Brake Hydraulic Issue - The 1947 - Present Chevrolet & GMC Truck Message Board Network

SCOTI · 12-09-2014, 12:51 PM

So..... last night I'm looking at/comparing the driver side upper arms (my modified OE unit, PB's, & the flat plate/ MMW ones) when I noticed something under the hood of my 89 CC dually.

The newest/latest master cylinder that I've installed is leaking in the same spot as the previous units. Brake fluid has f'd the paint on the booster yet again & you can see where its dripped down below. The leaks are coming from where the 'pin' pushes the plunger into the MC.

This is the 3rd time for this so something isn't right. I changed over from a Hydra-boost set-up to vacuum assist. I sourced parts based off a 3/4 ton suburban vac assist set-up.

The master cylinders were 2 different oreillys units: 1 reman & the other was a 'new' Brakebest/house brand. The current unit is a new Wagner model. They're not leaking from the lines. Anyone else had failures internally that seeped out where the piston/plunger enter the MC??

**nlped** · 12-09-2014, 01:08 PM

I haven't had it happen personally, but I've heard of it. I remember overhearing that the plunger was actuating to far, and causing it to leak past the internal seal in the "push rod hole". Not sure this would be your problem, but just my .02

SCOTI · 12-09-2014, 01:32 PM

Quote:

Originally Posted by nlped

I haven't had it happen personally, but I've heard of it. I remember overhearing that the plunger was actuating to far, and causing it to leak past the internal seal in the "push rod hole". Not sure this would be your problem, but just my .02

Hhmm..... definitely possible. I did have to make a new plunger as the vac set-up I started w/didn't have one & there was a difference in the depth of the HB unit vs the vac assist one. I made up the difference of lengths based on caliper measurements from the two units.

Unfortunately..... I recently cleaned house & tossed all the HB stuff which will make finding my answer that much harder. At least I kept the original HB push-rod.

Andy4639 · 12-09-2014, 09:21 PM

Have you made sure the foot pedal is always coming back to full rest and the rod from the brake pedal isn't keeping pressure on the unit?

SCOTI · 12-10-2014, 01:43 AM

Quote:

Originally Posted by Andy4639

Have you made sure the foot pedal is always coming back to full rest and the rod from the brake pedal isn't keeping pressure on the unit?

Yes. No residual pedal pressure. I'm going to start the hunt for a 3/4 ton vac assist set-up to get that pin.

Andy4639 · 12-10-2014, 02:13 AM

Can you not just cut yours down?

SCOTI · 12-10-2014, 02:29 AM

Quote:

Originally Posted by Andy4639

Can you not just cut yours down?

Well, I measured w/calipers for this round so it's hard to quantify how much needs to be cut off.

Andy4639 · 12-10-2014, 05:39 AM

Quote:

Originally Posted by SCOTI

Well, I measured w/calipers for this round so it's hard to quantify how much needs to be cut off.

Understand!

bent wrench · 12-15-2014, 08:04 PM

Loosen master cyl nuts and feel where plunger rod hits MC piston.
or
Add washers til pedal play is felt and that is how much clearance you need.

Many boosters will have an adjustable pushrod tip.

Painter D · 12-16-2014, 12:41 AM

Had this happen to me once, bought a Wilwood MC and that cured it. FYI

12-09-2014, 12:51 PM	#1
SCOTI Registered User Join Date: Apr 2001 Location: DALLAS,TX Posts: 22,064	Brake Hydraulic Issue So..... last night I'm looking at/comparing the driver side upper arms (my modified OE unit, PB's, & the flat plate/ MMW ones) when I noticed something under the hood of my 89 CC dually. The newest/latest master cylinder that I've installed is leaking in the same spot as the previous units. Brake fluid has f'd the paint on the booster yet again & you can see where its dripped down below. The leaks are coming from where the 'pin' pushes the plunger into the MC. This is the 3rd time for this so something isn't right. I changed over from a Hydra-boost set-up to vacuum assist. I sourced parts based off a 3/4 ton suburban vac assist set-up. The master cylinders were 2 different oreillys units: 1 reman & the other was a 'new' Brakebest/house brand. The current unit is a new Wagner model. They're not leaking from the lines. Anyone else had failures internally that seeped out where the piston/plunger enter the MC?? __________________ 67SWB-B.B.RetroRod 64SWB-Recycle 89CCDually-Driver/Tow Truck 99CCSWB Driver All Fleetsides @rattlecankustoms in IG Building a small, high rpm engine with the perfect bore, stroke and rod ratio is very impressive. It's like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar..... *Cubic inches is like Indiana Jones with a cheap pistol.*

12-09-2014, 01:08 PM	#2
nlped Senior Member Join Date: Jul 2009 Location: Hayden, Al. Posts: 4,148	Re: Brake Hydraulic Issue I haven't had it happen personally, but I've heard of it. I remember overhearing that the plunger was actuating to far, and causing it to leak past the internal seal in the "push rod hole". Not sure this would be your problem, but just my .02 __________________ Carter 1968 Chevy SWB Fleet... Walt 1963-1/2 Ford Falcon Futura...Martha

12-09-2014, 09:21 PM	#4
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,945	Re: Brake Hydraulic Issue Have you made sure the foot pedal is always coming back to full rest and the rod from the brake pedal isn't keeping pressure on the unit? __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

12-10-2014, 02:13 AM	#6
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,945	Re: Brake Hydraulic Issue Can you not just cut yours down? __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

12-15-2014, 08:04 PM	#9
bent wrench Registered User Join Date: Dec 2014 Location: Cornelius OR Posts: 2	Re: Brake Hydraulic Issue Loosen master cyl nuts and feel where plunger rod hits MC piston. or Add washers til pedal play is felt and that is how much clearance you need. Many boosters will have an adjustable pushrod tip. __________________ This is my brain on C-10

12-16-2014, 12:41 AM	#10
Painter D Registered User Join Date: Jun 2007 Location: DFW (Forney) Posts: 1,529	Re: Brake Hydraulic Issue Had this happen to me once, bought a Wilwood MC and that cured it. FYI __________________ '58 SWB Fleetside...Front & Rear Porterbuilt Dropmember, 6.0 LS /4L60E. Accuair E-level, 20 Billet Specialties (Vintecs) '63 Buick Riviera ... AccuAir E-level, 20" Billet Specialties (Vintecs) http://67-72chevytrucks.com/vboard/s...=528853&page=5

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