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 Post subject: Master Cylinder Help
PostPosted: June 15, 2017, 11:47 am 
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Location: Round Rock, TX
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Admittedly, I am no mechanic, but I replaced the Master Cylinder myself and then paid a shop to replace everything else related to the brake system. Shop cannot get full pressure in system and think that the problem is the master.

The master install was self explanatory, except for a little rubber disc. I placed it into the hole where the pedal shaft contacts the piston. Was that correct? The master was bench bled before mounting and bled after mounting several times as well.

Please help... this is about the only thing between getting the truck roadworthy. Thanks in advance.

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 Post subject: Re: Master Cylinder Help
PostPosted: June 15, 2017, 2:16 pm 
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I've never heard of placing anything between the pushrod and piston, so that rubber disk is probably not right. Bench bleeding was good. It is possible that the master cylinder is bad out of the box. Incorrect adjustment of drum brakes can make it seem as though the system is not working properly. If they are a rather typical modern shop, I suppose it is possible they don't know how to do that, though many newer vehicles do still have drums on the rear.

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 Post subject: Re: Master Cylinder Help
PostPosted: June 15, 2017, 2:52 pm 
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Just picked it up and there is no pressure at all. Pedal goes to the floor. it seems like there is a lot of movement before the rod even engages the piston. Are there different length rods for these trucks that maybe got switched out when someone replaced the master before?

I bought a new master and will post a pic of the piston hole and disc. It looks different than pics on Autozone's website. I bought both of mine at O'Reilly.

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 Post subject: Re: Master Cylinder Help
PostPosted: June 15, 2017, 3:24 pm 
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The pushrod is not typically replaced with the master cylinder. Did it work with the previous master cylinder?

There are different length pushrods that will fit and perhaps it was shortened at one time. After 50 or 60 years, it's hard to know what has been done in the past.

The pushrod is also adjustable. It is mounted using an eccentric bolt. If that is adjusted incorrectly, it can require quite a bit of pedal travel before the master cylinder is engaged.

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318 Y-block (292 +.070 bore, +.170 stroke), FMS T5-Z w/Mustang 10.5" diaphragm clutch.


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 Post subject: Re: Master Cylinder Help
PostPosted: June 15, 2017, 4:16 pm 
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Wasn't working before. I am going to play with adjusting the rod before removing the master. Thanks.

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 Post subject: Re: Master Cylinder Help
PostPosted: June 15, 2017, 5:17 pm 
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Is there a vacuum booster involved with this MC??

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 Post subject: Re: Master Cylinder Help
PostPosted: June 15, 2017, 6:36 pm 
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No. Single res manual.

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 Post subject: Re: Master Cylinder Help
PostPosted: June 15, 2017, 6:43 pm 
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shoe adjustment is important however not many of the single res mc are sold these days and it is possible its bad out of the box.
i would remove the brake line and have someone step on the brake pedal to see if fluid comes out, hold something in front of the hole to catch the fluid, then if it comes out put the line back in before letting up to keep from getting air in it.

also when bleeding the lines the mc must be kept full of fluid as it does not hold enough to do all the bleeding before running out of fluid.

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 Post subject: Re: Master Cylinder Help
PostPosted: June 17, 2017, 10:06 pm 
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Rod was non-adjustable and too short. Made a spacer and brakes work. Ordered an adjustable rod. Thanks everyone for your help.

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 Post subject: Re: Master Cylinder Help
PostPosted: June 18, 2017, 4:07 pm 
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That is correct, the rod itself is not adjustable. However, it is mounted to the pedal with an eccentric bolt which provides the adjustment. Do you have the eccentric bolt?

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 Post subject: Re: Master Cylinder Help
PostPosted: June 18, 2017, 9:56 pm 
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I don't think so. I took the bolt out several times and did not notice that it was an eccentric bolt. I think I would have noticed, but I will have to check that. Thanks.

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 Post subject: Re: Master Cylinder Help
PostPosted: June 18, 2017, 11:43 pm 
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If the brakes are fully bled:

Check to make sure the wheels are slightly dragging on the brake drums. If not adjust star adjuster so that when the wheel turns, there is a slight drag heard. Jack up a wheel, spin it and listen for a slight drag. With new shoes, they'll probably need to be a bit tighter than broken in shoes.

There should be an eccentric that allows adjustment for the M/C pushrod at the brake pedal. That would allow additional adjustment and if adjusted forward, ought to take up any remaining slack.

One additional thing to double check, are the shoes installed correctly? I always have to look, but IIRC - shoes with shorter liners to front, shoes with thicker liner to rear.

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