Scarebird front disc brake swap

[Dieselman966]

I bought my car with the swap already done.  The pedal effort seems pretty excessive for the amount of brake I get.  What master cylinder is recommended to run with the scarebird setup or what are you guys running with them?  The brake booster hoods vacuum so I'm guessing that's not the problem.  I have to replace rear axle seals also along with new shoes.  They are oil soaked now.

[67428GT500]

Scarebird? What are they from and on?

[Dieselman966]

Scarebird is a company that makes brackets to adapt off the shelf parts to swap to disc brakes.  My 65 galaxie 500 I used a mustang rotor not sure on the year and 95 s10 calipers.  They dont have a recommendation for a master cylinder though.

[67428GT500]

I thought you may be trying to do what I was going to and use the T-bird large calipers and 12" rotors that were part of the trans am conversion.  Are you using a disc brake master cylinder?  The factory disc brake master has a 1" bore. I don't know if that'll help you much.

[drdano]

I have the ScareBird adapter disk brakes on my '62 Galaxie.  What really attracted me to this kit was that it uses off the shelf parts you could get out on the road, not specialty calipers or rotors that you have no hope in hell to get replacements for if you have an issue.  Mine uses '68 Mustang rotors and single piston S10 calipers.  I decided to use a '68? Galaxie master cylinder for disk/drum brakes.  I cannot remember the bore diameter, my hunch is it's 1"+.  The pedal effort is stupid heavy and it's nearly impossible to lock up the front brakes unless you really He-Man the pedal hard. 

I think there are several issues with my setup.  First, I had to remove the power booster/fruit jar setup because the angle of the booster made it impossible to bolt in any off-the-shelf two-chamber master that would clear the hood.  So, I have no power assist at all.  The bore size may also be too large for this setup.  I called Wilwood and asked their recommendation and they thought a 7/8" bore master would work, but didn't ask me the caliper piston diameter or anything...so I think they recommended it based on my symptoms of hard pedal and difficult to lock up.  My gut tells me that the single piston S10 calipers are also causing a problem.  The single pistons are absolutely huge.  If I can find a direct swap in multi-piston caliper I'll likely try that as well. 

Let me know if you get a master that seems to work for you and helps.  I like this setup because it bolts in easily, but it really should work a bit better than it does.

[machoneman]

Too large of a master cylinder piston diameter will do that. See Wildwood's tutorial below:

https://www.wilwood.com/TechTip/TechTroubleshooting

[Dieselman966]

Ok. I'll pull the master cylinder off and see what I come up with for a piston size.

[mbrunson427]

If the master cylinder change works, can you please post up and let us know. I bought the same setup for my '62 but have not installed yet.

Similarly, I liked that it was common parts in case something needs to be replaced eventually.

[Dieselman966]

If the master cylinder change works, can you please post up and let us know. I bought the same setup for my '62 but have not installed yet.

Similarly, I liked that it was common parts in case something needs to be replaced eventually.

I'll definitely post what I come up with.  It sucks searching for an answer and finding the same problem but no solution.

[drdano]

I hate the idea of trial and error with this stuff.  "The MS bore is too large" I've heard before, but I'm unclear on how you determine if you need to go from 1" to 15/16" or to 7/8" without buying one of each, plumbing them in, bleeding the system, trying it out, etc.  If too small, you wont fully push the pistons out to stop before the MS is out of stroke or the pedal is on the floor.  Too large and you've got a gorilla leg trying to stop it like we have now.  Maybe there are online calculators that can help?  We already know the front piston diameter for the S10 rotors is 2.5" if I remember correctly.  I'm unsure what the factory rear drum brake piston diameters are.  But given those two, you've got to move a certain volume of fluid through the MS to each piston to travel some distance before the MS runs out of stroke.

[Dieselman966]

I just measured the master cylinder bore. It is 1 1/32"  now how do I find a master cylinder that has a smaller more with the bolt pattern I need? It there a guide out there for master cylinders?

[TomP]

If it is way too heavy with a 1" i'd skip the 15/16" and go to 7/8". There are even smaller ones than that. Don't go too small or it will take an unnerving amount of pedal stroke to stop.

[Dieselman966]

Here's the plumbing nightmare.  Does anyone have a schematic for the prop valve? Think I just might redo all this guys work.  I need a rear brake line now too.  Oh the joys of working on old csrs.

[machoneman]

If it is way too heavy with a 1" i'd skip the 15/16" and go to 7/8". There are even smaller ones than that. Don't go too small or it will take an unnerving amount of pedal stroke to stop.

I vote 7/8's as well. On the prop valve issue, I dumped mine (took out the internals) and added one of those aftermarket adjustable prop valves. Why? If you have modified the braking system, added different size and width wheels & tires, lightened the car, move the battery to the trunk, changed the OEM suspension (shocks, spring rate, etc.) it's pretty hard to get the best braking otherwise. Once you set the new prop valve, you can leave it alone forever.   

[machoneman]

I hate the idea of trial and error with this stuff.  "The MS bore is too large" I've heard before, but I'm unclear on how you determine if you need to go from 1" to 15/16" or to 7/8" without buying one of each, plumbing them in, bleeding the system, trying it out, etc.

I agree but there are way too many variables, for even top-notch firms like Wildwood, Baer, etc., for an equation to answer without have a lot of details specific to one vehicle. All the factors that go into even something as simple (seemingly) as the bore size of a master is affected by pedal stroke, pivot point, disc front + brake shoe rears, discs all around and more. That's why these Forums are often so helpful for those of us who have BTDT.