Front disc conversion on '65 Barracuda FS

[Bob Jasinski]

OK, so I have spent hours going through the sticky writeup, and numerous other posts about front disc conversins on early A bodies, but I need some input on implementation. I have a full KH setup, and now that I have my car finally out of the body shop, it's coming together. All the lines will be new, and I contacted Inline Tube about what lines to order as well as fittings. Since I'm going with a dual pot master cylinder, they said I should order the BLK 241 distribution block https://www.inlinetube.com/collections/all/?q=blk241 , the ADJP01 adjustable proportioning valve Products, and the PAB6402 Products Line kit.

I have the Raybestos MS36406 dual pot master with 15/16" bore ordered from Rock Auto. Currently there are new rear wheel cylinders installed that are stock units, (Dorman W78734) that are 15/16" (.9375') diameter. Rear brake shoes and drums (10") are new by Wagner. I know many have used the factory style "Texas" shaped distribution block with built in prop valve (I have a used one) but do not like it for a few reasons. First, it doesn't fit very well in place of the old brass drum-drum block, I'd have to drill some new hole(s) in the frame, I don't want to install the warning light in my dash, and as far a I can tell, it is not adjustable.

I've read in a number of places it would be better to go with a smaller diameter rear wheel cyls of 13/16" to provide better balance with the front discs. I'm willing to change these new ones out (system is still dry) but is it really needed with the adjustable prop valve? If I did go with smaller rear wheel cyls, would that eliminate the need for the prop valve? This will be a manual disc/drum brake system, and the car will have modern radials, same size all around, close to factory diameter but on 15" Ralleye wheels. Input is appreciated.

Here's some current project photos:

 

[66fs]

I've never had a problem with K-H discs and the standard rear wheel cylinders. I run the original small 10 x 1 3/4 brakes in the rear. My sons' 73 Dart has the 10 x 2 1/2 rear brakes and the standard 73 front discs and that had early rear brake lock up.

 

[LO23M8B]

Just beautiful. When I hit that $550,000,000 lotto I'll give ya a million dollars for it.

 

[Bob Jasinski]

I've never had a problem with K-H discs and the standard rear wheel cylinders. I run the original small 10 x 1 3/4 brakes in the rear. My sons' 73 Dart has the 10 x 2 1/2 rear brakes and the standard 73 front discs and that had early rear brake lock up.

66fs, No proportioning valve in your FS? If I could I'd do without it, as long as its safe.

 

[Bob Jasinski]

Just beautiful. When I hit that $550,000,000 lotto I'll give ya a million dollars for it.

Its a deal!!

 

[LO23M8B]

OK

 

[Car Nut]

Nice looking Barracuda!

 

[66fs]

66fs, No proportioning valve in your FS? If I could I'd do without it, as long as its safe.

I run a separate proportioning valve from a 67-68 A body. I would run your adjustable. That setup looks good, I had 15 in Rallye wheels on the 66. They are on the 68 Formula S now.

 

[Bob Jasinski]

I've been looking at Summit for the prop valve/distribution block offerings they have. Many (most) are non-adjustable. If adjustability is so important, why are the factory distribution blocks with prop valves all non adjustable? Is tire size (front/back) the issue? I'm going to run the same tire size on all four corners, am I overthinking this need for adjustability?

 

[RustyRatRod]

I've been looking at Summit for the prop valve/distribution block offerings they have. Many (most) are non-adjustable. If adjustability is so important, why are the factory distribution blocks with prop valves all non adjustable? Is tire size (front/back) the issue? I'm going to run the same tire size on all four corners, am I overthinking this need for adjustability?

Because the adjustment was engineered into the system. It doesn't need to be adjustable given the design of the entire vehicle.

 

[Bob Jasinski]

Because the adjustment was engineered into the system. It doesn't need to be adjustable given the design of the entire vehicle.

That makes good sense Rusty. I'd like to use a non-adjustable factory dual circuit type, but I think they all incorporated the light switch, trying to get away from that on this car. I may have to stick with an adjustable type like Inline tube recommends and just plumb it in.

 

[Bob Jasinski]

I run a separate proportioning valve from a 67-68 A body. I would run your adjustable. That setup looks good, I had 15 in Rallye wheels on the 66. They are on the 68 Formula S now.

66fs, I spoke with Inline Tube today about availability of the '67-'68 prop valve (they actually show it in their YouTube video) , and it mounts inline after the distribution block, I assume that is the one you are using. He said they are no longer available, I would have to find a used one or go with the adjustable type. I think the factory one is what I (ideally) would like to find. It would have the preset rear brake bias setting built in.

Edit: looks like Mega Parts carries these: Proportioning Valve 1967-70 A-Body Disc Brakes 1967-70 B-Body Disc Brakes 1970-71 E-Body Disc Brakes, Brake Junction/Distribution Blocks, 129-RBV004 Reproduction, NOS and Used Mopar Muscle Car Parts

 

[66fs]

66fs, I spoke with Inline Tube today about availability of the '67-'68 prop valve (they actually show it in their YouTube video) , and it mounts inline after the distribution block, I assume that is the one you are using. He said they are no longer available, I would have to find a used one or go with the adjustable type. I think the factory one is what I (ideally) would like to find. It would have the preset rear brake bias setting built in.

Edit: looks like Mega Parts carries these: Proportioning Valve 1967-70 A-Body Disc Brakes 1967-70 B-Body Disc Brakes 1970-71 E-Body Disc Brakes, Brake Junction/Distribution Blocks, 129-RBV004 Reproduction, NOS and Used Mopar Muscle Car Parts

Looks good.

 

[RustyRatRod]

That makes good sense Rusty. I'd like to use a non-adjustable factory dual circuit type, but I think they all incorporated the light switch, trying to get away from that on this car. I may have to stick with an adjustable type like Inline tube recommends and just plumb it in.

Just know that the further away you get from stock with stuff like tire sizes, the more you're outside the box that the factory designed it in, so bear that in mind.

 

[Bob Jasinski]

Just know that the further away you get from stock with stuff like tire sizes, the more you're outside the box that the factory designed it in, so bear that in mind.

Roger that Rusty. Tires will be same size radials all around, diameter the same or close to stock.

 

[RustyRatRod]

Roger that Rusty. Tires will be same size radials all around, diameter the same or close to stock.

I think that will be fine.

 

[1964cuda]

OK, so I have spent hours going through the sticky writeup, and numerous other posts about front disc conversins on early A bodies, but I need some input on implementation. I have a full KH setup, and now that I have my car finally out of the body shop, it's coming together. All the lines will be new, and I contacted Inline Tube about what lines to order as well as fittings. Since I'm going with a dual pot master cylinder, they said I should order the BLK 241 distribution block https://www.inlinetube.com/collections/all/?q=blk241 , the ADJP01 adjustable proportioning valve Products, and the PAB6402 Products Line kit.

I have the Raybestos MS36406 dual pot master with 15/16" bore ordered from Rock Auto. Currently there are new rear wheel cylinders installed that are stock units, (Dorman W78734) that are 15/16" (.9375') diameter. Rear brake shoes and drums (10") are new by Wagner. I know many have used the factory style "Texas" shaped distribution block with built in prop valve (I have a used one) but do not like it for a few reasons. First, it doesn't fit very well in place of the old brass drum-drum block, I'd have to drill some new hole(s) in the frame, I don't want to install the warning light in my dash, and as far a I can tell, it is not adjustable.

I've read in a number of places it would be better to go with a smaller diameter rear wheel cyls of 13/16" to provide better balance with the front discs. I'm willing to change these new ones out (system is still dry) but is it really needed with the adjustable prop valve? If I did go with smaller rear wheel cyls, would that eliminate the need for the prop valve? This will be a manual disc/drum brake system, and the car will have modern radials, same size all around, close to factory diameter but on 15" Ralleye wheels. Input is appreciated.

Here's some current project photos:

View attachment 1716363467View attachment 1716363468View attachment 1716363469View attachment 1716363470View attachment 1716363473

OK, so I have spent hours going through the sticky writeup, and numerous other posts about front disc conversins on early A bodies, but I need some input on implementation. I have a full KH setup, and now that I have my car finally out of the body shop, it's coming together. All the lines will be new, and I contacted Inline Tube about what lines to order as well as fittings. Since I'm going with a dual pot master cylinder, they said I should order the BLK 241 distribution block https://www.inlinetube.com/collections/all/?q=blk241 , the ADJP01 adjustable proportioning valve Products, and the PAB6402 Products Line kit.

I have the Raybestos MS36406 dual pot master with 15/16" bore ordered from Rock Auto. Currently there are new rear wheel cylinders installed that are stock units, (Dorman W78734) that are 15/16" (.9375') diameter. Rear brake shoes and drums (10") are new by Wagner. I know many have used the factory style "Texas" shaped distribution block with built in prop valve (I have a used one) but do not like it for a few reasons. First, it doesn't fit very well in place of the old brass drum-drum block, I'd have to drill some new hole(s) in the frame, I don't want to install the warning light in my dash, and as far a I can tell, it is not adjustable.

I've read in a number of places it would be better to go with a smaller diameter rear wheel cyls of 13/16" to provide better balance with the front discs. I'm willing to change these new ones out (system is still dry) but is it really needed with the adjustable prop valve? If I did go with smaller rear wheel cyls, would that eliminate the need for the prop valve? This will be a manual disc/drum brake system, and the car will have modern radials, same size all around, close to factory diameter but on 15" Ralleye wheels. Input is appreciated.

Here's some current project photos:

View attachment 1716363467View attachment 1716363468View attachment 1716363469View attachment 1716363470View attachment 1716363473

I upgraded my '64 Barracuda to KH 4 piston disc up front last spring with the same MC I believe you have. The rear is an 8 3/4" with 10"drum. I had issues with the rear locking up when I test drove. I read somewhere the same as you to put in smaller 13/16" rear W/C but once I got them in hand, I could see that they wouldn't fit the backing plate nor the brake shoes(pic) so I abandoned that. I broke down and added an adjustable proportioning valve after the newer style Combination valve in the rear line. Once the Adjustable was in place it immediately stopped the rear wheel lock up with out any adjusting. With a little stop testing and adjusting, the fronts do most of the work and the stop distances decreased dramatically and no lock up anymore.

Beautiful car BTW, I almost wish mine was a formula S but I am kind of fond of the P/B transmission and its uniqueness that only '64 had.

As stated before the factory parts may not work with change in tire size etc. I have 14" rally wheels (factory was 13"), SuperStock rear springs and 0.92" torsion bars. So not factory at all and with the higher spring rates can change the way the car handles.

 

[Bob Jasinski]

1964Cuda, Thanks for the feedback. I'm unclear as to what combination valve you have there, it may be just the dual circuit distribution block with the switch in it; as was used for '67 to late '69, '70. My research tells me those do not contain a proportioning valve, and the proportioning valve was a separate piece after the distribution block before it went to the rear axle for those years (see my link in post #12 above to the Mega Parts '67-'70 proportioning valve that I have ordered). Inline tube has a video showing the changes from '62 into the '70s.

 

[1964cuda]

1964Cuda, Thanks for the feedback. I'm unclear as to what combination valve you have there, it may be just the dual circuit distribution block with the switch in it; as was used for '67 to late '69, '70. My research tells me those do not contain a proportioning valve, and the proportioning valve was a separate piece after the distribution block before it went to the rear axle for those years (see my link in post #12 above to the Mega Parts '67-'70 proportioning valve that I have ordered). Inline tube has a video showing the changes from '62 into the '70s.

Hi Bob,
Yes I believe the one I got is for like a newer style aftermarket, may not be period Mopar correct, that is a combination valve with proportion and front hold off or metering all in one.this is what was sold to me with the master cylinder and all the lines bent to fit. Along with rebuilt calipers, LCA and new rotors.

 

[stillrunners]

Good stuff guys.....and nice build there !

 

[Bob Jasinski]

Hi Bob,
Yes I believe the one I got is for like a newer style aftermarket, may not be period Mopar correct, that is a combination valve with proportion and front hold off or metering all in one.this is what was sold to me with the master cylinder and all the lines bent to fit. Along with rebuilt calipers, LCA and new rotors.

View attachment 1716366598

I looked it up on Jegs website. Yes, its not correct for your Barracuda, its a GM valve. That's why you had to add the separate adjustable valve. As Rusty indicates in post #10, the fixed proportional valves are specific to the car design.

 

[scatpackbee]

I upgraded my '64 Barracuda to KH 4 piston disc up front last spring with the same MC I believe you have. The rear is an 8 3/4" with 10"drum. I had issues with the rear locking up when I test drove. I read somewhere the same as you to put in smaller 13/16" rear W/C but once I got them in hand, I could see that they wouldn't fit the backing plate nor the brake shoes(pic) so I abandoned that. I broke down and added an adjustable proportioning valve after the newer style Combination valve in the rear line. Once the Adjustable was in place it immediately stopped the rear wheel lock up with out any adjusting. With a little stop testing and adjusting, the fronts do most of the work and the stop distances decreased dramatically and no lock up anymore.

Beautiful car BTW, I almost wish mine was a formula S but I am kind of fond of the P/B transmission and its uniqueness that only '64 had.

As stated before the factory parts may not work with change in tire size etc. I have 14" rally wheels (factory was 13"), SuperStock rear springs and 0.92" torsion bars. So not factory at all and with the higher spring rates can change the way the car handles.



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Do your caliper dust boots rub on the rotor “step”?

 

[glhs0426]

I installed a budget system on a 66 barracuda and a rear proportioning valve was needed to prevent early lockup. It differed from your setup in that it was not the factory KH 4 piston calipers.

BTW that is an absolutely gorgeous 300 convertible! G correct?

 

[Dave999]

yeah i'll second that....mine has 9 inch drums on the back (60s style duo servo self energizing) and single pot (slider) disc front.
without a proportioning valve the rear would lock up... new tyres, old tyres,bigger wheels nothing fixed it until i got a brake bias.

presume with the 4 pot front and 10s on the back things will be worse

issue is disk brakes need more fluid to move (look at the bore of the caliper pistons) and a higher line pressure to work properly than drums

so without the valve, by the time you get your front disks 1/4 to 1/2 ON the rears are already full on like you used both feet on the peddle

the valve lets you get the best out of the discs up front well before you have over powered the tiny wheel cylinders out back

even more necessary with 60s duo servo brakes at the back, these self power-on as the shoes ride round on the mountings.... they altered the rear brakes over the years as disc fronts become more commonplace to reduce this self energizing action.
duo servo was totally appropriate with drums all round .....not so with discs up front

look to the master cylinder bore size if when all said and done, it still feels like your brake pads and shoes are polished wood (no progressive braking and a confident stop only when you really are standing on that peddle)

a smaller bore would give longer peddle travel, greater subtlety in brake application and less foot effort...

Pressure in system = Force of foot/x sectional area of master cylinder
make x section area smaller and for the same force with your foot you get higher line pressure and maximum effort with the foot would produce a much higher pressure in the brake lines than before meaning a wider range of application from brake off to brakes fully on.

smaller bore cylinders at the back reduce the peddle travel but also reduce the force they apply to the shoes for a given pressure in the line, so benefits there as well if you can find some that fit.......
big wheel cylinder bore
Pressure in brake line x Area of cylinder x section=Force on shoe
smaller wheel cylinder bore
PxA(smaller)=F(smaller)

its a balancing act between what you can get for your brake set up and the fact that with modern tyres and modified car, things have moved well away from 1968 cross ply n drums set up.

these days you need to stop in a style closer to an ABS equipped Audi.... not a 1968 dodge dart...and you can, with the right set up if you can modulate that peddle and keep off the clutch, in the panic of an emergency stop.


Dave

 

[Bob Jasinski]

I installed a budget system on a 66 barracuda and a rear proportioning valve was needed to prevent early lockup. It differed from your setup in that it was not the factory KH 4 piston calipers.

BTW that is an absolutely gorgeous 300 convertible! G correct?

Yes, it's a '61 300G, 1 of 337 convertibles built. I've owned it since 1978, I was 24 when I bought it.