Master Cylinder Swap

ABA · Post by **ABA** » October 1, 2006, 6:21 pm

I have read that when replacing a Slicks master cylinder with a newer dual resevior master cylinder you need to shorten the shaft.
How much does it have to be shortened?

I was thinking about just making a spacer plate to fit between firewall and master cylinder. Has anyone else tried this? I think it would be easier than cutting and welding shaft back together.

ICEMAN6166 · Post by **ICEMAN6166** » October 2, 2006, 1:26 pm

dont need to cut and weld anything back.

the single pot rod is too short.
the dual pot rod is too long.
someone give the correct measurement if known but i believe its around an inch.
take the short rod off the pedal.put the long rod in the end of the master cylinder.see how far the hole is past the pedal? cut that much off the end and round it back off as the inside of the mc piston is rounded.you have a little adjustment with the eccentric bolt used to hold the rod to the pedal so as you depress the pedal a hair before it contacts, do not make the length tight.

ABA · Post by **ABA** » October 2, 2006, 3:19 pm

Actually I thought of that till I got the dual pot off and seen that the push rod is held in place by some type of retainer. I've never rebuilt a master cylinder and didn't know what was involved in getting the push rod out.
It's off a '69 F150 btw.

Now that I think about it, I can't remember replacing a master cylinder that had the push rod held in place by a retainer. I've always used a screw driver to bench bleed them.

Truckfarmer · Post by **Truckfarmer** » October 2, 2006, 3:24 pm

This has been discussed before as an alternative to cutting the rod. If you use a spacer like you suggested, replacing a master cylinder while traveling might be a tick easier. Nothing worse than breaking custom made parts on a raodtrip. Imagine explaining that to the "pimply faced seventeen year-old" at an Autozone counter.

ABA · Post by **ABA** » October 2, 2006, 3:29 pm

That's the main reason I was thinking about a spacer plate too TF.

cdherman · Post by **cdherman** » October 2, 2006, 5:55 pm

I don't follow that a custom shortened rod is going to make future MC replacements so difficult.

Obviously, you need to remmeber what vehicle you used as a donor and get the same master. If the new master comes with a new pushrod, then just give it back with the core and keep using your custom cut one.

The ones that are stuck in with a retainer can be removed with a stiff pull, if my memory serves me correctly.

ICEMAN6166 · Post by **ICEMAN6166** » October 3, 2006, 12:30 pm

the rods in some of the mcs have a groove with a little clip on the end ,like cd says a good pull will get it out.

couple other things to know
if you have a 61-64 or f250 4x4 you need to keep the plate from the back of the single pot and the screws so as to be able to mount the new mc

the 65/66 f 100s accept the mc without the plate due to the firewall holes being correct.

couple ways to do the brake lights, either with a tee and the original style switch or harness extension and pedal operated switch.

last thing is which mc to use and there have been several.i personally use the 72 f250 4x4 drum/drum .

65TremecGT · Post by **65TremecGT** » October 3, 2006, 3:56 pm

My dad built an 1" spacer from alum for both of our F-100 disc brake swaps, hardly notice it and no cutting of parts required.

ABA · Post by **ABA** » October 3, 2006, 5:22 pm

ICEMAN6166 wrote:
couple ways to do the brake lights, either with a tee and the original style switch or harness extension and pedal operated switch.

.

Hmm, the T fitting is a good idea, simple too. Guess it wouldn't matter which location, font or rear, since they both produce pressure.

cdherman · Post by **cdherman** » October 3, 2006, 11:28 pm

Just understand -- the pressure activated switch, via a "T" fitting will light up you brakes later than a mechanical switch that is properly set up to light your brake lights as soon as you you put your foot on the pedal.

Those fractions of a second difference may be what keeps your expensive, irreplaceable tailgate and bumper in one piece.......

Todays idiots on the road that tailgate excessively need a few extra 10ths to slow down....

ABA · Post by **ABA** » October 4, 2006, 2:20 pm

Ahh, very good point CD.
Now would be good time to fab up a switch while I got the steering column out of the way.

cdherman · Post by **cdherman** » October 4, 2006, 7:23 pm

In my case, the swtich I fabbed was just a piece of 2" pipe, cut into thirds, about 6" long. Then I welded a tang on it, with a threaded hole in the tang. The switch goes in the hole (get one from any early 70's truck) and the whole assembly can be held with a couple pipe clamps in just the right spot on the steering column so that the brake pedal depresses the plunger when its up, and releases the plunger with even a 1/4" of downward travel.

Then, to be really non-committal, I just pulled the brake light switch wires into the cab via a hole in the firewall, and rigged up a new pigtail with bullet connectors, so that I did not modify the wiring harness at all.

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ABA · Post by **ABA** » October 4, 2006, 8:01 pm

So the original pressure switch wires will work on the newer brake switch?

cdherman · Post by **cdherman** » October 4, 2006, 9:56 pm

Well, the wires you see in my picture are my own creation, spade type connectors on one end and bullet on the other. They look nice, as I solder them, and also use a matching peice of shrink tube. They just adapt the bullet connectors to later spade connectors.

But, the switches function the same way, if that's what you mean. You don't need to do any fancy re-wiring of the vehicle.

The pressure switch waits to light up the taillights (make contact) until it has some decent pressure built up. In other words, you have started to actually apply the brakes.

The later switch is a N.O. (normally open) type swtich that is open (no contacts) when the plunger is depressed. As soon as the plunger is released, the contacts connect and your brakes light up.

Adjusted right, your brakes light up as soon as you rest your foot on the pedal, and NOT when you finally actually decide to apply the brakes. This is good if you are worried about being rear ended. Moreover, it is more similar to the way modern vehicles are set up, it that they too will light up the brake lights with minimal depression of the brake pedal.

66fourby · Post by **66fourby** » October 5, 2006, 2:54 pm

When I went to disks on my 66,I took the brake pedal switch from a 73, slit open a 2" long piece of heater hose,and put the switch inside the heater hose.I then put a hose clamp on the switch and heater hose and clamped it to the steering column so the switch arm contacts the brake pedal arm.Once you get it lined up and tightened up,works great.This was supposed to be temporary till I got a bracket made,but works so good,I decided to keep it this way.You can't see the hose clamp unless you stick your head under the dash.Yes ,I also used the wires from the original pressure switch.Have had this setup for two years.Still working great.

DV65CustomCab · Post by **DV65CustomCab** » October 5, 2006, 3:25 pm

Many answers here: http://www.mongrelmotorsports.homestead ... discs.html
No cutting or drilling with my instructions.

Cutting the pushrod isn't a big deal.
Finding the right fitting for the hydraulic switch can be a challenge. The switch doesn't have the same threads as the brake lines.

ABA · Post by **ABA** » October 5, 2006, 6:30 pm

Hey DV65, I already had your page book marked.

Well I just got though mounting the bracket for the switch to my brake pedal.
I drilled the spot welds on my donor truck's pedal switch bracket and popped it off with a chizel then marked it in the same location it came off on my '65 and drilled a couple bolt holes and now it's mounted.

Now to fab up another bracket for it to close on and I should be good to go.
I took some pics but the digital camera didn't want to act right. Batteries must be weak. Try again tomorrow.

ABA · Post by **ABA** » October 10, 2006, 4:47 pm

Well I got the camera to work right.

My brake light switch mod and newly installed 1in aluminum spacer plate for the master cylinder

Works like a charm, only thing now is I need to paint it to match the 40yr old dirt and rust color of my firewall.

Damn digital camera shows up everything.

ICEMAN6166 · Post by **ICEMAN6166** » October 12, 2006, 1:07 am

but i needed no special fitting. i just moved the stock tee up to the master cylinder.f250 4x4s, f350, and up with hydraulic brakes the switch is in a tee halfway back on the drivers side frame rail.
as for that other issue of the millisecond delay in switch activation, i have a sliding step bumper that sticks out a couple inches past the tailgate being in the down position so bash away and btw,what are you people riding so close to my bumper for.

the 65 f350 i put on the 4x4 frame will have to have a pedal switch because its brake system had no tee (72).

jimbob1021 · Post by **jimbob1021** » October 12, 2006, 8:47 am

i made a t fitting for my master cyl so i could install it right in the brake line you just set it up like the old style trailer brake setup i can take a picture of it very little money to make it and it looks like it belong's there and it works great an it's ez. to replace if it ever goes bad i dont know how to download a picture on this yet? but i can put a picture in my album if any one wants to see how i did it

jim.