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| | | | Joined: Apr 2020 Posts: 26 1952 Chevy Truck | | 1952 Chevy Truck Joined: Apr 2020 Posts: 26 | My master cylinder drips at the front boot. It has a 1 1/8" bore. I rebuilt it with part 72-256 from classicparts.com. Drip continued. Tried a 1 1/4" kit, but it doesn't fit... clearly a 1 1/8" bore.
I bled the brakes after both rebuilds.
What can I try next?
What am I missing?
The reservoir drains in 24 hours one drip at a time.
Last edited by Justhorsenround; 04/06/2020 3:57 PM. Reason: Spelling
1952 Chevy 3100 with GM Straight 6 250 engine
| | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | Did you inspect the bore for quality? Hones are available for cleaning up cylinder bores.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
| | | | | Joined: May 2005 Posts: 8,983 Sir Searchalot | | Sir Searchalot Joined: May 2005 Posts: 8,983 | The kit is probably 71-256. If it leaks on the boot end, it almost has to be the seal on that end of the piston. Bad seal right out of the box or........ got "crooked/pinched" during rebuild. (sounds like a big leak?)>>>>>> Is it possible something got on backwards?
As Ed indicates, did you think the bore looked/felt OK? not pitted/rusted? Did you lightly hone it? Hone kit is drill driven and cheap. Honing is a must-do on a rebuild.
Be sure its not coming from some fitting or? Other wise you will have to take it to the bench.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
| | | | | Joined: Apr 2020 Posts: 26 1952 Chevy Truck | | 1952 Chevy Truck Joined: Apr 2020 Posts: 26 | Thank you. I'm not a mechanic and you are the first to mention the word "honing." I'll look into that as an option... or I'll just buy a new master cylinder. Sadly I've spent close to $70 on two kits with the shipping.
Bad seal? Can't say. I have no clear instructions or pictures on how this is supposed to be assembled. I only put the new parts in the way the old parts came out.
Not sure what kind of a seal is supposed to be there.
Pits - I cleaned it and there are likely some small pits.
1952 Chevy 3100 with GM Straight 6 250 engine
| | | | | Joined: Apr 2020 Posts: 26 1952 Chevy Truck | | 1952 Chevy Truck Joined: Apr 2020 Posts: 26 | Thank you.
I'm not a mechanic and new to this... learning on YouTube.
I cleaned the bore but did not know about the need to hone. I've never heard of it until now.
No rust. Slight pit.
Not sure what fitting to look for. No instructions in the kit on the sequence of the parts. I put them back the way the old ones came out. A diagram and instructions would be useful.
1952 Chevy 3100 with GM Straight 6 250 engine
| | | | | Joined: May 2005 Posts: 8,983 Sir Searchalot | | Sir Searchalot Joined: May 2005 Posts: 8,983 | This may help a little until I find better. "Fittings" leaking, meaning the brake line attachments to the master cylinder could be leaking. Just wanting to be sure there is not a leak that is flowing from somewhere and dripping off the boot. If it's coming from inside the boot, it the internal piston seal. We all have made many mistakes along the way. Now you know you have to inspect the piston bore, hone it if it's savable and be real careful on reassembly. If you don't make mistakes, you are not doing anything. It is possible with Chinese rubber parts, that they have low reliability and short longevity. It is also possible, I think, to use the wrong brake fluid on some rubber parts.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
| | | | | Joined: Feb 2001 Posts: 1,094 'Bolter | | 'Bolter Joined: Feb 2001 Posts: 1,094 | Where are you in Louisiana?
Tommy
59 apache 1/2t
261 short stepside
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