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SR1 brake calipers

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GraemeD
(@graemed)
Reputable Member
Joined: 6 years ago
Posts: 220
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The Hispec brake calipers for the SR1 are the same as the SR3, so this information should be useful to SR3 owners

I mentioned I had a long pedal in the "brake / throttle overlap" post.  So that is why I did this. 

Disassembly, required blowing the pistons out. Mine were stuck pretty good. The first time, I got creative with blockoff plates and clamps. This time, expandable freeze plugs. Using various thickness pieces of wood, blow out a piston. Be careful, as the piston comes out with force and a bang, with spraying fluid. So cover everything with a thick shop rag. My pistons took over 100psi to get them to move in the seals 

IMG 5171
IMG 5169

clean everything well,  the pistons had a baked on build-up  where they contacted the pads. I very carefully removed this with a razor blade without a scratch. Then I polished the pistons using a cloth wheel and compound. 

IMG 5173

After a second cleaning of everything and a close visual inspection, I re assembled using a very lite coat of Dow Corning 111 lubricant (DC111). This is an inert lubricant that will stay on the seals and piston, it won't be dissolved by the brake fluid. I did read elsewhere about using Krytox grease. Most caliper manufacturers recommend using their proprietary  "special assembly lube" I am guessing it is silicone based. 

IMG 5176

The pistons slid into the calipers with "much" less force than when I assembled them with "Miller Red Rubber Grease" that is designed for brake systems. The red grease is brake fluid soluble, so it was entirely gone, by the many bleedings I did, by the time the calipers came apart. 

Reinstalled everything back on the car and a proper bleeding done. The brakes are hugely improved now with minimal pedal travel, it only moves about 1-1/8" with foot pressure now. And they should by easier to modulate because I am not loosing pad pressure to the stiff pistons. With slight hand pressure on the pedal, I can feel a drag from the pads, but none with the pedal relaxed. 


   
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CharleyH
(@charleyhradicalsportscarregistry-com)
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Joined: 6 years ago
Posts: 1822
 

Great post!  This is very helpful.

 

Charley


   
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Victor Ling
(@azwcat)
Estimable Member
Joined: 4 years ago
Posts: 89
 

Very nice post.  I just removed the pistons from one caliper last night and found it to be difficult without risking scratching when pulling them out.  These pistons don't have the outer ring part that are on other pistons I've seen, so there is nowhere to grab.  I'll go look for expandable freeze plugs for the next caliper.  That's a nice trick.

The pistons all show some areas of wear, which I found surprising.  Nothing deep, but just some hazy areas and marks that can be polished.  New pistons are $38 each so I'll probably give it a try.

 


   
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