| middle rear disc brakes [message #364622] |
Thu, 10 June 2021 20:55  |
joewilly
Messages: 40
Registered: April 2016
Location: Victor,Ia
Karma: -1
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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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| Re: [GMCnet] Re: middle rear disc brakes [message #364626 is a reply to message #364624] |
Fri, 11 June 2021 05:48  |
joewilly
Messages: 40
Registered: April 2016
Location: Victor,Ia
Karma: -1
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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
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| Re: [GMCnet] Re: middle rear disc brakes [message #364627 is a reply to message #364626] |
Fri, 11 June 2021 06:07 |
6cuda6
Messages: 975
Registered: June 2019
Karma: -6
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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
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| Re: middle rear disc brakes [message #364632 is a reply to message #364622] |
Fri, 11 June 2021 10:28 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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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
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| Re: middle rear disc brakes [message #364640 is a reply to message #364622] |
Fri, 11 June 2021 16:41 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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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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| [GMCnet] Re: middle rear disc brakes [message #364641 is a reply to message #364640] |
Fri, 11 June 2021 18:04 |
Russell Mehlenbacher
Messages: 128
Registered: June 2010
Karma: 1
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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:
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Russ & Linda Mehlenbacher
Rochester Hills, Michigan
'76 Eleganza
'74 Sequoia
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| Re: [GMCnet] Re: middle rear disc brakes [message #364648 is a reply to message #364641] |
Sat, 12 June 2021 08:33 |
joewilly
Messages: 40
Registered: April 2016
Location: Victor,Ia
Karma: -1
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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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| [GMCnet] Re: middle rear disc brakes [message #364655 is a reply to message #364648] |
Sat, 12 June 2021 19:46 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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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 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
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--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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