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Discussion Starter #1
got my vacuum up to about 19 at idle after the valve job, so decent vacuum for the power assist discs up front, drums in the rear. stock was four drums, so the disc setup is all after market.

so the brakes are better, but very "grabby" at slow speeds. first time i drove it i locked up the rears by accident just coming to a normal stop at only two or three miles per hour.

does this sound like a proportioning valve issue? thanks-

billy
 

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Yes, is the valve adjustable? If it is, you need more front bias, if is not, then it needs a rebuild.
 

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Discussion Starter #3
Yes, is the valve adjustable? If it is, you need more front bias, if is not, then it needs a rebuild.
there is no adjustment for this old valve. Don has a part on his website that is a combination distribution block and proportioning valve. i'm not sure my valve can be rebuilt?
 

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if you read the ford specs--they made a radical change in rear wheel cyl sizes with disc brakes especially in big block cars--you might want to start there as my 67 with factory disc brakes had a bad prop valve so i increased the rear cyl size 1/16 in (to slow them down )and did away with the prop valve---the prop is really just a time delay valve as i see it
doctordesoto
 

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could it be as simple as the rear brakes are adjusted to tight to begin with?
 

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Discussion Starter #6
could it be as simple as the rear brakes are adjusted to tight to begin with?
that is a good point Harvey. before the valve job, when the vacuum was really low, i had them pretty tight to make up for the low vacuum. might need to back off a bit.
 

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Been there, Tightenedem up enough that you barely had to touchem. Worem out in about a week. Being that tight they never really release either. Thankfully it wasn't on a road machine.
 

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A bad booster will make the brakes too sensitive, so will oil or brake fluid on the shoes. Make sure the emergency brakes aren't adjusted too tight.
 

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You may want to consider going through the system top to bottom and check and bleed everything. Start by doing the the brake cylinders (rebuild). That way you get any potential rust buildup and crap outta the lines.....if it's been more than 10 years or so it really needs it I promise. Check the fluid as it comes out and you may find gunk in it. Also, you can reduce any air that may have gotten in there. Like art says if you have any fluid on the shoes it will act up so be sure the brake cylinders aren't leaking and that you dont get anything on them....
 

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Discussion Starter #11
You may want to consider going through the system top to bottom and check and bleed everything. Start by doing the the brake cylinders (rebuild). That way you get any potential rust buildup and crap outta the lines.....if it's been more than 10 years or so it really needs it I promise. Check the fluid as it comes out and you may find gunk in it. Also, you can reduce any air that may have gotten in there. Like art says if you have any fluid on the shoes it will act up so be sure the brake cylinders aren't leaking and that you dont get anything on them....
i should add that almost everything in the brake system is been gone over. new brake booster, rear shoes and cylinders, master cylinder, calipers, pads, etc. bled to death trying to max the brakes efficiency when the vacuum was bad. only that has not been changed/upgraded since the after market discs in the early 90's - the distribution block and the proportioning valve.
 

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well,that is my distribution block. but that's not my proportioning valve. the question thought remains - how do i know if either needs to be rebuilt?
Okay, I'll bite, what's your proportioning valve look like then? Post a picture.
 

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Discussion Starter #15
Okay, I'll bite, what's your proportioning valve look like then? Post a picture.
that's gonna' be a tough photo to get, but i'll work on it tomorrow. could be it's totally wrong for my car. stay tuned. thanks for the help
 

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Discussion Starter #16
that's gonna' be a tough photo to get, but i'll work on it tomorrow. could be it's totally wrong for my car. stay tuned. thanks for the help
ok, got the picture. it wasn't easy, but i would like to know what this is if it's not a proportioning valve. all i gotta do is figure out how to add photos. photo.jpg
got it. anyone recognize this "proportioning valve". definitely not the cylindrical unit posted on the "how to rebuild" site
 

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It is the later model, service replacement part and you are correct, it looks nothing like the original.

Those things are always FUBAR. I've got a couple inops laying around if anyone would like to try their hand at rebuilding.
 

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Those things are always FUBAR. I've got a couple inops laying around if anyone would like to try their hand at rebuilding.
Art,

I want to refute your claim but given my current issues, I cannot. Having said that, I haven't had any problems with them (and don't think my current issue is attributable to it).

It has to be good, it's patented. :buck:
 

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Discussion Starter #20
Art,

I want to refute your claim but given my current issues, I cannot. Having said that, I haven't had any problems with them (and don't think my current issue is attributable to it).

It has to be good, it's patented. :buck:
just so i am clear, which one is FUBAR - mine or the cylindrical valve? my car is not a concourse car, so if there is a better way for the brakes to work, let me know=
 
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