Wolfgang,
I'm almost positive that when I last bled the dual-diagonal circuit brakes
on both my 5ktq and 5k manually (I use a home-made pressure bleeder now), I
could push the pedal to the floor when I had my friend crack the bleed screw
on one corner only. I checked on the net and there are warnings about not
pressing the pedal all the way to the floor:
http://forums.probetalk.com/showthre...1029134&page=1
(third post)
Maybe Chris' master cylinder is not malfunctioning......maybe?
Cheers!
Steve Sears
1987 Audi 5kTQ
1980 Audi 5k
1962 and '64 Auto Union DKW Junior deLuxes
(SPAM Blocker NOTE: Remove SHOES to reply)

"Wolfgang Pawlinetz" <w.pawlinetz@a1.net> wrote in message
news:1143560984.347220@news...
>
> Yep. I would just try to check if the circuits are still separated. That
> would make Me nervous.
>
> A simple check would be to bleed off the air in one circuit, leaving the
> other one open. Then apply foot pressure. The pedal still shouldn't creep
> to the floor, right?
>
> Regards
>
> W.

 

Wolfgang,
I'm almost positive that when I last bled the dual-diagonal circuit brakes
on both my 5ktq and 5k manually (I use a home-made pressure bleeder now), I
could push the pedal to the floor when I had my friend crack the bleed screw
on one corner only. I checked on the net and there are warnings about not
pressing the pedal all the way to the floor:
http://forums.probetalk.com/showthre...1029134&page=1
(third post)
Maybe Chris' master cylinder is not malfunctioning......maybe?
Cheers!
Steve Sears
1987 Audi 5kTQ
1980 Audi 5k
1962 and '64 Auto Union DKW Junior deLuxes
(SPAM Blocker NOTE: Remove SHOES to reply)

"Wolfgang Pawlinetz" <w.pawlinetz@a1.net> wrote in message
news:1143560984.347220@news...
>
> Yep. I would just try to check if the circuits are still separated. That
> would make Me nervous.
>
> A simple check would be to bleed off the air in one circuit, leaving the
> other one open. Then apply foot pressure. The pedal still shouldn't creep
> to the floor, right?
>
> Regards
>
> W.

 

"Wolfgang Pawlinetz" <w.pawlinetz@a1.net> wrote in message
news:1143558183.457287@news...
> IMO there's a second problem here.
>
> That car should have two separated braking circuits (i.e. left front
> operating together with right rear and left rear with right front).
>
> Both systems are actuated via one master cylinder which also separates the
> systems.
>
> This should make sure, that even if one braking line blows, the other
> should still be working so that you can still - although with higher foot
> pressure - bring the car to a stop with only two brakes in operation.
>
> If that car really lost it's brake completely there must be a leak between
> circuit 1 and 2, because only in this case the pressure in the second
> 'good' circuit could bleed away as well.
>
> Most likely the seal in the master cylinder between the two circuits is
> leaking. So you should check that too.
>
> With the loss of one braking line such a car must never lose all its
> braking power.

Yep, I can see the point, problem being that I didn't experience the failure
myself - my girlfriend said that the brakes *worked*, but that they needed
more strength than she could muster....

I can see from the pile of workshop-receipts from the previous owner that my
idea that the master cylinder was correct; he'd had it renewed at an Audi
dealer last november.

Well, I'll locate the source of the fluid mist on the rear tyre (it is
certainly from around the caliper somewhere) and see how that goes.

Steve: agreed with the braided lines; I use them on my motorcycle, but for a
car I've always favoured OE rubber lines - it's longevity I'm after on the
car, not brake feel

I'll come back with more when my bout of 'flu is over and I've had a chance
to deal with this.

--
Chris
: )

 

"Wolfgang Pawlinetz" <w.pawlinetz@a1.net> wrote in message
news:1143558183.457287@news...
> IMO there's a second problem here.
>
> That car should have two separated braking circuits (i.e. left front
> operating together with right rear and left rear with right front).
>
> Both systems are actuated via one master cylinder which also separates the
> systems.
>
> This should make sure, that even if one braking line blows, the other
> should still be working so that you can still - although with higher foot
> pressure - bring the car to a stop with only two brakes in operation.
>
> If that car really lost it's brake completely there must be a leak between
> circuit 1 and 2, because only in this case the pressure in the second
> 'good' circuit could bleed away as well.
>
> Most likely the seal in the master cylinder between the two circuits is
> leaking. So you should check that too.
>
> With the loss of one braking line such a car must never lose all its
> braking power.

Yep, I can see the point, problem being that I didn't experience the failure
myself - my girlfriend said that the brakes *worked*, but that they needed
more strength than she could muster....

I can see from the pile of workshop-receipts from the previous owner that my
idea that the master cylinder was correct; he'd had it renewed at an Audi
dealer last november.

Well, I'll locate the source of the fluid mist on the rear tyre (it is
certainly from around the caliper somewhere) and see how that goes.

Steve: agreed with the braided lines; I use them on my motorcycle, but for a
car I've always favoured OE rubber lines - it's longevity I'm after on the
car, not brake feel

I'll come back with more when my bout of 'flu is over and I've had a chance
to deal with this.

--
Chris
: )

 

"Wolfgang Pawlinetz" <w.pawlinetz@a1.net> wrote in message
news:1143558183.457287@news...
> IMO there's a second problem here.
>
> That car should have two separated braking circuits (i.e. left front
> operating together with right rear and left rear with right front).
>
> Both systems are actuated via one master cylinder which also separates the
> systems.
>
> This should make sure, that even if one braking line blows, the other
> should still be working so that you can still - although with higher foot
> pressure - bring the car to a stop with only two brakes in operation.
>
> If that car really lost it's brake completely there must be a leak between
> circuit 1 and 2, because only in this case the pressure in the second
> 'good' circuit could bleed away as well.
>
> Most likely the seal in the master cylinder between the two circuits is
> leaking. So you should check that too.
>
> With the loss of one braking line such a car must never lose all its
> braking power.

Yep, I can see the point, problem being that I didn't experience the failure
myself - my girlfriend said that the brakes *worked*, but that they needed
more strength than she could muster....

I can see from the pile of workshop-receipts from the previous owner that my
idea that the master cylinder was correct; he'd had it renewed at an Audi
dealer last november.

Well, I'll locate the source of the fluid mist on the rear tyre (it is
certainly from around the caliper somewhere) and see how that goes.

Steve: agreed with the braided lines; I use them on my motorcycle, but for a
car I've always favoured OE rubber lines - it's longevity I'm after on the
car, not brake feel

I'll come back with more when my bout of 'flu is over and I've had a chance
to deal with this.

--
Chris
: )

 

Steve Sears wrote:
> Wolfgang,
> I'm almost positive that when I last bled the dual-diagonal circuit brakes
> on both my 5ktq and 5k manually (I use a home-made pressure bleeder now), I
> could push the pedal to the floor when I had my friend crack the bleed screw
> on one corner only. I checked on the net and there are warnings about not
> pressing the pedal all the way to the floor:
> http://forums.probetalk.com/showthre...1029134&page=1
> (third post)
> Maybe Chris' master cylinder is not malfunctioning......maybe?

Maybe. I'm just wondering what sense it then makes to have a diagonal
separated system anyway.

Honestly I am pretty sure the pedal should not creep with one line
broken. At least that was told to me by my previous Ford Mech. The
principle is the same.

I'll try to check with my Audi garage in the next days.

Regards

Wolfgang

 

Steve Sears wrote:
> Wolfgang,
> I'm almost positive that when I last bled the dual-diagonal circuit brakes
> on both my 5ktq and 5k manually (I use a home-made pressure bleeder now), I
> could push the pedal to the floor when I had my friend crack the bleed screw
> on one corner only. I checked on the net and there are warnings about not
> pressing the pedal all the way to the floor:
> http://forums.probetalk.com/showthre...1029134&page=1
> (third post)
> Maybe Chris' master cylinder is not malfunctioning......maybe?

Maybe. I'm just wondering what sense it then makes to have a diagonal
separated system anyway.

Honestly I am pretty sure the pedal should not creep with one line
broken. At least that was told to me by my previous Ford Mech. The
principle is the same.

I'll try to check with my Audi garage in the next days.

Regards

Wolfgang

 

Steve Sears wrote:
> Wolfgang,
> I'm almost positive that when I last bled the dual-diagonal circuit brakes
> on both my 5ktq and 5k manually (I use a home-made pressure bleeder now), I
> could push the pedal to the floor when I had my friend crack the bleed screw
> on one corner only. I checked on the net and there are warnings about not
> pressing the pedal all the way to the floor:
> http://forums.probetalk.com/showthre...1029134&page=1
> (third post)
> Maybe Chris' master cylinder is not malfunctioning......maybe?

Maybe. I'm just wondering what sense it then makes to have a diagonal
separated system anyway.

Honestly I am pretty sure the pedal should not creep with one line
broken. At least that was told to me by my previous Ford Mech. The
principle is the same.

I'll try to check with my Audi garage in the next days.

Regards

Wolfgang

 

On Tue, 28 Mar 2006 19:10:29 +0200, "Chris G."
<bloodygreycat@hotmail.com> wrote:

>Yep, I can see the point, problem being that I didn't experience the failure
>myself - my girlfriend said that the brakes *worked*, but that they needed
>more strength than she could muster....

Ok. That sounds as if the spare circuit worked.

>I can see from the pile of workshop-receipts from the previous owner that my
>idea that the master cylinder was correct; he'd had it renewed at an Audi
>dealer last november.
>

Seems like a reasonable assumption that the master cylinder is ok.
Good luck with your project!

Regards

Wolfgang

 

On Tue, 28 Mar 2006 19:10:29 +0200, "Chris G."
<bloodygreycat@hotmail.com> wrote:

>Yep, I can see the point, problem being that I didn't experience the failure
>myself - my girlfriend said that the brakes *worked*, but that they needed
>more strength than she could muster....

Ok. That sounds as if the spare circuit worked.

>I can see from the pile of workshop-receipts from the previous owner that my
>idea that the master cylinder was correct; he'd had it renewed at an Audi
>dealer last november.
>

Seems like a reasonable assumption that the master cylinder is ok.
Good luck with your project!

Regards

Wolfgang