brake problems

[steve_k]

hi folks, looking for a bit of advise.

i'm in the process of getting a mates e30 ready for it's first mot in a good few years,

i've gone through everything with a fine tooth combe but i'm stuck with one little problem.

it's the brakes that have got me stumped.
a little background on the brakes.

the fronts are hi-spec billet 4 callipers with 285x25 discs, full one piece braided steel lines to the M/C (no abs),
rears are rebuilt touring spec callipers with one piece lines to a new rear T piece then one piece to the M/C.

the servo & master cylinder are off an E90 325i, the M/C was rebuilt with new seals & bench bled before fitting,
the one way valve on the servo is from an R56 mini cooper (2L),
brakes all bled properly using both the 2 man method & a pressure bleeder.

now the bit thats got me stumped is this,

with the engine off (keys in my pocket) if i press the brake pedal it's very firm, barely moves,
yet if i run the engine it's very soft & spongy & appears to go all the way down.

each time this happens i've bled the brakes again & there's no air in the lines at all.

i'm beginning to wonder if the one way valve is at fault as it seems like there's no vacuum in the servo.

has anyone else had this problem? if so how did you go about curing it?

help me out here folks i'm at my wits end with it.

[steve_k]

just had a look on bmwfans.info & it shows the non return valve as a simple straight connector (no valve inside).

would it be worth trying a simple hose connector??

[martauto]

Is it not the case that the servo is working which lets you press the brake pedal with ease as oppose to the engine not running?
Has this system ever worked in anger ?
You may as well try it with a straight connector, nothing to loose there.

Mart.

[steve_k]

Is it not the case that the servo is working which lets you press the brake pedal with ease as oppose to the engine not running?
Has this system ever worked in anger ?
You may as well try it with a straight connector, nothing to loose there.

Mart.

That's what I can't figure out,

I'm leaning towards the non return valve not working,

Going to try the straight connector & see what happens,

Also, no ot hasn't been used in anger yet.

[DanThe]

If the system is free of air and the pedal goes all the way down you are either losing fluid or it is circulating in the master cylinder (passing the piston seals)
The 'non return valve' mounted below the fusebox is actually a pressure valve, it stops the rear brakes coming on until a certain pressure is reached, it cannot allow the pedal to sink unless there is air in it or fluid is leaking from it,

Where did you get the cylinder seals from? 99% of so called rebuild kits are not fit for purpose in my opinion, cheap chinese shite has spread like a plauge and found its way into box's with even the best manufacturers names on it. For that reason I would rather buy a new master than rebuild one

[DanThe]

Oh and if the pedal is sinking to the floor I wouldnt want to drive it much let alone in anger!

[martauto]

Oh and if the pedal is sinking to the floor I wouldnt want to drive it much let alone in anger!

The "anger " bit was ment to be taken as "used" at all

Mart.

[steve_k]

If the system is free of air and the pedal goes all the way down you are either losing fluid or it is circulating in the master cylinder (passing the piston seals)
The 'non return valve' mounted below the fusebox is actually a pressure valve, it stops the rear brakes coming on until a certain pressure is reached, it cannot allow the pedal to sink unless there is air in it or fluid is leaking from it,

Where did you get the cylinder seals from? 99% of so called rebuild kits are not fit for purpose in my opinion, cheap chinese shite has spread like a plauge and found its way into box's with even the best manufacturers names on it. For that reason I would rather buy a new master than rebuild one

hi dan,

there's no loss of fluid as i've checked using talc on all the unions while the pedal was pressed several times.
the rebuild kit was purchased direct from bmw, though there is a brand new M/C on the way just in case.

the non return valve i mentioned is the one that goes into the servo from the TB, but from what i can see online the part number (e30 & e90) comes back as a simple connector so i'll be trying that in the next day or so (weather permitting) & see how that goes.

the pressure valve onder the fuse box was replaced with a tilton adjustable valve to stop the rear brakes locking up before the fronts (recommended by my rally driver father in law).

i'm starting to lean towards the servo being fubared to be honest.

[steve_k]

Oh and if the pedal is sinking to the floor I wouldnt want to drive it much let alone in anger!

The "anger " bit was ment to be taken as "used" at all

Mart.

it's only been "tested" on his drive way so far.

[martauto]

, though there is a brand new M/C on the way just in case.

My money is on this.................... sounds like your in the same camp ???

Mart.

[steve_k]

, though there is a brand new M/C on the way just in case.

My money is on this.................... sounds like your in the same camp ???

Mart.

i am slightly, going to test out the straight connector first (cheap/easy option) & go from there.

[ChrisHC]

There is a pull rod running across the car from the brake pedal to the M/C and if that is not properly adjusted it can give a very spongey feel to the pedal so that might be worth looking at, but would not account for the brakes being quite as bad as you describe.

[steve_k]

There is a pull rod running across the car from the brake pedal to the M/C and if that is not properly adjusted it can give a very spongey feel to the pedal so that might be worth looking at, but would not account for the brakes being quite as bad as you describe.

I'll check that again as it was adjusted to bring the pedal back up to its correct position.

[steve_k]

I better update this.

Checked the rod from the pedal to clevis & that's fine,

So I removed & checked the "check valve" on the servo.

Bear in mind this from an r56 mini Cooper,

With this removed, if I blow as hard as I can into it from the servo side the valve opens

But if I blow into it from the TB side there's nothing (like I'm blowing with my mouth closed).

I should have an "empty" L shaped connector tomorrow so I'll fit that & see what happens,

Dug out the old vacuum line from the e30 servo & it appears to be a simple "open" connector which is what comes up when I search the part number on Google,

So strange.

[martauto]

Is this what is supposed to happen as in hold the vacuum in the servo ?

Mart.

[steve_k]

Is this what is supposed to happen as in hold the vacuum in the servo ?

Mart.

I'll be honest I don't know but it's worth a try.

[DanThe]

Thats what it is supposed to do

This part will have no effect on the peal sinking

[fixedwheelnut]

Thats what it is supposed to do

This part will have no effect on the peal sinking

What Dan said, the one way valve is only there for safety it holds vacuum in the servo so in the event of engine failure there is enough vacuum held in the servo for approx six applications of the brakes before it is gone.

The pedal sinking if there are no leaks or air in the system is more than likely Master Cylinder seals.

Does the pedal sink regardless of engine on or off?

[steve_k]

Thats what it is supposed to do

This part will have no effect on the peal sinking

What Dan said, the one way valve is only there for safety it holds vacuum in the servo so in the event of engine failure there is enough vacuum held in the servo for approx six applications of the brakes before it is gone.

The pedal sinking if there are no leaks or air in the system is more than likely Master Cylinder seals.

Does the pedal sink regardless of engine on or off?

That's the thing, with the engine off the pedal is good & firm, engine running & it goes pretty low & feels soft.

I checked the M/C & can't see any signs of fluid leaking out.

[flybynite]

I checked the M/C & can't see any signs of fluid leaking out.

Doesn't have to leak to be buggered, it is just getting past the seals and 'recirculating' the fluid in the MC instead of pushing it down the pipe.

If the pedal is going to the floor and no fluid is leaking out then it has to be the MC.

[DanThe]

You could also have a situation where the diameter of the new master is wrong for the calipers, you could have picked a MC too small, what are the bore sizes of the MC?

[steve_k]

the M/C is a 25.5mm one from an e90 335D.

[DanThe]

That should be giving a very firm pedal

[steve_k]

That should be giving a very firm pedal

That's what I was expecting,

I'm leaning towards the M/C being fubar internally as you suggested,

I'll get hold of another to try & see how it goes,

[martauto]

Pressure is an exact item as it must have the correct components ALL working together with the same spec`s and if just one is not "up there" the whole system could throw all sorts of issues which you could spend , spend , spend.
We make a lot of hydraulic rams for the construction industry , maybe a couple of thousand a year, and each and every one is tested wayyyyyyyyy above their operating limits.
Seals DO fail even when new, thats why we test each one over and above.
Men in deep holes need to know it`s all correct.
Back on subject, the M/C seems to be the culprit, but the same principles apply .

Mart.

[steve_k]

Pressure is an exact item as it must have the correct components ALL working together with the same spec`s and if just one is not "up there" the whole system could throw all sorts of issues which you could spend , spend , spend.
We make a lot of hydraulic rams for the construction industry , maybe a couple of thousand a year, and each and every one is tested wayyyyyyyyy above their operating limits.
Seals DO fail even when new, thats why we test each one over and above.
Men in deep holes need to know it`s all correct.
Back on subject, the M/C seems to be the culprit, but the same principles apply .

Mart.

Cheers mart,

I'll get gold of another one & give that a try,
It's the only part that can be causing it.

[steve_k]

well i've found another e90 M/C to try, should be here next week so lets see whats happen this time.

[steve_k]

well i should have another M/C with me tomorrow so soon as i get that i'll fit it & try again, fingers crossed it sorts it.

[steve_k]

Well the new/replacement 25.5mm (335D) M/C arrived this morning,

I've checked it all over, looks to be in good condition,

I've bench bled it & thatsbworked fine so just got to wait for a dry day (very soon I hope) to get it fitted,

Once thats done I'll bleed the brakes again & keep my fingers crossed.

Let's good this sorts it as the owner (my mate) is itching to get back out in the car.

[martauto]

We all live in hope mate

Mart.

[steve_k]

We all live in hope mate

Mart.

So do I mart.

He keeps pexking my head over it, no way am I getting p*ss wet through just keep him happy.

[martauto]

We all live in hope mate

Mart.

So do I mart.

He keeps pexking my head over it, no way am I getting p*ss wet through just keep him happy.

Come over to my "open air" garage and we will both get wet and collapse with the cold

Mart.

[steve_k]

We all live in hope mate

Mart.

So do I mart.

He keeps pexking my head over it, no way am I getting p*ss wet through just keep him happy.

Come over to my "open air" garage and we will both get wet and collapse with the cold

Mart.

mines exactly the same, ideal in summer but a nightmare at this time of year, thank god for thermal undies