Help! More brake questions

Kisner · 03-14-2002, 02:04 PM

Just when I thought I had everything figured out and bought "all" new components for my entire brake system, I run into another roadblock. My 68 coupe came originally with standard drum brakes. When I received my new front brake lines yesterday and were comparing them with my old, they weren't close to matching (they manufactured new ones from the distribution block to the rubber hoses). To my ultimate horror (stupidity for never checking), the previous owner switched the front brakes from manual drum to disc. Now that's great for braking power, however, I know the original, optional power disc brakes for the 68 came with a power brake booster and proportioning valve. The previous owner didn't purchase these and left the old manual drum master cylinder and original distribution box. Is there any way to make these brakes work as non-power disc? I know some of the earlier Mustangs had non-power disc. Don't really have the $169 for a new pressure differential/proportioning valve and $200 or so bucks for a new booster.

Also, do I need to return my new drum master cylinder and exchange it for a disc master cylinder? Not sure if the master cylinder lines for the disc will still line up with my distribution block?

Clark Rodgers · 03-14-2002, 03:15 PM

Where do I start except to say you are between a rock and a hard place.
First, remember these are your brakes and they are important so don't try to make something work. If I was you I would change what I had to. The Dist. block is now available from NPD for $80, still expensive but not $160.

You can try and make the master cylinder work, use a disk one with the block or try the manual with an adjustable porportioning valve. The lines should be close enough to work with either.

I don't really feel good about rigging this, especially because look at how much trouble the brakes have caused you before.

Kisner · 03-14-2002, 11:11 PM

Well, if I have to I can cough up the $ for a new distribution block with proportioning valve. But what impact would it have if I ran my straight distribution block. In my little mind, I'm thinking I'd have fully functional disc brakes up front and fully functional drum brakes in the rear. Shop manual talks about how the primary (front) brakes are most often used depending on the braking situation, but the only real benefit I read was that the proportioning valve would, in most cases, prevent real wheel lockup on hard stops.

Also, I just read earlier today in the shop manual that the power vacuum booster was also an option, however, they did include it on all the 68's with disc brakes. Shouldn't the disc brakes work fine without a booster (I'm sure they'd be better with it but I can't afford all the bells and whistles).

I think I better swap out the master cylinder (haven't used the new one I just bought so that won't cost me anything) since the cars with disc brakes did use the one with the larger front brake reservoir. By the way, why does the front brakes have a larger reservoir any way?

Clark Rodgers · 03-15-2002, 10:32 AM

Kisner, I am on board with you not using the booster, it would be nice but I'm sure you could be ok without it.

If you decide to go with the old drum distribution block then you will get equal pressures at the wheels and not give you the best braking and possibly not enough fluid to apply good pressure on the discs. This answers your other question as well, the reservoirs are different sizes because the front discs need more fluid to operate, just compare the piston size in a caliper vs. wheel cylinder.

The front discs are the primary stopping system and need more pressure, so if that is through a dist. block or a adjustable valve they need more than the back drums.

thunderbolt · 03-15-2002, 12:01 PM

I will preface by saying I am sure about this.
Isn't the disk brake master cylinder larger than the drum brake one and hence pumps more volume. If you use the disk brake master cylinder then I think you should get the disk brake proportioning valve otherwise increaced fluid volume will only make the rear drums lock sooner. Maybe you could get and adjustable proportioning valve (I would but you may not be comfortable with one of these) and then dial in the correct proportioning yourself and not worry about right valve with right master cylinder.
Of course as I said earlier, I don't know any of this for fact.

Rev · 03-15-2002, 06:26 PM

I think yo'll need a non-power (manual ) master cylinder and an adjustable proportioning valve to do this correctly. Still shouldn't cost too much. Just exchange the MC and get the adjusable PV for asbout $50-60. You probably will need some short lines and fittings from the local auto supply.

Rev

Kisner · 03-16-2002, 11:00 PM

Thanks for all the advice. For the time-being, I'm decided to use the standard drum brake master cylinder and my original brake fluid distribution box. Went to return the drum master cylinder for a disc one, but the guy at AutoZone highly advised against it since I wouldn't be using a proportioning valve. In his opinion, the disc master cylinder won't work properly without a proportioning valve. Whenever I get to finally drive it (by year's end hopefully), and the brakes don't work good enough for me, I'll get the ideal setup.

By the way, it took me 2 days, but I finally got all my new lines installed with all new hoses, and bench bled the master cylinder late this evening. Will install the master cylinder tomorrow, bleed the brakes, and hope they work. The long line running from the front to the back was a total nightmare to install. Advice for new restorers - either pay someone or if you're installing new brake lines, do it with the transmission, engine, and exhaust removed! I need a skin graft for all my knuckles. Finally, if anyone needs new brake lines, the ones I got from National Parts Depot were virtually flawless, with precise bends and lengths identical to my originals.

03-14-2002, 02:04 PM	#1
Kisner Registered Member Join Date: Nov 2000 Posts: 290	Help! More brake questions Just when I thought I had everything figured out and bought "all" new components for my entire brake system, I run into another roadblock. My 68 coupe came originally with standard drum brakes. When I received my new front brake lines yesterday and were comparing them with my old, they weren't close to matching (they manufactured new ones from the distribution block to the rubber hoses). To my ultimate horror (stupidity for never checking), the previous owner switched the front brakes from manual drum to disc. Now that's great for braking power, however, I know the original, optional power disc brakes for the 68 came with a power brake booster and proportioning valve. The previous owner didn't purchase these and left the old manual drum master cylinder and original distribution box. Is there any way to make these brakes work as non-power disc? I know some of the earlier Mustangs had non-power disc. Don't really have the $169 for a new pressure differential/proportioning valve and $200 or so bucks for a new booster. Also, do I need to return my new drum master cylinder and exchange it for a disc master cylinder? Not sure if the master cylinder lines for the disc will still line up with my distribution block?

03-14-2002, 03:15 PM	#2
Clark Rodgers Registered Member Join Date: May 1999 Location: Rowlett,Texas Posts: 306	Where do I start except to say you are between a rock and a hard place. First, remember these are your brakes and they are important so don't try to make something work. If I was you I would change what I had to. The Dist. block is now available from NPD for $80, still expensive but not $160. You can try and make the master cylinder work, use a disk one with the block or try the manual with an adjustable porportioning valve. The lines should be close enough to work with either. I don't really feel good about rigging this, especially because look at how much trouble the brakes have caused you before. __________________ 69 393W Sportsroof deluxe

03-15-2002, 10:32 AM	#4
Clark Rodgers Registered Member Join Date: May 1999 Location: Rowlett,Texas Posts: 306	Kisner, I am on board with you not using the booster, it would be nice but I'm sure you could be ok without it. If you decide to go with the old drum distribution block then you will get equal pressures at the wheels and not give you the best braking and possibly not enough fluid to apply good pressure on the discs. This answers your other question as well, the reservoirs are different sizes because the front discs need more fluid to operate, just compare the piston size in a caliper vs. wheel cylinder. The front discs are the primary stopping system and need more pressure, so if that is through a dist. block or a adjustable valve they need more than the back drums. __________________ 69 393W Sportsroof deluxe

03-15-2002, 06:26 PM	#6
Rev Registered Member Join Date: Nov 1998 Location: Houston, Tx. Posts: 3,887	I think yo'll need a non-power (manual ) master cylinder and an adjustable proportioning valve to do this correctly. Still shouldn't cost too much. Just exchange the MC and get the adjusable PV for asbout $50-60. You probably will need some short lines and fittings from the local auto supply. Rev __________________ '66 Coupe, 306, 350-375 HP, C-4, 13.07 e.t., 104.8 mph, 1/4 mi. O.B.C. #2 '66 coupe

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03-14-2002, 11:11 PM	#3
Kisner Registered Member Join Date: Nov 2000 Posts: 290	Well, if I have to I can cough up the $ for a new distribution block with proportioning valve. But what impact would it have if I ran my straight distribution block. In my little mind, I'm thinking I'd have fully functional disc brakes up front and fully functional drum brakes in the rear. Shop manual talks about how the primary (front) brakes are most often used depending on the braking situation, but the only real benefit I read was that the proportioning valve would, in most cases, prevent real wheel lockup on hard stops. Also, I just read earlier today in the shop manual that the power vacuum booster was also an option, however, they did include it on all the 68's with disc brakes. Shouldn't the disc brakes work fine without a booster (I'm sure they'd be better with it but I can't afford all the bells and whistles). I think I better swap out the master cylinder (haven't used the new one I just bought so that won't cost me anything) since the cars with disc brakes did use the one with the larger front brake reservoir. By the way, why does the front brakes have a larger reservoir any way?

03-15-2002, 12:01 PM	#5
thunderbolt Registered Member Join Date: Oct 1998 Location: Houston, TX, USA Posts: 380	I will preface by saying I am sure about this. Isn't the disk brake master cylinder larger than the drum brake one and hence pumps more volume. If you use the disk brake master cylinder then I think you should get the disk brake proportioning valve otherwise increaced fluid volume will only make the rear drums lock sooner. Maybe you could get and adjustable proportioning valve (I would but you may not be comfortable with one of these) and then dial in the correct proportioning yourself and not worry about right valve with right master cylinder. Of course as I said earlier, I don't know any of this for fact.

03-16-2002, 11:00 PM	#7
Kisner Registered Member Join Date: Nov 2000 Posts: 290	Thanks for all the advice. For the time-being, I'm decided to use the standard drum brake master cylinder and my original brake fluid distribution box. Went to return the drum master cylinder for a disc one, but the guy at AutoZone highly advised against it since I wouldn't be using a proportioning valve. In his opinion, the disc master cylinder won't work properly without a proportioning valve. Whenever I get to finally drive it (by year's end hopefully), and the brakes don't work good enough for me, I'll get the ideal setup. By the way, it took me 2 days, but I finally got all my new lines installed with all new hoses, and bench bled the master cylinder late this evening. Will install the master cylinder tomorrow, bleed the brakes, and hope they work. The long line running from the front to the back was a total nightmare to install. Advice for new restorers - either pay someone or if you're installing new brake lines, do it with the transmission, engine, and exhaust removed! I need a skin graft for all my knuckles. Finally, if anyone needs new brake lines, the ones I got from National Parts Depot were virtually flawless, with precise bends and lengths identical to my originals.