Brake Master Cylinder question

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Brake Master Cylinder question

Postby dpuckett » Sun Nov 01, 2015 8:16 am

When I first bought my pickup in 2008 with a measly 275k mi, it had a soft pedal. Flushed the old fluid out. No improvement. Did all the other usual checks, bypassed the ABS, and decided to put a new master cylinder on it. Got a NEW Bendix from Rock Auto. Got it to bench bleed with both methods, put it on. Braking was improved, but not stellar. I just chalked it up to being a (then) 15- year old truck.

Fast forward 7 years and 185k (for a total of 460k) to now. Sheared 4 teeth off the original pinion, and installed a Dana 71, rather than put gears in my 3.54 D70. New brakes nd wheel cylinders. Got it bled, adjusted the rears, and pedal was still low.
Then I had a brainstorm (brain fart?). Unhooked the brake lines, hooked up the clear vinyl lines you use to bench bleed.

I kept an eye on the bubble in the lines. The line from the rear-feeding reservoir moved the bubble immediately, telling me the rears start to engage immediately. The line from the front-feeding reservoir didnt move til the pedal was almost halfway to the floor. Took it off, and put it in a vise. Had to push the cylinder ablut 5/16" before the fluid started moving from the big section of the MC.

My question is, shouldnt the fluid start flowing to the front and rear brakes t the same time? As it is, it appears my fronts arent getting any pressure build up until it has moved significantly. I have NEVER locked my brakes in this truck, despite bypassing the Govt-mandated "safety features".

It wold explain my lackluster braking, but I'm no brake expert, lol.
His- 93 W250 club cab LE, auto to Getrag conversion, piston lift pump, 3.54 LSD. 400k+
Hers- 04 QC 4x4. Built auto, Triple Dog, Air Dog. Funny Round truck that aint so quiet.
dpuckett
14mm rotor
 
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Location: Perryville MO

Re: Brake Master Cylinder question

Postby coodah » Tue Nov 03, 2015 7:28 pm

I had the opposite issue with my 90 cab chassis truck. It seamed as if I was always replacing front brakes and the back never saw any wear. I also had a problem with brake fluid blowing out under the reservoir lid. I had to constantly top off the front reservoir. This happened on two master cylinder/booster units I got from O'Reilly's. I finally got fed up with it on the last set of front pads I replaced. I went ahead and switched out the master cylinder/booster the same time, since it was lifetime warranty. My problem then went away. I think some of the rebuilt stuff is junk. Prior to this I checked the proportioning valve on the frame and also bi-passed the valve over the rear axle that meters brake fluid pressure depending on load level. I also disconnected the ABS.
To answer your original question I would think flow level should be equal coming out of the front and back reservoir as the pedal is depressed. Just my two cents.
Good Luck,
Curt
90 W350 Cab-Chassis Truck, 5 spd, 93 W250 CC 5spd
coodah
fuel screw!!!!
 
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Re: Brake Master Cylinder question

Postby dpuckett » Wed Nov 04, 2015 7:30 pm

Got a new one coming into NAPA in the morning.
His- 93 W250 club cab LE, auto to Getrag conversion, piston lift pump, 3.54 LSD. 400k+
Hers- 04 QC 4x4. Built auto, Triple Dog, Air Dog. Funny Round truck that aint so quiet.
dpuckett
14mm rotor
 
Posts: 2196
Joined: Wed Jan 03, 2007 4:33 pm
Location: Perryville MO
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Re: Brake Master Cylinder question

Postby cougar » Sat Nov 07, 2015 12:02 pm

Hope it is a new one and not a "re manufactured" one. After the 3rd in a row from Napa failed I bought a brand new Bendix.
RIP 91.5 W250 5 speed. The great experiment.
92 W250 HD 47RH with Compushift. Upgraded H1C to 62/60/16, Scheid Lightning VE, 60# valve springs, DAP 7X.010 injectors, 4" DE exhaust, home made cooler tubes.
01 2500 "the work truck".
cougar
14mm rotor
 
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