| p30 master cylinder [message #371506] |
Sun, 05 November 2023 12:11  |
skip2
Messages: 544
Registered: September 2011
Location: Winter Haven,FL (center o...
Karma: 3
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Hello to all watching,
I need to replace my P30 master cylinder it is leaking fluid out the back. I'd rebuild if I thought there was any decent rebuild kits. I look up P30 and I get all kinds of cylinders, some with viewable reservoir, some with 2 cap retainers, some with one. some with the plastic caps with the see through reservoir. I like the ideal of seeing the fluid level without taking the top off. Whats the latest greatest for replacement, anyone with one knows its a pain to pull the cap off and check. I certainly don't want to loose any stopping power though.
Skip Hartline
74 Canyon Lands, FiTech,
3.7 FD LSD, Manny Tranny,
Springfield Distributor,
2001 Chevy Tracker Ragtop Towd
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| Re: p30 master cylinder [message #371508 is a reply to message #371507] |
Mon, 06 November 2023 13:18  |
skip2
Messages: 544
Registered: September 2011
Location: Winter Haven,FL (center o...
Karma: 3
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Senior Member |
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Fronts are 80mm calipers, center is rear caddy disc with e brakes, rears are stock shoes
74 Canyon Lands, FiTech,
3.7 FD LSD, Manny Tranny,
Springfield Distributor,
2001 Chevy Tracker Ragtop Towd
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| Re: p30 master cylinder [message #371509 is a reply to message #371506] |
Mon, 06 November 2023 16:10 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Bob Stone did some volume testing and found the P30 is not a great choice for those with 80s front / Caddy stuff in rear . I would contact him before choosing a new MC as there may be better options now
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: p30 master cylinder [message #371510 is a reply to message #371509] |
Mon, 06 November 2023 19:05 |
skip2
Messages: 544
Registered: September 2011
Location: Winter Haven,FL (center o...
Karma: 3
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Is he on the blacklist
74 Canyon Lands, FiTech,
3.7 FD LSD, Manny Tranny,
Springfield Distributor,
2001 Chevy Tracker Ragtop Towd
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| Re: p30 master cylinder [message #371512 is a reply to message #371511] |
Tue, 07 November 2023 19:03 |
skip2
Messages: 544
Registered: September 2011
Location: Winter Haven,FL (center o...
Karma: 3
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I tried to PM guess it didn't work.
Been looking at a lot of Bob Stone's Posts and it seems there is a Napa M2580 MC that has good numbers but I can't really tell if the booster has to be updated I have changed my booster when I first got it 12 years ago. The PO had it in a box never installed. Is there a way to identify what booster I might have. Definitely want to fix it one last time the best possible way.
Skip Hartline
74 Canyon Lands, FiTech,
3.7 FD LSD, Manny Tranny,
Springfield Distributor,
2001 Chevy Tracker Ragtop Towd
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| Re: p30 master cylinder [message #371515 is a reply to message #371506] |
Wed, 08 November 2023 13:55 |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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Wally and others are correct that the M2580 will not work with a stock booster or the stock sensitized booster. It will work with the Metric sensitized booster.
Here is a picture of the quick take-up MC that I used and suggested by Walt Halley. NAPA # is M2580
http://www.gmcmhphotos.com/photos/new-style-master-cylinder/p68374-mc-from-late-model-gm-trucks.html
NAPA#
https://www.napaonline.com/en/p/NMCM2580
and Rock Auto has them for $107 Interesting a couple of months ago, Rock Auto had them on Closeout at under $30. I wonder what happened there.....
https://www.rockauto.com/en/moreinfo.php?pk=309794&jsn=266
There is however another MC out there with the same 40mm step bore, and a 1 1/8" primary bore. It is NAPA part #M2609. (https://www.napaonline.com/en/p/NMCM2609) Don't know how it would preform in our situation as it looks like it was intended for lighter duty vehicles. Might work with a stock GMCMH braking system putting more pressure into the system. I don't think it would be advisable to use with bigger brake systems as volume might not be there.
Other #’s for the 1 1/4” step bore are
RAYBESTOS MC39630
Cardone # for the 1 1/4" is 102029
Other #s for the 1 1/4 are Dynamic Friction #35547146, and Wagner # 110888
No need to change or modify the reservoirs. But because the reservoirs are smaller than stock, the step bore fits easily under the hood. Will need to pay attention to fluid level. Easy, they are translucent plastic.
Also, the reinforcement bracket will have to be modified. Simple, put it in a vice and bend it in a couple of spots to clear the upper reservoir and elongate the upper mount holes. Also may need a adjustable pushrod and a method of measuring the needed length of that pushrod. I used bluing ink on the rod end. Kept lengthening it until the bluing ink rubbed off. Backed off .010 a couple of times until ink remained intact. Tightened little at a time until it rubbed off and shortened it another .015. I think Walt used the stock pushrod….not sure of that.
The step bore MC works kinda like a quick lift floor jack. The 40mm with it's better volume brings the shoes/brake pads out to contact quick and then reverts to the 1 1/4" (31.7mm) bore for better pressure. That 1 1/4" bore is the same bore as the GMC original MC.
The P30 that you have been using has a 34mm bore, larger bore than the original so correspondingly lower pressure on full panic stop than the original 1 1/4" (31.7MM)stock GMC MC and with the shorter stroke and larger calipers, one could run out of volume. In addition, the P30 MC has a small flapper valve in it for return of fluid to the reservoir. That little valve has been known to have a piece of rust get caught in it and not closing up as I should resulting in NO Brakes. Many who had the P30 have converted back to the stock GMC MC. There are other brake options out there. Do your research and choose wisely.
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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| Re: p30 master cylinder [message #371517 is a reply to message #371513] |
Wed, 08 November 2023 17:56 |
skip2
Messages: 544
Registered: September 2011
Location: Winter Haven,FL (center o...
Karma: 3
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Senior Member |
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I found out that 3/8 16 and 10X1.5 are about identical threads and the nut is either 17mm or 11/16 diameter. still not sure other than the metric tap seems a smoother fit, any other ideals other than taking off the master cylinder. Where can adjustable push rods be obtained anyone know?
Skip Hartline
74 Canyon Lands, FiTech,
3.7 FD LSD, Manny Tranny,
Springfield Distributor,
2001 Chevy Tracker Ragtop Towd
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| Re: p30 master cylinder [message #371518 is a reply to message #371506] |
Wed, 08 November 2023 18:30 |
skip2
Messages: 544
Registered: September 2011
Location: Winter Haven,FL (center o...
Karma: 3
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Senior Member |
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Thank you all for all the info given to me.
Since I currently have a P30 Cylinder, which booster was it compatible with?
Skip Hartline
74 Canyon Lands, FiTech,
3.7 FD LSD, Manny Tranny,
Springfield Distributor,
2001 Chevy Tracker Ragtop Towd
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| Re: p30 master cylinder [message #371535 is a reply to message #371506] |
Tue, 21 November 2023 09:44 |
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SeanKidd
Messages: 747
Registered: June 2012
Location: Northern Neck Virginia
Karma: 4
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Is there a source/part number for the metric sensitized booster?
Sean and Stephanie
73 Ex-CanyonLands 26' #317 "Oliver"
Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1 LSD Honda 6500 inverter gen.
Colonial Travelers
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