1984 Audi 4000S Quattro brake bleeding
 

Hi,

I just found the following message on google while looking for hints
on brake fluid bleeding. It's two months old now, but it still cought
my attention (copied from google, my reply is below):

> From: - view profile
> Date: Mon, Jun 13 2005 6:28 pm
> Email:
> Groups: alt.autos.audi, rec.autos.tech
>
> Hi,
> I think there is air in my rear brake lines, but bleeding is a
> rediculous pain. I know the proportioning valve on the '84 is not
> adjustable, but is there a way to disable it? I know the first ones on
> Jeeps there was a button that could be held. I just want a way to keep
> normal pressure or lot's of pressure to the rears while bleeding.
> Right now I can bleed once and then the rears get closed off.
>
> My main problem is that I have either a leak or air in my lines, but I
> can't see a leak and don't seem to lose fluid. If I press my brake
> pedal slowly it goes about 3/4 or 7/8 to the floor, but still feels
> like a normal pedal. When it does this I get pressure to all 4 wheels,
> but probably about half of what I'd call normal pressure. If I push
> the pedal more rapidly or fast it will only go half way and feel like a
> normal pedal with full pressure, but only the front wheels will have
> pressure. I'm hoping it's just air in the rear lines and under lots of
> pressure that compressed enough to divert the flow and close off the
> rears. If it's something more serious then maybe there's a way I can
> make the fronts always have the pressure? Right now I can brake fine
> with the mostly depressed pedal, I'm just worried when I go to get the
> car inspected they will say it's inappropriate that way.

Hi Chris,

I am just guessing here, but could it be that the brake bomb is gone?
On my Audi 100, 1989 it took me quite a while before I realised that
this is the problem. In most posts about the brake bomb, they mention
that it's main purpose is to give brake assistance when the engine is
off. However, my impression is that the most important part is to have
a reservoir so that the brake assist works instantly. Before I
replaced my brake bomb, the brake worked normally when pressing it
slowly. Only when pressing it suddenly, there was a short
(~half-second) delay before the pump could build up the pressure and
then the brake paddle went down further. The above sounds very much
like this.

Indicators whether this could be the problem a

- Engine running: When the brake pedal is prest suddenly, it feels
hard first and then goes down further.

- While driving: When suddenly braking, the brakes are at first weaker
and then increase in strength as the pedal moves down.

- Just after the engine is switched off, the brake pedal is hard to
press down.

Working bomb: Just after the engine is switched off, the brakes still
work fine. After pressing the pedal down 20 to 70 times, it suddenly
becomes hard.

For more details on the brake bomb and how it works do a google serch.

Christoph

1984 Audi 4000S Quattro brake bleeding
 

My guess is that the bomb is not the problem.

More likely that the first poster is having the problem due to a failing master
cylinder.

Christoph Bollig wrote:
> Hi,
>
> I just found the following message on google while looking for hints
> on brake fluid bleeding. It's two months old now, but it still cought
> my attention (copied from google, my reply is below):
>
>
>>From: - view profile
>>Date: Mon, Jun 13 2005 6:28 pm
>>Email:
>>Groups: alt.autos.audi, rec.autos.tech
>>
>>Hi,
>> I think there is air in my rear brake lines, but bleeding is a
>>rediculous pain. I know the proportioning valve on the '84 is not
>>adjustable, but is there a way to disable it? I know the first ones on
>>Jeeps there was a button that could be held. I just want a way to keep
>>normal pressure or lot's of pressure to the rears while bleeding.
>>Right now I can bleed once and then the rears get closed off.
>>
>>My main problem is that I have either a leak or air in my lines, but I
>>can't see a leak and don't seem to lose fluid. If I press my brake
>>pedal slowly it goes about 3/4 or 7/8 to the floor, but still feels
>>like a normal pedal. When it does this I get pressure to all 4 wheels,
>>but probably about half of what I'd call normal pressure. If I push
>>the pedal more rapidly or fast it will only go half way and feel like a
>>normal pedal with full pressure, but only the front wheels will have
>>pressure. I'm hoping it's just air in the rear lines and under lots of
>>pressure that compressed enough to divert the flow and close off the
>>rears. If it's something more serious then maybe there's a way I can
>>make the fronts always have the pressure? Right now I can brake fine
>>with the mostly depressed pedal, I'm just worried when I go to get the
>>car inspected they will say it's inappropriate that way.
>
>
> Hi Chris,
>
> I am just guessing here, but could it be that the brake bomb is gone?
> On my Audi 100, 1989 it took me quite a while before I realised that
> this is the problem. In most posts about the brake bomb, they mention
> that it's main purpose is to give brake assistance when the engine is
> off. However, my impression is that the most important part is to have
> a reservoir so that the brake assist works instantly. Before I
> replaced my brake bomb, the brake worked normally when pressing it
> slowly. Only when pressing it suddenly, there was a short
> (~half-second) delay before the pump could build up the pressure and
> then the brake paddle went down further. The above sounds very much
> like this.
>
> Indicators whether this could be the problem a
>
> - Engine running: When the brake pedal is prest suddenly, it feels
> hard first and then goes down further.
>
> - While driving: When suddenly braking, the brakes are at first weaker
> and then increase in strength as the pedal moves down.
>
> - Just after the engine is switched off, the brake pedal is hard to
> press down.
>
> Working bomb: Just after the engine is switched off, the brakes still
> work fine. After pressing the pedal down 20 to 70 times, it suddenly
> becomes hard.
>
> For more details on the brake bomb and how it works do a google serch.
>
> Christoph

1984 Audi 4000S Quattro brake bleeding
 

I agree. I've driven cars with both a bad "bomb" (535i) and failing
master cylinders (various) and the OP's issue sounds like it's in the
MC, not the bomb. replace the MC first then look at the bomb if it's
still not quite right.

nate

Tony wrote:
> My guess is that the bomb is not the problem.
>
> More likely that the first poster is having the problem due to a failing
> master cylinder.
>
> Christoph Bollig wrote:
>
>> Hi,
>>
>> I just found the following message on google while looking for hints
>> on brake fluid bleeding. It's two months old now, but it still cought
>> my attention (copied from google, my reply is below):
>>
>>
>>> From: - view profile Date: Mon, Jun 13 2005
>>> 6:28 pm Email: Groups: alt.autos.audi,
>>> rec.autos.tech
>>> Hi, I think there is air in my rear brake lines, but bleeding is a
>>> rediculous pain. I know the proportioning valve on the '84 is not
>>> adjustable, but is there a way to disable it? I know the first ones
>>> on Jeeps there was a button that could be held. I just want a way to
>>> keep normal pressure or lot's of pressure to the rears while
>>> bleeding. Right now I can bleed once and then the rears get closed off.
>>> My main problem is that I have either a leak or air in my lines, but
>>> I can't see a leak and don't seem to lose fluid. If I press my brake
>>> pedal slowly it goes about 3/4 or 7/8 to the floor, but still feels
>>> like a normal pedal. When it does this I get pressure to all 4
>>> wheels, but probably about half of what I'd call normal pressure. If
>>> I push the pedal more rapidly or fast it will only go half way and
>>> feel like a normal pedal with full pressure, but only the front
>>> wheels will have pressure. I'm hoping it's just air in the rear
>>> lines and under lots of pressure that compressed enough to divert the
>>> flow and close off the rears. If it's something more serious then
>>> maybe there's a way I can make the fronts always have the pressure?
>>> Right now I can brake fine with the mostly depressed pedal, I'm just
>>> worried when I go to get the car inspected they will say it's
>>> inappropriate that way.
>>
>>
>>
>> Hi Chris,
>>
>> I am just guessing here, but could it be that the brake bomb is gone?
>> On my Audi 100, 1989 it took me quite a while before I realised that
>> this is the problem. In most posts about the brake bomb, they mention
>> that it's main purpose is to give brake assistance when the engine is
>> off. However, my impression is that the most important part is to have
>> a reservoir so that the brake assist works instantly. Before I
>> replaced my brake bomb, the brake worked normally when pressing it
>> slowly. Only when pressing it suddenly, there was a short
>> (~half-second) delay before the pump could build up the pressure and
>> then the brake paddle went down further. The above sounds very much
>> like this.
>>
>> Indicators whether this could be the problem a
>>
>> - Engine running: When the brake pedal is prest suddenly, it feels
>> hard first and then goes down further.
>> - While driving: When suddenly braking, the brakes are at first weaker
>> and then increase in strength as the pedal moves down.
>>
>> - Just after the engine is switched off, the brake pedal is hard to
>> press down.
>>
>> Working bomb: Just after the engine is switched off, the brakes still
>> work fine. After pressing the pedal down 20 to 70 times, it suddenly
>> becomes hard.
>>
>> For more details on the brake bomb and how it works do a google serch.
>>
>> Christoph


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