Problem With Brakes After Converting To Dual Ms On 66

[slymongoose]

i converted my 66 mustang (6-cylinder) over to the dual master cylinder, but now the brakes are not functioning nearly as well as they did before.
at first they 'worked' if i pumped the pedal enough; but when i was sitting in my driveway, pumping it up the other day, the brake cylinder on the drivers' side busted off. i ordered a new brake cylinder, installed it, pumped the brakes, and again the master cylinder blew.
i appear to have the correct master cylinder, in that the bowls are the same size and i have drum brakes all around.
has anyone experienced a problem like this? do i just have a bad new master cylinder?

 

[horse sence]

You have any pics of this ? It sounds like you have a lot of air in the lines . Are you talking about the master cylinder or a wheel cylinder . Either way i have never seen this happen .Is it aluminum?

 

[tos]

What do you mean when you say the master cyl blew? Did you install a new master cyl or used ? Is it period correct ?

 

[slymongoose]

it's a new master cylinder, i THOUGHT it was the right one for the job. after i thought about it, i figured i had installed one with the different sized bowls (for disk front brakes) but that's not the case. both bowls look equal size to me.
the master cylinder didn't blow. the wheel cylinder on the front drivers side (behind the tire) blew off because it was under too much pressure.
i'm not sure what else to try other than ordering a new master cylinder ....

 

[horse sence]

For a wheel cylinder to blow out you must have the brake shoes adjusted way to loose . They should just allow the drums to slide on and spin with slight drag but not a lot.If the shoes are to loose the puck inside the cylinder will move to far and blow out or leak. If it didn't tear the cups you can put it back together .

 

[slymongoose]

the first time i happened, i just assumed the wheel cylinder was bad, so i ordered a new one. but since the same thing happened almost immediately with the new one, i am pretty sure i can re-use it.

i'll try to make sure i have the shoes lined up and on right. i've done it so many times before, i figured it was all okay.
may be worth mentioning that, before i installed the new brake system, i switched over to a 5-lug bolt on the front and back wheels using parts from a 67.

if i were to just try a new master cylinder, would this one from rockauto ($38)
http://www.rockauto.com/catalog/moreinfo.php?pk=1628072&cc=1332313
work as well as this one from cj ($68)
http://www.cjponyparts.com/dual-bow...er-drum-brakes-oe-steel-kit-1965-1966/p/DBC1/

 

[slymongoose]

when searching through all the mustang forums, this was the closest thing i could find ... and in the end, this guy just ended up replacing the master cylinder and it fixed his problem

so i figured maybe that's where i start

 

[slymongoose]

allfordmustangs.com/forums/classic-tech/339729-66-6cyl-drum-brake-problem.html

 

[horse sence]

I don't know if the fittings will be the same .
Your master cylinder is probably good .I think the problem is the shoe adjustment ,if the shoes are to loose when you release the pedal they close up to far requiring you to pump the brakes just to expand them again .Adjust them first and i think you will fix all.

 

[slymongoose]

here's what happens when i push the brakes. here i push the brake 3 times, goes all the way to the floor each time. no resistance whatsoever the first time, a little bit the second and third time....but if i pump it any more, one of the sides of the wheel cylinder will eventually blow off, bending the pins that hold the shoes in place because it forces them out of the way

 

[tos]

First off you shouldn't be pumping them without the drum on there. the brake shoes only move a slight amount. adjust your star adjuster at the bottom there until your drum will have just a slight amount of resistance when you install it then rotate your drum to check again that you have a slight amount of resistance. this should be the way all your drums should feel. that's when you want to bleed your brakes. What your doing allows the pistons (there are two in each wheel cyl) to extend too far. They are not really blowing out, they are doing what they are supposed to do but you are exceeding there intended travel and that's why you are bending pins.

 

[horse sence]

Didn't know you do not have the brake drums on .They have to be on to bleed the lines or the pistons will push out every time you try to pump them up.

 

[slymongoose]

i did have the wheel and drum on before. all the times before. i just took it off this time so i could get a picture/video of it. it did the exact same thing with the wheel and hub on. it over expands the same way, and the pins were bent with the wheel on

 

[tos]

The only way it could expand that far is if your adjustment is way off or it has the wrong drum on there (too big). I can see by your video that it looks like the shoes are right and have plenty of meat on them so I would start by following my earlier post on adjustment but I would first take a quick measurement of the ID of the drum. I used to work for Midas as a young lad and did literally hundreds of brake jobs then 20 years in the Air Force as a jet engine mechanic also working on support equipment. Never saw this happen before though. Check the drum id then adjust with the star adjuster and see what you get. That shoe should only move a fraction to do its job.

 

[slymongoose]

i just noticed that my self-adjuster at the bottom says R instead of L (because i am on the drivers side).
i must have somehow mixed them up.
could that be causing the problem? everything else looks right...

 

[tos]

After looking at your video again before you push the brakes I can see that your adjustment is off somewhat. If you compare the distance of your shoes to the outer area of the backing plate then you will see they are inward at the bottom so you will at least need to adjust your star adjusters out some.

 

[tos]

That R means its a right hand thread not necessarily which side it goes on.

 

[tos]

If that one is the drivers side which it looks like it is then it should have a right hand thread so I think you have it on the correct side but just make sure it is right hand thread

 

[slymongoose]

ok, cool. i had never even looked at the adjuster that close, but i was cleaning everything off and noticed the R, and then i saw the L on my adjusting lever and so i was just unsure. (and you are correct, this is the driver's side)
i'll tinker with it some more later today and see if i can get anywhere. thank you so much for your replies

 

[tos]

So just to understand how the adjuster works, if you watch your video you will see the adjustment arm lift up when you hit the brakes, then when you take your foot off the brakes is when it does its adjustment. As the arm comes back down into position it catches the teeth on the star and turns it which lengthens the adjuster assembly taking up the slack between the shoes and drum. Understanding that should help you check that you have the correct adjuster on the proper side.