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Brake Master Cylinder Woe

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jjbunn

jjbunn

Jedi Knight
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A while back I replaced all the rubber parts in the brake master cylinder, and rebuilt it. It looked fine, but now I notice a small dribble of brake fluid from around the piston, which is dribbling down the pedal box and onto the brake pedal.

I'm going to have to replace the master cylinder, right?
 
'fraid so. Rats. May try a local supplier for another kit, but if it's leakin' it's likely now time to just bite th' bullet and replace it.
 
Check around... I got mine through VB a couple years back, and paid at least an arm, maybe part of a leg. The local guys (advance, orielly, etc) sell them too, but without the reservior... for quite a bit less.
 
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I'm going to have to replace the master cylinder, right?

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Yep.
 
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Check around... I got mine through VB a couple years back, and paid at least an arm, maybe part of a leg. The local guys (advance, orielly, etc) sell them too, but without the reservior... for quite a bit less.

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Rats indeed, Doc! Kenny: do you have a URL for these local guys? My reservoir is in good nick, so that may be a good route.
 
www.adanceautoparts.com actually a chain store... but they have a pretty good online ordering system.

Check on part # MC39086

It appears to even be the original metal box style reservior... (I've not seen those available for awhile - and my 77 had a plastic one from the factory, but my new clutch master cyl is even plastic res'ed whereas the original in mine was metal.) Plus it's half the cost of the next 2 I found...

Also, parts # 0722025 and MC39085

And they may be only available online... I've found stuff I wanted before, and went to the store (there's one 3 miles from the ohuse), and they couldn't pull it up.
 
Julian - Did you hone the cylinderbefore installing the new seals and reassembling? If not, that may be all you need to do to get it to stop leaking. You can get brake cylinder hones from local auto parts stores (be sure to mesure the ID of the M/C so you get the correct hone). Check the inside of the M/C for any deep pitting before trying to hone it. If there is deep pitting, then it is replacement time.
Cheers,
 
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Julian - Did you hone the cylinderbefore installing the new seals and reassembling? If not, that may be all you need to do to get it to stop leaking. You can get brake cylinder hones from local auto parts stores (be sure to mesure the ID of the M/C so you get the correct hone). Check the inside of the M/C for any deep pitting before trying to hone it. If there is deep pitting, then it is replacement time.
Cheers,

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Hi David. No, I didn't hone it. When it was apart I inspected the bore quite closely and saw no blemishes at all. So I thought it would be OK. I think I'm not going to take the risk of a DIY job, and will buy new.

Kenny: thanks for the links. Advance does show the one I need in stock (0722025) but it's quite a bit more dear ($320) than on Ebay or at Moss ($210).
 
Honeing not only cleans up the bore but it gives it a bit of tooth so the new seals seat correctly.
 
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Honeing not only cleans up the bore but it gives it a bit of tooth so the new seals seat correctly.

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Hi Jack ... I just ordered a new one from Victoria British at $170 ... considerably cheaper than anywhere else I could find.

It puzzles me that the same item can vary so much in price depending on where you shop: from $170 to $320 is a helluva variation!

I'm disappointed my "rebuild" of the existing cylinder didn't work out: guess I'll chalk it up to experience; In some cases it's best just to bite the bullet and pay up for new.
 
Ummm...not necessarily... I was under the impression (mistaken, obviously) that you'd honed it. Not too late! A "brake cylinder hone" and a Black & Decker drill. Some brake fluid as lube. Low speed and a "back-and forth" with the hone to get a 'cross-hatch' pattern uniformly along the bore.
 
My advice is to stick with the new one. Been there done that.This particular brake master is very difficult to get right and even with honing they'll still sometimes leak. Besides, taking everthing apart three times and putting it back together three times, because the second rebuild didn't take, is a real drag.
 
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I just ordered a new one from Victoria British at $170

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That's not a bad price...about $10 higher than me but still decent.
 
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I just ordered a new one from Victoria British at $170

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That's not a bad price...about $10 higher than me but still decent.

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Aaaargh! I didn't know you had them, Tony!

Any progress on finding the parts I did ask for?

Thanks!
 
Miss Agathas rule of thumb. If Tony dosn't have one he can get it.

Well he dosn't have a dog but borrows his neighbors from time to time.
 
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Any progress on finding the parts I did ask for?

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Got some of them - still going through used parts bins for the others (having a hard time finding a door cap on which I like the vinyl)
 
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Any progress on finding the parts I did ask for?

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Got some of them - still going through used parts bins for the others (having a hard time finding a door cap on which I like the vinyl)

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Thanks Tony, wonderful news!
 
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