What is normal brakepedal travel distance?

H

heinz wittenbecher

New member
Mar 1, 1998
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Still struggling with low brakepedal with engine running and without, The
difference being 2+ inches.

I've been trying to find the specs on what normal brakepedal travel
would/should be with and without engine running. Unfortunately I did not
take much notice of that before we started.

I've messed around so much by now that a clean start is needed.

BTW, geiser test negative, I.e. no spurts.

If it takes more fluid to apply calipers vs. drums, why the big diff when
engine is off or running? Should it not be same? or at least closer?

TIA - Heinz
 
>
>
> Heinz, sorry you are having such a problem with the brakes.
> With all the
> advice you have received regarding the sequence to bleed,
> have you tried
> either or both?
>

Yup, forwards and backwards :-) and then in reverse :-(

We bench-bled MC just in case though we were quite sure the MC didn't run
dry during changeover and changing of lines.

We went for a ride and the pedal is still quite low at hard braking.

Brakes become active (noticeable) at about half pedal travel.

At hard braking it stops about 1/2 in. above hitting bottom of pedal travel,
which is kinda' close I feel.

The pedal is not mushy, brakes appear solid at that point and it stops at
same spot each time.

Pedal is slightly higher when applied with parking brake on. (standing
still)

With cover off MC there is no gushing fluid when brake is released. I
would've expected a gusher if compressed air was forcing fluid back, no?

Clamped front brakehoses, no diff.

Is it possible that the master cylinder is not putting enough fluid through?
(The master cyl is original, but recently replaced [new, not rebuilt]). If
so, is there a solution?

Has anyone else installed all 4? TSM has sold a few. To anyone on the
gmcnet?

As my next move (of despearation?) I've ordered a Bleeder from Phoenix
Systems.

Heinz
 
Heinz:

Unless you've used the Chevy P-30 chassis master cylinder (MC) and the
brake rod (it's 0.010" longer than original), I doubt the original MC
has sufficient capacity for all-wheel disc brakes. In case you need the
numbers, as I know it, here they are: MC - GM 14009146, NAPA 39-622 and
Wagner F103239.

Paul Bartz

From: Heinz Wittenbecher [mailto:heinz]
Sent: Monday, July 27, 1998 6:12 PM
Subject: RE: GMC: What is normal brakepedal travel distance?

>
>
> Heinz, sorry you are having such a problem with the brakes.
> With all the
> advice you have received regarding the sequence to bleed,
> have you tried
> either or both?
>

Yup, forwards and backwards :-) and then in reverse :-(

We bench-bled MC just in case though we were quite sure the MC didn't
run
dry during changeover and changing of lines.

We went for a ride and the pedal is still quite low at hard braking.

Brakes become active (noticeable) at about half pedal travel.

At hard braking it stops about 1/2 in. above hitting bottom of pedal
travel,
which is kinda' close I feel.

The pedal is not mushy, brakes appear solid at that point and it stops
at
same spot each time.

Pedal is slightly higher when applied with parking brake on. (standing
still)

With cover off MC there is no gushing fluid when brake is released. I
would've expected a gusher if compressed air was forcing fluid back, no?

Clamped front brakehoses, no diff.

Is it possible that the master cylinder is not putting enough fluid
through?
(The master cyl is original, but recently replaced [new, not rebuilt]).
If
so, is there a solution?

Has anyone else installed all 4? TSM has sold a few. To anyone on the
gmcnet?

As my next move (of despearation?) I've ordered a Bleeder from Phoenix
Systems.

Heinz
 
Paul,

The one I have in there now is a replacement I got from Cinnebar last summer
so I assume it's stock.

The P-30 MC, is it a direct replacement? Any other pieces needed?

TIA - Heinz

>
> Heinz:
>
> Unless you've used the Chevy P-30 chassis master cylinder (MC) and the
> brake rod (it's 0.010" longer than original), I doubt the original MC
> has sufficient capacity for all-wheel disc brakes. In case
> you need the
> numbers, as I know it, here they are: MC - GM 14009146, NAPA
> 39-622 and
> Wagner F103239.
>
> Paul Bartz
>
> From: Heinz Wittenbecher [mailto:heinz]
> Sent: Monday, July 27, 1998 6:12 PM
> Subject: RE: GMC: What is normal brakepedal travel distance?
>
> >
> >
> > Heinz, sorry you are having such a problem with the brakes.
> > With all the
> > advice you have received regarding the sequence to bleed,
> > have you tried
> > either or both?
> >
>
> Yup, forwards and backwards :-) and then in reverse :-(
>
> We bench-bled MC just in case though we were quite sure the MC didn't
> run
> dry during changeover and changing of lines.
>
> We went for a ride and the pedal is still quite low at hard braking.
>
> Brakes become active (noticeable) at about half pedal travel.
>
> At hard braking it stops about 1/2 in. above hitting bottom of pedal
> travel,
> which is kinda' close I feel.
>
> The pedal is not mushy, brakes appear solid at that point and it stops
> at
> same spot each time.
>
> Pedal is slightly higher when applied with parking brake on. (standing
> still)
>
> With cover off MC there is no gushing fluid when brake is released. I
> would've expected a gusher if compressed air was forcing
> fluid back, no?
>
> Clamped front brakehoses, no diff.
>
> Is it possible that the master cylinder is not putting enough fluid
> through?
> (The master cyl is original, but recently replaced [new, not
> rebuilt]).
> If
> so, is there a solution?
>
> Has anyone else installed all 4? TSM has sold a few. To anyone on the
> gmcnet?
>
> As my next move (of despearation?) I've ordered a Bleeder from Phoenix
> Systems.
>
> Heinz
>
 
Heinz:

Sorry, but I neglected to mention that there is need for a different
mounting bracket.

If you contact Bobby Moore in Louisville, 502-964-6416, he can give you
specifics as he has done a few, including his coach. My system is from
Leigh Harrison, so I didn't have to fabricate one.

Since the P-30 MC is a larger capacity fluid reservoir, you'll need to
use something ( I used a cheap red colored ketchup dispenser, for
instance: turkey baster is another possibility) to get brake fluid into
it. It's also helpful to remove the rear bail that holds the cover in
place to get the cover off.

Paul

- -----Original Message-----
From: Heinz Wittenbecher [mailto:heinz]
Sent: Monday, July 27, 1998 6:42 PM
To: gmcmotorhome
Subject: RE: GMC: What is normal brakepedal travel distance?

Paul,

The one I have in there now is a replacement I got from Cinnebar last
summer
so I assume it's stock.

The P-30 MC, is it a direct replacement? Any other pieces needed?

TIA - Heinz

>
> Heinz:
>
> Unless you've used the Chevy P-30 chassis master cylinder (MC) and the
> brake rod (it's 0.010" longer than original), I doubt the original MC
> has sufficient capacity for all-wheel disc brakes. In case
> you need the
> numbers, as I know it, here they are: MC - GM 14009146, NAPA
> 39-622 and
> Wagner F103239.
>
> Paul Bartz
>
> From: Heinz Wittenbecher [mailto:heinz]
> Sent: Monday, July 27, 1998 6:12 PM
> Subject: RE: GMC: What is normal brakepedal travel distance?
>
> >
> >
> > Heinz, sorry you are having such a problem with the brakes.
> > With all the
> > advice you have received regarding the sequence to bleed,
> > have you tried
> > either or both?
> >
>
> Yup, forwards and backwards :-) and then in reverse :-(
>
> We bench-bled MC just in case though we were quite sure the MC didn't
> run
> dry during changeover and changing of lines.
>
> We went for a ride and the pedal is still quite low at hard braking.
>
> Brakes become active (noticeable) at about half pedal travel.
>
> At hard braking it stops about 1/2 in. above hitting bottom of pedal
> travel,
> which is kinda' close I feel.
>
> The pedal is not mushy, brakes appear solid at that point and it stops
> at
> same spot each time.
>
> Pedal is slightly higher when applied with parking brake on. (standing
> still)
>
> With cover off MC there is no gushing fluid when brake is released. I
> would've expected a gusher if compressed air was forcing
> fluid back, no?
>
> Clamped front brakehoses, no diff.
>
> Is it possible that the master cylinder is not putting enough fluid
> through?
> (The master cyl is original, but recently replaced [new, not
> rebuilt]).
> If
> so, is there a solution?
>
> Has anyone else installed all 4? TSM has sold a few. To anyone on the
> gmcnet?
>
> As my next move (of despearation?) I've ordered a Bleeder from Phoenix
> Systems.
>
> Heinz
>
 
I disagree.. Discs take less fluid to actuate than brake shoes since they
are in constant contact with the rotors and move less. Brake shoes are not
in contact with the brake drums.

Besides the system worked before the lines were replaced.

to start again have you bled the master cylinder and combination valve first
and than locked the combination valve open with the special tool? You have
an air pocket somewhere. In addition I believe that another problem stems
from the fact that you have to remove the rear calipers to bleed.

>Heinz:
>
>Unless you've used the Chevy P-30 chassis master cylinder (MC) and the
>brake rod (it's 0.010" longer than original), I doubt the original MC
>has sufficient capacity for all-wheel disc brakes. In case you need the
>numbers, as I know it, here they are: MC - GM 14009146, NAPA 39-622 and
>Wagner F103239.
>
> Paul Bartz
>
>From: Heinz Wittenbecher [mailto:heinz]
>Sent: Monday, July 27, 1998 6:12 PM
>Subject: RE: GMC: What is normal brakepedal travel distance?
>
>>
>>
>> Heinz, sorry you are having such a problem with the brakes.
>> With all the
>> advice you have received regarding the sequence to bleed,
>> have you tried
>> either or both?
>>
>
>Yup, forwards and backwards :-) and then in reverse :-(
>
>We bench-bled MC just in case though we were quite sure the MC didn't
>run
>dry during changeover and changing of lines.
>
>We went for a ride and the pedal is still quite low at hard braking.
>
>Brakes become active (noticeable) at about half pedal travel.
>
>At hard braking it stops about 1/2 in. above hitting bottom of pedal
>travel,
>which is kinda' close I feel.
>
>The pedal is not mushy, brakes appear solid at that point and it stops
>at
>same spot each time.
>
>Pedal is slightly higher when applied with parking brake on. (standing
>still)
>
>With cover off MC there is no gushing fluid when brake is released. I
>would've expected a gusher if compressed air was forcing fluid back, no?
>
>Clamped front brakehoses, no diff.
>
>Is it possible that the master cylinder is not putting enough fluid
>through?
>(The master cyl is original, but recently replaced [new, not rebuilt]).
>If
>so, is there a solution?
>
>Has anyone else installed all 4? TSM has sold a few. To anyone on the
>gmcnet?
>
>As my next move (of despearation?) I've ordered a Bleeder from Phoenix
>Systems.
>
>Heinz
>
>
 
Did not lock the combination valve as it only affects the front (the lock),
or at least thats what I gather from the manual and it's only locked open to
allow for less pressure to affect the bleed. Having gotten a good flow
together with the bleed valve being nicely on top and no change with fronts
pinched off I'm still looking at the rears to be the culprit.

Having said that, I'm going to start from scratch once the power bleeder
arrives later this week utilizing pointers and ideas received from the net
over the last few days.

Have had the comment/recommendation to bypass the metering valve altogether
as due to it's age it may be gummed up, etc. and that it's not really
neccessary on the coach as it was simply a carryover from the Toronado. Has
anyone done so (bypassed it)?

Air is still the number one suspect. Going to do another (one or more)
serious bleed sessions and hopefully by next week I'll be able to report on
what ultimately "worked for me".

I too am hoping that the standard MC will ultimately suffice, as from what
info I gathered sofar the larger reservor of the P30 MC should only be
necessary if the 80mm calipers were used.

Heinz

>
>
> I disagree.. Discs take less fluid to actuate than brake
> shoes since they
> are in constant contact with the rotors and move less. Brake
> shoes are not
> in contact with the brake drums.
>
> Besides the system worked before the lines were replaced.
>
> to start again have you bled the master cylinder and
> combination valve first
> and than locked the combination valve open with the special
> tool? You have
> an air pocket somewhere. In addition I believe that another
> problem stems
> from the fact that you have to remove the rear calipers to bleed.
>
>
>
>
>
>

> >Heinz:
> >
> >Unless you've used the Chevy P-30 chassis master cylinder
> (MC) and the
> >brake rod (it's 0.010" longer than original), I doubt the original MC
> >has sufficient capacity for all-wheel disc brakes. In case
> you need the
> >numbers, as I know it, here they are: MC - GM 14009146, NAPA
> 39-622 and
> >Wagner F103239.
> >
> > Paul Bartz
> >
> >From: Heinz Wittenbecher [mailto:heinz]
> >Sent: Monday, July 27, 1998 6:12 PM
> >Subject: RE: GMC: What is normal brakepedal travel distance?
> >
> >>
> >>
> >> Heinz, sorry you are having such a problem with the brakes.
> >> With all the
> >> advice you have received regarding the sequence to bleed,
> >> have you tried
> >> either or both?
> >>
> >
> >Yup, forwards and backwards :-) and then in reverse :-(
> >
> >We bench-bled MC just in case though we were quite sure the MC didn't
> >run
> >dry during changeover and changing of lines.
> >
> >We went for a ride and the pedal is still quite low at hard braking.
> >
> >Brakes become active (noticeable) at about half pedal travel.
> >
> >At hard braking it stops about 1/2 in. above hitting bottom of pedal
> >travel,
> >which is kinda' close I feel.
> >
> >The pedal is not mushy, brakes appear solid at that point
> and it stops
> >at
> >same spot each time.
> >
> >Pedal is slightly higher when applied with parking brake on.
> (standing
> >still)
> >
> >With cover off MC there is no gushing fluid when brake is released. I
> >would've expected a gusher if compressed air was forcing
> fluid back, no?
> >
> >Clamped front brakehoses, no diff.
> >
> >Is it possible that the master cylinder is not putting enough fluid
> >through?
> >(The master cyl is original, but recently replaced [new, not
> rebuilt]).
> >If
> >so, is there a solution?
> >
> >Has anyone else installed all 4? TSM has sold a few. To anyone on the
> >gmcnet?
> >
> >As my next move (of despearation?) I've ordered a Bleeder
> from Phoenix
> >Systems.
> >
> >Heinz
> >
> >
>
 
Tried all that and the reason for removal is to assure air doesn't get
trapped in caliper, i.e. it gets taken off to align bleed valve to the top
so that air can escape.

Got absolute clean flow out of the bleed valve but I also noticed in the
process how brakefluid can flow around an airbubble inside the plastic tube
and never come out until syphoned out so there is a good chance air is
trapped in the line rather than caliper.

But... going to do it all again from scratch in a day or so :-)

I'd still appreciate a difference of brakepedal travel between engine
running and not with a stock setup. Missed taking a note of that before
staring to tear stuff appart, 20/20 hindsight.

TIA - Heinz

>
> > an air pocket somewhere. In addition I believe that another
> problem >
> > stems from the fact that you have to remove the rear
> calipers to bleed.
>
> I think Tom is right on, turning those calipers ever so
> slightly during
> removal may have entraped some air that is not rising to the top/or
> whatever, to be bled out for some reason. What tricks could
> make those
> air bubbles break loose? Tapping on the chambers with a
> hammer, or maybe
> an air wrench held against the chambers and goosed a few times?
> --
>
> Regards,
> John Dolan
>
> jdolan
>
 
> an air pocket somewhere. In addition I believe that another problem >
> stems from the fact that you have to remove the rear calipers to bleed.

I think Tom is right on, turning those calipers ever so slightly during
removal may have entraped some air that is not rising to the top/or
whatever, to be bled out for some reason. What tricks could make those
air bubbles break loose? Tapping on the chambers with a hammer, or maybe
an air wrench held against the chambers and goosed a few times?
- --

Regards,
John Dolan

jdolan
 
The only difference engine running vs engine off is the power assist. You
are simply putting more pressure on the system. The same amount of fluid is
being moved. Since there are no giesers, forget bleeding, you have done that
well. You said the pedal is firm, just low. It's low because of the amount
of fluid displaced. You could adjust the master piston rod ever so slightly
longer to get more out of it, but that is the last resort. Do not cover the
compensating ports if you do adjust it or you'll get brake drag/burn. My
feeling is that you need a bigger master to move more volume. Caliper
alignment is something to think about. If the pads are not hitting squarely
then they will have to "twist" into place. Look for uneven wear on the pads,
if so then go after it. I could measure my pedal height if that would help.
'73 Desert

> -----Original Message-----
> From: owner-gmcmotorhome
> [mailto:owner-gmcmotorhome]On Behalf Of Heinz
> Wittenbecher
> Sent: Monday, July 27, 1998 1:39 PM
> To: GMCnet (E-mail)
> Subject: GMC: What is normal brakepedal travel distance?
>
>
> Still struggling with low brakepedal with engine running and without, The
> difference being 2+ inches.
>
> I've been trying to find the specs on what normal brakepedal travel
> would/should be with and without engine running. Unfortunately I did not
> take much notice of that before we started.
>
> I've messed around so much by now that a clean start is needed.
>
> BTW, geiser test negative, I.e. no spurts.
>
> If it takes more fluid to apply calipers vs. drums, why the big diff when
> engine is off or running? Should it not be same? or at least closer?
>
> TIA - Heinz
>
 
Heinz I found new combination valves here for about $50 US. Don't take it
off it sets up the ratio between front and rear brakeing pressure. Without
it you will be locking the rear brakes before the fronts.

>Did not lock the combination valve as it only affects the front (the lock),
>or at least thats what I gather from the manual and it's only locked open to
>allow for less pressure to affect the bleed. Having gotten a good flow
>together with the bleed valve being nicely on top and no change with fronts
>pinched off I'm still looking at the rears to be the culprit.
>
>Having said that, I'm going to start from scratch once the power bleeder
>arrives later this week utilizing pointers and ideas received from the net
>over the last few days.
>
>Have had the comment/recommendation to bypass the metering valve altogether
>as due to it's age it may be gummed up, etc. and that it's not really
>neccessary on the coach as it was simply a carryover from the Toronado. Has
>anyone done so (bypassed it)?
>
>Air is still the number one suspect. Going to do another (one or more)
>serious bleed sessions and hopefully by next week I'll be able to report on
>what ultimately "worked for me".
>
>I too am hoping that the standard MC will ultimately suffice, as from what
>info I gathered sofar the larger reservor of the P30 MC should only be
>necessary if the 80mm calipers were used.
>
>Heinz
>
>>
>>
>> I disagree.. Discs take less fluid to actuate than brake
>> shoes since they
>> are in constant contact with the rotors and move less. Brake
>> shoes are not
>> in contact with the brake drums.
>>
>> Besides the system worked before the lines were replaced.
>>
>> to start again have you bled the master cylinder and
>> combination valve first
>> and than locked the combination valve open with the special
>> tool? You have
>> an air pocket somewhere. In addition I believe that another
>> problem stems
>> from the fact that you have to remove the rear calipers to bleed.
>>
>>
>>
>>
>>
>>

>> >Heinz:
>> >
>> >Unless you've used the Chevy P-30 chassis master cylinder
>> (MC) and the
>> >brake rod (it's 0.010" longer than original), I doubt the original MC
>> >has sufficient capacity for all-wheel disc brakes. In case
>> you need the
>> >numbers, as I know it, here they are: MC - GM 14009146, NAPA
>> 39-622 and
>> >Wagner F103239.
>> >
>> > Paul Bartz
>> >
>> >From: Heinz Wittenbecher [mailto:heinz]
>> >Sent: Monday, July 27, 1998 6:12 PM
>> >Subject: RE: GMC: What is normal brakepedal travel distance?
>> >
>> >>
>> >>
>> >> Heinz, sorry you are having such a problem with the brakes.
>> >> With all the
>> >> advice you have received regarding the sequence to bleed,
>> >> have you tried
>> >> either or both?
>> >>
>> >
>> >Yup, forwards and backwards :-) and then in reverse :-(
>> >
>> >We bench-bled MC just in case though we were quite sure the MC didn't
>> >run
>> >dry during changeover and changing of lines.
>> >
>> >We went for a ride and the pedal is still quite low at hard braking.
>> >
>> >Brakes become active (noticeable) at about half pedal travel.
>> >
>> >At hard braking it stops about 1/2 in. above hitting bottom of pedal
>> >travel,
>> >which is kinda' close I feel.
>> >
>> >The pedal is not mushy, brakes appear solid at that point
>> and it stops
>> >at
>> >same spot each time.
>> >
>> >Pedal is slightly higher when applied with parking brake on.
>> (standing
>> >still)
>> >
>> >With cover off MC there is no gushing fluid when brake is released. I
>> >would've expected a gusher if compressed air was forcing
>> fluid back, no?
>> >
>> >Clamped front brakehoses, no diff.
>> >
>> >Is it possible that the master cylinder is not putting enough fluid
>> >through?
>> >(The master cyl is original, but recently replaced [new, not
>> rebuilt]).
>> >If
>> >so, is there a solution?
>> >
>> >Has anyone else installed all 4? TSM has sold a few. To anyone on the
>> >gmcnet?
>> >
>> >As my next move (of despearation?) I've ordered a Bleeder
>> from Phoenix
>> >Systems.
>> >
>> >Heinz
>> >
>> >
>>
>
>
>
 
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