Problem with bleeding brakes sets disc brake project back somewhat

H

heinz wittenbecher

New member
Mar 1, 1998
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I guess I should've known for it was going too good...

Did the roll-out today but didn't stay out long.

Brake pedal is up with engine off but as soon as I have vacuum boost it's
almost to the floor. Have gone though a few pennys of brakefluid today
bleeding and re-bleeding.

I'm in the middle of doing the rears again but have quit for the night.
Thought I might ask in the meantime in case I'm missing something.

The book talks about a tool to use on the metering valve but I gather that's
only so that you don't need 100+psi to bleed the front. We got clean (no
bubbles) out of all 6 bleed ports on the last go-around but still no pedal
when engine is running.

Of course the rears are complicated somewhat as the calipers have to be
removed to get the bleed valve to the top and then it's gravity bleed only
so as not to push on the pads while they're off the rotor.

If someone has some trick/ideas to suggest, I'm all ears (eyes).

Thanks in advance

Heinz
www.bytedesigns.com/gmc
 
If you have to bleed while the calipers are off the rotors, insert a block
between the pads approximately the same thickness as the rotors then bleed
away. Have you tried the "gieser test" for air ?

> -----Original Message-----
> From: owner-gmcmotorhome
> [mailto:owner-gmcmotorhome]On Behalf Of Heinz
> Wittenbecher
> Sent: Saturday, July 25, 1998 2:29 AM
> To: GMCnet (E-mail)
> Subject: GMC: Problem with bleeding brakes sets disc brake project back
> somewhat
>
>
> I guess I should've known for it was going too good...
>
> Did the roll-out today but didn't stay out long.
>
> Brake pedal is up with engine off but as soon as I have vacuum boost it's
> almost to the floor. Have gone though a few pennys of brakefluid today
> bleeding and re-bleeding.
>
> I'm in the middle of doing the rears again but have quit for the night.
> Thought I might ask in the meantime in case I'm missing something.
>
> The book talks about a tool to use on the metering valve but I
> gather that's
> only so that you don't need 100+psi to bleed the front. We got clean (no
> bubbles) out of all 6 bleed ports on the last go-around but still no pedal
> when engine is running.
>
> Of course the rears are complicated somewhat as the calipers have to be
> removed to get the bleed valve to the top and then it's gravity bleed only
> so as not to push on the pads while they're off the rotor.
>
> If someone has some trick/ideas to suggest, I'm all ears (eyes).
>
> Thanks in advance
>
> Heinz
> www.bytedesigns.com/gmc
>
 
>
>
> If you have to bleed while the calipers are off the rotors,
> insert a block
> between the pads approximately the same thickness as the
> rotors then bleed
> away.

Have tried/been doing that.

> Have you tried the "gieser test" for air ?

What's the gieser test ? :-)

>
> > -----Original Message-----
> > From: owner-gmcmotorhome
> > [mailto:owner-gmcmotorhome]On Behalf Of Heinz
> > Wittenbecher
> > Sent: Saturday, July 25, 1998 2:29 AM
> > To: GMCnet (E-mail)
> > Subject: GMC: Problem with bleeding brakes sets disc brake
> project back
> > somewhat
> >
> >
> > I guess I should've known for it was going too good...
> >
> > Did the roll-out today but didn't stay out long.
> >
> > Brake pedal is up with engine off but as soon as I have
> vacuum boost it's
> > almost to the floor. Have gone though a few pennys of
> brakefluid today
> > bleeding and re-bleeding.
> >
> > I'm in the middle of doing the rears again but have quit
> for the night.
> > Thought I might ask in the meantime in case I'm missing something.
> >
> > The book talks about a tool to use on the metering valve but I
> > gather that's
> > only so that you don't need 100+psi to bleed the front. We
> got clean (no
> > bubbles) out of all 6 bleed ports on the last go-around but
> still no pedal
> > when engine is running.
> >
> > Of course the rears are complicated somewhat as the
> calipers have to be
> > removed to get the bleed valve to the top and then it's
> gravity bleed only
> > so as not to push on the pads while they're off the rotor.
> >
> > If someone has some trick/ideas to suggest, I'm all ears (eyes).
> >
> > Thanks in advance
> >
> > Heinz
> > www.bytedesigns.com/gmc
> >
>
 
Could very well be.
Wonder what it was that "he took care of" after the fun ride around the
block :-)

I'm just totally stumped. After re-doing the bleed again... same problem.
Great pedal until I start the engine.

Open to any and all suggestions.

Heinz

> -----Original Message-----
> From: owner-gmcmotorhome
> [mailto:owner-gmcmotorhome]On Behalf Of
> CHill113
> Sent: Saturday, July 25, 1998 10:20 AM
> To: gmcmotorhome
> Subject: Re: GMC: Problem with bleeding brakes sets disc brake project
> back somewhat
>
>
> Heinz
> Let me say upfront that I don't know squat about what your
> problem is with the
> brakes, but I will ask a stupid question, based on an
> experience I had, since
> you apparently have installed disk brakes. I had some
> emergency brake work
> done in Portland, OR once and a new rotor installed. I paid
> the man and drove
> out on the street and nearly rear ended a couple vehicles
> until could go
> around the block. Oops he said, sorry I didn't take care of
> that saying that
> he should have done something to take care of that. Since you
> have six disk
> rather than two now, could what ever my problem was be
> causing your problem?
>
 
Thanks for the extra mile Justin.

The wheels do lock when down, i.e. it's not quite hitting the stop, but
almost.

The sequence we've been using is right rear/right front as they are the
furthest from the MC, then left rears, then fronts.

Guess I'm going to start putting plugs/caps in to isolate front/back,
left/right etc.

Grrrr.... and things were going so great :-)

>
>
> Heinz
> I decided to give my mechanic a call at home and see if he
> had any bright
> ideas. He worked for the GMC dealer back in 85 when I bought
> it, worked his
> way up to shop foreman and then Service Mgr of a major chevy
> dealer. He asked
> if the wheels lock when you apply the pedal all the way down?
> What have you
> changed out? Is there the possibility of a bad hose swelling
> and acting as an
> accumulator? His final comment was what sequence you are
> bleeding the brakes?
> He commented it is absolutely CRUCIAL that you bleed the
> fartherest from the
> master cylinder forward or you can trap an air pocket. I'm
> assuming you have
> done it correctly but here is the sequence he gave me:
> passenger side rear,
> driver side rear, passenger side middle, driver side middle,
> front passenger
> side and last driver side front. Good luck
> Justin
>
 
First question other than the rear disks is the rest of the system original?
ie; booster, master cylinder etc.

>Could very well be.
>Wonder what it was that "he took care of" after the fun ride around the
>block :-)
>
>I'm just totally stumped. After re-doing the bleed again... same problem.
>Great pedal until I start the engine.
>
>Open to any and all suggestions.
>
>Heinz
>
>> -----Original Message-----
>> From: owner-gmcmotorhome
>> [mailto:owner-gmcmotorhome]On Behalf Of
>> CHill113
>> Sent: Saturday, July 25, 1998 10:20 AM
>> To: gmcmotorhome
>> Subject: Re: GMC: Problem with bleeding brakes sets disc brake project
>> back somewhat
>>
>>
>> Heinz
>> Let me say upfront that I don't know squat about what your
>> problem is with the
>> brakes, but I will ask a stupid question, based on an
>> experience I had, since
>> you apparently have installed disk brakes. I had some
>> emergency brake work
>> done in Portland, OR once and a new rotor installed. I paid
>> the man and drove
>> out on the street and nearly rear ended a couple vehicles
>> until could go
>> around the block. Oops he said, sorry I didn't take care of
>> that saying that
>> he should have done something to take care of that. Since you
>> have six disk
>> rather than two now, could what ever my problem was be
>> causing your problem?
>>
>
>
>
 
>
>
> First question other than the rear disks is the rest of the
> system original?
> ie; booster, master cylinder etc.

Yup, all else except brakelines original. (no leaks).
 
Gieser test....pump the pedal several times (engine running) while an
observer watches the master with cap off. Release the pedal final time, look
for a "squirt" of brake fluid in the master. If YES=SQUIRT THEN=AIR. If NO
SQUIRT THEN=NO AIR. If AIR check bleed process. If NO AIR then check caliper
mounting alignment OR other. This test works on all disk brake systems and
even drum disk. Drums will have a small gieser due to return springs pulling
the shoes off the drum, disks will not have a gieser if they are normal.
What else is new to your brakes ? Does the pedal feel OK before you move the
coach ? If YES then look for run out issues. How much greater volume of
fluid are moving now than before the modification, lots ? Bigger master.
Haven't messed with my brakes, '73 Desert

> -----Original Message-----
> From: owner-gmcmotorhome
> [mailto:owner-gmcmotorhome]On Behalf Of Heinz
> Wittenbecher
> Sent: Saturday, July 25, 1998 10:02 AM
> To: gmcmotorhome
> Subject: RE: GMC: Problem with bleeding brakes sets disc brake project
> back somewhat
>
>
> >
> >
> > If you have to bleed while the calipers are off the rotors,
> > insert a block
> > between the pads approximately the same thickness as the
> > rotors then bleed
> > away.
>
> Have tried/been doing that.
>
>
>
> > Have you tried the "gieser test" for air ?
>
> What's the gieser test ? :-)
>
>
>
>
> >
> > > -----Original Message-----
> > > From: owner-gmcmotorhome
> > > [mailto:owner-gmcmotorhome]On Behalf Of Heinz
> > > Wittenbecher
> > > Sent: Saturday, July 25, 1998 2:29 AM
> > > To: GMCnet (E-mail)
> > > Subject: GMC: Problem with bleeding brakes sets disc brake
> > project back
> > > somewhat
> > >
> > >
> > > I guess I should've known for it was going too good...
> > >
> > > Did the roll-out today but didn't stay out long.
> > >
> > > Brake pedal is up with engine off but as soon as I have
> > vacuum boost it's
> > > almost to the floor. Have gone though a few pennys of
> > brakefluid today
> > > bleeding and re-bleeding.
> > >
> > > I'm in the middle of doing the rears again but have quit
> > for the night.
> > > Thought I might ask in the meantime in case I'm missing something.
> > >
> > > The book talks about a tool to use on the metering valve but I
> > > gather that's
> > > only so that you don't need 100+psi to bleed the front. We
> > got clean (no
> > > bubbles) out of all 6 bleed ports on the last go-around but
> > still no pedal
> > > when engine is running.
> > >
> > > Of course the rears are complicated somewhat as the
> > calipers have to be
> > > removed to get the bleed valve to the top and then it's
> > gravity bleed only
> > > so as not to push on the pads while they're off the rotor.
> > >
> > > If someone has some trick/ideas to suggest, I'm all ears (eyes).
> > >
> > > Thanks in advance
> > >
> > > Heinz
> > > www.bytedesigns.com/gmc
> > >
> >
>
 
If brakes worked before you put the new lines on the only thing it could be
is an air pocket in the lines. That is assuming that you got the lines all
correct at the combination valve. My book is not here so I am using a manual
for automobiles. Check your repair manual first.

Need to bleed brakes in the following sequence:

caution: if your rear disc brakes have 2 bleeder screws bleed the inner
first and the outer last.

Also if you are pressure bleeding disk brakes, they will close the metering
valve, and you will not be able to bleed the front brakes.

1. Master cylinder (has to be done first)
2. combination valve
3. passenger rearmost wheel
4. Passenger middle wheel
5. Drivers rearmost wheel
6. Drivers middle wheel
7. passenger front wheel
8. drivers front wheel.

If you are unsuccessful at this point in is necessary to deactivate the
metering valve. this is accomplished by either pushing in or pulling out a
button on the stem on the valve. It should remain deactivated while you
bleed the front brakes.

If at any point you let air into the system, you have to start all over again.

I will have my book tomorrow and will check this. Hope it helps

>>
>>
>> First question other than the rear disks is the rest of the
>> system original?
>> ie; booster, master cylinder etc.
>
>Yup, all else except brakelines original. (no leaks).
>
>
>
>
>
 
My 1973 Service Manual says to bleed the brakes in
this order...
1. Drivers side Front Wheel
2. Passenger side front Wheel
3. Drivers Side Front Bogie Wheel
4. Drivers Side Rear Bogie Wheel
5. Passenger Side Front Bogie Wheel
6. Passenger side Rear Wheel
I have never had any luck working on my brakes
myself...But decided to on the GMC. I only replaced
the front lines, Then did them by myself using
a Brake Bleeder Kit from Autozone ($4.95 I think ).
Took 5 minutes max.....They Work Great! Anyway..Is
this the order You are bleeding your brakes. It
looks like from the post that everbody is doing
just the reverse....Maybe I'm just reading the
post wrong.

> -----Original Message-----
> From: owner-gmcmotorhome
> [mailto:owner-gmcmotorhome]On Behalf Of
> RickStapls
> Sent: Sunday, July 26, 1998 2:16 AM
> To: gmcmotorhome
> Subject: Re: GMC: Problem with bleeding brakes sets disc brake project
> back somewhat
>
>

> >Brake pedal is up with engine off but as soon as I have vacuum boost it's
> >almost to the floor. Have gone though a few pennys of brakefluid today
> >bleeding and re-bleeding.
>
> Heinz,
> You have my sympathy as you pick through this can of worms. Some
> thoughts:
>
> 1 Disc brake caliper pistons are MUCH bigger than drum brake
> wheel cylinders.
> Hence, they displace more fluid as they apply. Theoretically
> they compensate
> for this by moving a shorter distance than drum brake cylinders, IF all is
> well. When Detroit, Wolfsburg, Hiroshima, et al did simple
> upgrades from drum
> to disc brakes (back in the '70s), they USUALLY went to a larger diameter
> master cylinder to supply the additional fluid needed, then added a power
> booster to help push that big cylinder. My point here is that
> your 6-wheel
> disc system is always going to be super-critical about air or
> other hydraulic
> weaknesses.
>
> 2. If you have to demount the calipers to bleed them, that
> speaks ill of the
> system design. Letting that go by, try to hold them in the
> position they were
> mounted in their original application while bleeding, not just
> "bleeder up".
>
> 3 When desparate, I try to divide and conquer. Block off or pinch off
> (using an appropriate smooth-jawed clamping tool) your hydraulic hoses.
> Confirm that you have a good pedal, then open up one hose at a
> time until the
> problem returns. The last subassembly reconnected should
> contain the cause
> of your trouble.
>
> 4 It may be that your problem isn't air in the hydraulics at all. Get a
> helper to repeatedly apply the brakes (engine running, booster
> working) while
> you crawl around checking things. Check for hoses that swell as
> pressure is
> applied. Closely observe your new calipers as brakes are applied. Do the
> calipers visibly move, flex, or twist? If so, they are not
> properly aligned
> with the discs (defective or misaligned caliper mounts). As they
> flex they
> use up a few CCs of brake fluid, which you can ill afflord.
>
> 5 Finally, there's a chance you may have a bad
> (internally-leaking) master
> cylinder, though these usually show up under LIGHT pedal pressure.
>
> Hope this gives you some ideas. Good luck
>
> Rick Staples
>
>
 
My 75 manual says to bleed them in the same sequence as the 73 manual.

Don

>My 1973 Service Manual says to bleed the brakes in
> this order...
>1. Drivers side Front Wheel
>2. Passenger side front Wheel
>3. Drivers Side Front Bogie Wheel
>4. Drivers Side Rear Bogie Wheel
>5. Passenger Side Front Bogie Wheel
>6. Passenger side Rear Wheel
>I have never had any luck working on my brakes
>myself...But decided to on the GMC. I only replaced
> the front lines, Then did them by myself using
> a Brake Bleeder Kit from Autozone ($4.95 I think ).
>Took 5 minutes max.....They Work Great! Anyway..Is
> this the order You are bleeding your brakes. It
> looks like from the post that everbody is doing
> just the reverse....Maybe I'm just reading the
> post wrong.
>
>> -----Original Message-----
>> From: owner-gmcmotorhome
>> [mailto:owner-gmcmotorhome]On Behalf Of
>> RickStapls
>> Sent: Sunday, July 26, 1998 2:16 AM
>> To: gmcmotorhome
>> Subject: Re: GMC: Problem with bleeding brakes sets disc brake project
>> back somewhat
>>
>>

>> >Brake pedal is up with engine off but as soon as I have vacuum boost
it's
>> >almost to the floor. Have gone though a few pennys of brakefluid today
>> >bleeding and re-bleeding.
>>
>> Heinz,
>> You have my sympathy as you pick through this can of worms. Some
>> thoughts:
>>
>> 1 Disc brake caliper pistons are MUCH bigger than drum brake
>> wheel cylinders.
>> Hence, they displace more fluid as they apply. Theoretically
>> they compensate
>> for this by moving a shorter distance than drum brake cylinders, IF all
is
>> well. When Detroit, Wolfsburg, Hiroshima, et al did simple
>> upgrades from drum
>> to disc brakes (back in the '70s), they USUALLY went to a larger diameter
>> master cylinder to supply the additional fluid needed, then added a power
>> booster to help push that big cylinder. My point here is that
>> your 6-wheel
>> disc system is always going to be super-critical about air or
>> other hydraulic
>> weaknesses.
>>
>> 2. If you have to demount the calipers to bleed them, that
>> speaks ill of the
>> system design. Letting that go by, try to hold them in the
>> position they were
>> mounted in their original application while bleeding, not just
>> "bleeder up".
>>
>> 3 When desparate, I try to divide and conquer. Block off or pinch off
>> (using an appropriate smooth-jawed clamping tool) your hydraulic hoses.
>> Confirm that you have a good pedal, then open up one hose at a
>> time until the
>> problem returns. The last subassembly reconnected should
>> contain the cause
>> of your trouble.
>>
>> 4 It may be that your problem isn't air in the hydraulics at all. Get
a
>> helper to repeatedly apply the brakes (engine running, booster
>> working) while
>> you crawl around checking things. Check for hoses that swell as
>> pressure is
>> applied. Closely observe your new calipers as brakes are applied. Do
the
>> calipers visibly move, flex, or twist? If so, they are not
>> properly aligned
>> with the discs (defective or misaligned caliper mounts). As they
>> flex they
>> use up a few CCs of brake fluid, which you can ill afflord.
>>
>> 5 Finally, there's a chance you may have a bad
>> (internally-leaking) master
>> cylinder, though these usually show up under LIGHT pedal pressure.
>>
>> Hope this gives you some ideas. Good luck
>>
>> Rick Staples
>>
>>
>
 
>
>
> My 75 manual says to bleed them in the same sequence as the 73 manual.
>
> Don
>

As does my '76 manual but many others' experiences, including my own, are
farthest to closest as noted by some of the posts.

I'd like to thank you all for you comments/suggestions. Some had already
been tried, some not. Going to leave the rig alone today and let it (and me)
'rest' :-)

One summation that one can take away from all the replies to my plight is
that there is no single solution to the matter of bleeding brakes. After
browsing www.phxsyss.com as suggested by Herm I'm more convinced of that
than ever. It just ain't as easy as any book says, i.e. one has to find the
right method for the occasion (and/or rig).

Well, hopefully success will come yet... yes it will :-)

Thanks again to all. New round of battle starts tomorrow.

Heinz

 
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