P30 or Stock master brake cylinder

[Bob Dunahugh]

I just installed 80 MM calipers at the front. Have had 74 MM at the middle for 2 years. With stock drums at the rear. Worked well. Now with my change to 80MM at the front. Some say that the stock master cylinder is fine. Others say that the P30 is needed. I still have the P30, and bracket from the burned 78 Royale. Bob Dunahugh 78 Royale

 

[powwerjon]

Bob,
I run the 80MM on the front and on the middle bogey and a very small slave cylinder on the rear drum. I should qualify my middle bogey setup as it is a Leigh Harrison 12 1/2” ford rotor. I have run the Cad disk on both the middle and rear and found the Harrison setup works well for me and our coach is a little more heavy that the 26’. v

I use the 7/8” bore slave that you can get from Autozone and it is Part@ 33769 on the rear drum. Some have not run any brake on the rear and left the drum on for the emergency brake function.

I use the Raybestos part# MC39075 that I get from Dave Lenzi which he modifies and also supplies the correct length intermediate pushrod. Not that expensive at all. It is a 1 1/4” bore unit and Bob stone has researched a 1 1/8” bore, AZ #NM11749

JR Wright
Michigan

>
> I just installed 80 MM calipers at the front. Have had 74 MM at the middle for 2 years. With stock drums at the rear. Worked well. Now with my change to 80MM at the front. Some say that the stock master cylinder is fine. Others say that the P30 is needed. I still have the P30, and bracket from the burned 78 Royale. Bob Dunahugh 78 Royale
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

 

[chris tyler]

What is the function of the rear slave? To assist the rear drums?
Are there pics of the setup?

I have stock [AFAIK] fromt disc and leading discs at the rear with a P30 MC that seems to be bypassing. I would prefer to have a stock type MC for
access reasons, but was tod the p30 was needed
So I have pretty much the same question.If there is a stck type master that will work adaqutly Id prefer to go with that

--
76 Glenbrook

 

[jim kanomata1]

When one has 6 tires on the ground, using only 4 for braking is very
questionable from our discussions with some people.
I have requested some test to see what happens on panic test.

On Thu, Oct 18, 2018 at 8:05 AM Chris Tyler
wrote:

> What is the function of the rear slave? To assist the rear drums?
> Are there pics of the setup?
>
> I have stock [AFAIK] fromt disc and leading discs at the rear with a P30
> MC that seems to be bypassing. I would prefer to have a stock type MC for
> access reasons, but was tod the p30 was needed
> So I have pretty much the same question.If there is a stck type master
> that will work adaqutly Id prefer to go with that
>
> --
> 76 Glenbrook
>
> _______________________________________________
> 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