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Author Topic: 77F rear caliper has me hot (with pictures)SOLVED I think  (Read 1808 times)

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Offline stever

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77F rear caliper has me hot (with pictures)SOLVED I think
« on: May 30, 2011, 03:00:19 PM »
OK I'm going bananas here. Trying to reassemble my caliper that was sold to me as a 77F rear caliper and the dam thing just won't go. I've been wrestling with this thing for 2 days. Heres the problem:


As you can see the stack of pads and disc are wider by about 3 mm than the distance between the end of the piston and the arms of the caliper.  The diameter of the piston is 38mm (the 77 diameter) and is fully retracted into the bore, a 77 F rebuild kit fits fine , and 77F pads fit nicely.  What the heck am I missing here?
« Last Edit: May 31, 2011, 09:43:01 AM by stever »
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Offline madmtnmotors

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Re: 77F rear caliper has me hot (with pictures)
« Reply #1 on: May 30, 2011, 03:53:54 PM »
400F?
550F?
750F?

Did you remove the piston and verify that the piston seal did not get pushed in behind the piston?
« Last Edit: May 30, 2011, 03:56:52 PM by madmtnmotors »
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Offline SOHC4ever

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Re: 77F rear caliper has me hot (with pictures)
« Reply #2 on: May 30, 2011, 03:59:13 PM »
Re you sure that the piston is fully retracted into the bore? It looks like it ought to go in a bit more. Maybe something got caught in there while you had it apart or the pieces just aren't happy?
Zen, zen.
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Offline BeSeeingYou

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Re: 77F rear caliper has me hot (with pictures)
« Reply #3 on: May 30, 2011, 04:38:06 PM »
Quote from: SOHC4ever on May 30, 2011, 03:59:13 PM
Re you sure that the piston is fully retracted into the bore? It looks like it ought to go in a bit more. Maybe something got caught in there while you had it apart or the pieces just aren't happy?
Zen, zen.

I think you may be right.  While I don't have that particular year of bike in my experience the piston should retract flush or close to it with the caliper.  Try a small c clamp to push the piston in.
« Last Edit: May 30, 2011, 04:39:50 PM by srust58 »
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Offline burnoutking1971

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Re: 77F rear caliper has me hot (with pictures)
« Reply #4 on: May 30, 2011, 04:52:52 PM »
I agree the piston looks like it is not all the way retracted. Did you use a new pistion or stainless steel aftermarket one? If so did you measure the piston lengh? Good luck the "C" clamp will work just be gentle and make sure your piston seal did not come disloged and is behind the piston. Can you post a pic of the set up just so I can have a look please?
Kind Regards
J
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Offline TwoTired

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Re: 77F rear caliper has me hot (with pictures)
« Reply #5 on: May 30, 2011, 04:59:16 PM »
I thought the rear caliper piston was shorter than the earlier front caliper pistons.

I don't have one apart right now to measure.  Just fuzzy memory.  I know the older front calipers use 38 mm pistons.

If my line of thinking is correct, (Hey miracles do happen  ;) ) could someone have put an older front caliper piston in the rear caliper?

...Just armchair ramblings.

Cheers,
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Offline Lamp

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Re: 77F rear caliper has me hot (with pictures)
« Reply #6 on: May 30, 2011, 05:34:42 PM »
I just rebuilt a 78ish supersport rear caliper for my bike. If yours is like mine, that piston is going to go in very tight at first. Right now it's yours isn't in all the way. That's why you have such a small gap. Also be sure to lube it up so it doesn't grab on the seal too much. BTW how clean is that piston. From what sticking out it looks pretty dirty.
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Offline stever

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Re: 77F rear caliper has me hot (with pictures)
« Reply #7 on: May 30, 2011, 06:52:31 PM »
Its for a 750. I agree it looks wrong, but its all the way in the bore. I swear. The fiche shows same part number front and back, so no dice on that thought. Maybe someone could measure the length of a known 77-80 piston for me? Would be nice to sort this out. I guess if push comes to shove I'll just get another one and hope its right. Steve
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Offline stever

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Re: 77F rear caliper has me hot (with pictures)SOLVED I think
« Reply #8 on: May 31, 2011, 09:46:06 AM »
Problem solved (I think). I found this Ebay ad for a new piston they claim is 35mm long.
http://cgi.ebay.com/ebaymotors/Honda-CB750-F-CBX-CBX1000-Rear-Brake-Caliper-Piston-/380342627094?pt=Motorcycles_Parts_Accessories&hash=item588e2feb16
 The one I have is 41 mm long. I've ordered a new one, we will see if thats the problem. Ah, the joy of assembling disparate parts into a whole.
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