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48hoopty

Bad News? 8.8 rear disc swap, Master cyl. Does it have to be power or can it be manual

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So I went to order the 2 pot master cylinder adapter from ECI and was told that the ford 8.8 discs will not operate in manual that they require a power booster. Definitely sucks since I scrounged a 3.55 limited slip disc rear. I've seen threads of others who have done this swap and would like some input. I was told that due to the small pistons it requires higher pressure to move them. I asked about compensating thru the proportioning valve and couldn't get an answer. For those that have done the swap did you stay with manual brakes or add a booster. With an adjustable proportioning valve were you able to get the brakes to operate. Are pedal pressures higher. I'm not looking forward to scrounging for a drum rear. I won't add a power booster to the firewall and don't really want to add one under the floor. I've read plenty of forums from the HAMB to here and nothing really discusses trials and tribulations of have a manual 8.8 disc setup. 

Thanks

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My understanding is that for general road use a 4 wheel disc setup does indeed need a power booster, I've run 4 wheel vented discs since the 1970's and the car stops well......yeh, o/k, my pedal box/master cylinder assembly is a pendant pedal arrangement, mounted on the firewall and I modified the firewall to accommodate the circular shape of the booster so thats how mine is but you maybe able to check around and see whether a remote mounted booster may be able to offer sufficient pressure to at least the front discs.........I'd be checking with a brake specific company like Willwood or similar..........andyd  

Edited by Andydodge

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3 hours ago, 48hoopty said:

So I went to order the 2 pot master cylinder adapter from ECI and was told that the ford 8.8 discs will not operate in manual that they require a power booster. Definitely sucks since I scrounged a 3.55 limited slip disc rear. I've seen threads of others who have done this swap and would like some input. I was told that due to the small pistons it requires higher pressure to move them. I asked about compensating thru the proportioning valve and couldn't get an answer. For those that have done the swap did you stay with manual brakes or add a booster. With an adjustable proportioning valve were you able to get the brakes to operate. Are pedal pressures higher. I'm not looking forward to scrounging for a drum rear. I won't add a power booster to the firewall and don't really want to add one under the floor. I've read plenty of forums from the HAMB to here and nothing really discusses trials and tribulations of have a manual 8.8 disc setup. 

Thanks

http://shoebox-central.com/1949-1950-1951-ford-deluxe-dual-reservoir-master-cylinder-conversion-kit

 

Look at the link above,and it you think you can make it work for you,call  them up first and ask them about it. Sure,it's for a 49-51 Ford,but I see no reason why you couldn't modify the mounting bracket to make it work with your P-15. They also sell a more expensive kit that has a mini-booster on it that sits below the floor if you think you need or want PB.

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Don't know if this correlates but my Studebaker truck has GM disc components on the front and Ford discs (Thunderbird) out back.  They are pressurized by a dual circuit Jeep master and work very well without any boost.  Guess you could hook it up, see if it meets needs, then retro a booster if you deem it necessary.

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This is what I was looking at 

http://www.ecihotrodbrakes.com/chrysler_master_assemblies.html

Spoke with their in house tech and was told about the pressure issue. Just wanted some feed back if anyone was running manual discs. I've done manual disc on others using Cadillac calipers and everything worked like a champ. In a simple hydraulic system the piston should still actuate regardless if there was a booster or not. Wonder if it just makes peddle pressure so hard it's not acceptable. Really a pain in the donkey since I've got a disc rear ready to bolt in, with all new parts on it. 

Can always go to a larger piston master cylinder to get more volume and pressure. 

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3 hours ago, 48hoopty said:

(snip) Can always go to a larger piston master cylinder to get more volume and pressure. 

Not quite; a larger master cylinder will give you more volume but less pressure.

 

Marty

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It is my understanding that the "power brake booster" does the actual work of applying the force to the master cylinder push rod when your foot pushes the pedal. Without the booster, your leg muscles are providing the force to the master cylinder pushrod. Disc brakes, I think might need more effort than "self energizing" drum brakes, thus requiring more input from your leg muscles. With disc, the harder you push, the better they work (with in their operating parameters) and the more work you have to do. The booster just reduces the "strain" on your left leg.

 

I also don't believe the "booster" applies any more pressure, or increases the force to the master cylinder than what you could apply with your muscles in a non-power brake system. And it does not do it any faster either. Any of the dirt modified race cars I have worked on are 4 wheel disc with out power boosters......and they stop......and they stop fast.  Well, most of the time. Sometimes they stop real fast without even using the brakes. A concrete wall is a pretty effective braking system.

 

Since this is my opinion, feel free to correct or add  info needed.

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4 hours ago, martybose said:

Not quite; a larger master cylinder will give you more volume but less pressure.

 

Marty

I knew that in my brain just didn't type it right. As the master cylinders provided with the kit both have 1" piston. I could drop down to a 15/16 or even a 7/8" mc that should increase line pressure. Typical brake systems operate at 1000 to about 1200 lbs. But with the small pistons in the ford caliper  what kind of pressure is needed to actuate the piston. The other avenue is the pedal pivot ratio. I could change that via bell crank to increase pressure and lessen pedal effort as well. I've done a lot of work on race cars with either manual discs or hydroboost. Since hydroboost is out of the question, I'm left with manual. I'm more inclined to use a mc with remote reservoirs. 

Also thinking that a power booster isn't a fail proof part and I can't see allowing the brakes to just crap out on an explorer since there isn't any power assist. So evidently the OEM mc on an explorer provides sufficient line pressure in manual mode to adequately stop the vehicle. So do I use the explorer mc. A call to wilwoodhas already been made will know more tomorrow when they return my call with answers.

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Using 4 wheel disc without booster, no problem. Ford 8.8 disc on the back and disc conversion on front. I use a Ford explorer disc brake MC and a residual valve on each line. Will require a bit more foot pressure with manual braking but No problem stopping. 

Edited by 50 coupe

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1 hour ago, 50 coupe said:

Using 4 wheel disc without booster, no problem. Ford 8.8 disc on the back and disc conversion on front. I use a Ford explorer disc brake MC and a residual valve on each line. Will require a bit more foot pressure with manual braking but No problem stopping. 

Thanks...exactly what I was looking for. ECI has a bracket that comes with either a corvette or mustang MC. Both are 1". The OEM explorer is also a 1". I was looking at wilwood with either 15/16 or 7/8 remote reservoir MCs. Didn't think there would be an issue except maybe a little more leg pressure. 

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