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middle rear disc brakes

JW
Joe williams
Fri, Jun 11, 2021 1:55 AM

having a problem with the middle axle disc brakes hanging up-not releasing.maybe fronts also

I have the Lee Harrison disc brake with I think is the P30 master cyl

I was driving along and slowed down going through small town and that is when I think they didn't release

Not knowing I kept driving for about 5 miles and and was having trouble maintaining 55mph so I pulled over and checked brakes with the laser gun and
found the middle dics  at 450+ deg. front discs were hot also about 350 rear drums where at 265.

can anyone point me in the right direction as what to look for that could cause this?

proportioning valve? master cyl?

your input/ideas would be appreciated

thanks
joe

Joe Williams
1978 Royale rear twin

having a problem with the middle axle disc brakes hanging up-not releasing.maybe fronts also I have the Lee Harrison disc brake with I think is the P30 master cyl I was driving along and slowed down going through small town and that is when I think they didn't release Not knowing I kept driving for about 5 miles and and was having trouble maintaining 55mph so I pulled over and checked brakes with the laser gun and found the middle dics at 450+ deg. front discs were hot also about 350 rear drums where at 265. can anyone point me in the right direction as what to look for that could cause this? proportioning valve? master cyl? your input/ideas would be appreciated thanks joe -- Joe Williams 1978 Royale rear twin
JH
James Hupy
Fri, Jun 11, 2021 4:41 AM

Brake hoses perhaps collapsed internally. They can look fine on the
outside, and pass fluid under higher pressures, but not bleed back. Worth a
look-see.
Jim Hupy
Salem, Oregon

On Thu, Jun 10, 2021, 6:55 PM Joe williams jwillms@netins.net wrote:

having a problem with the middle axle disc brakes hanging up-not
releasing.maybe fronts also

I have the Lee Harrison disc brake with I think is the P30 master cyl

I was driving along and slowed down going through small town and that is
when I think they didn't release

Not knowing I kept driving for about 5 miles and and was having trouble
maintaining 55mph so I pulled over and checked brakes with the laser gun and
found the middle dics  at 450+ deg. front discs were hot also about 350
rear drums where at 265.

can anyone point me in the right direction as what to look for that could
cause this?

proportioning valve? master cyl?

your input/ideas would be appreciated

thanks
joe

Joe Williams
1978 Royale rear twin


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Brake hoses perhaps collapsed internally. They can look fine on the outside, and pass fluid under higher pressures, but not bleed back. Worth a look-see. Jim Hupy Salem, Oregon On Thu, Jun 10, 2021, 6:55 PM Joe williams <jwillms@netins.net> wrote: > having a problem with the middle axle disc brakes hanging up-not > releasing.maybe fronts also > > I have the Lee Harrison disc brake with I think is the P30 master cyl > > I was driving along and slowed down going through small town and that is > when I think they didn't release > > Not knowing I kept driving for about 5 miles and and was having trouble > maintaining 55mph so I pulled over and checked brakes with the laser gun and > found the middle dics at 450+ deg. front discs were hot also about 350 > rear drums where at 265. > > can anyone point me in the right direction as what to look for that could > cause this? > > proportioning valve? master cyl? > > your input/ideas would be appreciated > > thanks > joe > -- > Joe Williams > 1978 Royale rear twin > _______________________________________________ > GMCnet mailing list > Unsubscribe or Change List Options: >
JW
Joe williams
Fri, Jun 11, 2021 10:48 AM

Thanks James,I'll take a look at them this morning, the lines where all replaced with stainless and new hoses when disc conversion was done in 2004,
only about 9000 miles driven since then.

Joe Williams
1978 Royale rear twin

Thanks James,I'll take a look at them this morning, the lines where all replaced with stainless and new hoses when disc conversion was done in 2004, only about 9000 miles driven since then. -- Joe Williams 1978 Royale rear twin
6
6cuda6@gmail.com
Fri, Jun 11, 2021 11:07 AM

Pump up the brakes then open a bleeder on the caliper....if you have brake fluid spray out and the caliper releases you probably have bad hoses like
Jim said....if it just drips out like when normally gravity bleeding brakes and caliper doesnt release (still cant turn the disc) you have a seized
caliper.

You could have other problems but start there as its the easiest.

Rich Mondor,

Brockville, ON

77 Hughes 2600

Pump up the brakes then open a bleeder on the caliper....if you have brake fluid spray out and the caliper releases you probably have bad hoses like Jim said....if it just drips out like when normally gravity bleeding brakes and caliper doesnt release (still cant turn the disc) you have a seized caliper. You could have other problems but start there as its the easiest. -- Rich Mondor, Brockville, ON 77 Hughes 2600
KB
Ken Burton
Fri, Jun 11, 2021 3:28 PM

My anaylysis of this is:

While a defective hose could cause this problem (usually on a single wheel), I know of no hose in the system that would affect multiple wheels in both
the front and rear at the same time.  Also since you have both front and rears failing / getting hot at the same time, those involve two separate
hydraulic systems.  So the questuion what is common to both?

The only place they are combined is mechanically in the master cylinder.  (I did consider the combination valve)  I have seen this failure while
testing the rod lengths between the master cylinder and the brake booster.  The too long one caused the master cylinder to fail to return completely
to it's home or at rest position.  When that happened the hydraulic pressure was not completely released causing the brakes to drag.  Since we know
in your case that rod can not get longer on it's own, we need to look at why the master cylinder is not returning to it's home / at rest position.

I would be looking at the brake pedal return spring, or something in the brake booster and master cylinder area including dirt or crap in the brake
fluid in the master cylinder itself.

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

My anaylysis of this is: While a defective hose could cause this problem (usually on a single wheel), I know of no hose in the system that would affect multiple wheels in both the front and rear at the same time. Also since you have both front and rears failing / getting hot at the same time, those involve two separate hydraulic systems. So the questuion what is common to both? The only place they are combined is mechanically in the master cylinder. (I did consider the combination valve) I have seen this failure while testing the rod lengths between the master cylinder and the brake booster. The too long one caused the master cylinder to fail to return completely to it's home or at rest position. When that happened the hydraulic pressure was not completely released causing the brakes to drag. Since we know in your case that rod can not get longer on it's own, we need to look at why the master cylinder is not returning to it's home / at rest position. I would be looking at the brake pedal return spring, or something in the brake booster and master cylinder area including dirt or crap in the brake fluid in the master cylinder itself. -- Ken Burton - N9KB 76 Palm Beach Hebron, Indiana
JB
Johnny Bridges
Fri, Jun 11, 2021 9:41 PM

Check the pin pushing the MC since you have a non - OEM MC.  Dave Lenzi wrote up a procedure for checking the length, Ken Henderson had another way of
checking it.  Lenzi also sells pins of different lengths to correct the problem Ken B speaks of.  Quick n dirty check for caliper movement binding -
look for asymmetric wear of the pads on each caliper.  If one side is mamrkedly thinner than the other, the caliper isn't moving on the mounting pins
to stay centered.

--johnny

Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs.  They must answer to me in hell

Check the pin pushing the MC since you have a non - OEM MC. Dave Lenzi wrote up a procedure for checking the length, Ken Henderson had another way of checking it. Lenzi also sells pins of different lengths to correct the problem Ken B speaks of. Quick n dirty check for caliper movement binding - look for asymmetric wear of the pads on each caliper. If one side is mamrkedly thinner than the other, the caliper isn't moving on the mounting pins to stay centered. --johnny -- Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons. Braselton, Ga. I forgive them all, save those who hurt the dogs. They must answer to me in hell
RM
Russell Mehlenbacher
Fri, Jun 11, 2021 11:04 PM

I recently had one of my mid calipers (TSM) drag in a big way. I think the
root cause was the caliper pin sleeves had rusted up and bonded to the
rubber O-ring in the caliper ears. A hard brake pushed it out of it's
'happy spot' and it wasn't going back. Took it all apart, turned the
rotors, cleaned the sleeves, removed the rubber rings and removed the rust
in their grooves. New pads of course.
Russ

On Fri, Jun 11, 2021, 4:41 PM Johnny Bridges via Gmclist <
gmclist@list.gmcnet.org> wrote:

Check the pin pushing the MC since you have a non - OEM MC.  Dave Lenzi
wrote up a procedure for checking the length, Ken Henderson had another way
of
checking it.  Lenzi also sells pins of different lengths to correct the
problem Ken B speaks of.  Quick n dirty check for caliper movement binding -
look for asymmetric wear of the pads on each caliper.  If one side is
mamrkedly thinner than the other, the caliper isn't moving on the mounting
pins
to stay centered.

--johnny

Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs.  They must answer to me
in hell


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I recently had one of my mid calipers (TSM) drag in a big way. I think the root cause was the caliper pin sleeves had rusted up and bonded to the rubber O-ring in the caliper ears. A hard brake pushed it out of it's 'happy spot' and it wasn't going back. Took it all apart, turned the rotors, cleaned the sleeves, removed the rubber rings and removed the rust in their grooves. New pads of course. Russ On Fri, Jun 11, 2021, 4:41 PM Johnny Bridges via Gmclist < gmclist@list.gmcnet.org> wrote: > Check the pin pushing the MC since you have a non - OEM MC. Dave Lenzi > wrote up a procedure for checking the length, Ken Henderson had another way > of > checking it. Lenzi also sells pins of different lengths to correct the > problem Ken B speaks of. Quick n dirty check for caliper movement binding - > look for asymmetric wear of the pads on each caliper. If one side is > mamrkedly thinner than the other, the caliper isn't moving on the mounting > pins > to stay centered. > > --johnny > -- > Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons. > Braselton, Ga. > I forgive them all, save those who hurt the dogs. They must answer to me > in hell > _______________________________________________ > GMCnet mailing list > Unsubscribe or Change List Options: >
JW
Joe williams
Sat, Jun 12, 2021 1:33 PM

thanks to all, I have talked with Dave Lenzi and concluded it is most likely the MC , new one on the way.
will let you all know if this fixes it, fingers crossed

--
Joe Williams
1978 Royale rear twin

thanks to all, I have talked with Dave Lenzi and concluded it is most likely the MC , new one on the way. will let you all know if this fixes it, fingers crossed -- Joe Williams 1978 Royale rear twin
JK
Jim Kanomata
Sun, Jun 13, 2021 12:46 AM

My way of thinking says that if one wheel is dragging, then it is not  the
Master cylinder.

On Sat, Jun 12, 2021 at 6:33 AM Joe williams jwillms@netins.net wrote:

thanks to all, I have talked with Dave Lenzi and concluded it is most
likely the MC , new one on the way.
will let you all know if this fixes it, fingers crossed

--
Joe Williams
1978 Royale rear twin


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--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502

My way of thinking says that if one wheel is dragging, then it is not the Master cylinder. On Sat, Jun 12, 2021 at 6:33 AM Joe williams <jwillms@netins.net> wrote: > thanks to all, I have talked with Dave Lenzi and concluded it is most > likely the MC , new one on the way. > will let you all know if this fixes it, fingers crossed > > > -- > Joe Williams > 1978 Royale rear twin > _______________________________________________ > GMCnet mailing list > Unsubscribe or Change List Options: > -- Jim Kanomata ASE Applied/GMC, Newark,CA jimk@appliedairfilters.com http://www.gmcrvparts.com 1-800-752-7502