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Scarebird Disc Brake Conversion; P15


Sam Buchanan

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One of the items at the top of my punch list when the P15 was purchased was the conversion to a dual-chamber master cylinder and front disc brakes. For various reasons I elected to rebuild the stock brakes when I returned the car to service, but the time has come to make the jump to discs. Traffic is getting increasingly hectic in our rapidly growing area and I think the $$$$'s will be well-spent for peace of mind and added safety.

 

Based on positive reviews on this forum I elected to go with the Scarebird conversion. This thread will offer details of the upgrade so future readers will have a resource for consideration. My kit includes aluminum hubs but I see this option is no longer listed on the Scarebird website. In its place is a more bare-bones conversion that requires modification of the stock spindles. But here is what was included in my kit--documentation is included and the components appear to be of high quality.

 

disc-conversion-1.jpg.4aff2618b69cdc83d4b19d23a60d076d.jpg

 

 

The first step is to remove the stock drums and backing plates with all the original components. The photo below shows why the front brakes have not had optimum stopping power because half of each shoe is barely touching the drum. This is most likely due to improper major shoe adjustment. But one reason I want to move away from the drum brakes is because of the finicky adjustment process which sometimes requires chants and the sprinkling of chicken blood around the shop......

 

 

disc-conversion-2.jpg.5f37f6af12658ddc1fec3ab45f8b78e4.jpg

 

 

No longer needed:

 

 

disc-conversion-3.jpg.387672f00b3fa498cc3fb13e5f1407e8.jpg

 

 

Here is the spindle with all the stock brake components removed along with decades of caked on grease and road debris. This will be a great opportunity to make sure all the grease zerks are functional.

 

disc-conversion-4.jpg.4f128de2f363279006e4cbdd21f18bba.jpg

 

 

Here is the kit caliper bracket bolted to the stock spindle, the fit is perfect.

 

 

disc-conversion-5.jpg.c02b6567454588f22061c50ffdb16794.jpg

 

More to come.

 

 

 

 

 

Edited by Sam Buchanan
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The bearings and seals were installed in the hubs and the assembly secured to the spindle with the stock washer and nut. I had to grind a few thousandths off the back of the nut to get clearance for the cotter pin which was included in the kit. 

 

disc-conversion-6.jpg.c3901ec6e6c20160d679db4780e81f1c.jpg

 

 

I've read reports of the kit dust cap not staying in place but the stock cap is too small....we'll see what happens. The rotor is a precise fit on the hub and I temporarily secured it with a couple of 1/2"-20 lug nuts from a local parts store. The threads on both hubs are right-hand.

 

disc-conversion-7.jpg.c18c8ef6d84bcf404d7bfc33fd7c90fb.jpg

 

 

The calipers I purchased came with bolts and seals and everything lined up perfectly on the adapter plates. I'm waiting on hoses to arrive over-night so I can complete the installation.

 

Parts List:

Rotors; 1991-92 Lincoln Mark VII rear

Calipers; 1990 Chevy Celebrity

Pads; 1990 Chevy Celebrity

Hoses; 1979 Cadillac Seville front

 

*Rotors, calipers and pads purchased from Rock Auto.

 

More to come....interested to see if everything plays nice with the stock 15" wheels.

 

 

Edited by Sam Buchanan
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I like the dog point studs.  Did you happen to see my conversion of the spindle nut to a newer adjusting setup?  Makes setting up the end play much more precise, especially for a disc setup. 

 

 

 

Edited by Sniper
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15 minutes ago, Sniper said:

I like the dog point studs.  Did you happen to see my conversion of the spindle nut to a newer adjusting setup?  Makes setting up the end play much more precise, especially for a disc setup. 

 

 

 

 

I like that, may pick up a couple of those kits. However, so far I'm ok with the preload setting with the stock nut, but the Dorman kit definitely offers more adjustability. Thanks for the tip!

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I put a Scarebird kit with their new hubs on my DeSoto and found dust caps that fit perfectly at my local hardware store. They were in an aisle with replacement utility trailer parts. 

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The Caddie brake hoses arrived this morning so one side is finished. I used 15" hoses, the only mod needed was to slightly enlarge the hole in the frame bracket so the hose fitting would insert fully into the bracket.

 

 

disc-conversion-8.jpg.f79c742f2243e5d40770dc557219067f.jpg

 

 

Then the big moment........would there be any interference between the caliper and wheel??

 

NONE!

 

When I installed the Wilwood dual-chamber master cylinder I mounted the remote reservoirs high on the firewall. I was able to open the caliper bleeder and the caliper basically bled itself as gravity did its thing. After the bubbles disappeared, I had a decent pedal. All four corners will get another bleed after everything is finished.

 

One more side to finish then the test drive....more to come.

Edited by Sam Buchanan
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Been driving the P15 around town to bed in the pads even though it still needs a final bleed. I haven't seen the need to remove the residual valve in the Wilwood dual-chamber master cylinder, the calipers release just fine. Haven't had any wheel/tire interference issues, the Scarebird installation seems to be trouble-free. I don't know if the front track changed any, didn't take any measurements pre-installation.

 

Happy camper.  ?

Edited by Sam Buchanan
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I might do that maybe a year or so after I get it on the road. Going to be a while.  Just too much going on right now.   After I drive it and really get the feel for original brakes, might change (before I hit a deer).   Keep us informed.

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To close the loop on this installation.....bled the brakes again and think it's probably as good as it'll get. The brakes work well but a second pump of the pedal brings it up a little higher than the first pump. This leads me to wonder if the master cylinder is a little under size or maybe a stronger residual valve might help. The Wilwood is available with a larger bore, if doing this again I would consider upsizing a bit. But without side-by-side comparison I can't make a definitive judgment.

 

Overall, well pleased with the conversion....think I've done about all I can do to upgrade the P15 brakes.

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1 hour ago, Sniper said:

Assuming no other inherent issues (M/C volume off, air in the lines, etc) a double pump usually means the drums need adjusting.  Did you check the rear drum adjustment?

Beat me to it Sniper!    On disks, it can also be an issue with 'pad knockback' due to disk runout.

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Just now, kencombs said:

Beat me to it Sniper!    On disks, it can also be an issue with 'pad knockback' due to disk runout.

 

A good point as well.  Which is why I converted my front spindle nut to the later style adjusters.  Just in case, lol. 

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1 hour ago, Sniper said:

Assuming no other inherent issues (M/C volume off, air in the lines, etc) a double pump usually means the drums need adjusting.  Did you check the rear drum adjustment?

 

I haven't for a while but I have that on my list for this week along with a valve adjustment. The difference in the first and second pump is very slight, still have a good pedal on first pump. I'll do another bleed in a few weeks after everything has settled in.

 

Not concerned about rotor runout, the hub bearing adjustment is good.

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On 6/12/2022 at 8:24 AM, Sam Buchanan said:

To close the loop on this installation.....bled the brakes again and think it's probably as good as it'll get. The brakes work well but a second pump of the pedal brings it up a little higher than the first pump. This leads me to wonder if the master cylinder is a little under size or maybe a stronger residual valve might help. The Wilwood is available with a larger bore, if doing this again I would consider upsizing a bit. But without side-by-side comparison I can't make a definitive judgment.

 

Overall, well pleased with the conversion....think I've done about all I can do to upgrade the P15 brakes.

 

Final update:

 

Bled the brakes again, adjusted the rear brakes, and all is well. Good pedal on first pump and the discs work nicely. Not as powerful as a modern car due to no boost.....but good.

 

The Wilwood 1" dual-chamber master cylinder is a good upgrade and very compatible with our brakes. Highly recommended.....love the remote reservoirs!

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12 hours ago, Sam Buchanan said:

 

Final update:

 

Bled the brakes again, adjusted the rear brakes, and all is well. Good pedal on first pump and the discs work nicely. Not as powerful as a modern car due to no boost.....but good.

 

The Wilwood 1" dual-chamber master cylinder is a good upgrade and very compatible with our brakes. Highly recommended.....love the remote reservoirs!

I'm glad to hear that!  My plan is also an unboosted disk/drum setup.  I'll be using a 1 1/32" master as that was what is available in my unique situation.   Using suspended pedals for a 60 truck in my 56.  The 60 setup used a 4 bolt master mount, same as the early 70 dual chamber disk/drum pickups.  So that is what my new one is.  I was hoping a booster wouldn't be needed and your experience is close enough in diameter to give me some confidence that it will work OK.

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  • 2 weeks later...

The new  Economy Scarebird kit (only one available now for P15s) uses different calipers and rotors, does not include hubs or bearings. The steel mounting plate is also different.

You have to use the hubs from the old brake drums.

 

Don't know why the photo of the spindle is shown sideways. I can't fix it.

scarebird 3.jpg

scarebird 4.jpg

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5 hours ago, jfish said:

The new  Economy Scarebird kit (only one available now for P15s) uses different calipers and rotors, does not include hubs or bearings. The steel mounting plate is also different.

You have to use the hubs from the old brake drums.

 

Don't know why the photo of the spindle is shown sideways. I can't fix it.

scarebird 3.jpg

scarebird 4.jpg

What rotors are they telling you to use? Seems like they only eliminated the hubs on this kit.

 

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  • 2 weeks later...

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