Technical How likely is this to brake and I loose all braking…?

Ok update:

so I bleed the brakes and have a firm pedal that stops front wheels (have them jacked up off the ground) with pedal about 1-2 inches from floor and I can still push harder to floor.

Actually got to test dual reservoir because I kept hearing fluid dripping and finally noticed I didn’t fully tighten rear brake line on master cylinder. Front wheels still stopped (rather slowly but better than nothing) with that rather large leak. Plus after tightening that line they still stopped with rear bleed screw open.

With everything closed and bleed front wheel stops good, going to jack up back tomorrow and test how they stop. Then I’m going to make sure parking brake is configured correctly (aka: works) then take up and down driveway then street.

I’ll keep you all posted

 

Sadly the maths (I'm English!) of 4:1 and 1.125" just won't generate enough pressure for decent stopping power, unless a decent sized booster is used (I'm not suggesting that in this case!). It'll feel fine on stands though .

Pedal ratio in the 6+:1 region and probably a 1" master required.

The pushrod throw of the pedal needs to be around the line parallel to the master mounting face too. Too much off that and the ratio starts to fall away as well as other problems. It also needs to be able to fully stroke the master. 1" is getting there but might be falling short. The 'clocking' of the pushrod / pedal arm inferred above will limit the throw if not in the correct position.

Chris

 

Yes. Going from a 1" master cylinder to 1⅛" means a ±27% increase in the required force on the pedal. It's equivalent to going from a 4:1 pedal ratio to 3.16:1!

 

Thank you all for the info.

It’s not the things I know that’s going to cause brakes to fail (that master cylinder mount breaking) it’s the things I didn’t know: 1 1/8 bore…

I’ll install a 1 inch bore tomorrow night. Just ordered one

 

Still need to figure out how to get a better ratio so you don't need to use extreme pedal pressure to stop. Sometimes this can be accomplished by just lengthening the arm on the pedal, or by drilling another pivot hole to get the best ratio. I've done it both ways and either works if you can do this. I added two inches of arm length to one of mine when I went from power assist back to manual, and the brakes stop better than they did when it was power assist. A cam change required me to delete the booster since I had low vacuum with the big cam.

 

When you say lengthening the arm on the pedal, that’s literally the distance from the pivot point to the pedal? I may try to find another pedal setup that has the larger arm so I don’t mess with the one I have.

in other news I’ve gone way off the deep end reading this thread: https://fordbarn.com/forum/showthread.php?p=2383768&posted=1

so I may try the cardone 10-1905 MC referenced by Gleen

https://www.finditparts.com/product...dBf0kZluyuaUX6FYAqkDl77SVbOUqMS1wB_qNdmpnSk6h

 

Looking at the Cardone master I am sure that it is for a brake booster system and not a non boosted system. If you look at your post #2 you will see the M/C piston has a deep bore and a piston retaining circlip. If you look at the Cardone M/C you will see it has neither. So the piston can pop out and there is nothing to stop the pedal push rod just dropping away from the M/C piston. Then you end up with no brakes.

 

Ohhhh good catch! I had not noticed that. Thank you for the heads up, I understand potential risk now

 

Day 8 of my slow decent into insanity…

4 new master cylinders arrived today and a glimmer of hope has emerged only to be slapped down. 2 steps forward, one step back.

I found that a 68 mustang drum/drum master cylinder has the same bolt pattern as my current mount and I only had to grind a little off the top to clear the back side of the mount and it’s a 1 inch bore.

Only annoying thing is the metal clip that holds the cap on hits the angle portion of the back side of the mount. I ground some of the angled portion off, about 1/8 inch and it seems to clear now.

done for the night and have family stuff all weekend so won’t get back to this till Monday…

 

Enjoy your weekend with the family.

 

He thinned the flange, how would grade 8 hardware help that?

 

True on flange. I found a 68 ford master cylinder that needed only minor grinding of the top of the flange…. I’ll probably have a local rod shop make me a new mounting plate

any thoughts on 1 1/4 vs 1 3/8 wheel cylinders for front wheel cylinders with 1 inch bore master cylinder?

 

It does not need help.

The material removed does not endanger the strength meaningfully.

You are conflating a hardware suggestion with an unrelated materials strength assessment.

 

Actually they're interrelated. He originally asked if drilling out the holes would make the master cylinder more likely to break.

Of course, it's cast iron and thinner than it was, so the part overall is weaker. So the answer is it's weaker but may still not break under regular usage conditions.

You recommended grade 8 hardware. A seemingly good idea, however I'd suggest it's 1) Unnecessary, and 2) adds to the likelihood of failure.

Grade 8 hardware requires higher torque to be more resistant to fatigue and for it to be worthwhile to use the stronger fastener. Higher compressive force on a thinned out cast iron mounting ear is more likely to crack/fracture that ear.

Also, grade 5 is more likely to deform before failing. Assuming the strength of grade 5 is sufficient for the application, the more ductile bolt is better for a braking application where an outright failure of the bolt could be catastrophic.

Can we say that removing material from a cast iron part does not change the strength of the part meaningfully on a part that is compressed when mounted? Keeping in mind that cast iron fails in a brittle manner and may be quite porous? Not with high confidence.

 

Yeah, no.

If you would like to argue with the laws of physics, and the basic tenets of material science, you can do that on your own time, with somebody else.

I'm not playing that game.

 

Don't make haphazard suggestions if you don't like them fact checked. This is far from the first time this month you've done so.

 

If you don't start conflicts, there won't be any.

And...now your nonsense is blocked!

 

X2
Always modify/reinforce the mounting bracketry instead of modifying the master cylinder or any other consumable parts on the car.
If you ever need to replace it on the side of the road a standard replacement part will bolt straight in without any hassles.

 

Yeah good idea. I’ll hopefully get this back together and driving and then get the local shop to make me a new mount.

now I’m debating swapping my 1 1/4 front wheel cylinders for 1 3/8 ones but they maybe something I’ll do when the current ones start leaking because quality of products these days…

 

A Grade 5 bolt will reach its ultimate tensile strength (120ksi) and fail before a Grade 8 bolt even reaches its yield strength (130ksi) and begins to deform.

This nonsense about Grade 8 bolts being brittle and Grade 5 being better because they yield needs to die a very public death.

 

Guys are pulling BBC out of cars with engine plate mounted to the 5/16" grade 2 or so studs in an aluminum intake manifold and some how guys here think there going to break the bolts holding that master cylinder on ?
I have one race car that has a plastic master cylinder LOL .

 

If you don't increase your torque value, the Grade 8 is more likely to initiate fatigue cracks. There's a lot more to it than just the tensile and yield strengths. You should use the lowest grade bolt that has sufficient strength.