Author Topic: Reverse bleeding rear drums  (Read 3493 times)

1stgen68

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Reverse bleeding rear drums
« on: December 13, 2019, 08:07:20 PM »
Replaced master cylinder due to brake fluid being rusted. Pulling in air at the new master after air bubbles appear even after bench bleeding. Was going to try a reverse bleed from the passenger right and cannot push the fluid through and only comes gushing out of the bleeder screw no matter if it's barely cracked or almost all the way open.  The fronts are bled and only have the back wheels that i cannot push the fluid through. Makes me wonder if i have a corroded line somewhere not allowing the fluid to pass. The steel line coming off the master is taped off and have it attached to a bottle (catch) can if i ever get it to flow correctly.  Would the only option that i have is to start chasing which line or lines contain the blockage starting from both rear wheels and on up to the master?

z28z11

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Re: Reverse bleeding rear drums
« Reply #1 on: December 13, 2019, 10:14:13 PM »
Rebuild the distribution block and/or proportioning valve (if so equipped) ? Rusty fuid is not a good sign for whatever you haven't rebuilt downstream - you might disassemble and refresh everything just to be safe. Including flushing the lines - 

Regards,
Steve
1968 Z28 M21/U17 BRG/W 1967 Chevy ll Nova SS 
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06  1949 3100 5wd 235/6

1stgen68

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Re: Reverse bleeding rear drums
« Reply #2 on: December 13, 2019, 10:21:58 PM »
Yea it has a proportioning valve and maybe that good ole rust has seized the piston inside and needs to be replaced.

KurtS

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Re: Reverse bleeding rear drums
« Reply #3 on: December 13, 2019, 11:32:28 PM »
Rebuild. There's a guy that makes quality rebuild kits for all the valves.
Kurt S
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z28z11

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Re: Reverse bleeding rear drums
« Reply #4 on: December 14, 2019, 05:09:54 AM »
Check this out and I believe you'll find your solution(s). I've got several to do myself -

https://www.musclecarresearch.com/

Regards,
Steve
1968 Z28 M21/U17 BRG/W 1967 Chevy ll Nova SS 
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06  1949 3100 5wd 235/6

x66 714

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Re: Reverse bleeding rear drums
« Reply #5 on: December 14, 2019, 11:40:17 AM »
I just did one on my 69. Not too bad. Lots of clean up. Had lots of junk in it. Only 3 little seals in their kits.....Joe
See America's First, Chevrolet

1968 Z/28 Corvette Bronze. Black Hounds Tooth. 02E Los Angeles born 3/13/1968 pnt OO. Purchased March 1976
1969 SS396 Yellow/Yellow 08E Norwood born 8/28/1969 pnt 76E. Purchased April 1981

z28z11

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Re: Reverse bleeding rear drums
« Reply #6 on: December 14, 2019, 06:15:02 PM »
I just did one on my 69. Not too bad. Lots of clean up. Had lots of junk in it. Only 3 little seals in their kits.....Joe

And the right seals, and seal materials. Friend of mine sent his out to a known rebuilder, leaked like a sieve when he installed it, went back and forth a couple of times to get right. I'd rather not trust the import look-alikes, master cylinders, either.

Regards,
Steve
1968 Z28 M21/U17 BRG/W 1967 Chevy ll Nova SS 
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06  1949 3100 5wd 235/6

x66 714

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Re: Reverse bleeding rear drums
« Reply #7 on: December 14, 2019, 07:54:37 PM »
I just did one on my 69. Not too bad. Lots of clean up. Had lots of junk in it. Only 3 little seals in their kits.....Joe

And the right seals, and seal materials. Friend of mine sent his out to a known rebuilder, leaked like a sieve when he installed it, went back and forth a couple of times to get right. I'd rather not trust the import look-alikes, master cylinders, either.

Regards,
Steve
The kit I used was from the link you provided.
I had to get some brass brushes to get the tarnish off. Need good light & rinses really good with brake cleaner. Maybe I will put a little air to mine now that it's rebuilt. I don't need any leaks...Joe
See America's First, Chevrolet

1968 Z/28 Corvette Bronze. Black Hounds Tooth. 02E Los Angeles born 3/13/1968 pnt OO. Purchased March 1976
1969 SS396 Yellow/Yellow 08E Norwood born 8/28/1969 pnt 76E. Purchased April 1981

KurtS

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Re: Reverse bleeding rear drums
« Reply #8 on: December 14, 2019, 08:21:08 PM »
Kurt S
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sabino56

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Re: Reverse bleeding rear drums
« Reply #9 on: December 16, 2019, 03:09:46 PM »
I just went thru similar on my 68 drums all around.  It sat and got rust in MC, rears would not flow. 
You may want to consider reverse flushing brake lines.  In my case, a rear brake cylinder leaked while sitting so there was flow into lines going to rear over time.  I had to reverse flush lines until clear with a pressure bleeder to get them to flow freely.  Also good time to replace soft line if you’re in that far.
I sent my MC and distribution block to Whitepost and they seem to have done a good job.