Replace Master Cylinder or MC plus Booster?

[james wack]

Seeking part number and source for brake booster and MC assembly, or just the correct booster. Background: When pressure bleeding the brakes
following rear axle caliper replacement, I developed a leak at the back of the MC where it meets the booster assembly. I see the booster/MC seal is
available for $40ish from several Corvette resto shops, but then age of the MC and booster are unknown and from their appearance, could well be
original. I previously bought a new Wagner MC (Part No. MC79821), but am now thinking, for that level of effort, I should replace the booster as well.
Just not sure what I'm getting into regarding the Booster replacement. It seems straight forward enough, except for the uncertainty with finding the
correct replacement parts. I cannot find a cross for the GM 18001970 or 18002562 booster. No luck at http://gmcmhparts.com. I've read quite a bit
of discussion on the topic of the MC mounting bracket and booster seal, but not so much on replacing this entire assembly. Anyone done this?
--
Wackster - 1976 23' Crestmont
Baltimore, Maryland

 

[jim kanomata1]

Save some time and contact a GMC coach parts supplier for information.

> Seeking part number and source for brake booster and MC assembly, or just
> the correct booster. Background: When pressure bleeding the brakes
> following rear axle caliper replacement, I developed a leak at the back of
> the MC where it meets the booster assembly. I see the booster/MC seal is
> available for $40ish from several Corvette resto shops, but then age of
> the MC and booster are unknown and from their appearance, could well be
> original. I previously bought a new Wagner MC (Part No. MC79821), but am
> now thinking, for that level of effort, I should replace the booster as
> well.
> Just not sure what I'm getting into regarding the Booster replacement.
> It seems straight forward enough, except for the uncertainty with finding
> the
> correct replacement parts. I cannot find a cross for the GM 18001970 or
> 18002562 booster. No luck at http://gmcmhparts.com. I've read quite a
> bit
> of discussion on the topic of the MC mounting bracket and booster seal,
> but not so much on replacing this entire assembly. Anyone done this?
> --
> Wackster - 1976 23' Crestmont
> Baltimore, Maryland
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502

 

[Jim Hupy]

The booster replacement is not the easiest process, but, involves removing
the bezel on the dash, then the air valves in the dash. This will allow
access to the clip that secures the brake pedal linkage pin to the piston
operating rod as well as the 4 nuts that secure the booster to the
bulkhead. Depending upon the year model. There is also a mounting bracket
that is accessed from under the drivers side hatch that braces the
booster/master cylinder assembly. Sometimes, there is a black, nasty,
sealant that has been applied to the bulkhead that makes removing the
assembly difficult as well. Best advice, refer to the shop manual.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> Seeking part number and source for brake booster and MC assembly, or just
> the correct booster. Background: When pressure bleeding the brakes
> following rear axle caliper replacement, I developed a leak at the back of
> the MC where it meets the booster assembly. I see the booster/MC seal is
> available for $40ish from several Corvette resto shops, but then age of
> the MC and booster are unknown and from their appearance, could well be
> original. I previously bought a new Wagner MC (Part No. MC79821), but am
> now thinking, for that level of effort, I should replace the booster as
> well.
> Just not sure what I'm getting into regarding the Booster replacement.
> It seems straight forward enough, except for the uncertainty with finding
> the
> correct replacement parts. I cannot find a cross for the GM 18001970 or
> 18002562 booster. No luck at http://gmcmhparts.com. I've read quite a
> bit
> of discussion on the topic of the MC mounting bracket and booster seal,
> but not so much on replacing this entire assembly. Anyone done this?
> --
> Wackster - 1976 23' Crestmont
> Baltimore, Maryland
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[robert mueller]

James,

The cup seal between the M/C and booster does not seal fluid in the master cylinder, it keeps vacuum in the booster, keeps brake
fluid from the M/C entering the booster and locates the M/C "tail" in the booster.

If you have fluid coming from in between the M/C and booster the rear seal in the M/C is leaking.

Here are two sources for a master cylinder and booster:

Applied GMC:

http://www.appliedgmc.com/index.itml

Dave Lenzi:

http://www.bdub.net/lenzi/index.html

While you're at it I would suggest you ask about / consider a sensitized booster.

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808


-----Original Message-----
From: Gmclist [mailto:gmclist-bounces] On Behalf Of James Wack
Sent: Friday, December 22, 2017 12:29 PM
To: gmclist
Subject: [GMCnet] Replace Master Cylinder or MC plus Booster?

Seeking part number and source for brake booster and MC assembly, or just the correct booster. Background: When pressure bleeding
the brakes following rear axle caliper replacement, I developed a leak at the back of the MC where it meets the booster assembly. I
see the booster/MC seal is available for $40ish from several Corvette resto shops, but then age of the MC and booster are unknown
and from their appearance, could well be original. I previously bought a new Wagner MC (Part No. MC79821), but am now thinking, for
that level of effort, I should replace the booster as well.
Just not sure what I'm getting into regarding the Booster replacement. It seems straight forward enough, except for the uncertainty
with finding the correct replacement parts. I cannot find a cross for the GM 18001970 or 18002562 booster. No luck at
http://gmcmhparts.com. I've read quite a bit of discussion on the topic of the MC mounting bracket and booster seal, but not so
much on replacing this entire assembly. Anyone done this?
--
Wackster - 1976 23' Crestmont
Baltimore, Maryland

 

[aaron bush]

There are potential problems with the new MC's that you buy off the shelf - they simply are not made to the same specs they used to be even though
part numbers may still be the same. I think this is an item that you should buy from one of the two sources in Rob's link Jim K. at Applied or Dave
Lenzi) to avoid complications and possible problems.

Dave and Jim both will also be happy to talk to you about parts and the issues.


--
78 Royale, rear dinette

 

[jerry sitzlar]

Jim Bounds also sells a sensitized booster outright (no trade in required). I just installed one this past summer and it works great on my coach. I
also replaced every component in the brake system except for the original calipers. It took about an hour to replace the booster on my 77 model. It
took longer to figure out how to do it without cutting up the dash. It was pretty tight for a 74 yo geezer.

Jerry
--
Jerry Sitzlar..... 77 Eleganza II, Twin bed, dry bath......
Lenoir City, TN