Thread: Brake troubles

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In post 34 you show a 33* angle in the brake pedal arm---and stated later that you had 3/4 inch travel in master rod-----thats not a very good mech leverage ratio-looks like maybe a 3 inch arm and a 7-1 would get it out to 21 inches? 5-1 maybe 15? you can raise the pressure by a better leverage/geometry and even a smaller diameter bore master. maybe down to 7/8? there are graphs out there that show the volumes/pressure differances-------

Keep in mind there is a difference in pressure & volume, If you unhooked the caliper and put a gauge on the front and back and got the same pressure (you did) that means that you still could have a volume issue or stuck piston, as of now you know that the fronts collapse at 600 psi and the rears don't, I still believe the easiest and no cost option would be to swap calipers on one side, those fronts could collapse at 600 psi as could the rears but the volume could be to much of a difference to ever get full pressure on the rear, it would also check your plumbing (valves, etc) if the rear don't collapse on the front rotor and the front does on the rear you now simply have a stuck piston or volume issue, and all else is kosher.
It doesn't mean your booster is bad either. A person can exert alot of force in a panic stop when his back is against the seat and he's using his legs, keep in mind that 99% of the time you don't exert full force on a brake pedal because you don't normally panic stop (normally), pedal leverage as Jerry said is mechanical advantage, as well as a smaller diameter master cylinder normally the pedal ratio is different for power brakes than non power.

stick a fork in me i'm done.

Ok I'm back on the job, it looks like I'll be doing some remodeling of brake pedal mounts and ratio. Had to walk away for a bit. Building aircraft is so much easier than getting a bunch of mismatched brake parts to work.
What I hate is that I'm going to have to cut the bracket on my frame and it's all painted etc.
Thanks for the help guys, I'll keep you posted.

Originally Posted by Navy7797

Had to walk away for a bit.
What I hate is that I'm going to have to cut the bracket on my frame and it's all painted etc.

Imagine if it was powder coated! At least the paint can be blended / patched / insert your term here...

Originally Posted by 34_40

Imagine if it was powder coated! At least the paint can be blended / patched / insert your term here...

Oh the HORROR, the HORROR

Before you cut your pedal, did you check the power booster to master cylinder rod adjustment?

Originally Posted by 36 sedan

Before you cut your pedal, did you check the power booster to master cylinder rod adjustment?

OK perhaps some slack can be taken up?, right now the rod is screwed onto the threaded rod coming out of the booster and that pushes in 1/4 " before it hits solid but I believe thats correct, its acts just like the other boosters I've looked at.

Quick and easy way of testing the rod length adjustment (from Jegs site);

Use the following procedure to check the push rod adjustment.
CAUTION: Wear protective goggles when performing the following procedure! Brake fluid may erupt from the master cylinder with sufficient force to cause personal injury.
1. Remove the master cylinder reservoir cap or cover.
2. While an assistant slightly depresses the brake pedal, watch for fluid to erupt in the reservoir when the pedal is depressed 3/8” to 1/2”. This indicates correct push rod length. On dual system master cylinder, fluid may spurt only from the front reservoir.
3. If the pedal travels more than 1/2” before master cylinder fluid erupts, the push rod is too short. If nothing happens no matter how far the pedal is depressed, the push rod is probably too long.

Originally Posted by 36 sedan

Quick and easy way of testing the rod length adjustment (from Jegs site);

Use the following procedure to check the push rod adjustment.
CAUTION: Wear protective goggles when performing the following procedure! Brake fluid may erupt from the master cylinder with sufficient force to cause personal injury.
1. Remove the master cylinder reservoir cap or cover.
2. While an assistant slightly depresses the brake pedal, watch for fluid to erupt in the reservoir when the pedal is depressed 3/8” to 1/2”. This indicates correct push rod length. On dual system master cylinder, fluid may spurt only from the front reservoir.
3. If the pedal travels more than 1/2” before master cylinder fluid erupts, the push rod is too short. If nothing happens no matter how far the pedal is depressed, the push rod is probably too long.

Mine does exactly what you have written in # 2. , all is set right.

Navy
I hope you get this figured out, because I have the same setup on my 34 ,an have the same problem. Except I ran mine for about 30,000 mile probably on the front brakes. But parked it an haven't drove it in about 7 years been meaning to get back on it .Jonathan

Navy-since you have power steering and need to redo the pedal/mounting bracket----think about using a hydroboost master cylinder from a late mustang AND the ford rear disc package from ford performance parts--------

Originally Posted by jerry clayton

Navy-since you have power steering and need to redo the pedal/mounting bracket----think about using a hydroboost master cylinder from a late mustang AND the ford rear disc package from ford performance parts--------

Thanks for the info Jerry, It just makes me mad, I've spent so much time and $ getting to this point and this has really slowed the build.

Navy-know what you mean--------however I have seen numerous (over many years since disc brakes )times that a package didn't work but that the person had no idea that his rear brakes weren't even working(post #86) ---when I get involved in something with 4 wheel brakes I take a very close look at an exact replication of something OEM-------Corvettes work fine, Lincolns, and Mustangs plus since so many use Ford 9iners rears , (or even 8.8) the explorer package does too. If not a race car I will look at the combo valves/masters from an oem and not mix anything up-------You got to remember that Speedway thinks brakes are to toss the vehicle sideways entering a turn on a dirt surface-usually ovals

Originally Posted by jerry clayton

Navy-know what you mean--------however I have seen numerous (over many years since disc brakes )times that a package didn't work but that the person had no idea that his rear brakes weren't even working(post #86) ---when I get involved in something with 4 wheel brakes I take a very close look at an exact replication of something OEM-------Corvettes work fine, Lincolns, and Mustangs plus since so many use Ford 9iners rears , (or even 8.8) the explorer package does too. If not a race car I will look at the combo valves/masters from an oem and not mix anything up-------You got to remember that Speedway thinks brakes are to toss the vehicle sideways entering a turn on a dirt surface-usually ovals

Jerry: I think I'm going to do just that, use stuff off a Ford. I've had this stuff from speedway since March 2015, painted parts etc. so they won't take it back. Why does education have to cost me so much time and money ! I'm just hoping that a match will work to match my GM front end-spindles, calipers etc. Most likely not but I'll try. Gotta have brakes on all 4'S.