No brake pedal return

[Cooper1999]

Evening all,
I'm hoping someone in the forum might be able to point me in the right direction. I'm building a Mini Marcos based on the old classic mini. Now I've got a problem with the brake system which is proving a bit of a problem to diagnose. Thing is the brake pedal no longer has any return - you press it down and it stays there.
The brake linkage looks to move freely up to the servo, the master cylinder doesn't look to be losing any fluid. So I suspect the master cylinder itself. Is this a correct assumption?
The spring which assists with returns the pedal looks to be a little long for this application, but I now don't think this is the root cause - there's no real pressure behind the pedal and as I say, it remains down even when released.
All ideas/suggestions welcome

[GreenV8S]

If you take all the hydraulics out of the equation and just push the pedal down, the return spring should pull it back up again. If yours doesn't, that's your first problem.

[E-bmw]

^^^^ Wot 'e said.

That is your first port of call.

[227bhp]

When there is enough air in the system the pedal will go beyond the fulcrum point which the spring works in and stay down.
The problem is simple; too much air in the system, work out why that is, bleed it off and it'll be ok.

[GreenV8S]

227bhp said:

When there is enough air in the system the pedal will go beyond the fulcrum point which the spring works in and stay down.

In my opinion, if the spring doesn't return the pedal there's a fault. It's perfectly normal to pump the pedal to the floor when bleeding brakes and it should return on its own.

[227bhp]

GreenV8S said:

227bhp said:

When there is enough air in the system the pedal will go beyond the fulcrum point which the spring works in and stay down.

In my opinion, if the spring doesn't return the pedal there's a fault. It's perfectly normal to pump the pedal to the floor when bleeding brakes and it should return on its own.

Except this doesn't happen in the real World, as per above ^

[E-bmw]

But surely as air is springy it should assist pushing the pedal back?

On top of that it must be an extremely poor design to allow the pedal to be able to go past the fulcrum point at all.

[227bhp]

E-bmw said:

But surely as air is springy it should assist pushing the pedal back?

On top of that it must be an extremely poor design to allow the pedal to be able to go past the fulcrum point at all.

You're right actually, I was thinking of the clutch, not brake as I had one do it to me the other day!

[Cooper1999]

Thanks all, for the suggestions.
I was hoping for a 'mechanical' problem so looked at the return spring first. Now in this application (mini pedal box/servo etc.) I think the (later model) servo mechanism return spring is a little too long to fully return the spring. However, what I'm finding is the pedal has no return whatsoever - that is, there is tension on the return spring.
I've ordered a replacement spring so that I can play around with modifying the end hooks to effectively make the spring shorter. I've also ordered an early model (mini), non-servo, twin leg pedal return spring (later servo cars were equipped with a single leg pedal spring assisted by the servo mech return spring. This is what I have).

I will look at bleeding the brakes next, but would've thought if there was a leak I would be seeing the master cylinder level going down? I should add, the brakes were working correctly (albeit the car isn't IVA'd/on the road yet).

[Penelope Stopit]

I suspect the master cylinder is playing up but you know what guessing can create

[Cooper1999]

Okay, so yesterday I tried to bleed the (front) brakes.
On both sides, after a very soft initial showing of fluid after opening the bleed nipple (pedal pressed), further pedal action didn't really show any further fluid being pumped through.
I haven't bled or tried to bleed the rear brakes but am I right in thinking, with a split system, this shouldn't make any difference? That is - if the master cylinder is working properly even if there was air in the rear brakes, depressing the pedal down should show fluid through the front brakes?
(I think I know the answer to this but just want to make sure I'm not suffering a 'senior moment').

So - all signs pointing to the master cylinder, do we think?

Thanks again.

[E-bmw]

Cooper1999 said:

Okay, so yesterday I tried to bleed the (front) brakes.
On both sides, after a very soft initial showing of fluid after opening the bleed nipple (pedal pressed), further pedal action didn't really show any further fluid being pumped through.
I haven't bled or tried to bleed the rear brakes but am I right in thinking, with a split system, this shouldn't make any difference? That is - if the master cylinder is working properly even if there was air in the rear brakes, depressing the pedal down should show fluid through the front brakes?
(I think I know the answer to this but just want to make sure I'm not suffering a 'senior moment').

So - all signs pointing to the master cylinder, do we think?

Thanks again.

Not really a huge amount of detail there so the obvious questions:

1. Does "very soft initial showing of fluid after opening the bleed nipple (pedal pressed)" mean you opened the bleed nipple when pressing the pedal down? as it actually seems to be saying the other way round with pedal pressed written after bleed nipple open.

2. Does "further pedal action" mean you closed the nipple at the bottom of its travel, let the pedal rise and opened the bleed nipple again when pressing the pedal down again?

General consensus when bleeding brakes is to start at the furthest bleed nipple from the master cylinder.

[Cooper1999]

Morning all,
Sorry (again) for the delay in getting back on this topic - work gets in the way during the week, and I've just come back from the British MotoGP where my son's and I were cheering on Valentino Rossi (I was watching Vale win GP before they were born!).

Anyway - to bleed the brakes it was:
1. press pedal
2. open bleed nipple
3. close bleed nipple
4. release pedal
5. repeat
This is the way I've always done it and think it's correct?

So I'll try and bleed the rear brakes this afternoon and see if it makes any difference.
Thanks again and enjoy your sunny Bank Holiday.

[GreenV8S]

Cooper1999 said:

This is the way I've always done it and think it's correct?

You should close the bleed nipple before the pedal reaches the bottom of the stroke so that you feel resistance in the pedal, rather than push the pedal down and hold it while you close the nipple. Unclear which way you have been doing it.

[Boosted LS1]

I've had brakes that refuse to bleed properly using the pumping method. An Easybleed kit works best for me.

[Cooper1999]

So I tried to bleed the rear brakes this past weekend and using the previously described method and the rears seemed to work correctly (as I expect when bleeding). Grabbing hold of the rear drums, with the pedal pressed the drums look to brake (cannot be turned by hand). So it appears it's only the fronts that aren't pressurising.
Does this point towards the master cylinder being defective? Or something else?
Thanks,