Home » Public Forums » GMCnet » Re: [GMCnet] update on master cylinder replace
| Re: [GMCnet] update on master cylinder replace [message #198131] |
Mon, 11 February 2013 14:17  |
KB
Messages: 1262
Registered: September 2009
Karma: 0
|
Senior Member |
|
|
As long as I'm bothering the experts with silly questions... :-)
If I understand it, one should not use master cylinders designed for an all-disc
system on a vehicle that has drum brakes, because some (most? all?) wheel
cylinders need residual pressure to retract fully and keep the cup seals closed.
Most disc-disc master cylinders don't include the necessary valve(s). This could
result in dragging brakes and/or air in the wheel cylinders.
Any truth to this??
thanks
Karen
1973 23'
1975 26'
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Karen
1975 26'
San Jose, CA
|
|
|
|
|
|
| Re: [GMCnet] update on master cylinder replace [message #198173 is a reply to message #198131] |
Mon, 11 February 2013 22:37  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
|
Senior Member |
|
|
Karen,
I'm confused by that statement/question: You speak of disc master
cylinders and wheel "cylinders" rather than "calipers". Calipers do not
need residual pressure valves unless the master cylinder is located below
the calipers, as on some hot rods. And the purpose is not to retract the
pads but to prevent them from retracting too much when the fluid runs back
to the master cylinder. Normally, caliper pistons are retracted by the
hysteresis of their rubber seals, by disc run-out, and by play in the wheel
bearings.
Ken H.
On Mon, Feb 11, 2013 at 3:17 PM, KB wrote:
> As long as I'm bothering the experts with silly questions... :-)
>
> If I understand it, one should not use master cylinders designed for an
> all-disc
> system on a vehicle that has drum brakes, because some (most? all?) wheel
> cylinders need residual pressure to retract fully and keep the cup seals
> closed.
> Most disc-disc master cylinders don't include the necessary valve(s).
> This could
> result in dragging brakes and/or air in the wheel cylinders.
>
> Any truth to this??
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
|
|
|
|
| Re: [GMCnet] update on master cylinder replace [message #198193 is a reply to message #198131] |
Tue, 12 February 2013 07:13 |
 |
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
|
Senior Member |
|
|
| KB wrote on Mon, 11 February 2013 15:17 |
As long as I'm bothering the experts with silly questions... 
If I understand it, one should not use master cylinders designed for an all-disc system on a vehicle that has drum brakes, because some (most? all?) wheel cylinders need residual pressure to retract fully and keep the cup seals closed.
Most disc-disc master cylinders don't include the necessary valve(s). This could result in dragging brakes and/or air in the wheel cylinders.
Any truth to this??
thanks
Karen
|
Karen,
The simple short answer is - NO.
No brake system that I know of expects there to be residual pressure in the brake system (anymore).
A little history...
Back in the days of single master cylinder and before self adjusting drum brakes actually worked, master cylinders did have a check valve arrangement in the piston seals so one could, if the brakes were out of adjustment, "pump them up" with a few short jabs of the brake pedal at the morning start-up. I bet you can't even find one of those if you wanted one.
Oh, and just for future reference, the only silly question is the one you are afraid to ask for fear of sounding uniformed.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
|
|
|
|
| Re: [GMCnet] update on master cylinder replace [message #198235 is a reply to message #198193] |
Tue, 12 February 2013 13:47 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
|
Senior Member |
|
|
| Matt Colie wrote on Tue, 12 February 2013 07:13 |
The simple short answer is - NO.
No brake system that I know of expects there to be residual pressure in the brake system (anymore).
Matt
|
Matt I thought in a Disk/drum configuration there should be a 2lb residual valve int he drum circuit to keep the drum cylinders in contact with the shoes so there wasn't a delay on brake application as the cylinders pumped up.
So I've read in the street rod building materials....
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
|
|
|
|
|
|
|
|
| Re: [GMCnet] update on master cylinder replace [message #198304 is a reply to message #198262] |
Wed, 13 February 2013 06:50 |
|
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
|
Senior Member |
|
|
| bwevers wrote on Tue, 12 February 2013 19:59 |
KB brings up an interesting point for people who like to
use master cylinders from rear disk brake applications on
the GMC. If you have rear drums you need the check valve.
Regards,
Bill
|
Bill,
Can you tell me where that diagram is from?
When they do this, do they get to omit the springs inside the
wheel cylinders?
The people that have fit disks on the rear should be really scared. And those that reversed the service of the MC so the front is using the other port are in trouble too. If the coach had/has this valve.
Admittedly, I left the brake labs over 20 years ago, but there have been no major changes that I was aware of in the intervening time. I know my coach doesn't have this feature, the inserts in the MC are just so the inverted flare does not have to be machined into the cast iron. I know this because we used to get shipped finished castings and the parts to assemble them for a specific test.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
|
|
|
|
|
|
|
|
| Re: [GMCnet] update on master cylinder replace [message #198358 is a reply to message #198254] |
Wed, 13 February 2013 17:11 |
GMC Cruse
Messages: 606
Registered: June 2009
Location: SE Michigan
Karma: 3
|
Senior Member |
|
|
| Matt Colie wrote on Tue, 12 February 2013 19:17 |
| Keith V wrote on Tue, 12 February 2013 14:47 |
| Matt Colie wrote on Tue, 12 February 2013 07:13 |
The simple short answer is - NO.
No brake system that I know of expects there to be residual pressure in the brake system (anymore).
Matt
|
Matt I thought in a Disk/drum configuration there should be a 2lb residual valve int he drum circuit to keep the drum cylinders in contact with the shoes so there wasn't a delay on brake application as the cylinders pumped up.
So I've read in the street rod building materials....
|
Keith,
That would be a new one on me.
I'm not saying it can't be done, but every drum cylinder I have ever had apart had a spring inside it for just that purpose.
Matt
|
The manufacturers have been using the rubber residual check valve for atleast 42 years. In 1980, I built a '27 Ford and used '70 Mustang front discs, booster and master cylinder. I used a '75 Vette rearend with disc brakes. I had to remove the rubber check valve from the master cylinder rear brake port due to the discs on the rearend. I still have the car and the brakes work great.
Mike K.
'75 PB
Southeast Michigan
|
|
|
|
|
|
| Re: [GMCnet] update on master cylinder replace [message #198383 is a reply to message #198380] |
Wed, 13 February 2013 20:04 |
 |
mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
|
Senior Member |
|
|
| Matt Colie wrote on Wed, 13 February 2013 17:51 |
I have got to do more research on this, I have just finished working my through nine factory manuals. Though some have strange proportioning valves, I have not yet found a residual pressure valve or mention of it. It could be buried in the differential switch or possibly the proportioning valve.
...
|
I have always had the impression that the residual pressure check valve was one of the several functions of the combination valve. (AKA: proportional valve.)
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
|
|
|
|
| Re: [GMCnet] update on master cylinder replace [message #198387 is a reply to message #198383] |
Wed, 13 February 2013 20:18 |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
|
Senior Member |
|
|
G'day,
I don't know what's going on but there are two threads with the same Subject currently on the Forum. I sent in the following
response to the other one:
G'day,
I just read Maintenance Manual (MM) X-7525, Section 5 Brakes, Pages 5-1 through 5-13 which covers General Information and Brake
System Trouble Diagnosis. I also skimmed pages 5-14 through 5-46 and I could NOT find any reference to a residual valve anywhere. I
then moved on to MM X-7625 and MM X-7725 there was no reference in either one of those manuals.
Returning to MM X-7525 Section 5, Page 5-27 I found Figure 32 - Master Cylinder (Exploded View). There is no residual valve in that
figure. There is, however, two "inserts" in the ports that feed the combination valve. It is possible that there are residual valves
in those inserts. However, considering the level of detail shown in the rest of the figure I don't believe there is.
I then checked Parts Book 78Z, Section 4 Brakes, Page 4-10, Figure 4.010 - Cylinder - Master, and it had the same level of detail.
It shows Key 5 - INSERT - tube fitting.
It seems to me that if either one of Key 5 were residual valves the parts book would call them residual valves NOT tube fitting.
IIRC when looking at a GMC Master Cylinder the insert is made of brass.
I did a bit more research into the way the brakes on a GMC work and noted a couple of things that could / would negate the necessity
for a residual valve.
1) Here's a cross section of the Combination valve that will be helpful to reference when reading the paragraph below.
http://www.gmcmhphotos.com/photos/member-galleries/p37696-combination-valve-cros.html
Ref: MM X-7525, Section 5 Brakes, Page 5-3 COMBINATION VALVE - METERING VALVE FUNCTION The metering section of the combination valve
operates to 'hold off' hydraulic flow (pressure) until about 130 psi has been built up in the system before applying the front
brakes. The pressure then blends to a full line pressure at approximately 400-600 psi line pressure. There is no flow restriction
when the brakes are released.
The metering valve is the spring and poppet on left side of the brass combination valve.
Below is a photograph that KenH took showing the internal parts of the OEM Combination valve. From what I can see I don’t believe
there is a residual valve in it. There could be one in the part Ken called the Brass Seat (part with screw extractor in it).
http://www.gmcmhphotos.com/photos/deciphering-the-combination-valve/p5329.html
or in the port on the left of this photo:
http://www.gmcmhphotos.com/photos/deciphering-the-combination-valve/p5323.html
But to me it looks like a clear passageway.
2) The rear brake shoes automatically adjust when the brakes are applied when backing up which leads me to assume they are kept
close enough to the drums to provide braking without having to depress the brake pedal very far.
Well' that's my $0.02's on the subject.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Mike Miller
Sent: Thursday, February 14, 2013 1:05 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] update on master cylinder replace
Matt Colie wrote on Wed, 13 February 2013 17:51
> I have got to do more research on this, I have just finished working my through nine factory manuals. Though some have strange
proportioning valves, I have not yet found a residual pressure valve or mention of it. It could be buried in the differential
switch or possibly the proportioning valve.
> ...
I have always had the impression that the residual pressure check valve was one of the several functions of the combination valve.
(AKA: proportional valve.)
--
Mike Miller -- Hillsboro, OR -- on the Black list
(#1)'73 26' exPainted D. -- (#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
http://m000035.blogspot.com
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
|
|
|
|
| Re: [GMCnet] update on master cylinder replace [message #198408 is a reply to message #198352] |
Wed, 13 February 2013 22:27 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
|
Senior Member |
|
|
Good references, Keith. The residual valve was really unfamiliar to me
except for the 2 psi version used to prevent drain-back into a
lower-than-caliper master cylinder. While I don't doubt the statement that
they've been used for a long time, I've never encountered one. But then,
most of my MC rebuilding experience was a LONG time ago. :-(
Still, I can assure you, based on the GMC service manuals, my own tear-down
and study of the GMC combination valve, and hands-on of all other parts of
the brake system, there is not one in the OEM GMC system.
Ken H.
On Wed, Feb 13, 2013 at 5:04 PM, Keith V wrote:
>
> OMG my image is shattered!
> whay has the world come to ...
> can it be true?
> Is Matt wr....I can't even say it!
>
> Here's 2 quick references;
>
> http://www.thebrakeman.com/valvetechi
>
> Very simply, the residual valve found in the drum brake systems is not
> compatible with the disc brake conversions.....
>
>
> http://www.mbmbrakeboosters.com/index.php?option=com_content&view=category&layout=blog&id=8&Itemid=16
>
> Drum brakes require a 10 lb. residual pressure (RPV10) to counteract the
> spring tension in the drum system which tends to pull the shoes away from
> the drums.
>
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
|
|
|
|
| Re: [GMCnet] update on master cylinder replace [message #198451 is a reply to message #198408] |
Thu, 14 February 2013 11:20 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
|
Senior Member |
|
|
I wonder if the hold off feature of the combo valve replaces the residual valve.
They seem to do the same kind of function, the the hold off probably doing things a little better.
Street rod guys are not always that knowledgeable about how things actually work I've found...
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
|
|
|
|
| Re: [GMCnet] update on master cylinder replace [message #198459 is a reply to message #198451] |
Thu, 14 February 2013 11:53 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
|
Senior Member |
|
|
Keith,
I suspect your right about the metering valve in our combination valve
eliminating the need for a residual pressure valve. Along with the
self-adjusting feature of the drum brakes.
The stated purpose of the metering valve is to delay front disc brake
application until the drums become effective. The stated purpose of the 10
psi residual pressure valve is to enable the drums to take effect
immediately. Kinda sound like saying the same thing with two different
sets of words when it's put that way, doesn't it? "Wait here" vs "Hurry up
there".
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Thu, Feb 14, 2013 at 12:20 PM, Keith V <my427v8@hotmail.com> wrote:
>
>
> I wonder if the hold off feature of the combo valve replaces the residual
> valve.
>
> They seem to do the same kind of function, the the hold off probably doing
> things a little better.
>
> Street rod guys are not always that knowledgeable about how things
> actually work I've found...
> --
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
|
|
|
|
Goto Forum:
Current Time: Sat Oct 05 04:29:15 CDT 2024
Total time taken to generate the page: 0.02681 seconds
|
GMCforum
Search
Help
Register
Login
Home
