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Caliper Rebuild

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jcatnite

jcatnite

Jedi Knight
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Ok, looks like I botched the first attempt at a caliper rebuild for my 76 Midget. This has been the brake job from you know where and it looks like it just got a little longer. Evidently, when I was pressing the cup back into one of the calipers I pinched the inner seal and even though it bled well, when I put a little brake pressure on with the pedal, fluid poured out of the caliper. Is there proven way to push the cups back into the calipers? I just used a large socked and tapped it in. Felt like it went in straight but like I said, fluid flowed with no feedback on the pedal. I would like to test my rebuild before I go so far next time. Does anyone know what pressures are developed by the system. I suspect it is pretty high but I thought an air rig with a banjo bolt would be a good way to test it before I went through the trouble of putting it on the car and filling the system for the 4th time. There is a story behind each attempt to fill the system...lol
Thanks,
JC
 
I've heard the only suggested way to push the caliper back in is by hand. No tapping or using a clamp. It's really important to clean the seal grooves until they are spotless so the seal can sit all the way in .. all the way around. I used a rag wrapped around a piece of solid wire (filed/sanded so no chance of scratching) and brake fluid to clean mine. Also wore a magnified visor to really inspect that it was clean.

Once you have that and the seal is lubricated with brake fluid or caliper seal grease then it should go in with firm but 'not-excessive' hand pressure.

I used 110 psi to remove my pistons for the rebuild and they came out slow. I would think that would be enough to see if the seals are holding but it's just a guess.

Cheers,
John
 
Thanks John,
110psi would have shot mine across the garage. Only needed around 40# to get mine out.
JC
 
I remember now my air fitting to caliper was leaking quite a bit and the seals were pretty old. That's why it probably took so much pressure. I made sure to put a wood spacer between the pistons so there would be no 'flying through the garage' action. Some people need to resort to hydraulic grease guns to get the pistons out. The guys over at https://www.brakecylinder.com say they have a hydraulic pump loaded with brake fluid that develops about 3500psi /bcforum/images/%%GRAEMLIN_URL%%/hammer.gif
 
Ok let me ask something else. The air is great for half the caliper but what about the other? I used a clamp on the piston cup in the half with the brake fitting after making sure both would move. Then I used a piece of brass for a drift though the banjo bolt hole to knock the second one out. Did you seperate them and then use air on both or what?

Thanks again,
JC
 
I got the pistons loose before splitting the calipers. Once split you would need to plug the holes that connect both halves .. not sure how that would be done.

I first put a spacer that was thick enough to let one piston move but not for it to pop out. Then I pushed that piston back in and clamped an aluminum spacer bar across it so only the other piston could move. Then used air pressure to get the other side to move a bit. Once both sides had moved in an out a few times, I split the calipers and removed them by hand or with channel locks .. I wasn't worried about chewing up the edges of the pistons since I was replacing them with new SS ones. Of course having something like this would be nice:

piston removal wrench
 
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