Brake Piston Insertion

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Dr. Frankenstein
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Brake Piston Insertion

#1

Post by Dr. Frankenstein »

As paranoid as I am about putting together new brakes, I want to make sure I don't mar or otherwise mess up the new, very expensive new brake pistons I just got for the front and rear brakes on my '78 GL1000. I'm working on the rear brakes and have a bit of a size difference in the pistons - 42.84mm for the old ones, and 43.00mm for the new ones...that's like, what...one sixteenth of a millimeter difference..?

The reason I ask is, the old ones will slide right in by hand as per the manual instructions; the New ones (from Brakecrafters for the '78 GL1000) seem to hang up or 'stick', and I don't know if it's because they're new, or if they are just a fraction of a millimeter bigger...and I don't want to press them in for fear of buggering up the brakes and the piston.

My question is, am I just being paranoid and the seals and pistons are stiff because they're new, or are they indeed too big?? I'm thinking about putting them in the vise and pressing them in, but I've read that if they don't 'go in', somethings wrong, and I do NOT want to mess this up.
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Re: Brake Piston Insertion

#2

Post by cfairweather »

I would first remove the seal from the groove and then you will be able to slide the old one in and out easily. Then compare it to the new one. After you polish the cylinder, the new one should easily slide in and out just like the old one.
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Re: Brake Piston Insertion

#3

Post by Figor »

When I pulled the seals out of mine the grooves were really caked with crud. Took a while to get them cleaned out good.
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cfairweather
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Re: Brake Piston Insertion

#4

Post by cfairweather »

A good way to clean the groove is with a Dremel using a fine wire wheel.
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Re: Brake Piston Insertion

#5

Post by pidjones »

With the seal out and the bore clean, the piston should drop right in (lubricated with brake fluid first). If it doesn't, send it back.
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flyin900
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Re: Brake Piston Insertion

#6

Post by flyin900 »

Figor wrote: Thu Oct 14, 2021 7:44 pm When I pulled the seals out of mine the grooves were really caked with crud. Took a while to get them cleaned out good.
The most overlooked part of a caliper rebuild and the most important for an easier assembly. If there is any residue of dried old brake fluid still in that seal groove it will extend the seal slightly and stop the piston from sliding into the cavity easily.
That said, if your putting those parts in dry with no brake fluid or seal grease, it will also hang up and not go together easily.

Brakecrafters has a good reputation from my recollection. Just like painting; its all in the prep work and cleaning of the parts.

If everything is cleaned properly and lubed, you should be able to push the piston into the caliper by hand, if not I would contact the supplier for further info.
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Re: Brake Piston Insertion

#7

Post by NotSoLilCrippseys »

I'd contact Brakecrafters. Not promising anything, as I have no relationship to them beyond being a customer, but I had a similar-sounding experience with a GL1100 front piston last winter and Brakecrafters took care of me.

My son rebuilt 3 dual-piston calipers (front/rear) with Brakecrafters kits, and one of the pistons in one kit went in hard but wouldn't slide back out. He followed their tutorials, and everything was clean enough to eat from. I swore that piston had to be bigger than spec.

I emailed them about the issue, claiming that one of the pistons had to be too large. They had me mail the offending caliper out to them. They pulled the stuck piston, replaced seals with new, and shipped it back for a basic shipping charge. Report was something about us botching the seal install, not using enough grease, or the like. No shaming. No hassle. Turnaround was about 5 days round trip.

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Re: Brake Piston Insertion

#8

Post by Sidecar Bob »

cfairweather wrote: Thu Oct 14, 2021 7:47 pm A good way to clean the groove is with a Dremel using a fine wire wheel.
Make sure you use a brass wire wheel not a steel one (check with a magnet - there are brass plated steel ones). Steel is harder than aluminum....
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Dr. Frankenstein
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Re: Brake Piston Insertion

#9

Post by Dr. Frankenstein »

Actually I did get back in touch with Brakecrafters, they said the machinist they use made a batch of the wrong size. They sent me out the correct ones, I sent them back the wrong ones, and all is good. They're a great bunch!

(And Yes, I did use a brass dremel to clean the groove).
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