Brake pedal travel

R

randy1

New member
Jul 5, 2007
1,979
0
0
Confession - I have not been driving my coach as much as I should.

Stock Front Disk / Rear Drum setup and prefer to stay that way.

I took the coach out and the pedal seems to go almost to the floor before any braking resistance is felt. With engine off brake pedal gets firm after
pumping it and goes down after starting up. All brake flex hoses replaced with teflon about 5 years ago. No obvious external fluid leaks. Booster line
intact and connected. No brake shoe/pad noise.

Any ideas as to what these symptoms point to?
--
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ
 
Bad master cylinder with internal leak.

Emery Stora
77 Kingsley
Frederick, CO

>
> Confession - I have not been driving my coach as much as I should.
>
> Stock Front Disk / Rear Drum setup and prefer to stay that way.
>
> I took the coach out and the pedal seems to go almost to the floor before any braking resistance is felt. With engine off brake pedal gets firm after
> pumping it and goes down after starting up. All brake flex hoses replaced with teflon about 5 years ago. No obvious external fluid leaks. Booster line
> intact and connected. No brake shoe/pad noise.
>
> Any ideas as to what these symptoms point to?
> --
> Randy
> 1973 26' Painted Desert
> Ahwatukee (Phoenix) AZ
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
What emery said is most likely cause of low pedal. Fairly ez fix, for
confirmation as well.
Jim Hupy

> Bad master cylinder with internal leak.
>
> Emery Stora
> 77 Kingsley
> Frederick, CO
>

> >
> > Confession - I have not been driving my coach as much as I should.
> >
> > Stock Front Disk / Rear Drum setup and prefer to stay that way.
> >
> > I took the coach out and the pedal seems to go almost to the floor
> before any braking resistance is felt. With engine off brake pedal gets
> firm after
> > pumping it and goes down after starting up. All brake flex hoses
> replaced with teflon about 5 years ago. No obvious external fluid leaks.
> Booster line
> > intact and connected. No brake shoe/pad noise.
> >
> > Any ideas as to what these symptoms point to?
> > --
> > Randy
> > 1973 26' Painted Desert
> > Ahwatukee (Phoenix) AZ
> >
> >
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
I would look at the more of the basics first. Fluid level and condition (clear). You may have a rear cylinder leak and that won't hit the ground for
a while. Hidden leak. Maybe back up in a parking lot and firm apply to adjust rears several times. Or the booster gives enough assist to drop the
pedal-- that part is odd An internal MC leak past seals can also cause this.
--
John Lebetski
Woodstock, IL
77 Eleganza II
Source America First
 
Inactivity is a huge enemy of braking systems. Sudden loss of pedal is
never a good sign. In any case a FULL INSPECTION of the entire system is
called for here. Jack it off the ground, block it like your life depends
upon it (it does) pull all wheels and tires, pull the rear drums (pita) and
you will find the culprit. One HUGE ADVANTAGE of disc systems, ease of
brake inspections.
Jim Hupy
Salem, Or. (presently snowed in)

> I would look at the more of the basics first. Fluid level and condition
> (clear). You may have a rear cylinder leak and that won't hit the ground
> for
> a while. Hidden leak. Maybe back up in a parking lot and firm apply to
> adjust rears several times. Or the booster gives enough assist to drop the
> pedal-- that part is odd An internal MC leak past seals can also cause
> this.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> Source America First
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
> Confession - I have not been driving my coach as much as I should.
>
> Stock Front Disk / Rear Drum setup and prefer to stay that way.
>
> I took the coach out and the pedal seems to go almost to the floor before any braking resistance is felt. With engine off brake pedal gets firm
> after pumping it and goes down after starting up. All brake flex hoses replaced with teflon about 5 years ago. No obvious external fluid leaks.
> Booster line intact and connected. No brake shoe/pad noise.
>
> Any ideas as to what these symptoms point to?

Randy,

With no vacuum source(?) the pedal will get real hard after a pump or two, but if you were rolling, you would also realize that you then have no
brakes.....

After you check the fluid level, do this test with the engine idling:
- Press the pedal once and note the travel or distance from floor.
- Pump the pedal three/four times and hold the last.
?? Did the pedal come up ??
If yes, it could be rear brake adjustment.
If no, it could be air in the system.
- Wait 15 minutes and try again. (It can take a while for the shoes to move back.)
?? Same result ?? See above.

To adjust the rear brakes, (hope no bozo removed the self adjusters) go to an empty lot. Put everything that is loose and or fragile on the floor or
someplace it can't fall/fly.
- Reverse Smartly, Jam on the Brakes.
- Repeat four times. The self adjusters cannot over adjust the brakes.
- Wait a bit again and asses the pedal travel now.

If it didn't get better, then you do probably have air in the system. I don't know how it happens, but I have had air accumulate in the brakes of a
vehicle that I had bled to solid some time before. It is rare, but it does happen.

Let us know how this worked out.

Matt

--
Matt & Mary Colie - Members GMCMI, GMCGL, GMCES
'73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
Now with both true Keyless and remote entry
SE Michigan - Twixt A2 and Detroit
 
I'd like to bleed them with my Mityvac ( pedal helpers always seem to find something better to do halfway through). Does it matter if the pedal is up
or fully depressed when bleeding from the wheel?
--
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ
 
The pedal needs to be up when bleeding from the wheel. Otherwise there is no path for the fluid to flow from the reservoir. When there is a big system
(like 4 wheel cylinders) coupled with a small reservoir,(like in the GMC), the level in the reservoir needs to be closely monitored as the shoes wear.
This is especially evident when breaking in new brake shoes or if the self adjusters are not working properly or getting used enough as the shoes
wear.
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.
 
Maybe you should jack up each side real quick and spin the wheels to see if the brakes are all properly adjusted. If one or more is not adjusted out
for wear, adjusting it manually may force air at the top of the system back out of the master cylinder and into the reservoir. Then you wont have to
bleed the system. This same scenario just happened to me and it was just the fluid going low because the shoes were wearing in and I had not been
doing my dutiful back up stops for the amount of braking that I did over the past several months.
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.
 
The pedel should be at the bottom. Suggest you put a 2x4 board to limit
travel.

> I'd like to bleed them with my Mityvac ( pedal helpers always seem to find
> something better to do halfway through). Does it matter if the pedal is up
> or fully depressed when bleeding from the wheel?
> --
> Randy
> 1973 26' Painted Desert
> Ahwatukee (Phoenix) AZ
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
> I'd like to bleed them with my Mityvac ( pedal helpers always seem to find something better to do halfway through). Does it matter if the pedal is
> up or fully depressed when bleeding from the wheel?

Randy,

You have that answer from Terry, but I have been vacuum (and gravity) bleeding for years because so many of my vehicles were simply not amenable to
pressure bleeding.

Very early on I discovered that the leakage on the threads is a problem two ways. The corrosion caused by the brake fluid in the threads may not be a
big issue in Arizona (I thought I remembered you living the NW), but the leakage while vacuum bleeding can be deceiving and cause you to bleed way
more than might be needed.
To deal with this, either wrap the threads with teflon tape (any color) (or I used to glom them up with a teflon filled pipe thread dope). The teflon
tape is cleaner and neater. It works well if you have a spare bleed screw so you can remover and replace. Then you can clean that one and use it for
the next. The amount of future grief this will prevent is amazing. I can't even remember the last time I broke (common thing in Michigan) a bleed
screw in one of my own vehicles.

If the little rubber caps are gone, they are good to have.

Matt
--
Matt & Mary Colie - Members GMCMI, GMCGL, GMCES
'73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
Now with both true Keyless and remote entry
SE Michigan - Twixt A2 and Detroit
 
> The pedal needs to be up when bleeding from the wheel. Otherwise there is no path for the fluid to flow from the reservoir. When there is a big
> system (like 4 wheel cylinders) coupled with a small reservoir,(like in the GMC), the level in the reservoir needs to be closely monitored as the
> shoes wear. This is especially evident when breaking in new brake shoes or if the self adjusters are not working properly or getting used enough as
> the shoes wear.
If the rear brakes stay adjusted (either by the self adjusters or manually), the fluid in the master cylinder will never be depleted by wear of the
shoes. Depletion of the master cylinder results from the wear of the disk brake pads on the front. On the OEM system (and if there are no leaks) the
master cylinder reservoir holds enough fluid to allow the front pads to wear completely out without getting too low of fluid.

But all of that goes out the window when the vehicle gets to be 40 years old and things don't work like they did from the factory, or POs have done
stuff that is non-OEM.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."
 
If your MC is good now, there is a good chance it will soon fail. Moving the pedal to push pistons to areas of the bore "that have never been charted"
tends to destroy the lip seals as they scrape over crusty bore. So be aware and best to use less than full depressions when bleeding or testing.
--
John Lebetski
Woodstock, IL
77 Eleganza II
Source America First
 
Fed master cyl reservoir almost empty. Filled and seems fine. No obvious external leaks.
--
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ
 
OEM master cylinder front reservoir supplies fluid for rear brakes. Might be time to check rear brakes.
Preaching to the choir.
Tom, MS II
--
1975 GMC Avion
KA4CSG
 
> Fwd master cyl reservoir almost empty. Filled and seems fine. No obvious external leaks.

Randy,

That reservoir should not go down unless there is a leak. Have adjusted the rear brakes?
If you don't want to climb under there at least find a big area that you can jam the brakes while backing up.
If the brakes got that far out, it can really truly take a dozen stops to set the brakes up right.
When doing this, expect to rearrange everything that is loose.

Matt
--
Matt & Mary Colie - Members GMCMI, GMCGL, GMCES
'73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
Now with both true Keyless and remote entry
SE Michigan - Twixt A2 and Detroit
 
my rear leaked for about 2 years. I checked and topped it off before every trip, and when I stopped. sometimes it was fine, sometimes I added a a
bit of fluid. I never noticed any external fluid leakage, but when I finally did re-build the rear brakes, you could tell a few of the brake
cylinders were leaking.

Chances are you have a rear brake cylinder leaking.
--
Jon Roche
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/
 
Anytime you lose fluid in the master cylinder reservoir, you have a leak.
Brakes are THE MOST CRITICAL SYSTEM in your coach. They need to be 100% all
the time. People's lives depend upon their condition. Find that leak, and
repair it, sooner than later.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> my rear leaked for about 2 years. I checked and topped it off before
> every trip, and when I stopped. sometimes it was fine, sometimes I added
> a a
> bit of fluid. I never noticed any external fluid leakage, but when I
> finally did re-build the rear brakes, you could tell a few of the brake
> cylinders were leaking.
>
>
> Chances are you have a rear brake cylinder leaking.
> --
> Jon Roche
> 75 palm beach
> St. Cloud, MN
> http://lqqkatjon.blogspot.com/
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
> Anytime you lose fluid in the master cylinder reservoir, you have a leak. ...
As the front pads wear, the fluid in its reservoir drops. On the OEM system, the front reservoir is the rear brakes. If the system has been altered so
that the front reservoir is the front brakes, there is a good chance a drop in fluid means nothing except that the pads are wearing.

Hard to diagnose anything on a 40 yo vehicle (that may not be all OEM) without complete information.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."
 
You must log in or register to reply here.
Get your shine on at www.cruzingear.co
GMCMI Fall 2026 Rally

Share this page

Share this page
Top Bottom
Back