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franklin28

Air in brake lines

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After installing the dual master cylinder I find I must still have air in the system as I have a low pedal and can raise its by pumping the brake pedal.

I bench bled the master cylinder before installing it. I then used a vaccum pump to pull the brake fluid through the system. Next I bled each wheel cylinder until I got only brake fluid in the bled hose dumping into a bottle ful of brake fluid. I Constantly kept an eye on the master cylinder to make sure it always had at least 1/4 full of fluid then I would fill it up again. I have bled the wheel cylinders about 10 times and gone through 2 quarts of brake fluid bleding the brakes. To eliminate the question of brake shoe to drum clearances I have the shoes set hard against the drums.

The system has a proportioning valve and 10# regulator valves in each line as reccomended for drum brakes.

I can still raise the pedal by pumping the brake pedal and am at a loss on how to get rid of the traped air ( assuming that is what is causing my problem). I noticed that there are several places in the system where the brake lines are at least 6: above the wheel cylinders and the master cylinder is under the floor which is also below the wheel cylinders.

The original master cylinder had its resivoir mounted on the firewall well above all wheel cylinders and all brake lines and hoses. I thaught that was for convience having a remote resivoir. I am now wondering if it is important to have the resivoir high like this.

Does anyone have any suggestions for me to get all the air out of the system?

Thanks, Bob

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Just remove the floorboards and get a set of moto-cross boots. It worked for Fred Flintstone!

Next time you are up in Vacation land I will loan you my aircraft bleeder. It pushes the fluid from the wheels back to the master. I have had great luck with it.

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It sounds like you are sucking air someplace where you dont have a tight seal..

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Is your pedal spongy? If not, the problem may have more to do with the fact that you replaced a 1 1/4" Franklin master cylinder with a 1 1/8 master cylinder.

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Bob , Are you sure the brake shoes are in full and correct adjustment? My dad had the same problem.He had brakes on the 32 pickup but low pedal.... He bled and bled them. The pedal was hard the first time down but low. I put the truck on the lift and spent about 6 hours centering and adjustinging the shoes per the owners manual and PRESTO!They were fixed. He was being fooled that there was air because low pedal ,but in fact the shoes needed to get closer to the drums. Just a though...also if working alone you can fill the master cyl ,crack the bleeders and it will self bleed as long as your new master cyl is higher that everything else. Mike PS As long as were on brakes ,the last set of shoes I had relined I set to FT WAYNE IND and had woven linings installed with brass thread. They are a wonderull improvement to to the hard linings . FYI....

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Bob , Are you sure the brake shoes are in full and correct adjustment? My dad had the same problem.He had brakes on the 32 pickup but low pedal.... He bled and bled them. The pedal was hard the first time down but low. I put the truck on the lift and spent about 6 hours centering and adjustinging the shoes per the owners manual and PRESTO!They were fixed. He was being fooled that there was air because low pedal ,but in fact the shoes needed to get closer to the drums. Just a though...also if working alone you can fill the master cyl ,crack the bleeders and it will self bleed as long as your new master cyl is higher that everything else. Mike PS As long as were on brakes ,the last set of shoes I had relined I set to FT WAYNE IND and had woven linings installed with brass thread. They are a wonderull improvement to to the hard linings . FYI....

Thanks for feedback Mike.

Yes, the brakes were adjusted properly. To eliminate that concern I actually adjusted all shoes out fully so that they are in firm contact with the drums.

I thought that would eliminate the stroke of the wheel cylinders while I tried to rid the system of air. I had help while bleeding the brakes at one point so that I would not re introduce air. Someone suggested that with the simple Franklin system I actually don't need a proportioning valve or pressure controls. That person thought I had introduced un necessary components and many plaves for air to become traped. I will try eliminating everything and go back to a simple set up still with the dual cylinder.

Bob

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Not to insult by any means, but did you bleed the wheel cylinders starting with the farthest wheel cylinder from the master cylinder and gradually moving closer to the closest wheel cylinder to the master cylinder?

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Not to insult by any means, but did you bleed the wheel cylinders starting with the farthest wheel cylinder from the master cylinder and gradually moving closer to the closest wheel cylinder to the master cylinder?

Yes I did.Bench blead Master then started with wheel cylinder furthest from master cylinder.

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When we installed a dual master on a Series 16, we found we had to install the check valves or the brake fluid would run back to the master. I don't know if they were #10's or not, but you must have them. If they are installed backward, the brakes will work, but will still bleed back, causing the need to pump up the pedal. We did not install a proportioning valve with the master we used.

Something is surely odd...can the valves possibly be in backwards?

Tom

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I think I have them in correctly but will check again.

Can't work on car until next week. Other projects, like grand children, will be taking priority

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I finally got back to the brake job and discovered that one of the 10 #regulator / check valves was defective as it would not stop flow in either direction.

I installed a new 10# / regulator check valve and now the pedal seems to be correct . For the record I also installed a remote resevoir prior to changing check valve without any effect. I had also reversed flushed the system without any sucess so it apears that the 10# regulattor / check valve was the problem.

Bob

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