Master Brake Cylinder Bad?

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pontiacgp

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Mar 31, 2006
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I converted to manual brakes using a Chrysler manual master. I had the master stored in my house for a few years and finally got around to the conversion this year. The brakes don't feel right and I had a hard time bleeding the rears. I removed the brake lines to the master and the port to the front brakes had brake fluid dripping out but the back brakes had no fluid coming from the port. I decided to bench bleed the master again so I lifted the back of the car and made sure the master was sitting flat. I bench bled the brakes using clear lines and made sure that there was no air in the master. I removed the bleeders from the master and there was fluid to the front brakes coming from the port but the port for the back brakes had no fluid flowing at all. I installed the lines in the master and opened the rear bleeder. I gravity bled both sides of the rear and the brake fluid was flowing great which surprised me since the fluid from the port in the master wasn't flowing. I let both sides bleed a long time, closed the bleeders and checked the feel of the brake pedal. I pumped the pedal a few times but it did not feel right. I opened the bleeders for the back brakes, one at a time, and neither side would bench bleed. I'm thinking the master is bad but I'm wondering what you guys think........
:popcorn:
 

pontiacgp

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Mar 31, 2006
29,270
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Kitchener, Ontario
The push rod has a little slack so it's not putting any pressure on the piston if that is what you mean.
 

pontiacgp

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Mar 31, 2006
29,270
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Kitchener, Ontario
I still have drums in the rear. When bench bleeding the rear bleeds and with a helper pumping the pedal I can bleed the rear cylinders. There should be flow at the port on the master for the rear brakes with the brake line off but I can leave that port open with the reservoir full and the cap off for as long as it takes to drink a beer and not a drop of brake fluid. The port for the front brakes flows freely with the brake line removed. Test driving the rear drums heat up so I know the rear brakes are working but the pedal is hard and there is very little modulation.
 
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pontiacgp

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Mar 31, 2006
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Kitchener, Ontario
I picked up another master from Napa and there is a difference with the one on my GP. When you remove the filler cap on the one on my GP there is what looks like a brass filter in the resevoir where the fluid would go to the master. With the one from Napa there is no valve and the holes in the master are visible. .....:unsure:

Before I remove the master in the GP i'll remove the reservoir to see what those brass inserts are. I didn't test the pressure when I bench bled it and maybe the "filter" is blocking the flow.
 
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fleming442

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Dec 26, 2013
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I had a similar problem with my car- it would lock the right rear occasionally and the pedal would get hard. The m/c had a snap ring out of place under the reservoir; it's been fine since. Maybe yours will straighten up with the new one.
 
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pontiacgp

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Mar 31, 2006
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Kitchener, Ontario
I'll see if that filter is blocked and see if I can clean it if it is. The new master has some fluid in it, I guess to protect it and I'm wondering if leaving the master sitting around for 3 or 4 years caused the fluid to dry up and clog the filter. I sent an email to Sherlock Holmes to see if he can help solve the mystery...
 
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