No brake fluid from new master cylinder (2 Viewers)

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Sep 9, 2018
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78 FJ40 with dual reservoir master cylinder. I replaced the master cylinder with a new Aisin along with all new brake lines in the front. I couldn’t get any brake fluid out of the rear wheels, so I’m about to start taking every brake line connection loose to diagnose the problem. I started at the new master cylinder. I pulled the brake line for the rear brakes off (between the 2 reservoirs), pumped the brakes, and no fluid comes out of the reservoir. Am I missing something or is my new Aisin MC a dude?

I was able to bleed the front brakes and if I loosen the brake line at the MC for the front brakes I do get fluid coming out.
 
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No. I didn’t even know about bench bleeding until researching why my rear wheels wouldn’t bleed. It sounded like it wasn’t necessary, but it would make bleeding the brakes easier.
 
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Bench bleeding can be done with the master installed, usually new master come with some bleed hoses. Make sure the rear wheel cylinders are purged of air (should be a couple of threads on this issue) and make certain the rear shoes are adjusted properly. Mine seemed to work best when they really dragged on the drums.

Each little thing adds up to good brakes. I got mine pretty good, then replaced the booster and that was the icing on the cake.
 
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Sep 9, 2018
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Little Rock, Arkansas
Thanks for help guys and for responding. I just can’t get past something.....shouldn’t I get brake fluid coming out of the master cylinder if I step on the brake pedal? Nothings coming out.
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You need to put a bleeder nipple in the master and run a hose into the resorvoir. Then start pumping it pushes and pulls fluid. When you let go of the pedal like you have it it sucks air back in.
 
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Even in this condition, fluid will come out. When the pedal is relaxed, fluid will fill into the piston column and when depressed, it will have no choice but to come out the hole. If you cannot get fluid out as shown, then fluid is not getting into the piston shaft. Of course I am not seeing everything, but , I am sure you are at the same spot.
 
Joined
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Little Rock, Arkansas
Front is fine. And if I just loosen the front brake line at the MC and push the pedal fluid leaks out. The brake pedal does feel soft, but I can and did bleed the front brakes. I do know I’ll have to redo the front. I started bleeding left rear, and when that didn’t work I moved around trying to figure this out. Even went and bought a vacuum bleeder. I guess I’ll pull the MC off tomorrow and see if the piston is retracting.
 
Joined
Nov 6, 2013
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Try tilting the MC with the front slightly elevated then pump.
Sometimes air can get trapped and cause problems.
 
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Take a look at this, fittings may be different but concept is the same. Ensure at the bench all is well.

 
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Is your pedal moving the piston all the way in and out? do you have free play at the top of the pedal?
 
Joined
Sep 9, 2018
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Little Rock, Arkansas
Well I left it open over night and break fluid did eventually come out of the reservoir. The bad news it dripped over my freshly repainted steering box. If it’s not working this afternoon I’ll pull it off and bench bleed it. Thanks everyone.

Oh and there is just a little bit of free brake pedal before the pistons engage which seems about right.
 
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Just b/c fluid came out doesnt mean all the air is out of the MC. If any air is still in the MC, it will be very hard to get that air all the way to the rear wheel cylinder. Bench bleeding is done for a reason.

You need to bench bleed both front and rear at the same time. So, you need to disconnect the front. I dont think it will work with the front still hooked up because you can get a full stroke of the pedal.
 
Joined
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I pulled it off tonight to bench bleed as everyone suggested. I got it put back on the 40, but I was too hot and sweaty to keep going. What an ordeal. I pulled and reinstalled the entire drivetrain. That was nothing compared to these damn brakes.
 

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