Master Cylinder replacement needed

H

heinz wittenbecher

New member
Mar 1, 1998
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Finally got a good caliper today and when all the smoke and brakefluid
cleared, the pedal keept going down as soon as boosted pressure is applied,
i.e. vacuum pump on. Goes right to the floor, slowly.

I'm suspecting the master cylinder is bleeding back? Any other
hints/suggestion as to what it could be are welcomed. No external leaks,
pretty sure no air, but even if still air it should pump up to spongy and
not go to the floor. ( Am I wrong?)

Of course all this happened too late to call Cinnebar. Hopefully they or the
Florida G's will have a new one as I'd prefer not to deal with an unknown
rebuild.

However, I recall that some of you folks have changed master cylinders and
some have found an equivilant replacement?

Is there something out there that'll updated/improve the master cyl?

Is there a current direct replacement?

There goes my weekend test drive :-)
but perhaps not if there is a direct replacement someone has firsthand
experience with.

TIA - Heinz
 
> -- [ From: Eugene Fisher * EMC.Ver #2.5.3 ] --
>
> Was this an old MS ?? Was working before the caliper change ?? should
> not need bench bleed.

About 2 years old, maybe 3. Had it replaced in Ottawa on last vacation trip
(Maritimes).
I can't remember if it was a new or rebuilt. It came from Cinnebar and if
there was a choice I would've taken a one.

It was never without fluid during bleed/caliper chnage/bleed.

Do you have a Wagner number?

Heinz

>
> Mine went out in Roseburg two months ago, same thing , one day a little
> spongey next day all the way to the floor. Ilooked everywhere in
> Roseburg , no Wagner so I got a NEW master cyl that was listed as a
> replacement, I took what ever I could get there, I do not even know the
> brand but of course they said"same as, made by, etc, wagner. It was
> working last I saw it.
> gene
>
> -------- REPLY, Original message follows --------
>
> Date: Friday, 21-May-99 10:58 PM
>
> From: Heinz Wittenbecher \ Internet: (heinz)
> To: gmclist \ Internet: (gmcmotorhome
> .org)
>
> Attachment: mimemsg.doc Code: 034U7A5 \ Created: Unknown [3 Kb]
>
> Subject: GMC: Master Cylinder replacement needed
>
> Finally got a good caliper today and when all the smoke and brakefluid
> cleared, the pedal keept going down as soon as boosted pressure is
> applied, i.e. vacuum pump on. Goes right to the floor, slowly.
>
> I'm suspecting the master cylinder is bleeding back? Any other
> hints/suggestion as to what it could be are welcomed. No external leaks,
> pretty sure no air, but even if still air it should pump up to spongy
> and not go to the floor. ( Am I wrong?)
>
> Of course all this happened too late to call Cinnebar. Hopefully they or
> the Florida G's will have a new one as I'd prefer not to deal with an
> unknown rebuild.
>
> However, I recall that some of you folks have changed master cylinders
> and some have found an equivilant replacement?
>
> Is there something out there that'll updated/improve the master cyl?
>
> Is there a current direct replacement?
>
> There goes my weekend test drive :-)
> but perhaps not if there is a direct replacement someone has firsthand
> experience with.
>
> TIA - Heinz
>
>
>
>
> -------- REPLY, End of original message --------
>
>
> --
> Gene 76Palm Beach /Or/CA
>
> GMC Technical Information
> http://www.california.com/~eagle/
>
>
 
>
> > the pedal keept going down as soon as boosted pressure is applied,
> > i.e. vacuum pump on. Goes right to the floor, slowly.
> >
> > I'm suspecting the master cylinder is bleeding back? Any other
> > hints/suggestion as to what it could be are welcomed. No external
leaks,
> > pretty sure no air, but even if still air it should pump up to spongy
and
> > not go to the floor. ( Am I wrong?)
>
> Heinz,
> You sound right to me. Trapped air MAY allow the pedal to go to the
> floor, but not slowly. If the pedal is initially firm, and then sinks
away,
> with no loss of fluid, it's leaking back into the master. Only possible
> exception would be a severely restricted line with air in
> line/cylinders/calipers beyond the restriction (pretty rare combination),
> which could give you the same symptoms.
> HTH.
>
> Rick Staples
> '75 Eleganza
> Louisville, CO
>

Thanks for the comments, Rick.
No restriction as we had no trouble bleeding with 17 pounds of pressure.
Going for the MC in AM. Need that 24 hour parts store :-)

Heinz
 
Do you know who built the Autozone ones?

I did have fluid behind the old master cylinder. I have a Raybestos in there
now but didn't get a chance to drive with it. Still puttering around.

Sure would be nice to get a real and honest comparison between generic and
Cinnebar/GMC. I don't have a problem with 175 bucks, but if all they do is
rebox it I'd be a little peeved.

The pedal does stay up now, but I'll reserve judgement until I drive it.

I'm going to order a Cinnebar one tomorrow, just in case. I need (hope) to
be on the road by Wednesday or Thursday, though I may not make it :-)

Heinz

> In a message dated 5/21/99 10:56:45 PM Eastern Daylight Time,

>
> cleared, the pedal keept going down as soon as boosted pressure is
applied,
> i.e. vacuum pump on. Goes right to the floor, slowly.
>
> I'm suspecting the master cylinder is bleeding back? Any other
> hints/suggestion as to what it could be are welcomed. No external leaks,
> pretty sure no air, but even if still air it should pump up to spongy and
> not go to the floor. ( Am I wrong?) >>
> Heinz -- the two Autozone master cylinders exhibited this same problem.
This
> is usually a sign that their is internal leakage in the master cylinder.
I
> called Cinnabar and talked to Wes and he claimed that there is a
difference
> in porting and possibly in the design of the piston (valume??). I had
them
> ship me one of the GM master cylinders for $175.00 plus $45.00 overnight
> freight. When it came it had the exact casting numbers on the side as the
> Autozone one. When I installed it though, it worked. Expensive, but I
was
> able to leave for my trip!
>
> Emery Stora
> 77 Kingsley
> Santa Fe, NM
>
>
 
>
> Heinz -- the two Autozone master cylinders exhibited this same problem.

Emery,

I thought you got your master cylinders at NAPA? I installed the NAPA
39075 with no probems. The AZ master cylinders are probably rebuilt,
while the NAPA 39075 is a new one. Price was reasonable too.

Patrick
- --
Patrick Flowers
Mailto:patrick

The GMC Motorhome Page
http://www.gmcmotorhome.com
 
> I thought you got your master cylinders at NAPA? I installed the NAPA
> 39075 with no probems. The AZ master cylinders are probably rebuilt,
> while the NAPA 39075 is a new one. Price was reasonable too.
>
> Patrick

Patrick,

Do I gather correctly that you're running a NAPA Master Cylinder?

I'm just wondering how many others are running "replacements".

Speak up lurkers :-)

Heinz
...still waiting for that testdrive. Got into rewiring coach charger system
while adding some more genset soundproofing [g].
 
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