Low Disc brake pedal fix!

Realise every one of these disc brake set ups are not like the other!!
I have my master cylinder and Booster mounted behind the rad, about where the engine belts are. This alows for a brake booster.

I had to have an offset 12" long push rod to clear the rad tank. That rod alowed flex and eventually failed.
I replaced it with a lever mechanism I built.
My full brakes applied pedal used to be about 3.5" off the floor, which was about half the overall pedal travel.
Now the pedal travel is about 1 and 3/4" giving me an applied high of about 5 and 1/4".

I think that would please alot of you guys with disc brakes complaning of low pedal.

The problen with the low pedal (if all else is correct) is the leverage built into the original brake pedal arm.

If you have or are planning disc brakes, I recomend a master with a bore of not less then 1 + 1/8" , and a double dighram 7" dia booster and increase the leverage of the brake pedal arm by about 1".

The lever I built gives a mechanical advantage of 1". The master usually needs to plunge about 3/4". Now I get the bottom of the pedal arm moves 3/8" and through the lever the booster puch rod moves about 7/8". which translates into the pedal moving 1 + 3/4". It feels great and very solid.

You might be able to build something like I did or build a whole new brake arm like sparky did and add the mechanical advantage right into the pedal or maybe weld an extension to the bottom of your exsisting pedal to relocate the push rod hole lower.(by how much you will have to calculate based on your van).






brakes applied



pedal at rest



M1D

Nice work. I suspect if you wanted to build those set-up 4 or 5 at a time you could sell them here.

Changing the lever has given a higher pedal but it is a little harder to push now, thats why I recomend more booster then I have. I have a single 7" diaphram booster. I made a welded bracket to attach it to the frame rail just behind the rad. I can access the lid from the dog house. I had to use the 7" due to space issuse but I could have got away with a dual 7" diaphram booster.

If you click on the picture you will get the whole image.










M1D

You might get some luck on the 'difficulty' of pedal push, by adding up to a 45° bend in your pivot arm.

Between the two points of travel axis', up to a 45° positional change between the two traveling attachment points, (pedal and rod), along the primary (fixed) axis, relative to the current distance between the three, should result in a beneficial parabola of needed force on the pedal.

Instead of having all three attachment points in a straight line from the fixed axis, changing the angle, using the middle attachment point as radius center, rotating the outer free point off the main axis just far enough to put points 2, 3, and 4 (the MC), 'in line' again at it's furthest travel, well, it should help.

I'm thinkin' 'in' to the line of travel, but try flipping the new arm either way, to see if it matters, angle in or out.

By the end of the pedal travel, the ratio should change for the better.


You might also gain a small some in the application, by changing the upper rod.

A pinned and cottered yoke, like the end on lower rod, welded or threaded directly



to your existing threaded hex-stock 'adjustment nut', replacing the lower of the two of the upper rod's ball joints might help, by removing one inline angle over 45°, straightening the 'line of march' your foot's pressure makes to the MC by >..< this much.

woohoo!

And it might also help by removing the need for another adjustment and zerk fitting in a very 'fun' area of an early.

A knuckle saver for sure.

Any of this makin' sense?

Don't throw away the one you have in there yet, cause my thought is still in beta.

You do nice work though.

If I hook the graple gromet to the wood piston throught the vortex generator right next to the dilithium cristal???????? I havn't got a clue what your sayen Bro! You lost me on the second sentence.

But I appreciate the intention and knowlege on your part. Thanks for that.

You will have to try again in kindergarden language with a picture drawn in cryons for me to follow. hehehe!

You have to realise the travel on that rod is about 3/4" to 1" off to full brakes.
I do need thast kind of leverage dynamic on my accelerator because I can't leave a stop line without too much throtle. Its always not enough or bam! too much throtle at first movement.

M1D

See if this works...

There are some inconsistencies in the drawing and scale, but the idea is there.
Both of these pivot arms and their construction lines are hastily drawn in a fully extended max position, and would only retract from this point in reverse direction of force, around the axis of fixed position 1.
As long as you don't have hole 3 being pushed past center-line between holes 2 and 4, you should be good to go.
If you can determine exactly where that theoretical line is, that should tell you what the offset angle should be, so that holes 2, 3 and 4 almost (but not quite) line up at max braking.
This should give you both, less pedal travel to that top of the brakes , and almost a 1:1 'pressure ratio' when you stand on'um and beg the 'Powers That Be' to spare you and your van whatever it's headed for.
Not necessarily in that order.
If you were as fat as me, you'd make that out of a bit heavier stock to go along with your nice Grade 8's...
The hole at position 1 could be slightly enlarged and using a bit more of the the long sleeve material you've got on one side, it could be welded in and the two become a one piece unit 'T', without need for shims or washers, stiffening the angles for force directing, by allowing the pivot arm to twist only on one axis, the one you want.
Find a nice long shouldered bolt, or you can actually use a snug good quality drift pin and cotter key at this point, that fits nice and smooth through the 'T' for it's axis, and your set.
Hopefully.

Hmmm, a real engineer!

Thank you for that, I understand completely. I can see clear how the rate of mechanical advantage changes through the throw.

I am miles away from ever getting over centre and I wouldn't want to cut it close because brake pedal drops as brakes ware out and an over centering of that linkage would be a disaster.

Currently the brake pedal rod intersects the lever at 90* as does the master cylinder rod. (at rest) When brakes are applied full the rod moves only about 3/4" which off the top of my mind looks top be about a 15* angle change.

I will contemplate you sugestions.
I will incorperate your idea into my accelerator linkage as I re-design it. Right now I have too much throtle for too little pedal movment off idle so its very hard to leave a stop line smoothly, My passangers think I'm jabbing the pedal on purpose.
Thanks
M1D

m1dadio wrote:Hmmm, a real engineer!...

Whoa, not even close! I just had the benefit of working near some very smart people for a while.

I'm pretty sure that reversing the arm, (flipping the proposed pivot arm pic horizontally) so the angle is 'out' will reduce your throttle linkage problem, by making you move the pedal further for less 'arm throw' at the carburetor.

So-?? What part # & brand booster & mastrer did you use ??

Probobly the least expensive of the aftermarket guys.
Tuffstuff.

http://www.tuffstuffperformance.com/

under special boosters

http://www.tuffstuffperformance.com/index.cfm/page/ptype=results/Category_ID=200/home_id=241/mode=cat/cat200.htm

These guys also have the brake master to use. Thay have the low profile corvett 1.125" master with lines on the left or both sides. Look in thier master department.

M1D

this is what I have now a duel diaphragm 7"





and a vacuum boost canister




M1D