to a few things mentioned above, the lines are all nearly new and are a combination of flexi and copper. I've also used the 'wedging the brake pedal down overnight trick' in the past on a clutch, but the pedal is so soft for so much of its travel that there must be a lot of air still present somehow.

I will try clamping the wheels, particularly both rears as these seem to be causing the problem and see what effect that has.

 

[K@rlos]

Always bleed the wheel furthest from master cylinder 1st.

 

[Moseley]

Right, I tried clamping off both rears (can't do all four wheels as not got enough clamping devices!) and the pedal didn't change in the slightest. It still had resistance free travel right up until the last inch, where the pedal goes solid and the front wheels lock up.

I whipped off the MC and disassembled - but doesn't look like anything wrong with it. The first seal however, does have what looks like an indented ring around it's sealing face, although it isn't passing fluid. The other seal has a 'linear' sealing face for want of a better description. I'm wondering if this is causing air to enter the rear system.

Anyway, I put it all back together and re-bled for the sake of it, but still exactly the same symptoms and air forever streaming out of both rear nipples and not a great deal of fluid.

 

[westy1]

had same prob on an early bay, has the front callipers got 2 bleed nipples on each one? if so bleed bottom one first then top one, one side of mine only had 1 bottom nipple i had to swop callipers over to get nipple to the top,
i also found that the rear flexi x2 looked ok but had collapsed and would not let letting enough fluid out,

good look

 

[Moseley]

had same prob on an early bay, has the front callipers got 2 bleed nipples on each one? if so bleed bottom one first then top one, one side of mine only had 1 bottom nipple i had to swop callipers over to get nipple to the top,
i also found that the rear flexi x2 looked ok but had collapsed and would not let letting enough fluid out,

good look

I've got drums all round, no compensators, no servo. So the system is as basic as it could be with one bleed nipple on each.

Mine doesn't seem to be an issue with the fluid getting through - just that the rears are seemingly drawing in air from somewhere as I'm getting an endless amount of bubbles coming from both sides. The fronts bled fine, and when the pedal does finally go solid, the front brakes lock up.

It makes sense in my head about the MC pulling in air, and it even sounds like it is full of air when pumping the pedal from underneath, but it just doesn't seem overly common having it allowing this to happen. Unfortunately, the only past threads I found on here with similar symptoms, the OP didn't post back with what solved it.

Guess there's only one way of finding out...

 

[Moseley]

Right, just to update on this, I've just changed the master cylinder and then bled all wheels again to see what effect this has had. The fluid is running much cleaner, and more positively from all wheels.

The pedal was still travelling a long way before going solid, as before, so I've given the MC a bleed on the bus (hold pedal down, crack off hard line, then re-tighten and release pedal). This released a small amount of air from the rears.

I haven't re-bled yet, but I can now pump up the pedal where I couldn't beforehand, so am hoping that this points to just the system needing a better bleed and that the MC is now actually holding pressure / not drawing air in.

Fingers crossed for tomorrow evening...

 

[vwcanuck]

Good to hear you probably found the major problem but as others have said ... bleed from the furthest wheel first to the nearest last to get all of the air out.

 

[bigdaz]

In know you said you adjusted the shoes but wondering if they arnt quite tight enough this would make the pedal travel as it takes up the slack.

Sent from my GT-P5210 using Tapatalk

 

[Moseley]

Subject: Bleeding brakes doing my nut

In know you said you adjusted the shoes but wondering if they arnt quite tight enough this would make the pedal travel as it takes up the slack.

Sent from my GT-P5210 using Tapatalk

I'll give you half a gold star, just because I hadn't updated this with my solution!

It did in part turn out to be the front brake adjustment. I'd wound the brakes out to how they should be, but I think as I'd been working my way round, the pads had re-centred / cylinders retracted further and it was causing a lot of free play in the pedal. Once re-adjusted, I now have a lovely solid pedal, and feel like I've earned a degree in brake bleeding and adjustment!

I think the original problem was still the MC letting in air, as once the new one was fitted, the fluid ran clean from the nipples, and although initially the pedal travel was still long, it was marginally more positive, as if it was moving fluid rather than air.

These things are sent to try us!!

 

[Hilly_70]

Hi bud ..

Just read your thread with interest .. As its exactly what im getting!

just cant bleed them .. pushesclean fluid through rears too but cant get pedal pressure ..

Mines a 70 too .. did you manage to get a master cylinder easily enough?

cheers

Hilly

 

[Moseley]

Hi bud ..

Just read your thread with interest .. As its exactly what im getting!

just cant bleed them .. pushesclean fluid through rears too but cant get pedal pressure ..

Mines a 70 too .. did you manage to get a master cylinder easily enough?

cheers

Hilly

I did gain a few grey hairs whilst trying to figure it out, and used a lot of brake fluid!

Assuming that you're confident that the rest of the system is all good, personally, I'd wind the adjusters out on all cylinders so that the shoes are all dragging. This will ensure that each pump on the pedal is forcing fluid out of the bleed nipples. And not just taking up slack in the pistons which can be confused with air in the system.

If this fails then master cylinders can be had from heritage - however, I think I ordered the wrong one as although all the pipes line up etc, it only has a port for one brake switch, not the two that it had on before (assuming that was as it left the factory?)

If I ever get round to it, I'll probably try to rebuild the original.

 

[Hilly_70]

Cheers dude!

I'll try winding them all out tomorrow but pretty sure theyre nearly there already!

Just did my head in this afternoon! .. Ive had the bus nearly 10 years and never had a prob till today!
It worked before I touched it today!..thats the wierd thing..

Anyway .. got tomorrow off to try again with more patience and less swearing!

Cheers bud

Hilly