Master cylinder bore

[53 stickfigure]

That v8 s10 I recently purchased has a really hard brake pedal. It stops but takes alot of effort. I was told a smaller diameter bore will solve the problem. If the master cylinder that is on it is factory for 1987, it has a 1 1/4 bore. I found a master cylinder at autozone for a 78 malibu with manual brakes with a 7/8 bore. They look identical with one exception, the s10 master cylinder new is $55, and the one for the malibu is $195. Im not familiar with many cars built with plastic reservoir master cylinders. I don't want to spend that kinda money but when it comes to brakes, i will to be safe. Will the malibu cylinder work without modification? I haven't been feeling well for a while now and don't feel like getting too involved in anything right now. Im trying to stick to simple bolt on and go things right now. I need to work on my health so i can get another project going.

 

[earthman]

Don't know anything about the fitment but i will agree the smaller bore will be easier to push.

 

[Dr Crankenstein]

How is the current MC mounted? Do you know the actual bore size?

S10's of that era could have power or manual brakes. If manual, the MC is mounted higher on the firewall and the pushrod connects higher on the brake pedal, providing necessary higher pedal ratio.

Get a photo (or three) at the firewall. There should be an "adapter" plate to mount the MC high...

.

 

[Skip]

How is the current MC mounted? Do you know the actual bore size?

S10's of that era could have power or manual brakes. If manual, the MC is mounted higher on the firewall and the pushrod connects higher on the brake pedal, providing necessary higher pedal ratio.

Get a photo (or three) at the firewall. There should be an "adapter" plate to mount the MC high...

.

Thanks for this, Dr C. My setup is manual from an 89 S10. I moved it all over to my 39. I have been thinking about adding a booster if I don't like the brake performance. Will the higher pedal ratio be too much? Or will it just stop on the proverbial dime?

Sounds like a proper change to power brakes would call for a new booster, MC, and pedal.

I hope I like it the way it is.

 

[smallfoot]

All the higher pedal ratio will do is make it easier on your leg to exert the same pressure on the pedal.
I did a long pedal to increase the ratio and am pleased with the results. I've been running manual drums all around until now. I'm tired of walking into a parts store...in Florida...USA and not being able to score enough parts in one trip to do a Ford...For God's sake! I'm right in the middle of swapping to chevy discs up front. From now on I don't care what they do with Ford brakes ....
I know my stuff is over 50 years old. But it's Ford. Shouldn't happen..jeez!

 

[53 stickfigure]

How is the current MC mounted? Do you know the actual bore size?

S10's of that era could have power or manual brakes. If manual, the MC is mounted higher on the firewall and the pushrod connects higher on the brake pedal, providing necessary higher pedal ratio.

Get a photo (or three) at the firewall. There should be an "adapter" plate to mount the MC high...

.

The way the master cylinder is mounted looks like factory manual brakes. Ive never driven a s10 with manual brakes so i have nothing to compare the pedal feel to. All i know is the pedal is way too hard.

 

[Old Iron]

Very first thing to check is the proportioning valve to make sure it is centered.
If it isn't centered, you'll only have brakes on the front or rear and that will give a real hard pedal because only one end is working.
Second, if the master isn't 1" or smaller, that will also give a hard pedal.

 

[Dr Crankenstein]

The mount is correct for factory manual brakes. (Thanks for the pics.)

I agree with Old Iron.

I'm also curious if the previous owner performed a poor swap from power. Does the push rod (from the pedal) run straight and level?

.

 

[53 stickfigure]

I just took her down the road and really paid close attention to the brakes. Its too late to jack her up, but i dont think the front brakes are working. I did some real hard braking and couldn't lock up the front or back, just slowed to a stop. I read somewhere that these master cylinders have some sort of bypass that can go bad?

 

[Dr Crankenstein]

Your MC should only bypass if it leaks internally... since you have a hard pedal, I doubt this is your problem.

Start at the start...

- put the rear on stands and run it in gear... can you stop the rear wheels? Add a little throttle... can you hold them?

- put the front on stands and hire a gorilla to spin the wheels... can you stop and hold them?

Those two tests ^^^ should prove the prop valve is working.

I'll ask again, is the push rod running straight and level? Does it have proper free play? If the push rod is connected to the pedal in the lower (power brake) position, you're sacrificing pedal ratio and stroke. If you lack free play, you're pushing the same fluid back and forth in a "vacuum".

.

 

[53 stickfigure]

The rod is straight but i have very little freeplay and see no way to adjust it. Should i cut about a 1/4 inch off the rod and weld it back together? The brake pedal is 8 inches higher than the gas pedal.