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Old 03-06-2008, 08:26 PM
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mounting master clyinder under floor, how to locate?

I want to put my master clyinder under the floor on my '29 dodge.

the body is off of the frame.

How do I know where to mount it?

I know where the firewall should be.

is there a specific distnce from the firewall or something??

Thanks
Keith

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Old 03-06-2008, 09:49 PM
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Every car is different to some degree, But my 32 Ford was done by knowing where the firewall and toe board was and the pedal just clears it. The advantage of a 32 Ford over all the other early Fords is that the 32 is the only one that the firewall bolts out out, making it easy to mock up fitment.





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Old 03-06-2008, 10:25 PM
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I've made a wooden template of the kickboard referencing a body mounting hole and set them up that way.

Set the pedal up so the pedal and arm will swing the furthest through the floorboard, and still keep the master cylinder below the floorboard enough to clear the cap and bails.

Usually the upper pedal stop is a peice of rubber mounted on the bottom of the floorboard, positioned so the pedal arm hits it and stops when retracted.

1/4" rubber is plenty thick enough for a bumper allowance..


Later, mikey.
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Old 03-07-2008, 07:05 AM
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Thanks Guys.
So it looks like I'll wait untill the body is on the frame then, otherwise I'm just guessing.
Unless I make a template like Mikey does
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Old 03-11-2008, 07:50 AM
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427v8...........Consider VERY carefully and do plenty of research before welding up your underfloor brake system. Many factors are involved because the master cylinder is only part of the system and all brake components should be considered with consultation with a brake system expert.

Here are a few things to consider: Depending on your type of wheel brake, disc or shoe, two piston or four, will reguire a given volumn of fluid to flow from the master cylinder to each wheel to provide proper braking. The diameter of the master cylinder piston and the length of the stroke is critical in moving the right amount of fluid. The geometry of the pedal arm and the ratio is very important.

A poorly designed system might require a 6" stroke of the pedal for normal braking and you would not be happy with that. Normal breaking might require exceptional force on the pedal, even with a power booster. The small boosters used for "under the floor" mounting are OK for normal breaking but under a panic stop, will not get the job done. Many of the street rods with underfloor systems have this problem and if you talk to the owners they will confirm this if they give you an honest answer.

The double diaphram booster improves on the problem, provided the entire brake system is designed correctly. Again, talk to an expert and consider the entire system as a whole when selecting your components.

You also need to consider how much available vacuum your engine can produce at idle to power your brake booster. If it will be less than 15" hg then you might need an electric booster vacuum pump with resevoir.

You might also look into a "Hydro-Boost" which uses and engine driven hydraulic pump like a power steering pump to provide "pedal assist" instead of vacuum.

Jim
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Old 02-20-2009, 02:38 PM
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I know this is an older thread but I thought it might be a good kickoff to my question. Why mount the master cylinder under the floor? I've never built a hotrod and have been reading up for a model a I wish to build. Is it just to keep the engine compartment clean, are there performance benefits, is it easier/harder? It seems to me the only benefit is a cleaner engine compartment, maybe some clearance issues are solved, but the underfloor location is going to be dirtier and more prone to damage from the elements. Any insight would be great.
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Old 02-20-2009, 03:28 PM
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There are no performance benefits, in fact, you need to add residual pressure valves to the lines if the master cylinder is lower than the calipers/wheel cylinders. Getting enough stroke at the master cylinder to properly run a tandem MC is always iffy, because the pedal will only swing so far due to it's shape. Changing pedal ratios is a PITA as well. Checking, bleeding and filling the resevoirs is fun too.
Floor mounted pedals in early cars always seem to get in the way of the column and you wind up with no room for a gas pedal.

You are right also in that the master cylinder under the floor is a bad place, as the pushrod ends are always facing into the direction of crud and moisture from the road and motor.
Exhaust in an early car is always close to the master cyl, which heats up the fluid.
If a car came with the mc under the floor, and you want to convert it, you usually have to brace the firewall. There are kits that will brace between the dash and firewall that have a swing pedal, some have the MC under the cowl, and operate through a bellcrank to make the master cylinder 90 or 180* from the pedal swing. Some put the mc on the outside of the firewall.

Early cars came with the pedals under the floor because brakes were cable or rod operated, and there was room for all the linkages and stuff.

You will have to do a bit of work to mount an MC on the firewall in a Model A, the sideways ones work too, but they need fab work to make them fit right. The under the cowl master cylinders are really fun to fill.....NOT!

Given the choice, I'd want mine on the firewall. Irregardless of how they look.

Later, mikey
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Last edited by powerrodsmike; 02-20-2009 at 03:33 PM.
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